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SULPHURIC    ACID    AND    ALKALI 


WORKS  BY    SAME  AUTHOR. 

The  Manufacture  of  Sulphuric  Acid  and  Alkali* 

A  Theoretical  and  Practical  Treatise. 

Vol.  I.  in  Two  Parts  (1200  pp.),  not  sold  separately.  Sul- 
phuric Acid.  Third  and  much  Enlarged  Edition. 
Just  published  -  -       £2  12     6 

Vol.  II. — Salt  CakCy  Hydrochloric  Acid^  and  Lcblanc  Soda. 
(900  pp.)   Second  Edition,  revised  and  enlarged  £2    2    0 

Vol.  III. — The  Ammonia-Soda  and  various  other  processes 
of  Alkali-makinff,  &c.  (800  pp.)  Second  Edition 
revised  and  enlarged  -  -  -       £2     2    0 

Coal-Tar  and  Ammonia*  Third  and  Enlarged  Edition. 
(900  pp.)  -  -  -  -  -£220 

Handbook     of     Technical     GaS'Analysis*      By 

Clement  Winkler,  Ph.D.,  and  translated  by  George 
Lunge,  Ph.D.  (200  pp.)   Second  English  Edition  lOs.  6d. 


GURNEY  &  JACKSON,  Paternoster  Row,  London,  E.C. 
(Successors  to  Mr.  Van  Voorst.) 


THEORETICAL  AND  PRACTICAL  TREATISE 

ON  THX 

MANUFACTURE 

SULPHURIC  ACID  AND  ALKALI, 

WITH   THB 

COLLATERAL     BRANCHES. 
GEORGE   LUNGE,  Ph.D., 

rROFUSOR   OF  TICHHICjtL  OIIMIBTKT  AT  THB   FKDRRAL  POLmCDKIC  ICHOOL,  miCH. 
(FOaHBRLV  UANAOBB  OF  THR  TYHB  ALKALI-WOBEB,  SOUTH  BHIBLDB.) 


THIRD  EDITION,  REVISED  AND  ENLARGED. 


VOLUME    I.— Part   ] 
SULPHURIC    ACID. 


LONDON: 

GURNEY  AND  JACKSON,  PATERNOSTER  ROW. 

(Sdccbbbobs  to  Mr,  VAN  VOORST.) 


CW«ywN.%c\c^(^,03 


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■■il 


-  X        i        '     .  '     ?      V 


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LKAJ^A^0^ 


PBIVTSD     BY     TAYLOB     AND     FRAVCIS, 
BBD  LION  COURT,  FLEET  STREET. 


PREFACE. 


The  Second  Edition  of  Vol.  I.  of  'Sulphuric  Acid  and  Alkali/ 
embracing  the  Manufacture  of  Sulphuric  Acid,  appeared  in  1891^ 
but  a  copious  Appendix  at  the  end  of  Vol.  III.  brought  the  subject 
down  to  1896.  It  might  perhaps  appear  somewhat  early  to  publish 
another  edition  of  such  a  voluminous  treatise  *^  but  the  first  glance 
at  this  book  will  prove  that  there  was  sufficient  cause  for  such 
a  proceeding.  Not  merely  the  enormous  development  of  the 
manufacture  of  sulphuric  anhydride  and  even  of  sulphuric  acid 
itself  by  the  contact-process  required  an  altogether  new  treatment 
of  the  subject,  but  also  the  vitriol-chamber  process  with  all  its 
ramifications,  which  in  all  probability  will  yield  the  principal 
portion  of  ordinary  sulphuric  acid  for  many  years  to  come,  has 
experienced  so  many  changes  and  improvements  that  its  descrip- 
tion ought  to  be  once  more  brought  up  to  date. 

A  mere  compilation  of  the  voluminous  literature  of  the  subject, 
of  patent  specifications,  and  so  forth,  even  combined  with  frequent 
visits  to  acid-works,  would  not  have  achieved  my  purpose — to 
furnish  chemical  manufacturers  with  a  trustworthy  guide  for  actual 
practice,  as  well  as  exhaustive  scientific  and  technological  informa- 
tion for  all  students  of  this  branch  of  industry.  But  fortunately 
I  have  been  able  to  enlist  for  this  edition,  like  its  predecessors, 
the  co-operation  of  a  large  number  of  experienced  practical  acid- 

*  It  is  not  intended  to  publish  a  third  edition  of  Vols.  II.  and  III.  for  some 
time  to  come. 

a2 


IV  PREFACE. 


maniifactttrers  who  are  far-seeing  and  large-hearted  enough  to 
place  their  knowledge  at  my  disposal  for  this  book^  and  therefore 
for  everybody  in  a  similar  position,  without  giving  way  to  the 
somewhat  narrow-minded  apprehension  that  by  enlightening  their 
neighbours  they  might  injure  their  own  interests.  This  senti- 
ment has  certainly  not  been  universal.  The  great  acid-trusts  in 
several  countries  do  not  give  any  information,  even  on  such 
apparently  trivial  matters  as  statistics.  On  the  other  hand, 
the  United  States  Census  Bulletin,  No.  210,  compiled  by  Messrs. 
Munroe  and  Chatard,  and  issued  in  June  1902,  contains  much 
that  is  welcome  to  all  practical  men,  over  and  above  the  com- 
pletest  and  most  carefully  worked  out  statistics  ever  published 
in  that  line. 

If  a  jealous  restriction  of  experience  within  the  precincts  of 
one's  own  business  circle  were  really  practised  in  all  cases,  it  would 
be  a  very  bad  thing,  not  merely  for  the  cause  of  technology  and 
therewith  of  technical  progress  in  general,  but  even  for  the  largest 
and  most  potent  manufacturers,  who,  after  all^  are  not  all-powerful 
or  omniscient.  But  that  such  a  spirit  is  fortunately  far  from 
universal,  is  best  proved  by  the  possibility  of  compiling  a  book 
like  the  present. 

For  the  lead-chamber  process  I  have  received  (irrespective  of  a 
number  of  smaller  notes)  valuable  remarks  or  long  communications 
from  the  following  gentlemen  or  firms,  to  whom  my  best  thanks 
are  herewith  publicly  tendered  * : — 

P.  Benker,  129  Rue  Martre,  Clichy,  Paris;  Dr.  Brauning, 
Manager  of  the  Government  Works  at  Oker;  G.  E.  Davis, 
32  Blackfriars  Street,  Manchester;  The  Royal  Saxon  Govern- 
ment Works,  Muldenerhiitte,  Freiberg;  Herman  Prasch,  Cleve- 
land,  Ohio;    W.   C.   Heraeus,   Hanau;    L.   Kessler,   Clermont- 

*  This  refers  merely  to  the  third  edition ;  the  names  of  those  who  rendered 
similar  services  to  me  iu  the  previous  editions  are  not  repeated  here. 


PREFACE.  V 

Ferrand ;  Dr.  G.  Krell,  Hiisten  -  Bruchhausen  (Westphalia) ; 
Metallnrgische  Oesellschaft^  Frankfurt-a.-M.;  H.  H.Niedenfuhr^ 
3  Friedrich-Wilhelmstrasse^  Berlin  N.;  Chemische  Fabrik  Rhe- 
nania^  Stolberg  (through  the  late  Dr.  B.  Hasenclever);  Dr.  A. 
Zanner  (Brussels). 

So  far  as  the  contact-process  is  concerned,  I  have  been  enabled 
through  the  special  communications  of  nearly  all  those  who  have 
been  mainly  instrumental  in  developing  it^  especially  of  the  large 
firms  concerned^  to  completely  elucidate,  for  the  first  time,  the 
history  of  this  branch  of  industry  which  has  now  acquired  such 
great  proportions^  and  to  describe  its  present  state  so  far  as  this  is 
compatible  with  business  interests.  A  host  of  hitherto  unknown 
facts  is  contained  in  the  communications  of  Dr.  Arndt,  Dr.  Jacob, 
Dr.  Krauss  (Hochst),  Dr.  Messel,  Monsieur  Meunier  -  DoUfus, 
Dr.  Babe,  Dr.  Schroeder,  Verein  chemischer  Fabriken  in  Mannheim, 
and  Professor  Clemens  Winkler.  The  Badische  Anilin-  und 
Sodafabrik  had  already  allowed  Dr.  Knietsch  to  publish  a  great 
number  of  interesting  facts  in  his  celebrated  lecture  delivered 
before  the  Berlin  Chemical  Society,  and  that  firm  has  favoured  me 
also  with  new  valuable  information  for  this  book. 

All  contributions  to  this  book  by  other  persons  are  acknowledged 
as  such  in  their  proper  places. 

The  mass  of  material  thus  placed  at  my  disposal  would  have 
swelled  this  book  to  an  altogether  inconvenient  size^  if  I  had  not 
made  some  room  by  cutting  out  part  of  the  former  contents. 
When  preparing  this  third  edition,  I  adopted  the  same  plan  as  in 
the  second  edition — shortening  many  descriptions  and  discussions 
and  entirely  omitting  others,  also  making  innumerable  alterations 
in  details  and  rewriting  whole  chapters.  But  all  the  more 
important  omissions  of  this  kind  are  pointed  out  in  the  text 
with  reference  to  the  former  editions,  so  that  the  reader  of  this 
third  edition  is  always  made   aware  of  the  existence  of  older 


n  PREFACE. 


materials.  This  seems  the  proper  course  for  a  work  of  this  kind^ 
whose  object^  among  others^  is  to  be  of  service  to  inventors  as  a 
book  of  reference,  to  show  them  what  has  been  previously  done  in 
the  field,  and  thus,  on  the  one  hand,  to  suggest  to  them  ideas  for 
further  improvements,  and,  on  the  other  hand,  to  spare  them 
disappointments  in  patent  matters.  Some,  indeed,  will  miss  in 
this  edition  various  items  contained  in  its  predecessors,  whilst 
others  may  think  that  I  ought  to  have  restricted  myself  to  a 
description  of  such  materials  and  apparatus  as  are  still  in  use,  and 
of  such  views  as  are  now  prevalent.  It  will  never  be  possible  to 
supply  each  reader  with  everything,  and  only  everything,  he 
happens  to  require ;  I  had  to  content  myself  with  taking  a  middle 
course. 

In  this  edition  I  have  not  scrupled  to  replace  even  valuable  and 
voluminous  illustrations  by  new  ones,  where  I  was  able  to  obtain 
the  most  recent  descriptions.  No  doubt  some  readers  will  miss, 
for  example,  the  splendid  drawings  of  Schaffner^s  shelf-burner, 
from  which  hundreds  of  such  burners  have  been  erected,  but  I 
thought  it  a  waste  of  space  to  give  these  again,  along  with  the  new 
drawings  by  Niedenfiihr.  In  the  same  way  I  have  sacrificed  my 
own  drawings  of  the  Glover  tower,  of  the  vitriol-chambers,  and 
many  others.  Those  who  wish  to  consult  them  will  find  the 
former  editions  referred  to  in  the  respective  places.  A  copious 
index  will  facilitate  the  use  of  this  book. 

It  is  now  twenty-four  years  since  the  first  edition  of  this  volume 
saw  the  light.  The  two  former  editions  have  earned  for  the 
author  every  commendation  he  could  desire,  and  more  than  he 
honestly  could  have  claimed  for  himself.  It  will  not,  I  hope,  be 
thought  egotistic  if  I  say  that  hardly  anybody  is  better  able  to 
appreciate  the  weak  sides  of  this  work  than  its  author.  Errors, 
omissions,  matters  of  questionable  value  will  be  found  by  the 
expert  reader  here  and  there.      This  third  edition  is  still  very 


PREFACE.  Vn 

far  removed  from  the  ideal  of  such  a  treatise  as  it  exists  in  the 
mind  of  the  author.  But  nobody  can  do  more  than  is  in  his 
power,  and  such  readers  as  know  (or  think  they  know)  this  or 
that  thing  better,  and  who  may  be  inclined  to  sharp  criticism, 
had  best  ask  themselves  the  question  whether  they  would  come 
up  to  the  ideal  if  they  had  to  write  such  a  book,  and  whether 
they  cannot  derive  some  valuable  information  even  from  this  im- 
perfect performance,  which  probably  represents  the  last  opportunity 
the  author  will  have  of  treating  the  subject. 

Zurich,  August  tfth,  1903. 


CONTENTS. 


Page 
Fb£fac£ iii 

GoHTisirn ix 

IlTTROOUOlION     8 

Definition  of  Snlphurio  Acid  and  Alkali  Manufacture,  3  ;  Sulphuric 
Acid,  4;  Sulphate,  Leblanc  process,  Hydrochloric  Acid,  '5; 
Eecovery  of  Sulphur,  6. 

CHAPTEK  I. 

HiSTOBlCAL  AND  GeNEBAL  NoTES   ON   THE   MaNUFACTUBE  OF  SuLPHUBIC 

Acid 7 

History  of  the  Manufacture  of  Sulphuric  Acid,  7. 
General  Principles  of   the  Manufacture  of  Sulphuric  Acid,    11; 
Division  of  the  Subject,  13. 

CHAPTER  II. 

The  Baw  Matbeials  of  the  Svlphubic-Acid  Manufaotube  (ineluding 

NiT&ic  Acid)    14 

1.  Natural  Sulphur  (Brimstone)     14 

Historical,  14;  properties  of  sulphur,  15;  allotropio  conditions,  15; 

thermic  properties,  16 ;    combinations,  solubility,  16 ;   refined 

sulphur,  16. 
Natural  occurrence  of  sulphur,  17 ;  Sicilian  sulphur  industry,  17 ; 

new  processes  for  extracting  sulphur,  18 ;  analyses  of  Sicilian 

sulphur,   19 ;    prices,   exportation,  20 ;    sulphur   in   Northern 


X  CONTENTS. 

Page 

Italy,  20 ;  Spain,  Germany,  Austria,  Russia,  21 ;  Africa, 
Iceland,  Japan,  22  ;  New  Zealand,  United  States,  23 ;  other 
parts  of  America,  24. 

Sulphur  manufactured  from  other  materials,  25 ;  from  spent  oxide 
of  iron,  23 ;  from  pyrites,  26  ;  from  sulphur  dioxide,  sul- 
phuretted hydrogen,  29. 

World's  production  of  sulphur,  30. 

Technical  analysis  of  sulphur,  31 ;  commercial  grades,  3 1 ;  detection 
of  arsenic,  31 ;  selenium,  32  ;  direct  estimation  by  solubility  in 
carbon  disulphide,  32 ;  degree  of  fineness,  Chancel's  sulphuri- 
meter,  33  ;  refined  sulphur,  flowers  of  sulphur,  34. 

2.  Pyntes     34 

Properties  of  pyrites,  34 ;  of  mareasitie,  35  ;  magnetic  pyrites  (pyr- 
rhotite),  36 ;  copper-pyrites,  36. 

First  application  of  pyrites,  37 ;  introduction  of  cupreous  pyrites,  39. 

Sources  of  pyrites,  40 ;  Great  Britain,  40  ;  Ireland,  41  ;  coal-brasses, 
41 ;  importations  of  foreign  pyrites  into  Great  Britain,  42 ; 
pyrites  in  Germany,  42 ;  in  Austria,  45  ;  Switzerland,  Poland, 
Belgium,  46 ;  France,  47 ;  Italy,  50  ;  Sweden,  Norway,  5J ; 
Spain  and  Portugal,  53;  United  States,  57;  Canada,  New- 
foundland, Australia,  59. 

World's  production  of  pyrites,  59 ;  average  composition  of  the 
world's  pyrites,  60 ;  prices,  61 ;  proportional  value  of  poor 
and  rich  pyrites,  61. 

Analysis  of  pyrites,  62 ;  decomposing  the  ore  in  the  wet  way,  62 ; 
precipitating  by  barium  chloride,  64  ;  previous  removal  of  the 
iron,  66 ;  Lunge's  method,  67 ;  other  methods,  69 ;  estimation 
of  sulphates  by  titration,  70 ;  estimation  of  available  sulphur, 
72 ;  expeditious  pyrites  assays,  74 ;  testing  burnt-ore,  75 ; 
magnetic  pyrites,  76 ;  marcasite,  76 ;  estimation  of  other  con- 
stituents of  pyrites,  77 ;  arsenic,  77. 

3.  Zinc-blende 79 

Occurrence,  79  ;  composition,  80 ;  analysb,  81. 

4.  Other  Metallic  Sulphides     81 

Noxious  vapours,  82 ;  total  acids  contained  in  these,  83 ;  from 
copper-pyrites,  83 ;  materials  used  at  Oker,  83 ;  galena,  85 ; 
coarse  metal,  85  ;  lead-matte,  85. 


CONTENTS.  XI 

Page 

5.  By-jproducU  of  other  Manufaetureg    85 

Spent  oxide  of  gas-works,  85 ;  alkali  waste,  88 ;  sulpharetted 
hydrogen  £rom  the  manufacture  of  sulphate  of  ammonia,  89 ; 
other  sources  of  sulphur  dioxide,  89. 

6.  NiiraU  of  Soda   89 

Properties,  89 ;    solubility,  90 ;   occurrence  in  Chili,  91 ;    in  other 

places,  93 ;  potassium  nitrate,  93 ;  consumption,  93  ;  treatment 
of  nitre-bags,  94 ;  composition  of  commercial  nitrate  of  soda, 
94 ;  occurrence  of  potassium  and  of  perchlorate,  95 ;  analysis 
of  nitrate  of  soda,  96 ;  ''  refraction,"  96  ;  nitrometer  method,  96. 

7.  NUrie  Acid '. 98 

Boiling-points,  98 ;  specific  gravities,  99 ;  correction  for  temperature, 

101 ;  influence  of  lower  nitrogen  oxides,  102 ;  oxidizing  pro- 
perties, 103. 

Manufacture  of  nitric  acid,  103 ;  French  cylinders,  104 ;  Griesheim 
cylinders,  107;  French  stiUs,  111;  Valentiner's  stills,  111; 
Guttmann's  still,  114;  other  stills,  115;  Prentice's  continuous 
still,  115;  Uebel's  process,  116. 

Cement  for  nitric  acid,  120  ;  asbestos  cement,  120. 

Gases  and  vapours  evolved  during  the  working  of  the  retorts,  121 ; 
Volney*8  observations,  121. 

Condensation  of  nitric  acid,  123 ;  old  receiver  apparatus,  123 ; 
cooling  pipes  and  worms,  124 ;  condensing  exit-gases  by  coke- 
towers,  124 ;  by  plate-towers,  125  ;  Bohrmann-Lunge*8  system, 
125;  recovering  nitric  acid  from  lower  oxides,  125;  Nieden- 
fiihr's  apparatus  for  this  purpose,  127 ;  refining  or  bleaching 
nitric  acid,  127 ;  Griesheim  condensing-process,  129 ;  Gutt- 
mann's  system,  131  ;  various  systems,  132  ;  Valentiner's 
vacuum  process,  134. 

Concentration  of  nitric  acid,  139. 

Nitre-cake,  139. 

Cost  of  manufacturing  nitric  acid,  140. 

Utilization  of  nitric  acid  from  nitrating  processes  (nitrobenzene, 
nitroglycerine,  &c.),  141. 

Various  processes  for  the  manufacture  of  nitric  acid,  142. 

Protection  against  accidents  by  nitric  acid,  145. 

Transportation  of  nitric  acid,  145. 

Pumping  of  nitric  acid,  Pulsometers,  146. 

Analysis  of  nitric  add,  147  ;  impurities  in  commercial  nitric  add,  147. 


XII  CONTENTS. 

CHAPTER  III. 

Page 
The  Pbopbbtibs  ajtd  Analtbib  of  the  Tbohnicallt  £hplot£d  Oxides 

and  aoidb  of  sulphub    149 

Stdphur  Dioxide  (Sulphurous  Add)    149 

Properties  of  sulphur  dioxide,  149 ;  reactions,  151. 

Sulphurous  aoid,  152 ;  soluhility,  152 ;  production  from  sulphuric 

acid  and  charcoal,  153 ;  salts,  154. 
Injurious  action  of  SOj  on  health  and  vegetation,  154 ;    noxious 

vapours  (acid-smoke),  154. 
Detection  and  estimation  of  sulphurous  acid  and  sulphur  dioxide, 

159  ;  qualitative  reactions,  159  ;  quantitative  estimation,  160. 
Applications  of  sulphurous  acid  (sulphur  dioxide),  161. 

Sulphuric  Anhydride  (Sulphur  Triaxide) 162 

Pyrondphuric  Acid 164 

Nordhausen  or  fuming  oil  of  vitriol,  165 ;  melting-  and  boiling- 
points,  166 ;  specific  gravities,  166 ;  specific  heats,  169 ;  heats 
of  solution,  170  ;  various  properties,  170. 

Sulphuric  Acid    170 

Occurrence,  170;  monohydrated  sulphuric  acid,  171;  dissociation, 
vapours,  172 ;  formation,  172 ;  sulphuric  acid  containing 
water,  173  ;  distilled  acid  (critical  concentration),  173 ; 
absorption  of  SO,  at  that  concentration,  175  ;  rectified  oil 
of  vitriol,  176 ;  hydrometers,  176 ;  Baume's  hydrometer, 
176 ;  Twaddell's  hydrometer,  ]  78 ;  specific  gravities  of  dilute 
sulphuric  acid,  179  ;  table  by  Lunge,  Isler,  and  Naef,  180 ; 
maximum  density,  186;  correction  for  temperature,  186; 
hydrates  of  sulphuric  acid,  187 ;  influence  of  impurities  on  spe- 
cific gravities  of  sulphuric  acid,  187  ;  of  sulphurous  acid,  188  ; 
of  nitrogen  acids,  189 ;  of  arsenic,  189  ;  of  lead  sulphate,  190  ; 
unreliability  of  hydrometric  testing  for  high  specific  gravities, 
190 ;  Anthon's  table  for  mixtures  of  sulphuric  acid  and  water, 
190  ;  melting-points  of  sulphuric  acid,  191 ;  boiling  sulphuric 
acid,  193 ;  boiling-points,  193 ;  tension  of  aqueous  vapour  in 
sulphuric  acid,  195 ;  specific  heat  of  sulphuric  acid,  197. 

Chemical  behaviour  of  sulphuric  acid,  198 ;  rise  of  temperature  on 
mixing  sulphuric  acid  with  water,  198 ;  effects  of  the  affinity  of 
sulphuric  aoid  for  water^  200 ;  decomposition  of  sulphuric  acid, 


1 


CONTENTS.  XUl 

Page 

201 ;  add  propertiefi,  201 ;  salts  (stdphates),  202 ;  action  on 
metals,  202  ;  on  platinum,  203 ;  on  cast-iron,  203  ;  ou  wrought- 
iron,  204 ;  on  lead,  206  ;  sine,  tin,  211. 

Behaviour  of  sulphurous  and  sulphuric  add  towards  the  oxides  of 
nitrogen,  212 ;  nitrous  oxide,  212  ;  nitric  oxide,  21 2 ;  nitrous  acid, 
213 ;  chamher-crystals  (nitrososulphuric  add),  215 ;  nitrogen 
peroxide,  221 ;  tendon  of  nitrous  add  in  presence  of  dilute 
sulphuric  acid,  227  (tahles,  228)  ;  behaviour  of  nitrososulphuric 
acid  towards  reducing-agents :  sulphur  dioxide,  227,  coke, 
231. 

Analysis  of  sulphuric  add,  2S2 ;  qualitative  detection,  232 ;  quanti- 
tative estimation,  233 ;  volumetrical  estimation,  233 ;  litmus, 
phenolphthalein,  methyl-orange,  234 ;  standard  alkaline  solutiou, 
236;  standard  acid,  236 ;  analysis  of  fuming  oil  of  vitriol,  238. 

Taking  the  sample,  238 ;  weighing  in  bulbs,  239 ;  in  glass  tap-tubes, 
240 ;  bulb-tap  pipette,  241 ;  sampling  solid  anhydride,  242 ; 
Frdberg  method,  242 ;  table  for  comparing  free  and  combined 
SO,,  243;  producing  mixtures  with  a  given  strength  of  SO,,  244; 
influence  of  SO,  on  testing,  244 ;  testing-methods  based  on 
suppressing  the  filming,  24t5 ;  definition  of  percentage  of  SO,, 
247. 

Estimation  of  the   impurities  of  sulphuric   acid,   248  ;  qualitative 

detection,  248 ;  arsenic,  248  ;  volatile  impurities,  249  ;  nitrogen  I 

adds,   249  ;  selenium,   252 ;  quantitative  estimation,  252 ;   of  ^ 

nitrogen  acids,  253 ;  total  nitrogen  acids,  253 ;  nitrometer  method, 
253 ;  reduction  of  gas-volumes  fpr  normal  conditions  of  pressure  ] 

and  temperature,  258  ;  gas-volumeter,  259;  estimation  of  nitrous  j 

acid  (nitrososulphuric  acid)  by  the  permanganate  method,  262; 
table  for  testing  nitrous  vitriol,  264  ;  colorimetric  estimation  of 
small  quantities  of  nitrous  acid,  266 ;  of  nitric  acid,  267. 

CHAPTER  IV. 

The  Pboductioh  of  Sulphub  Dioxide    268 

A.  Brimstone-burners 268 

Old  burners,  268;  improved  burners,  272;  Stahl's  burners  with 
boiling-down  pans,  274  ;  coutinuous  burners,  277  ;  Blair's,  277  ; 
H.  Glover's,  279 ;  de  Hemptinne's,  280  ;  burners  for  wood-pulp 
works,  283  ;  residue  from  sulphur-burners,  285  ;  cooling  the  gas 
from  brimstone-burners,  286. 


XIV  CONTENTS. 

Pag© 
B.  The  Production  of  Sulphur  Dioxide  from  Pi/rites 286 

1.  Breaking  ihspyrites   286 

Breaking  by  hand,  286 ;  Bieving,  287 ;  mechanical  stone-breakers, 

287. 

2.  PtfriteS'humers  for  lumps    29J 

Necessity  of  keeping  lumps  and  smalls  apart,  291  ;  burning  in  heaps, 
292 ;  in  kilns  or  burners,  292 ;  Freiberg  kilns,  293 ;  burners 
with  grates  and  ash-pits,  295;  English  grate-burners,  296;  gas- 
flue,  300  ;  grate-bars,  300 ;  ash-pit,  303  ;  tilting-box  for  dis- 
charging the  burnt  ore,  303  ;  arrangements  for  preventing  any 
blowing  out  during  discharging,  303 ;  Rhenania  burners  with 
such  arrangement,  305 ;  doors  of  burners,  307 ;  brickwork,  307 ; 
size  of  burners,  308 ;  grate-surface,  308  ;  sets  of  burners,  309  ; 
concentrating-pans  placed  on  top  of  burners,  310 ;  potting  the 
nitre  in  burners,  311 ;  special  kinds  of  pyrites-burners,  311 ; 
burners  for  copper-matte,  312. 

Working  of  the  pyrites-burners  for  lumps,  313;  starting  the  burners, 
313;  objects  aimed  at,  314;  sulphur  remaining  in  cinders,  315; 
appearance  of  cinders,  315 ;  testing  them  for  sulphur,  316 ; 
composition  of  cinders,  316 ;  residue  from  treating  metallurgical 
products,  318 ;  admission  of  air,  319 ;  subliming  of  sulphur, 
319  ;  slags  (scars),  319 ;  behaviour  of  different  ores,  320  ;  regu- 
lation of  draught,  321 ;  work  of  burner-men,  323 ;  regulating 
the  heat,  324 ;  influence  of  dampness,  326 ;  general  remarks, 
326. 

3.  Burning  pyrites-smalls    327 

Burning  smalls  together  with  lumps,  327;  balls  made  with  clay, 
328:  (a)  burning  smalls  in  coal-fired  furnaces,  329;  (b)  by 
the  heat  of  burners  for  lumps,  330;  Olivier  &  Ferret's 
furnace,  330 ;  Hasenclever  &  Helbig's  tower-furnace,  331 : 
(c)  burning  smalls  without  external  heat,  331 ;  balling  pyrites- 
dust  by  grinding  with  water  and  drying  (pugging),  331; 
Gerstenhofer  furnace,  332 ;  Maletra's  shelf-burner,  334 ; 
Aussig  burner,  337  ;  working  shelf-burners,  339  :  combination 
with  lump-burners,  342 ;  other  descriptions  of  shelf-burners, 
343. 

Mechanical  dust-burners,  343 ;  MacDougall's  furnace,  343 ;  modifi- 
cations, 346 ;  Frasch's  burner,  348  ;  Herreshoff  burner,  349  ; 


CONTENTS.  XV 

Page 

other  mechanical  dust-burners,  351;  Spence's  dust-bumer»  352; 
other  burners,  356;  Bruckner's,  367;  Walter's  burner  for 
"  peas,"  367. 

4.  Furnaces  for  roasting  zine-hlende 368 

Nuisance  caused  by  the  open  roasting  of  blende,  368 ;  development 
of  processes  for  utilizing  the  sulphur.  368 ;  Hasendever  and 
Helbig's  furnace,  369  ;  Liebig's  furnace,  360 ;  Khenania  furnace, 
361 ;  other  blende-furnaces,  363 ;  mechanical  furnaces,  364 ; 
treatment  of  complex  ores  containing  blende,  366. 

5.  Burners  for  the  spent  oxide  of  gas-worJes 366 

6.  Burners  for  sulphuretted  hydrogen 367 

7.  Processes  for  absorbing  sulphur  dioicide  contained  in  aeid-smohe, 

fire-gases^  and  the  like 370 

Dealing  with  ordinary  coal-smoke,  370 ;  chimneys,  371 ;  dilution  with 
air,  371 ;  smoke  from  glass-works,  372 ;  condensing  by  water, 
372 ;  by  sulphuric  acid,  373 ;  absorption  by  caustic  lime,  373 ; 
by  limestone,  374;  by  magnesium  or  aluminium  hydrate, 
376  ;  by  zinc  carbonate  or  oxide,  376 ;  by  ferric  oxide  and  coal, 
376 ;  by  metallic  iron,  copper,  zinc,  377 ;  by  copper  and  air, 
377 ;  by  hydrogen  sulphide,  377 ;  by  calcium  or  barium  sul- 
phide, 378 ;  by  vegetable  charcoal,  379  ;  by  passing  over  red- 
hot  coals,  379. 

8.  Preparation  of  sulphur  dioonde  in  the  pure  state 379 

Old  methods,  379 ;  from  sulphuric  acid  and  coal,  379 ;  from  sulphuric 
acid  and  sulphur,  380  ;  from  sulphuric  acid  and  ferrous  sulphide, 
380 ;  by  heating  ferroas  sulphate  with  sulphur,  380 ;  by  burning 
sulphur  in  air,  381 ;  process  of  Schroeder  and  Haenisch  for  the 
preparation  of  liquid  sulphur  dioxide,  381 ;  vessels  for  sending 
out  liquid  sulphur  dioxide,  386 ;  uses  for  liquid  sulphur 
dioxide,  387. 

9.  Draught^pipes  and  flues 388 

Cooling  the  gases  by  cast-iron  pipes,  388 ;  utilizing  the  heat  of  the 

gases,  389 ;  Albert's  process,  389. 
Flue-dust,    390;    removal,    392;    dust-chambers,    393;    Freiberg 

cooling-flues,  394  ;  centrifugal  dust-catcher,  396. 
Purification  of  sulphur  dioxide  from  SO,  for  the  manufacture  of 

wood-pulp,  397. 


XVI  CONTENTS. 

Page 
10.  ITie  burner^as 397 

CompoBition  of  the  burner-gas  from  burning  brimstone,  397. 

Composition  of  the  bomer-gas  from  burning  pyrites,  399. 

Sulphur  dioxide  for  manufacturing  calcium  bisulphite  (in  the  manu- 
facture of  wood-pulp  &c.),  401. 

Composition  of  the  gas  from  blende-furnaces,  401. 

Sulphuric  anhydride  in  burner-gas,  402. 

Actual  percentage  of  snlphur  dioxide  in  burner-gas,  407 ;  in  gases 
from  poor  ores,  408. 

Comparison  of  brimstone  and  pyrites  as  material  for  sulphuric-acid 
making,  409. 

The  quantitative  estimation  of  sulphur  dioxide  in  burner-gas,  411 ; 
Reich's  method,  411 ;  Lunge's  test  for  total  acids  in  the  burner- 
gas,  416 ;  estimation  of  oxygen  in  burner-  and  chamber-gases, 
417 ;  by  pyrogallol,  417 ;  by  phosphorus,  418 ;  estimation  of 
the  oxides  and  acids  of  nitrogen  in  gaseous  mixtures,  419 ; 
Lunge  and  Naef's  method,  419  ;  estimation  of  nitrous  oxide, 
419. 


CHAPTER  V. 

CovsTBrcnoN  of  the  Lbad  Chambkbs 421 

Necessity  of  large  spaces,  421 ;  suitability  of  lead,  421 ;  proposals 
for  other  materials,  422. 

The  erection  of  lead  chambers  above  ground,  422 ;  foundation,  423 ; 
pillars,  423  ;  of  wood,  423 ;  of  brickwork,  424 ;  of  stone,  425 ; 
of  iron,  425 ;  sleepers  and  joists,  426  ;  floor,  427 ;  frame  of 
wood,  428  ;  of  angle-iron,  430  ;  lead  for  chambers,  430  ;  thick- 
ness, 430 ;  quality,  431 ;  joining  lead  by  solder,  433 ;  by 
rabbets,  433 ;  by  burning,  433 ;  erecting  a  lead  chamber,  437 ; 
straps,  438 ;  chamber-top,  441 ;  chamber-bottom,  445 ;  details 
of  chamber  construction  on  the  English  plan,  448 ;  chamber 
buildings,  450. 

Renewal  of  the  chambers,  450 ;  repairs,  450 ;  pulling-down,  452 ; 
wear  and  tear  of  chambers,  453. 

Shape  of  lead  chambers,  454;  Rhenania  chambers,  454;  H.  A. 
Smith's  proposal,  455  ;  Delplace's  chambers,  455 ;  Th.  Meyer's 
tangential  chambers,  455. 

Combination  of  chambers  to  sets,  458;   Benker's  chambers,  459 
size  of  chambers,  460 ;  connecting-tubes,  464. 


CONTENTS.  XVll 

Page 

Total  cubical  contenta  of  chambers,  465 ;  forced  or  high-pressure 
work,  468  ;  chambers  worked  by  G.  E.  Davis,  469 ;  chamber- 
space  for  poor  ores,  470 ;  iuflueuce  of  consumption  of  nitre, 
470 ;  of  temperature,  470 ;  various  terms  of  expressing  chamber- 
space,  471. 

Proposals  for  diminishing  cTiamher- space,  471.  Use  of  pure  oxygen, 
471 ;  employment  of  a  very  large  quantity  of  nitre,  472  ;  better 
mixture  of  gases  and  increase  of  condensing^pace,  472 ;  Ward's 
glass  sheets,  472 ;  chambers  with  glass  partitions,  474 ;  with 
brick  partitions,  475 ;  filled  with  coke,  475 ;  apparatus  of 
Verstraet,  476  ;  of  Lardani  and  Susini,  476  ;  of  Richters,  476 ; 
of  Pratt,  476  ;  Burgemeister's  cooling-shafts,  477. 

Mixing-  and  cooling-towers,  477 ;  Thyss  towers,  477 ;  Sorel's  plan, 
478 ;  Lunge's  plate-towers,  478 ;  theory,  478 ;  construction,  480 ; 
functions,  484 ;  practical  application  of  plate-towers,  487  ;  ex- 
periences made  in  various  places,  488 ;  prescriptions  for  erecting 
plate-towers,  492 ;  NiedenfUhr's  plan  of  acid-making  by  plate- 
towers  only,  493 ;  by  a  combination  of  plate- towers  and  cham- 
bers, 496 ;  practical  results  obtained  by  adding  plate-towers  to 
chambers,  497 ;  differences  of  temperature  and  pressure  in  that 
case,  498. 

Other  apparatus  on  the  principle  of  plate-towers,  498 ;  Hacker  and 
Gilehnst's  pipe-towers,  499 ;  Benker's  towers,  499 ;  Guttmann's 
balls,  600  ;  cone-towers,  500. 

Question  of  completely  abolishing  the  lead  chambers,  501. 

Chamber  fittings^  501.  Drawing  off  the  acid  by  taps,  501  ;  siphons, 
502 ;  acid-valves,  506 ;  acid-dishes  (drips),  506 ;  dippers  for 
taking  samples  of  acid,  507 ;  man-holes,  507 ;  thermometers, 
508  ;  pressure-gauges,  508 ;  acid-gauges,  509  ;  sights,  510. 

Apparatus  for  introducing  nitric  acid  into  the  chambers,  511.  Com- 
parison of  "potting"  and  of  the  use  of  liquid  nitric  acid,  511  ; 
introduction  of  nitric  acid  as  vapour  ("potting''),  513;  in- 
troduction of  vapours  from  ordinary  retorts,  517  ;  introduction 
of  liquid  nitric  acid,  517 ;  Mariotte  bottles,  519 ;  tambours, 
519  ;  cascades,  521 ;  introduction  through  the  Glover  towers, 
522;  by  means  of  spray-producers  (injectors),  523;  storing 
nitric  acid,  527 ;  introduction  of  nitre  as  aqueous  solution  of 
nitrate  of  soda,  527. 

Feeding  the  chambers  with  nitrous  gases  obtained  as  a  by*product, 
529  ;  Dunlop's  process,  529. 
VOL.  I.  b 


XYlll  CONTENTS* 

Page 

Supply  of  water  as  steam  or  spray ^  530.  Steam,  530  ;  steam-boilers, 
530 ;  use  of  exhaust-steam,  531 ;  registering  steam-gauges, 
531 ;  steam-pipes,  531 ;  branches  and  taps,  532 ;  pressure- 
gauge  behind  tap,  533  ;  automatic  steam-regulators,  533 ;  place 
of  steam-jets,  533  ;  regulating  steam -jets  from  one  place,  534 : 
total  quantity  of  steam  required,  535 ;  emplo3*ment  of  water  in 
the  place  of  spray,  536 ;  Sprengel's  system,  536 ;  Griesheim 
system,  537 ;  objections  to  water-sprays  and  refutation  thereof, 
538 ;  Benker's  spray-producers,  540 ;  Korting's  spray-producers, 
541 ;  modification  of  these  with  glass  nozzle,  541 ;  filtering 
water  for  this  purpose,  542;  Benker*s  chambers  for  high- 
pressure  style  with  water-sprays,  543. 

Arrangements  for  producing  the  draught  in  viirioUchamhers,  544. 
Calculation  of  draught  from  the  composition  and  temperature  of 
the  gases,  544 :  effects  of  excessive  draught,  547 ;  draught  by 
outlet-pipe  from  the  last  chamber,  549 ;  by  steam-injectors, 
549 ;  by  chimneys,  550 ;  by  the  Gay-Lussac  tower,  551 ; 
working  more  than  one  chamber  by  the  same  chimney,  552 ; 
introducing  air  into  the  first  chamber,  553  ;  draught  produced 
by  Glover  tower,  553;  regulating  the  draught  by  dampers, 
653 ;  by  a  diaphragm  in  the  *'  sight,"  554 ;  by  automatic 
arrangements,  555 ;  Strype's  regulator,  556 ;  mechanical  pro- 
duction of  draught,  559  ;  fan-blasts,  559  ;  anemometers,  562 ; 
Fletcher's,  562  ;  tables  for,  567 ;  Swan's,  570 ;  various,  571 : 
Seger's,  572. 

Calculation  of  the  volume  of  chamber-gases  according  to  temperature 
and  moisture,  573. 

CHAPTEK  VI. 
The  Recovery  of  the  Nitrogen  Compounds 575 

Reasons  for  this,  575 ;  reactions  of  nitrogen  oxides  towards  sulphuric 
acid,  575 ;  invention  of  Gay-Lussac's  tower,  576 ;  of  Glovers 
tower,  576 ;  principle  of  Gay-Lussac  tower,  577 ;  towers  in 
series,  578 ;  width,  579 ;  dimensions,  580 ;  foundations,  581 ; 
framework,  581 ;  leadwork,  582 :  stone-towers,  583 ;  packing, 
584 ;  coke,  584 ;  stoneware  packing,  586  ;  plate-towers,  586  ; 
repacking  towers,  587 ;  dealing  with  dangerous  gases,  588 ; 
complete  design  of  a  Gay-Lussac  tower,  589 ;  other  apparatus 
on  the  same  principle,  590. 


1 


CONTENTS.  XIX 

Page 
Distribution  of  the  feeding-acid,  592;  acid-wbeels,  593;  overflow 

apparatus,  595 ;  regulation  of  supply,  598 ;  Mariotte's  yessel, 
598 ;  balancing-apparatus,  599 ;  box-apparatus,  601  ;  "  Semper 
idem "  apparatus,  602 ;  regulation  by  pulsometers,  603 ;  cen- 
tralized system  (Griesheim),  603  ;  pumping-apparatus,  605  ; 
air-pumps,  606 ;  acid-eggs,  607  ;  automatic,  611 ;  prevention  of 
splashing,  612 ;  combination  of  acid-eggs,  614 ;  Laurent's 
pulsomefcer,  614  ;  Kestner's,  618 ;  tanks  or  reservoirs  for  acid, 
619. 

Working  the  Gay-Lussac  tower,  620 ;  drying  and  cooling  the  gas, 
620 ;  cooling  the  acid,  620 ;  quantity  of  acid  for  feeding  the 
tower,  623 ;  quality  of  nitrous  vitriol,  624 ;  presence  of  nitric 
acid  in  nitrous  vitriol,  625  ;  of  nitrogen  peroxide,  626  ;  process 
of  Brivet,  Lasne,  &  Benker,  626  ;  Benker's  introduction  of  gas 
containing  SO^  before  the  tower,  627 ;  regulation  of  the  draught, 
627  ;  faulty  working  of  the  tower,  628 ;  loss  of  nitre  from  this 
cause,  628  ;  exit-gases,  ruddy  vapours,  629  ;  acids  in  exit, 
629  ;  proposals  for  absorbing  these,  630. 

Various  plans  for  recovering  the  nitre  in  otber  ways,  631. 

Denitration  of  the  nitrous  vitrol,  631 ;  necessity  for,  631  ;  shelf- 
apparatus,  632  ;  Gay-Lussac's  denitrificateur,  632 ;  steam-boxes, 
634 ;  steam-columns,  636. 

Glover  tower,  639 ;  history,  639 ;  objection  raised  against  it  and 
refutation  thereof,  639 ;  functions  of  the  Glover  tower,  643 ; 
construction  of  a  Glover  tower,  644 ;  materials  for  lining,  645  ; 
foundation,  646 ;  frame,  646 ;  leadwork,  647 ;  lip,  648 ;  top, 
649  ;  inlet-  and  outlet-pipes,  649  ;  lining,  651 ;  arch,  652 ; 
packing,  652  ;  avoiding  excessive  height  of  towers,  657  ;  distri- 
bution of  acid,  657  ;  cubic  contents,  658  ;  description  of  complete 
Glover  towers,  658  ;  circular  towers,  659 ;  Liity's  towers,  660  ; 
Niedenfuhr's  tower,  661 ;  placing  Glover  and  Gay-Lussac  towers 
together,  662 ;  working  of  the  Glover  tower,  663  ;  acid  used  for 
feeding,  663 ;  mixing  the  nitrous  vitriol  and  chamber-acid  out- 
side the  tower,  664 ;  temperature  of  acid  and  gas,  665  ;  Glover 
towers  connected  with  shelf-burners,  &c.,  666  ;  with  brimstone- 
burners,  666 ;  working  Glover  towers  for  various  functions,  667 ; 
extent  of  denitration,  667 ;  concentrating  action,  668  ;  forma- 
tion of  fresh  acid,  668 ;  time  occupied  by  each  transfer  of 
oxygen,  670 ;  proportion  of  Glover-tower  space  to  chamber- 
space  with  reference  to  the  formation  of  acid,  671 ;  proposal  for 


XX  CONTENTS. 

Page 

pushing  the  work  in  the  Glover  tower  heyond  the  usual  rate, 
672  ;  drawbacks  of  the  Glover  tower,  673  ;  impure  acid,  673. 
Denitration  bj  other  means,  674. 

CHAPTER  VII. 
The  Chambek-Procbss     675 

Starting  the  chambers,  675  :  use  of  acid  for  luting  the  chambers,  675 ; 
introduction  of  nitre  and  steam,  676 ;  stopping  chambers  for 
repairs,  677. 
Supply  of  air,  677 :  objects,  677 ;  indications  of  draught,  678 ; 
percentage  of  oxygen  in  exit-gases,  679 ;  action  of  excessive 
draught,  680 ;  of  insufficient  draught,  681 ;  regulation  of  draught, 
681 ;  increasing  draught  from  Glover  tower  by  a  gas-siphon, 
682 ;  admitting  air  behind  burners,  682 ;  influence  of  atmo- 
spheric conditions  on  draught,  683;  quantitative  data  on 
draught,  683 ;  influence  of  difierence  of  level,  684 ;  uselessness 
of  mathematical  formulae,  686. 

Supply  of  water  (steam),  686 :  regulation,  686 ;  streugth  of 
chamber-acids  and  drips,  687 ;  effects  of  a  wrong  supply  of 
water,  693.  Supply  of  nitre,  695  :  colour  of  chambers,  698 ; 
testing  chamber-acids  for  nitre,  699 ;  effects  of  too  much  or  too 
little  nitre,  701 ;  modified  processes  for  introducing  nitre,  703 ; 
total  quantity  of  nitre  circulating  in  chambers,  704.  Irregular 
ivorking,  loss  of  nitre,  705 :  formation  of  nitrous  oxide,  707 ; 
mechanical  losses,  707. 

Tem2)erature,  710 :  at  various  works,  711 ;  observations,  713  ;  by 
Lunge  and  Naef,  714  ;  by  Sorel,  720  ;  abnormal  cases,  720. 

DepHi  of  acid,  721 :  general  remarks,  722. 

DistribtUion  of  gases  and  rate  of  formation  in  the  various  parts  of  the 
vitriol-chambers,  722  :  views  of  H.  A.  Smith,  723 ;  observations 
made  on  acid-trays  by  Mactear,  723 ;  by  Naef,  724  ;  by  Mactear 
on  rate  of  formation  of  acid,  725  :  by  Lunge  &  Naef  at  Uetikon, 
727  ;  absence  of  "  free  "  nitrogen  peroxide  in  normally  working 
chambers,  727 ;  appearance  of  free  nitrogen  peroxide  in  the 
presence  of  an  excess  of  nitre,  729  ;  their  observations  on  the 
distribution  of  gases  and  the  progress  of  the  process  in  the 
chambers,  730  ;  observations  on  the  revival  of  the  process  when 
the  gases  pass  into  the  next  chamber,  731 ;  on  the  mixture  of 


CONTENTS.  XXI 

Page 
the  gases,  732 ;  Abraham's  ideas  as  to  the  path  which  the  gases 
take  within  the  chambers,  734. 

Carbon  dioxide  in  chamber-gases,  735. 

Duration  of  passage  through  the  chambers,  735. 

Testing  the  ehamber-exitSj  736 :  low-level  escapes,  736 ;  high-level 
escapes,  736 ;  limits  imposed  by  Alkali  Act,  736 ;  continuous 
testing,  737  ;  Mactear's  plan,  737  ;  simpler  plans,  73S  ;  Strype's 
apparatus,  739 ;  prescriptions  of  British  Alkali  Makers'  Asso- 
ciation, 743  ;  improvement  by  Carpenter  &  Linder,  746  ; 
shape  of  absorbing-vessels,  740 ;  estimation  of  nitric  oxide, 
748 ;  estimating  sulphur  burnt  from  oxygen  in  exit-gases,  749. 

Theory  of  the  formation  of  sulphuric  acid  in  the  lead-chambers,  750  : 
views  of  Clement  &  Desormes,  750  ;  of  Davy,  751 ;  of  Gmelin, 
752 ;  of  Berzelius,  752 ;  of .  Feligot,  753 ;  of  Weber,  754  ;  of 
Winkler,  757 ;  Lunge's  former  views,  758 ;  Lunge  &  Naefs 
investigations,  759 ;  Raschig's  theory,  761 ;  Lunge's  new  theory, 
762 ;  SoreFs  views,  769 ;  influence  of  change  of  temperature, 
771 ;  the  chamber-process  considered  as  a  catalytic  one,  773  ; 
attempts  at  establishing  theories  on  the  action  of  masses, 
774;  laws  of  chemical  dynamics,  775;  velocity  of  reactions, 
777 ;  impossibility  of  subjecting  the  chamber-process  to  mathe- 
matical treatment,  779. 


CHAPTER  YIII. 
The  PrBiFiCATioN  of  Sulphuric  Acid    780 

Impurities  found  in  chamber-acid,  780;  injurious  action  of  these, 
781 ;  methods  of  purification,  781 ;  clarifying  muddy  acid,  782. 

Purification  of  Sulphuric  Acid  from  Arsefiiic,  782 :  arsenic  in  brim- 
stone-acid, 782 ;  arsenic  in  pyrites,  782 ;  arsenic  in  pyrites- 
acid,  783 ;  cases  where  the  arsenic  does  no  harm,  784 ;  cases 
where  arsenic  is  not  allowable,  785  ;  acids  absolutely  free  from 
arsenic,  785. 

Removal  of  arsenic  by  distillation,  786 ;  as  arsenic  trichloride,  787  ; 
precipitation  of  arsenic  as  sulphide,  788  ;  by  barium  sulphide, 
788 ;  by  other  sulphides,  789 ;  by  thiosulphates,  789  ;  by 
gaseous  hydrogen  sulphide,  790 ;  Freiberg  process,  790  (genera- 
tion of  sulphuretted  hydrogen,  792  ;  precipitation  of  the  arsenic 
in  the  tower,  793 ;  tests,  793 ;  filtering  and  washing  of  the 


XXll  CONTENTS. 

Page 
arsenic  sulphide,  796) ;  other  methods,  799 ;  evolution  of  sulphu- 
retted hydrogen  in  other  ways,  800 ;  damage  caused  hy  going 
too  far  in  that  treatment,  801 ;  cost  of  treatment,  801 ;  effect 
of  treatment,  801 ;  acid  for  storage-batteries,  802. 

Purification  fro^n  Nitrogen  Compounds^  802:  by  sulphur  dioxide, 
802 ;  by  brimstone,  803 ;  by  organic  substances,  803 ;  by 
ammonium  sulphate,  803. 

Purification  hy  special  methods.  Electrolysis,  ^c,  804. 

Coloured  Add^  805 :  removal  of  selenium,  806, 

Chemically-pure  Sulphuric  Add,  806 :  distillation,  807. 

CHAPTER  IX. 
The  Concentration  of  Sulphuric  Acid 810 

Necessity  for  concentration,  810 ;  action  taking  place  during  boiling- 
down,  810;  material  of  concentrating-vessels,  811;  lead  pans,  811. 

1.  Lead  pans  heaied  from  the  fo/>,  812 :  construction,  813;  Hasen- 

clever  pans,  816  ;  pans  fired  by  producer-gas,  817. 

2.  Lead  pans  with  bottom  heat,  817  :  way  of  firing  the  pans,  819 ; 

drawings  of  pans,  820 ;  various  systems,  822. 

3.  Lead  pans  fired  hy  waste  heat,  823 :  on  pyrit-es-burners,  823 ; 

drawings  of  such,  824 ;  objections,  827 ;  pans  on  brimstone- 
burners,  828. 

4.  Concenirathig-pans  heated  hy  steam,  828  :  Duisburg  pans,  828  ; 

precautions,  829 ;  multitubular  pans,  831 ;  remarks  on  steam- 
pans,  832. 

5.  Concentration  to  144°  Tw.  in  platinum  vessels,  833. 

The  last  co^icentration  of  Sulphuric  Acid,  834 :  various  plans,  834 ; 

reasons  for  higher  concentration,  835. 
Manufacture  of  ordinary  Rectified  Oil  of  Vitriol,  836 :  first  use  ot 

glass  retorts,  836 ;  of  platinum  vessels,  837  ;  present  state,  838. 
Concentration  in  glass  retorts,  838;   ordinary  English   plan,  838; 

improvements,  842 ;  Gridley-Chance  system,  844 ;  similar  plans, 

846 ;  cost  of  concentrating  in  glass,  847. 
Concentration  in  porcelain  dishes  or  heahers,  848;  Negrier's  apparatus, 

848 ;  Benker's  apparatus,  850  ;  Webb's  beaker-apparatus,  851 ; 

similar  apparatus,  854  ;  various  other  apparatus,  855. 
Conctntration  in  platinum  stills,  856 :  older  stills,  856 ;  Prentice's 

stills,   856  ;    Delplace's  stills,  858  ;    Desmoutis'    stills,    863 ; 

firing  platinum  stills,  865 ;  by  Liegel's  gas-producers,  ^6iy. 


CONTENTS.  XX41I 

Page 
CombinadoD  of  platinum  dishes  with  lead  hoods  (Faure  &  Kessler's 

system),  866. 
Other  forms  of  platinum  stills,  875, 
Loss  of  platinum  in  the  concentration  of  sulphuric  acid,  875 ;  prices 

of  platinum  stills,  876. 
Gold-lined  platinum  stills,  877. 
Crusts  formed  in  platinum  stills,  879 ;  explosion  in  clearing  out  a 

stiU,  881. 
Concentration  in  iron,  881 :  suitable  strength  of  acid,  881  ;  various 

shapes  of  pans  or  retorts,  882 ;  pans  used  by  Quinan  at  Pinole, 

884 ;  combination  of  cast-iron  pans  and  platinum  covers,  888 ; 

Clayton  Aniline  Company's  pan,  889  ;  Krell's  apparatus,  891  ; 

other  plans,  892. 
Concentration  in  wrought-iron,  896. 
Action  of  sulphuric  acid  on  cast-iron,  896. 
Recovery  of  strong  Sulphuric  Add  from  waste   acids   (acid-tar, 

sludge-acid),  896. 
Cast-iron  pans  protected  hy  enamel  or  otherwise,  899. 
Concentration  of  Sidphuric  Acid  hy  hot  gases,  901 :  apparatus  of 

Gossage,  901 ;  various,  902 ;  Kessler^s  furnace,  903 ;  Kessler's 

new  apparatus,  908  ;  Zanner's  pans,  909 ;  apparatus  of  Quinan, 

912. 
Concentration  in  vacuum-retorts,  913 :  apparatus  of  de  Hemptinne, 

913;  of  Krell,  914 ;  German  form,  914  ;  various  apparatus,  915  ; 

vacuum-retorts  for  acid-tar,  916, 
Concentration  hy  electricity,  916. 
General  remarks,  917. 

Monchydrated  Sulphuric  Acid,  917  :  Lunge's  process,  918. 
Packages  for  Sidphuric   Acid^    920  :    carboys,    920  ;    filling    and 

emptying  carboys,  922  ;  tank-waggons,  925  ;  acid-boats,  926  ; 

sea-transport  of  acid,  927. 

CHAPTER  X. 

ARBAM6EME5T   OP   A   SXTLPHITRIC-ACID  WoBKS    ON  THE  CuiJiBEB  PlAN  ; 

Yields  and  Costs     928 

General  remarks,  928  ;  arrangement  of  chamber-plant,  029  ;  designs 
of  modern  chamber-plant,  931 ;  estimate  of  cost  for  same,  933  ; 
designs  for  a  combination  of  chambers  and  towers,  934 ;  cost  of 
chamber-plant  in  France,  935. 


XXIV  CONTENTS. 

Page 

Yields  and  costs,  936  ;  terms  for  expressing  the  consumption  of  nitre 
and  the  yield  of  acid,  937  ;  (i)  consumption  of  nitre,  938 ; 
(ii)  yield  of  sulphuric  acid,  940 ;  consumption  of  coals,  942 ; 
results  at  French  factories,  942  ;  at  Hamburg,  944. 

Cause  of  losses  in  the  manufacture  of  sulphuric  acid,  945. 

Statements  of  costs  for  the  manufacture  of  sulphuric  acid:  (1)  from 
brimstone,  946 ;  (2)  from  pyrites  in  England,  947 ;  in  France, 
948 ;  in  Germany,  949  ;  statements  by  l^iedenfiihr  and  Luty  for 
the  old  system,  950;  for  a  combination  of  chambers  and  towers, 
952;  for  the  contact-process,  953  ;  for  concentrated  acid,  953; 
comparison  of  both  processes,  955  ;  cost  in  America,  956. 


CHAPTER  XI. 

The  Manufactdee  op  Norbhausen  or  Fuming  Oil  of  Vitriol  and 

OF  Sulphuric  Anhydride    959 

Introduction,  959 :  the  manufacture  of  fuming  oil  of  vitriol  in 
Bohemia,  960. 

The  production  of  sulphuric  anhydride  and  fuming  of  vitriol  from 
artificially-prepared  sulphates,  965 ;  from  ferric  sulphate,  965  : 
by  the  vacuum  process,  966 ;  from  acid-tar,  967  ;  from  ferrous 
sulphate,  968 ;  from  magnesium  sulphate,  968 ;  from  sodium 
pyrosulphate,  968. 

Utilization  of  SO^,  contained  in  pyrites-kiln  gases,  971 ;  dehydration 
of  sulphuric  acid  by  metaphosphoric  acid,  971 ;  SOg  from 
chamber-crystals,  972  ;  SO,  by  electricity,  972. 

The  manufacture  of  sulphuric  anhydride  (also  of  fuming  and  ordinar}- 
sulphuric  acid)  by  "  contact  '^-processes,  973  ;  historical,  973  ; 
first  observations  on  contact-reactions,  974  ;  generalization  of 
Berzelius,  974  ;  discovery  of  the  synthesis  of  SO^  by  platinum  by 
Peregrine  Phillips,  975  ;  following  investigations,  975 ;  Schnei- 
der's process,  976 ;  processes  of  Jullion,  Petrie,  Piria,  Laming, 
977  ;  Blondeau,  Woehler  &  Mahla,  978 ;  Robb,  Trueman, 
Schmersahl  &  Bouck,  979  ;  employment  of  silica  by  Petrie  and 
Hunt,  979 ;  experiments  made  by  Plattner  and  Reich,  980 : 
process  of  Deacon,  980  ;  common  shortcomings  of  former  in- 
ventors, 981 ;  demand  springing  up  for  fuming  acid,  982. 

New  epoch  inaugurated  by  Winkler's  paper  in  1875,  983 ;  Squire 
&  Messel's  process,  983 ;  Winkler's  paper,  984 ;  efifects  of  it, 
985 ;  manufacture  of  fuming  acid  by  Jacob,  988 ;  at  Thann, 


CONTENTS.  XXV 

Pago 
989  ;  in  Germany,  by  Winkler's  process,  990 ;  modifications 

of  this,  991 ;  process  of  Schroeder  &  Haenisch  with  pure 
sulphur  dioxide,  993 ;  processes  employing  pure  oxygen,  994 ; 
employment  of  burner-gases,  994. 
Theory  of  the  contact-processes  for  the  manufacture  of  sulphuric 
anhydride,  996 ;  views  of  Berzelius,  Liebig,  996 ;  Bunsen, 
Ostwald,  997;  modem  views  on  catalyzers,  998;  views  of 
Sackur,  999 ;  Kassell  &  Smith,  1000  ;  experiments  and  views 
of  Knietsch,  1001 ;  of  Brode,  1007 ;  paper  by  Lunge  &  Pollitt, 
1008 ;  maximum  yield  theoretically  obtainable,  1009  ;  vapour- 
tensions  of  sulphates  in  contact-processes,  1011. 

Present   state  of   the  Manufacture  of  Sulphuric  Anhydride   and 

Sulphuric  Acid  by  the  Contact-process 1011 

I.  The  process  of  the  Badische  Anilin-  und  Sodafabrik  at  Lud- 
wigshafen,  1012;    statements  of  Knietsch  and  of  the  patent 
specifications,  1012 ;  contribution  by  the  firm,  1026. 
II.  Process  of  the  Farbwerke,  vorm.  Meister,  Lucius,  &  Briining,  at 

Hochst,  1039. 
HI.  The  Schroeder-Grillo  process,  1057. 

IV.  The  process  of  the  Mannheimer  Verein,  1067. 
V.  The  Freiberg  process,  1073. 

VI.  Babe's  process,  1078. 

Recent  proposods  for  impt^oving  the  Manufacture  of  Sulphuric  Acid 

by  the  Contact-process    •   10S2 

A.  Purification  of  the  gases,  1082.  B.  Contact^apparatus,  1083. 
C.  Absorbing-apparatus,  1085.  D.  Contact-substances,  1086. 
E.  Manufacture  of  8O3  from  by-products,  1091. 

CHAPTER  XIL 

Other  Pbocssses  fob  Manufactukinq  Sulphuric  Acid 1092 

I.  Oxidation  of  sulphurous  acid  by  means  of  nitrous  acid,  but 

without  lead-chambers,  1092. 
II.  Processes  dispensing  with  nitre,  1096. 

III.  Sulphuric  Acid  from  sulphates,  1097 ;  from  calcium  sulphate, 
1097 ;  production  of  SO^  from  gypsum,  1098  ;  sulphuric  acid 
direct  from  gyjwum,  1099. 

IV.  Calcining  pyrites  with  salt,  1100. 

V.  By  electricity,  1100. 

VOL,  I.  c 


XXVI  CONTENTS. 


CHAPTER  XIII. 

Page 
Br-rB0DucT8  of  the  Manufactctbe  of  Sulphubic  Acid   1102 

Utilization  of  cinders  from  non-cupreous  pyrites  as  ballast,  1102  ; 
for  absorbing  H,8,  1102;  for  absorbing  HCl,  1103;  for 
manufacturing  iron  compounds,  1103.  Manufacture  of  iron 
from  pyrites-cinders,  1104. 

Recovery  of  mw?  from  pyrites-cinders,  1107. 

Recovery  of  ihallium^  1110  ;  oi  selenium,  1113. 

The  extraction  of  copper  from  pyrites-cinderSy  1116  :  general,  1115; 
lirst  attempts,  1117 ;  recent  process,  1117 ;  composition  of 
cinders,  1118  ;  grinding,  1121  ;  calcining-fumacesy  1121  ; 
reverberatory  furnaces,  112L;  blind  roasters  (muffles),  1126; 
mechanical  furnaces,  1129  ;  mode  of  operating  the  calcination, 
1133;  tests,  1138;  condensation  of  the  calcination -gas, 
1138.  Lixiviation  of  the  calcined  mixture,  1139;  residue 
(purple  ox%  blue  billy),  1141;  extraction  of  lead,  1142; 
copper-liquors,  1143;  process  at  Oker,  1144,  Precipitation 
of  the  copper  from  the  liquors,  1146;  Gibb's  H^S  process, 
1146;  use  of  scrap-iron,  1147;  use  of  spongy  iron,  1148; 
furnace  for  making  spongy  iron,  1148 ;  operating  it,  1151 ; 
composition  of  spongy  iron,  1153;  composition  of  coppcr- 
prccipitate,  1154;  furnaces  for  smelting  it,  1156;  pure 
copper,  1157.  Extraction  of  tJie  sHver  contained  in  burnt 
p}'rites,  1158;  Claudet*s  process,  1158;  other  processes, 
1160.  Waste-liquors  from  the  copper  extraction^  1162. 
Working-results,  1165. 

Other  copper-extracting  processes,  1165.     Treatment  of  very  poor 
cupreous  cinders,  1167.    General,  1168. 


CHAPTER  XIV. 

Afplicatioks  of  Sulphubic  Acid  and  Statistics     1169 

Principal  applications,  1169. 

Statistics  for  the  United  Kingdom,  1170 ;  Germany,  1172  ;  France, 

Austria,  Belgium,  Italy,  1174;  Russia^  United  States,  1175; 

Japan,  1177. 


CONTENTS.  XXVll 


ADDENDA. 

Brimstone  as  raw  material  for  sulphuric-acid  making,  Boiling- 
point  of  sulphur.  Exportation  of  sulphur  from  Sicily,  1178. 
Sulphur  in  Transylvania,  Greece,  Japan,  North  America,  1179. 
Sulphur  from  sulphides,  1179.  World's  production  of  sulphur, 
1180.  Analysis  of  crude  sulphur.  Detection  of  arsenic  and 
selenium,  1180.  Grinding  and  sifting  sulphur,  Examination 
of  sulphur  for  fineness,  &c.,  1181. 

Pyrites  in  Germany,  Austria,  1181 ;  in  America,  1182.  Leached 
ores  from  Spain,  1182.  World's  production  of  iron-pyrites, 
1182.    Estimation  of  carhon  in  pyrites,  1183. 

Snlphuric  acid  from  hydrogen  sulphide,  1183. 

Nitrate  of  soda  in  California,  1183.    Statistics,  1183. 

Hydrates  of  nitric  acid,  1183;  nitric-acid  retorts,  1183;  con- 
densation of  nitric  acid,  1184  ;  clear  concentrated  nitric  acid, 
1185;  utilization  of  nitre-cake,  1185,  1186;  recovery  of 
nitric  acid  from  waste  acids,  1186;  production  of  nitric  acid 
from  atmospheric  air,  1186  ;  from  ammonia,  1187* 

Scsquioxide  of  sulphur,  1187. 

Acid-smoke,  1187. 

Specific  gravities  of  sulphuric  acid,  1187;  influence  of  impurities 
on  specific  gravity,  1188  ;  action  of  sulphuric  acid  on  platinum, 
1188  ;  analysis  of  fuming  sulphuric  acid,  1188 ;  detection  and 
ostimation  of  arseuic  in  sulphuric  acid,  1189. 

Herreshoflf  furnaces,  1192. 

Mechanical  furnaces  for  hlende,  1193. 

Cooling  the  gases  in  chamhers,  1193. 

Keaction-towers,  1193 ;  pipe-towers,  1193. 

Mechanical  calculation  of  the  weight  of  acid  in  the  chamhers,  1193. 

lutrodttction  of  water  as  spray,  1194. 

Fan-blasts  for  producing  draught  in  chambers,  1194. 

Measurement  of  the  velocity  of  a  current  of  gas,  1194. 

Path  which  the  gases  travel  in  the  chambers,  1194. 


Page 


IHDEX 1195 


FIRST    BOOK. 


STJLFHUBIC    ACID. 


VOL.  1.  » 


INTRODUCTION; 


Formerly  the  term  ^^ alkali  manufacture'^  nearly  always  com- 
prised a  cycle  of  operations^  beginning  with  the  manufacture  of 
sulphnric  acid  and  proceeding  to  that  of  sulphate  of  soda  (salt- 
cake),  hydrochloric  acid,  soda-ash  (with  caustic  soda,  soda- 
crystals,  fee),  and  bleaching-powder.  This  cycle  is  not  completed 
in  all  factories,  but  frequently  (at  the  present  day  even  more  so 
than  formerly)  the  operation  stops  at  sulphuric  acid  or  sulphate 
of  soda ;  but  we  may  embrace  all  this  under  the  general  term  of 
"  Sulphuric  Acid  and  Alkali  Manufacture/' 

In  this  wider  meaning  the  products  of  alkali-making  are 
necessary  materials  for  many  metallurgical  processes,  for  the 
manufacture  of  artificial  manures,  soap,  fatty  and  mineral  oils^ 
glass,  paper,  many  inorganic  and  organic  colouring-matters 
(especially  nearly  all  coal-tar  dyes),  and  even  of  many  articles  of 
food, — that  is  to  say,  for  nearly  all  branches  of  manufacturing 
chemistry.  In  fact,  among  all  branches  of  chemical  industry 
the  cycle  of  technical  operations  connected  with  alkali-making  is 
preeminent,  not  merely  from  the  magnitude  of  the  works  and  the 
absolute  bulk  of  the  raw  material  used  and  the  quantity  produced, 
but  also  from  the  fact  that  most  other  chemical  products  require 
one  or  more  branches  of  alkali-making  as  the  conditions  of  their 
own  existence.  It  can  be  truly  said  that  the  manufacture  of 
acids  and  alkali  is  the  foundation  upon  which  the  whole  chemical 
industry  of  our  times  is  built  up,  and  that  such  industry  cannot 

b2 


INTRODUCTION. 


be  much  developed  in  any  country  not  possessing  a  flourishing 
alkali  trade^  or  not  being  at  least  specially  well  situated  for  buying 
the  produce  of  the  latter.  It  is  thus  evident  how  great  is  the 
importance  of  the  alkali  trade  in  its  wider  meaning  to  the 
civilization  of  mankind^  though  we  should  certainly  be  going  too 
far  if  we  measured^  as  some  have  done^  the  civilization  of  a 
country  by  the  development  of  this  special  industry. 

Formerly  the  whole  cycle  of  processes  here  described  was 
intimately  connected  with  the  great  invention  of  Leblanc,  now 
rather  more  than  a  century  old.  Twenty  years  ago,  although  the 
ammonia-soda  process  had  then  already  more  than  proved  its  right 
to  be  considered  a  full  success,  it  had  not  yet  shaken  in  any  tangible 
degree  the  supremacy  of  the  Leblanc  process,  at  least  not  in  Great 
Britain.  In  the  latter  process  the  different  branches  of  '^  alkali- 
making  ^'  mentioned  above  are  connected  in  such  a  manner  that 
only  under  special  local  conditions  can  one  or  more  of  the 
principal  substances  be  omitted.  Formerly  this  was  the  case  even 
less  than  now,  as  the  competition  of  ammonia-soda  ash  has 
completely  altered  some  of  the  conditions  of  trade,  making  it 
unremunerative  in  many  cases  to  convert  the  sulphate  of  soda 
into  the  carbonate.  Thus  there  exist  now  many  works  stopping 
at  the  manufacture  of  sulphuric  acid,  and  others  which  go  as  far 
as  sulphate  of  soda,  tpgether  with  chlorine  products ;  but  very 
many  proceed  still  further,  going  on  to  the  manufacture  of  soda  in 
its  various  branches. 

The  manufacture  of  sulphuric  acid  is  in  reality  a  very  large 
industry,  quite  apart  from  its  connection  with  the  Leblanc 
process.  Enormous  quantities  of  it  are  required  for  the  manu- 
facture of  artificial  manures*  (fertilizers),  and  therefore  every 
large  manure  factory  makes  its  own  sulphuric  acid.  This  is  done 
also  by  the  largest  sulphate-of-ammonia  works,  petroleum  refiners 
coal-tar  dye  manufacturers,  and  in  a  few  other  cases.  Some  works 
in  England,  aud  many  on  the  Continent,  make  sulphuric  acid  to 
a  great  extent,  or  even  entirely,  not  for  their  own  use,  but  for 
sale.     Since  this  acid  is  no  longer  sent  out  in  any  considerable 


INTRODUCTION.  5 

quaBtity  in  glass  carboys,  but  in  iron  tank -waggons,  it  can  be 
carried  to  considerable  distances  at  moderate  cost. 

As  sulphuric  acid  is  mostly  made  from  pyrites,  its  manufacture 
is  intimately  connected  with  the  recovery  of  copper  from  the 
cinders,  in  which  process  iron  oxide,  silver,  and  other  by-products 
are  obtained. 

A  very  large  (formerly  even  the  largest)  quantity  of  sulphuric 
acid  is  used  up  at  the  works  themselves  for  the  manufacture  of 
stdphaie  of  soda  {salt-cake)  and  sulphate  of  potash,  in  which  hydro^ 
chloric  add  is  a  necessary  by-product.  Sometimes  salt-cake  is 
obtained  without  previously  manufacturing  siQphuric  acid,  as  a 
by-product  of  other  manufactures  or  by  the  ''  direct  process  '*  of 
Hargreaves  and  Robinson.  There  is  only  one  use  of  salt-cake 
on  a  large  scale,  except  for  alkali-making,  namely,  for  the  manu- 
facture of  glass ;  but  a  much  larger  quantity  of  salt-cake  still 
enters  into  the  Leblanc  process  for  manufacturing  soda.  This 
article  is  mostly  the  final  product,  either  in  the  calcined  or 
crystallized  or  caustic  state^  and  the  series  of  operations  is  thus 
brought  to  a  close  in  this  direction. 

Hydrochloric  acid  {muriatic  add)  is,  of  course,  sold  as  such  to 
some  extent,  but  in  nothing  like  such  large  quantities  as  sulphuric 
acid,  as  its  carriage  is  impossible  in  metallic  vessels^  and  there- 
fore more  expensive  and  troublesome.  Most  of  it  is  at  once, 
sometimes  even  without  condensation  to  liquid  acid,  converted 
into  chlorine,  which,  being  a  gas,  is  immediately  worked  up  into 
bleaching-powder  or  chlorate  of  potash,  or  occasionally  into  other 
products ;  a  comparatively  small  quantity  of  it  is  sold  in  the  state 
of  liquid  chlorine.  The  time  when  the  hydrochloric  acid  was 
condensed  merely  to  satisfy  the  exigencies  of  laws  made  for 
protecting  the  health  and  vegetation  of  a  neighbourhood,  and  was 
then  run  to  waste  into  the  Acarest  watercourse,  is  now  past,  since 
the  process  of  decomposing  salt  by  sulphuric  acid  is  only  profitable 
if  the  hydrochloric  acid  is  fully  utilized  :  this  acid  has  thus  risen 
from  the  rank  of  a  by-product  to  that  of  the  best-paying  principal 
product. 


6  .INTRODUCTION. 

Once  more  the  conditions  of  the  Leblanc  process  were  changed 
by  the  solution  of  the  problem  of  the  recovery  of  sulphur  from  the 
alkali  waste^  and  it  has  now  been  made  into  a  real  cycle,  into  which 
common  salt  and  coal  enter  at  one  end,  alkali  and  chlorine  issuing 
at  the  other,  whilst  sulphur  and  possibly  even  lime  are  made  to  do 
service  over  and  over  again.  This,  however,  appears  most  clearly 
in  Vols.  II.  &  III.  of  this  Treatise ;  to  which  we  also  refer  for  such 
general  observations  as  the  ammonia  process  of  soda  manufacture 
calls  for. 


HISTORY  OF  SULPHURIC  ACID. 


CHAPTER  I. 

HISTOKICAL^AND  GENERAL  NOTES  ON  THE  MANUFACTURE 

OF  SULPHURIC  ACID. 

History  of  the  Manufacture  of  Sulphuric  Add. 

According  to  Rod  well  (^  Birth  of  Chemistry^)  it  is  very  probable 
that  sulphuric  acid  was  already  known  to  the  ancients ;  but  usually 
its  firsts  although  indistinct^  mention  is  ascribed  to  the  Arab 
Geber,  who  speaks  of  the  '^  spirit  ^'  which  can  be  expelled  from 
alum  and  which  possesses  solvent  powers.  Geber  is,  however,  a 
mythical  personage,  and  many  of  his  alleged  numerous  discoveries 
have  wrongfully  crept  into  the  Latin  "  translations  '^  of  his  pre- 
tended writings,  as  proved  by  Berthelot  and  Steinschneider  (comp. 
Lippmann,  Zsch.  angew.  Chem.  1901,  p.  646),  who  show  that 
sulphuric  acid  was  unknown  to  Arabian  writers  about  975  a.d. 
Others  give  the  honour  of  its  discovery  to  the  Persian  alchemist 
Abu-Bekr-Alrhases,  who  is  said  to  have  died  in  9iO.  Vincentius 
de  Beauvais  (about  1250)  alludes  to  it;  and  Albertus  Magnus 
(1193-1280)  speaks  of  a  spiritus  vitrioli  Romani,  which  can  only 
have  been  sulphuric  acid ;  his  '^  sulphur  philosophorum  '^  is  the 
same  thing. 

With  all  distinctness  Basilius  Valentinus,  in  his  ^  Revelation  of 
the  Hidden  Manipulations/  describes  its  preparation  from  cal- 
cined  copperas  and  silica,  and,  in  his  '  Triumphal  Car  of  Antimony/ 
also  its  preparation  by  burning  sulphur  with  saltpetre  (Kopp, 
'  Geschichte  der  Chemie,^  iii.  p.  303) ;  but  he  took  the  two  to  be 
different  substances. 

Gerhard  Domaeus  (1570)  described  its  properties  accurately; 
Libavius  (1595)  recognized  the  identity  of  the  acids  from  different 
processes  of  preparation ;  the  same  was  done  by  Angelus  Sala 
(1613),  who  pointed  out  the  fact,  which  had  sunk  into  oblivion 
since  Basilius,  that  sulphuric  acid  can  be  obtained  by  burning 
sulphur  in  moist  vessels  (of  course  with  access  of  air) ;  after  that 


8  HISTORICAL  AND  GENERAL  NOTES. 

time  it  was  prepared  by  the  apothecaries  in  this  way.  An 
essential  improvement,  ^iz.  the  addition  of  a  little  saltpetre,  was 
introduced  in  1666  by  Nicolas  le  Fevre  and  Nicolas  Lemeiy. 
This  caused  a  sort  of  manufacture  of  vitriol  which  is  said  to  have 
been  introduced  into  England  by  Cornelius  Drebbel :  this  only  is 
certain — that  a  quack  doctor  of  the  name  of  Ward  first  carried 
on  sulphuric-acid  making  on  a  large  scale  at  Richmond  near 
London,  probably  a  little  before  1740.  Ward  employed  large 
glass  vessels  up  to  66  gallons  capacity,  which  stood  in  two  rows 
in  a  sand-bath,  and  which  were  provided  with  horizontally  pro- 
jecting necks ;  at  the  bottom  they  contained  a  little  water.  In 
each  neck  there  was  an  earthenware  pot,  and  on  this  a  small  red- 
hot  iron  dish,  into  which  a  mixture  of  one  part  saltpetre  and  eight 
parts  of  brimstone  were  put ;  then  the  neck  of  the  bottle  was 
closed  with  a  wooden  plug;  on  the  combustion  being  finished, 
fresh  air  was  allowed  to  enter  the  vessel,  and  the  operation  was 
repeated  till  the  acid  had  become  strong  enough  to  pay  for  con- 
centrating in  glass  retorts. 

Ward  called  the  product  '^oil  of  vitriol  made  by  the  bell'' 
(already  Basilius  Valentinus  had  used  the  expression  "percam- 
panam''  in  this  sense),  in  order  to  distinguish  the  spirit  of  vitriol 
made  from  brimstone  from  that  distilled  from  sulphate  of  iron, 
the  latter  having  been  made  on  a  kind  of  manufacturing  scale  in 
England  previously :  an  exact  description  of  this  is  given  by 
J.  C.  Bernhardt  in  his  ^  Chemische  Versuche  und  Erfahrungen,' 
17.55.  Ward's  process,  troublesome  as  it  is,  reduced  the  price 
of  the  acid  from  2*.  6d.  per  ounce  (the  price  of  the  acid  from 
copperas  or  from  burning  brimstone  under  a  moist  glass  jar)  to 
2$.  per  lb. 

An  extremely  important  improvement  in  this  process  was  the 
introduction  of  the  lead  chambei's,  which  by  general  consent  is 
ascribed  to  a  Dr.  Roebuck  of  Birmingham,  who  in  174f6  erected 
such  a  chamber  6  feet  square,  and  in  1749,  in  partnership  with 
Mr.  Garbett,  built  a  factory,  founded  thereon,  at  Prestonpans  in 
Scotland,  in  order  to  supply  acid  for  the  bleaching  of  linen.  The 
mixture  of  brimstone  and  saltpetre  in  the  above  proportion  was 
put  into  small  iron  waggons  which  were  run  into  the  chamber 
on  a  railway  :  the  chamber  was  closed,  and  the  process  carried  on 
intermittently  in  this  way.  Guttmann  (Journ.  Soc.  Chem.  Ind. 
1901,  p.  5)  gives  a  detailed  description  and  some  drawings  of  such 


LEAD  CHAMBERS  IN  ENGLAND.  9 

*'  lead-houses ''  and  their  style  of  working  from  a  manuscript  by  a 
Birmingham  chemist^  W.  E.  Sheffield^  written  between  1771  and 
1 790.  The  cost  of  acid  of  spec.  grav.  1'844  per  ton  was  £22  6*.  4rf. 
without  labour. 

Soon  other  works  followed  at  Bridgenorth^  and  at  Dowles  in 
Worcestershire,  where  the  chambers  were  already  made  10  feet 
square;  in  1772  a  factory  was  erected  in  London  with  71  cylin- 
drical lead  chambers,  each  6  feet  in  diameter  and  6  feet  high. 
In  1797  there  were  already  six  or  eight  works  in  Glasgow  alone. 
According  to  the  statements  given  in  Mactear's  ^  Report  of  the 
Alkali  and  Bleaching-Powdcr  Manufacture  in  the  Glasgow 
District^  (p.  8),  the  acid  at  that  time  cost  the  Glasgow  manu- 
facturers £32  per  ton,  and  was  sold  at  £64:.  At  Radcliffe^  near 
Manchester,  it  cost,  in  1799,  £21  10*.  per  ton,  without  interest 
on  capital.  In  the  latter  place  there  were  six  chambers  12  feet 
long,  12  feet  wide,  and  10  feet  high,  with  roofs  like  those  of 
houses,  and  valves  opened  between  each  operation;  on  their 
bottom  were  8  or  9  inches  of  water ;  every  four  hours  a 
mixture  of  1  lb.  saltpeti*e  and  7  lb.  brimstone  was  burnt  in  each 
chamber  on  iron  shelves,  of  which  each  chamber  contained  four, 
4  inches  distant  one  from  another.  The  shelves  were  made  of 
very  thin  iron,  in  order  to  get  heated  very  quickly,  and  rested 
on  iron  frames,  by  means  of  which  they  could  be  slid  in  and 
out ;  a  quarter  of  an  hour  before  each  operation  the  valves  and 
doors  were  opened  in  ordei*  to  allow  air  to  enter.  Thus,  weekly, 
1386  lb.  of  brimstone  and  198  lb.  of  saltpetre  were  burnt,  yielding 
1800  lb.  of  oil  of  vitriol — that  is,  130  per  cent,  of  the  sulphur  with 
a  consumption  of  14''28  per  cent,  saltpetre  on  the  same.  In  six 
weeks  the  strength  of  the  acid  attained  only  1*250  sp.  gr. ;  it  was 
thus  run  off  and  concentrated  up  to  1*375  sp.  gr.,  in  which  state 
it  was  used  and  sold.  At  Prestonpans,  in  1800,  a  yield  of  only 
111  per  cent,  on  the  sulphur  was  attained,  with  a  consumption  of 
13  per  cent,  saltpetre  on  the  brimstone ;  in  1813  there  were  in 
that  place  108  chambers  of  14  feet  length,  10  feet  height,  and 
4J  feet  width.  In  1805  there  existed  at  Burntisland  a  factory 
with  360  chambers  of  a  capacity  of  19  cubic  feet  each.  11.  Forbes 
Carpenter  and  W.  F.  Reid  also  give  some  interesting  notes  on  the 
early  manufacture  of  sulphuric  acid  (Journ.  Soc.  Chem.  Ind.  1901, 
p.  7).  The  former  mentions  acid-charabers  erected  in  Cornwall 
from  dressed  granite,  with  lead  top  and  bottom. 


10  HISTORICAL  AXD  GENERAL  NOTES. 

Ill  the  meantime  the  first  lead  chamber  in  France  had  been 
erected  at  Rouen  by  Holker  in  1766.  In  177 J*,  in  that  place,  on 
the  advice  of  De  la  FoUie,  an  important  improvement  was  intro- 
duced, viz.  the  introduction  of  steam  into  the  chambers  during 
the  combustion  of  brimstone.  In  1793  Clement  and  Desormes 
showed  that  the  acid- chambers  can  be  fed  by  a  continuous  current 
of  air,  by  which  a  great  deal  of  saltpetre  could  be  saved.  They 
showed  that  the  oxidation  of  sulphurous  acid  takes  place  to  the 
extent  of  nine  tenths  at  the  expense  of  atmospheric  oxygen,  and 
that  the  saltpetre  plays  only  the  part  of  intermediary  between  the 
air  and  the  sulphurous  acid.  By  this  the  modem  theory  of  the 
essence  of  the  sulpliuric-acid-making  process  was  established ;  but 
it  took  a  remarkable  long  time  before  the  difficulties  were  over- 
come which  stood  in  the  way  of  introducing  the  continuous 
system  into  practice.  Usually  the  introduction  of  the  continuous 
burning  of  brimstone  is  ascribed  to  Jean  Holker  (a  grandson  of 
the  first  Holker),  in  1810;  but,  according  to  Mactear,  a  con- 
tinuous system  had  been  introduced  at  St.  RoUox,  at  least 
partially,  already  in  1807 :  steam  was  first  introduced  there  in 
1813  or  1814. 

In  Germanv  the  first  lead  chambers  seem  to  have  been  those 
at  liingkuhl,  near  Cassel.  One  of  the  oldest  chambers  was  that 
erected  by  Dr.  Richard  at  Potschappel  near  Dresden  in  1820;  as 
he  had  no  plumber  at  his  disposal,  he  had  to  solder  the  chamber 
himself  with  soft  solder  and  a  smoothing-iron  (Bode,  in  his  transla- 
tion of  H.  A.  Smith's  ^  Sulphuric  Acid  Manufacture,'  p.  96).  This 
chamber  was  still  charged  intermittently,  100  lb.  of  brimstone 
yielding  only  150  lb.  of  vitriol. 

Lampadius,  in  a  treatise  published  in  1815  *,  speaking  of 
sulphuric  acid  as  then  made  in  England  and  at  Schwemsal  near 
Leipzig,  describes  the  lead  chambers  as  '^  rooms,"  about  25  feet 
square  with  a  stone  floor,  lined  throughout  with  lead,  with  two 
doors  through  which  sulphur  is  introduced  and  burned  on  iron 
dishes,  holding  J  cwt.  of  brimstone,  mixed  with  20  per  cent, 
nitrate  of  potash,  steam  being  introduced  from  a  copper  outside 
the  room.  Through  four  pipes  and  taps,  during  the  later  stages 
of  the  combustion  (which  lasted  three  hours),  a  little  air  was 
admitted.     The  ''  room ''  was  exposed  to  great  strain  through  the 

*  Quoted  by  CI.  Wiukler,  Zsch.  angew.  Chem.  1900,  p.  731.     Some  of  the 
following  statements  are  also  taken  from  this  paper. 


GENERAL  PRINCIPLES.  11 

strong  expansion  and  subsequent  contraction  of  the  atmosphere 
inside.  The  dilute  acid  formed  was  boiled  down  in  glass  retorts 
to  spec.  grav.  1*800. 

The  invention  of  soldering  lead  with  the  same  material  or 
"  burning  ^'  by  means  of  the  hydrogen  blowpipe  is  due  to 
Debaissayns  de  Richemond,  in  1838.  As  late  as  1846  PrechtPs 
'Technical- Encyclopaedia'  (xiv.  p.  246)  mentions  the  chamber- 
sides  as  being  sometimes  covered  with  a  crust  of  chamber- 
crystals,  i  or  1  inch  thick^  which  proves  the  want  of  under- 
standing the  process  at  that  time. 

Kestner,  of  Thann  in  Alsace,  was  the  first  to  collect  the  products 
of  condensation  at  the  chamber-sides  in  order  to  regulate  the 
working  of  the  chambers  thereby.  This  innovation  was  at  once 
considered  of  such  importance  that  Kestner  was  called  to  Glasgow 
in  order  to  introduce  his  plan  into  Tennant's  works. 

In  1827  Gay-Lussac's  condensing-apparatus  for  the  nitre-gas 
escaping  from  the  cjiambers  was  invented  :  at  Chauny  this  appa- 
ratus was  erected  in  1842,  at  Glasgow  in  1844.  But  we  have  now 
come  so  near  the  present  time  that  we  may  conclude  the  historical 
part  of  our  task. 

General  Principles  of  the  Manufacture  of  Sulphuric  Acid. 

Sulphuric  acid  can  be  obtained  on  a  large  scale  in  one  of  two 
ways — viz.,  first,  by  burning  sulphur  or  sulphides  into  sulphur 
dioxide  and  further  oxidizing  the  latter,  or,  secondly,  by  decompos- 
ing natural  or  artificially  prepared  sulphates.  The  latter  process, 
apart  from  several  proposals  so  far  not  carried  out  practically, 
until  quite  recently  served  for  making  fuming  oil  of  vitriol,  which 
will  be  treated  of  hereafter ;  by  far  the  greater  portion  of  sulphuric 
acid  has  always  been  obtained  by  the  former  process,  which  will 
occupy  us  in  the  first  instance.  We  shall,  at  first,  only  describe 
those  apparatus  and  processes  which  actually  serve  for  manufac- 
turing on  a  large  scale ;  and  we  shall  close  by  mentioning  the 
alterations  whicb  have  merely  remained  as  proposals,  as  well  as 
the  processes  founded  on  totally  new  principles. 

By  the  combustion  of  sulphur,  either  free  (as  brimstone,  gas- 
sulphur,  &c.)  or  combined  with  metals  or  with  hydrogen,  sulphur 
'  dioxide  (SO2)  is  always  formed  at  first.  Sulphuretted  hydrogen,  even 
when  mixed  with  as  much  as  70  per  cent,  of  inert  gases  (nitrogen), 
can  be  lighted  like  illuminating-gas  and  continues  burning  without 


12  HISTORICAL  AND  GENERAL  NOTES. 

any  difficulty^  aqueous  vapour  being  formed  at  the  same  time  as 
SO2.  Brimstone  ignites  in  the  air  at  a  temperature  rather  below 
300°  C. ;  and  when  once  it  has  begun  to  bum,  the  heat  generated 
suffices  to  raise  the  whole  of  the  sulphur  to  the  point  of  ignition^ 
provided  that  sufficient  air  be  present.  A  number  of  metallic 
sulphides  behave  similarly :  the  most  important  of  these  for  our 
purpose  is  the  iron  disulphide,  FeSg ;  but  here  special  precautions 
must  be  taken,  so  that  the  whole  mass  may  be  completely  burnt 
(roasted).  In  both  cases,  along  with  sulphur  dioxide^  SO2,  a  little 
trioxide  (sulphuric  anhydride),  SO3,  is  always  formed,  and,  in  the 
presence  of  water  or  steam,  also  sulphuric  acid,  SO4H2,  more  or 
less  diluted  with  water.  Moreover  an  aqueous  solution  of  sulphu- 
rous acid  in  contact  with  air  gradually  changes  into  sulphuric  acid. 
In  both  cases  it  is,  of  course,  the  oxygen  of  the  air  which  converts 
the  SO2  into  SO,?  or  SO4H2 ;  but  this  reaction  at  the  ordinary  or 
only  moderately  elevated  temperature  goes  on  far  too  slowly  to  be 
applicable  for  technical  purposes. 

There  are  two  ways  of  increasing  the  velocity  of  the  oxidation 
of  sulphur  dioxide.  One  of  these^  which  is  principally  applicable 
to  dry  gases  and  therefore  leads  to  the  preparation  of  sulphur 
trioxide  in  the  anhydrous  state,  is  the  employment  of  '^  catalytic  ^^ 
substances.  We  shall  discuss  this  in  Chapter  XI.,  devoted  to  the 
"  Contact  processes" 

The  second  way,  which  is  exclusively  applicable  to  the  produc« 
tion  of  real  sulphuric  acid,  H2SO4,  is  founded  on  the  property  of 
the  acids  of  nitrogen  to  serve  as  carriers  of  oxygen  from  atmo- 
spheric air  upon  sulphur  dioxide  and  water,  the  original  nitrogen 
oxide  being  always  re-formed.  This  process  will  be  explained  in 
detail  when  we  treat  of  the  theory  of  the  formation  of  sulphuric 
acid ;  it  is  called  the  vitriol-chamber  process. 

The  reaction  between  nitrogen  acids  and  sulphur  dioxide  only 
goes  on  in  the  presence  of  water  ;  and  we  must  add  at  once  that, 
in  practice,  much  more  water  is  needed  than  suffices  for  the 
formation  of  SO4H.2  ;  the  sulphuric  acid  formed  is  therefore 
always  dilute,  and  must  be  concentrated  for  most  purposes. 

For  some  purposes  the  acid  must  also  be  deprived  of  certain 
foreign  substances  which  get  into  it  from  the  raw  materials  and 
the  apparatus  ;  and  in  such  cases  the  sulphuric  acid  has  to  be 
purified. 


DIVISION  OF  THE  SVliJECT.  13 

Thus  our  subject  subdivides  itself  into  the  following  headings  : — 

1.  An  examination  of  the  raw  materials  oi  the  sulphuric- acid 
manufacture,  and  an  account  of  the  properties  of  the  oxides  and 
acids  of  sulphur » 

2.  The  generation  of  sulphur  dioxide.  Since  the  processes 
diflfer  very  much,  both  as  to  apparatus  and  the  method  of  pro- 
ceeding, we  have  to  distinguish  between  (a)  sulphur  dioxide 
from  brimstone,  (A)  from  metallic  sulphides,  (c)  from  sulphuretted 
hydrogen. 

3.  The  conversion  of  sulphur  dioxide  into  sulphuric  acid  in  tlic 
so-called  vitriol-chambers. 

4.  The  purification, 

5.  The  concentration  of  sulphuric  acid. 

6.  The  contact  processes, 

7.  The  utilization  of  the  by-products. 


14  RAW  MATERIALS  OF  MANUFACTURE, 


CHAFTER  II- 

THE  RAW  MATERIALS  OF  THE  SULPHURIC-ACID 
MANUFACTURE  (including  NITRIC  ACID). 

1.  Natural  Sulphur  (Brimstone). 

Brimstone,  owing  to  its  being  found  in  nature  in  the  free  state, 
has  been  known  to  mankind  since  very  ancient  times.  It  is  hardly 
necessary  to  point  to  its  being  noticed  in  the  Bible ;  it  is  also  men- 
tioned several  times  in  the  Homeric  poems.  The  Romans  evidently 
obtained  it  in  the  same  way  as  is  done  now,  by  melting  it  out  of 
its  mixture  with  marl,  &c.  The  ancients  employed  it  principally 
for  fumigating  purposes,  both  on  account  of  its  disinfecting  pro- 
perties and  as  a  religious  rite  (compare  the  well-known  passage 
from  the  Odyssey,  where  Ulysses  purifies  his  house  after  slaying 
the  intruders),  but  also  for  many  of  the  uses  to  which  it  is  put 
at  the  present  day,  as  for  cleaning  wine-casks,  for  destroying 
fungus-growths  in  vineyards  and  orchards,  for  plasters  in  skin- 
diseases,  for  lighting  fires  and  preparing  torches,  for  cementing 
glass,  for  bleaching,  for  "  niello  '*  work  on  metals  ■'^. 

In  modern  times  brimstone  has  been  used  for  most  of  the  just- 
mentioned  purposes  and  for  many  others  ;  but  we  are  here  con- 
cerned only  with  its  use  for  the  manufacture  of  sulpliuric  acid. 
Brimstone  is  undoubtedly  the  most  convenient  raw  material  for 
this  manufacture,  and  for  a  long  tiibe  all  the  sulphuric  acid  of 
commerce  was  made  from  it ;  but  its  use  in  this  respect  has  been 
almost  entirely  abandoned  in  most  localities,  and  is  not  likely  to 
be  revived,  since  iron-pyrites,  and  more  especially  that  containing  a 
few  per  cent,  of  copper,  supplies  sulphur  for  the  above  purpose  far 
more  cheaply  than  natural  brimstone  ever  can  do.  In  spite  of  this» 
brimstone  is  still  a  principal  raw  material  for  the  manufacture  of 
sulphuric  acid  in  America  (where,  however,  it  has  lost  its  former 

*  I  owe  these  historical  notes  to  a  treatise  by  Professor  Blumner,  of  Zurich 
in  the  *  Festschrift  zur  Begriissiing  der  Philologen-Versammlung '  ^Ziltich,  1887), 
p.  23  et  seq. 


PROPERTIES  OP  SULPHUR.  15 

exclusive  sway),  and  it  is  also  used  to  some  considerable  extent  in 
England  for  that  purpose,  but  very  little  indeed  in  other  European 
countries. 

A  somewhat  considerable  quantity  of  brimstone  is  also  consumed 
in  the  manufacture  of  sulphurous  acid^  principally  in  order  to 
prepare  bisulphate  of  lime  for  the  manufacture  of  wood-pulp. 

Sulphur  is  an  element  whose  atomic  weight  is  now  assumed  to 
be  32'06  (oxygen  =  16).  It  is  very  brittle  ;  its  hardness  is  from 
1*5  to  2'5  of  the  ordinary  mineralogical  scale  ;  its  specific  gravity 
is  2'07.  As  usually  occurring,  it  is  semi-transparent  at  the  edges 
and  of  the  well-known  bright  yellow  colour,  which  darkens  with 
an  increase  of  temperature  ;  at  —50°  it  is  nearly  devoid  of  colour. 
Its  taste  and  smell  are  very  slight.  It  does  not  conduct  electricity, 
but  itself  becomes  electric  by  friction  ;  and  it  is  therefore  difficult 
to  powder  finely,  as  it  adheres  to  the  mortar  and  pestle. 

Sulphur  melts  at  lll°-5  C,  and  forms  a  thin,  light-yellow  liquid,, 
which,  on  being  more  strongly  heated,  becomes  darker  and  thicker; 
at  250°  to  260°  C.  it  is  nearly  black,  and  so  viscid  that  it  does 
not  run  out  when  the  vessel  is  upset ;  at  a  still  higher  temperature 
it  becomes  thinner  again,  keeping  its  brown  colour ;  and  at  440°  C. 
it  boils,  forming  a  brownish-red  vapour ;  but  it  begins  to  volatilize 
before  boiling ;  and  its  action  on  silver  seems  to  show  that  it  doea 
so  to  a  slight  extent  even  at  the  ordinary  temperature  (unless  there 
is  formation  of  H^S  in  this  case). 

Sulphur  exists  in  different  allotropic  conditions.  That  occurring 
in  nature  often  appears  in  rhombic  crystals,  mostly  pointed 
rhombic  octahedra,  whose  physical  properties  have  been  described 
above ;  this  a-modification  is  also  obtained  by  crystallizing  sul- 
phur from  its  solution  in  carbon  disulphide.  The  /8-modification 
is  obtained  by  slowly  cooling  melted  sulphur,  and  pouring  off  the 
liquid  portion  when  another  portion  has  crystallized ;  it  consists, 
of  long  thin  oblique  rhombic  prisms,  belonging  to  the  monoclino- 
hedric  system,  of  a  brownish-yellow  colour,  transparent,  spec.  grav. 
1'982  ;  they  gradually  pass  over  into  the  a-modification,  com- 
pletely so  after  a  few  days,  even  at  the  ordinary  temperature — 
suddenly  by  shaking  or  scratching  ;  the  colour  then  becomes 
light  yellow;  and  the  crystals  lose  their  transparency,  but  remain 
as  pseudomorphs  of  the  )3-sulphur.  The  sulphur  in  rolls  consists, 
when  fresh,  of  /8-sulphur — after  a  short  time,  of  a-sulphur. 
When  sulphur  has  been  heated  up  to  the  point  of  viscosity,  and 


16  RAW  MATERIALS  OP  MANUFACTURE. 

is  then  poured  into  very  cold  water,  the  7- modification  is  formed, 
viz.  amorphous,  soft,  tough,  reddish-brown  sulphur,  of  1'957  spec, 
grav.  ;  this  also  is  gradually  converted  into  a-sulphur  ;  but  it  takes 
some  time  before  this  conversion  is  complete.  The  tough  state 
lasts  very  much  longer  if  resinous  substances,  iodine,  &c.  are  mixed 
with  the  sulphur,  even  in  very  small  quantity.  This  modification 
is  partly  contained  in  the  "  flowers  "  of  sulphur. 

Heated  in  the  air  to  250°  C.  *,  sulphur  inflames  and  burns  with 
a  purplish-blue  flame,  forming  sulphur  dioxide  (SOo),  and  giving 
out  2221  metrical  units  of  heat  per  gram  of  sulphur.     More  exactly, 
.according  to  Thomsen  (Berl.  Ber.  1880,  p.  959),  the  heat  evolved 
in  burning  the  different  modifications  of  sulphur,  expressed  in 
atomic  calories  (that  is,  applied  to  32  grams  of  sulphur),  is: — 
S  (rhombic,  octahedric)  +02  =  S02=  +71,080  cal. 
S  (monoclinic)  .     .     .     +0^=802= +71,720  cal. 
Hence  the  conversion  of  32  parts  by  weight  of  monoclinic  into 
rhombic  sulphur  is  accompanied  by  the  evolution  of  640  calories. 
Berthelot,  however  (Compt.  rend.  xc.  p.  14=19),  states  the  figure  for 
octahedric  sulphur  =  +69260  atom.  cal.  =  2164  gram- calories. 

Hydrogen  combines  with  sulphur  very  slightly  at  a  temperature 
of  120°,  very  sensibly  so  at  200°.  On  boiling  sulphur  with  water, 
hydrogen  sulphide  is  evolved  and  sulphuric  acid  is  found  in  the 
residue  (Cross  &  Higgin,  J.  Chem.  Soc,  xxxv.  p.  249;  comp. 
also  Colson,  Bull.  Soc.  Chim,  [2]  xxxiv.  p.  66 ;  Bohm,  Jahresb. 
1883,  p.  225). 

Sulphur  is  insoluble  in  water,  a  very  little  soluble  in  alcohol  and 
in  glycerine,  rather  more  so  in  essential  oils,  but  easily  soluble 
(excepting  the  7-modification)  in  disulphide  of  carbon  and  in 
chloride  of  sulphur. 

The  sulphur  occurring  in  commerce  as  refined  sulphur,  in  rolls 
or  as  '^  rock-sulphur,"  is  frequently  almost  chemically  pure. 
^'  Flowers  of  sulphur  "  always  contains  a  little  sulphurous  acid, 
also  some  sulphuric  acid,  persistently  retained  in  spite  of  prolonged 
washing  ;  it  owes  its  greater  efficacy  agaiust  diseases  of  the  vine 
(oidium)  and  other  cases  principally  to  this  property. 

O.  Roessler  (Arch.  d.  Pharm,  1887,  p.  845)  states  that  sulphur 
ill  rolls  is  practically  free  from  acids  of  any  sort.  Flowers  of 
sulphur  contains  a  somewhat  considerable  quantity  of  sulphurous 

*  Comp.  J.  R.  Hill,  Chem.  News,  1890,  Ixi.  p.  126. 


NATURAL  OCCURREXCE  OF  SULPHUR.  17 

acid  (100  grams  up  to  3*14  c.c.  of  SOj),  which  may  be  partially 
oxidized  to  sulphuric  acid  ;  thiosulphuric  acid  is  not  found  in  it^ 
but  in  milk  of  sulphur  (up  to  015  per  cent.). 

Natural  Occurrence  of  Sulphur. 

Sulphur  occurs  in  nature  in  very  large  quantities,  both  in  the 
free  state  and  in  combination  with  other  bodies  as  sulphides  and 
sulphates.  Deposits  of  sulphur  are  forming  at  the  present  day, 
especially  in  volcanic  countries,  by  the  decomposition  of  sulphur- 
etted hydrogen  and  of  sulphurous  acid. 

Daubree  (Compt.  rend.  xcii.  p.  101)  noticed  a  recent  formation 
of  sulphur  in  the  subsoil  of  Paris,  from  the  action  of  organic  sub- 
stances on  sulphates  ;  and  the  same  action  has  been  observed  in 
many  mineral  springs,  where  it  is  especially  attributed  to  the 
action  of  Algse,  such  as  Beggiatoa,  Osdllaria^  and  Ulothrix  (Compt. 
rend.  xcv.  pp.  846  &  1363). 

But  of  far  more  consequeuce  are  the  beds  of  sulphur  deposited 
in  former  geological  periods.  The  most  important  of  all  are  those 
of  Sicily,  in  the  chalk  ;  next,  those  in  the  Romagna  and  in  other 
parts  of  Italy.  The  Sicilian  sulphur  industry  is  described  in 
detail  by  Angelo  Barbaglia  in  Hof  mann's  Official  Report  on  the 
Vienna  Exhibition,  i.  p.  144,  and  by  Parodi  (Berichte  d.  deutsch. 
chem*.  Ges.  1874,  p.  358),  According  to  the  latter,  the  disposable 
stock  of  sulphur  in  Sicily  is  said  to  amount  to  ten  millions  of 
tons  ;  so  that  it  would  be  exhausted  about  1950.  Other  calcula- 
tions gave  more  than  twice  that  amount.  The  apparatus  for  melting 
the  sulphur  out  of  the  "  sulphur-earth  *'  in  Sicily  is  also  described 
by  Barbaglia. 

Further  descriptions  of  the  Sicilian  sulphur  industry  are  found 
iQ  the  '  Chemiker-Zeitung '  of  1882,  pp.  1389,  1405,  1421  ;  also 
in  '  Zeitsch.  f .  angew.  Chemie,*  1890,  p.  56,  in  the  '  Journal  of  the 
Society  of  Chemical  Industry,'  1890,  p.  118  ;  by  Bechhold,  '  Zsch. 
angw.  Ch.'  1894,  p.  33  ;  by  Frank,  ibid.  1900,  p.  843 ;  by  Inng- 
fleisch  (Monat.  Scient.  1901,  p.  511). 

Probably  the  most  exhaustive  description  of  the  modern  Italian 
sulphur  industry  is  that  given  by  Aichino,  in  '  Mineral  Industry,' 
viii.  p.  592. 

Here  we  quote  only' a  few  brief  notes  on  more  recent  processes 
or  proposals  for  extracting  sulphur  from  its  ores  (whether  intended 
for  Sicilian  sulphur  or  that  from  other  localities). 

VOL.  1.  c 


18  RAW  MATERIALS  OF  MANUFACTURE. 

In  recent  years  the  "  Gill  kilns  "  have  rapidly  gained  ground  in 
replacing  the  calcarone  methods,  and  they  incrjease  the  output  of 
sulphur  by  50  per  cent.  These  kilns  consist  of  an  oven  covered 
by  a  cupola,  called  a  "  cell ; "  inside  there  is  a  smaller  cupola, 
within  which  a  coke  fire  is  burning.  Each  cell  holds  from 
5  to  30  cubic  metres  of  ore.  There  are  generally  six  cells  working 
in  an  angular  battery.  The  gases  generated  in  the  first  cell  pass 
by  lateral  channels  into  the  next;  by  the  time  the  fusion  is 
completed  in  the  first  cell,  the  contents  of  the  second  cell  are 
already  heated  up  to  the  igniting-point  by  the  gases,  and  so  on. 
The  gases  heavily  charged  with  sulphur  are  not  lost  as  in  the 
calcarone  method  ;  the  yield  is  much  larger,  the  time  shorter 
(three  or  four  days  for  each  cell),  and  as  the  quantity  of  smoke  is 
much  less,  the  work  can  be  continued  almost  all  the  year  round 
without  danger  to  the  crops.  In  1888  there  were  only  365  cells 
in  40  mines,  in  1894  the  number  had  increased  to  1821  cells  in 
225  mines,  that  is  over  two-thirds  of  the  total. 

E.  F.  White  (Eng.  Min.  Journ.  Ixii.  p.  536)  extracts  sulphur  from 
sulphur-ores  by  passing  the  latter  downwards  between  two  conical 
steam-heated  vessels,  where  the  sulphur  is  fused  and  runs  out  at 
the  bottom. 

De  la  Tour  de  Breuil  (Compt.  rend,  xciii.  p.  456)  employs  a 
66-per-cent.  solution  of  calcium  chloride  for  the  same  purpose. 
C.  Vincent  recommends  this  process  (Bull.  Soc.  Chim.  xl. 
p.  528). 

K.  Walter,  in  Milan,  has  patented  an  apparatus  for  continu- 
ously melting  out  sulphur  by  combustion  of  part  of  the  sulphur 
itself,  and  converting  the  sulphur  dioxide  formed  into  sulphuric 
acid  in  lead  chambers  (Chem.  Zeit.  1886,  p.  1199). 

The  American  patents  of  P.  Dickert,  Nos.  298,734  and  301,222, 
describe  an  apparatus  for  melting  sulphur,  consisting  of  a  jacketed 
pan  connected  by  a  perforated  diaphragm  with  another  jacketed 
pan  turned  bottom  upwards.  The  melting  is  produced  by  means 
of  steam  introduced  into  the  jacket. 

Very  ingenious  is  the  process  of  Herman  Frasch  (U.S. 
pat.  461429,  461430,  461431  of  1891),  which  is  applied  to  the 
Louisiana  sulphur,  where  quicksand  makes  it  impossible  to  use 
the  ordinary  methods.  A  well  is  sunk  by  drilling  in  the  same 
way  as  for  petroleum.  This  well  is  cased  with  an  iron  pipe 
10  in.  in  diameter,  reaching  10  feet  into  the  rock  overlying  the 


FRASCH  PROCESS  FOR  SULPHUR-EXTRACTION.  J  9 

sulphur-bed.  Inside  this  there  is  a  6-in.  pipe,  inside  the  latter 
a  3-in.  pipe,  and,  finally,  in  the  centre  a  1-in.  pipe.  The  well  is 
carried  down  to  the  bottom  of  the  sulphur-bed,  and  the  6-in.  pipe 
and  smaller  pipes  are  dropped  nearly  to  the  bottom  of  the  lode. 
Water  heated  to  166°  C.  is  forced  down  the  10-in.  and  6-in.  pipes 
under  corresponding  pressures,  and  on  coming  in  contact  with 
the  sulphur  it  is  melted  and  collects  in  the  well.  Ordinary 
pumping  not  haying  answered,  compressed  air  is  forced  down 
through  the  1-in.  pipe,  which  mixes  with  the  molten  sulphur  and 
reduces  its  specific  gravity  so  that  it  rises  in  the  3-in.  pipe  to  the 
top  with  great  rapidity.  As  much  as  150  tons  of  sulphur  has  been 
pumped  in  24  hours.  About  50  tons  of  coal  per  day  are  burned 
under  the  boilers. 

The  loss  of  heat  is,  of  course,  very  great,  and  there  is  an 
uncertainty  about  the  way  in  which  the  impurities  present  may 
choke  up  the  pipes.  In  1896  one  hole,  sunk  in  very  pure  sulphur, 
produced  2100  tons;  this  was  continued  in  1898,  bringing  up  the 
total  to  4509  tons.  However,  according  to  vol.  vii.  of  '  Mineral 
Industry,^  p.  643,  in  1898  the  conclusion  was  reached  that  the 
process  was  unprofitable ;  but  this  is  entirely  wrong.  In 
February  1902  I  received  from  the  inventor  (Mr.  Frasch)  a  set 
of  photographs,  taken  on  the  spot  a  few  weeks  before,  exhibiting 
the  manufacture  on  a  large  scale,  the  pumps  discharging  a  full 
3-in.  stream  of  liquid  sulphur  all  through.  The  boiler-power  is 
being  increased  from  2100  to  4300  H.P.  With  the  present 
(lower)  power  the  average  production  is  100  tons  per  day  from 
one  well;  up  to  250  tons  per  day  has  been  realized  before. 
The  liquid  sulphur  is  discharged  into  bins  up  to  a  size  of 
72  ft.  X  60  ft.  X  5  ft.,  where  it  solidifies  and  is  broken  up  for 
shipment.  Many  thousand  tons  have  been  pumped  and  shipped, 
and  there  are  large  stocks  on  hand  shown  in  those  bins. 

Analyses  of  Sicilian  sulphur  (Mene,  Monit.  Scient.  1867, 
p.  400)  :— 

Sulphur  soluble  in  OS2 96*2      921      921  91-3  901  900  887 

Sulpbur  ingoluble  in  CSj 15  2  0  21  17 

Carbonaceous  matter 05        10        11        07  10  11  10 

Sand 1-5        23        28        33  23  28  55 

limestone    and    strontium!      j.g        ^.j        3.Q        0.5  4.1  ^.q  2*8 

Bidpbate  J  ^     ^        

10000      99-5      990      993      99*5      990      997 

[Mine's  samples  are  evidently  of  a  very  low  quality.] 

c2 


20  RAW  MATERIALS  OF  MANUFACTURE. 

The  average  price  of  sulphur  in  Sicily  in  1881  was  115  lire,  in 
1882  105  lire,  in  1887  only  69  lire  (say  £2  15«.)  per  ton. 

A  Report  by  the  Italian  Minister  of  Agriculture  for  the  year 
1894  (Chem.  lud.  1895,  p.  182)  describes  the  depressed  state  of 
the  Sicilian  sulphur  industry. 

In  1896,  by  the  formation  of  the  Anglo-Sicilian  Sulphur 
Company,  working  with  English  capital,  the  Sicilian  sulphur 
industry  was  at  last  placed  on  an  economically  sound  basis,  ami 
at  the  same  time  the  ruinous  cutting  down  of  prices  ceased. 
During  1900  the  average  price  for  '^  best  thirds  '^  was  £3  13«.  6rf. 
per  ton  f.o.b.  Catania. 

The  total  exportation  of  sulphur  in  Sicily  during  the  year 
ending  June  30,  1900,  was  517,741  tons;  during  the  year  ending: 
June  30,  1901,  521,497  tons.  This  quantity  was  exported  ta 
different  countries  as  follows : — 

1900-1901.  1899-1900. 

Tons.  Tons. 

United  States  147,094  138,846 

France 98,455  98,393 

Italy      85,210  101,624 

Germany  30,549  26,290 

Norway,  Sweden,  Denmark   ...  27,373  18,313 

Greece  and  Turkey     22,304  19,795 

Great  Britain  ....! 19,923  25,933 

Russia  19,878  16,815 

Austria     19,647  23,067 

Holland 15,813  11,781 

Portugal  11,315  11,462 

Belgium 9,316  8,845 

Spain    3,566  6,298 

Other  countries   11,059  10,259 

(The  quantities  for  a  number  of  years  previously  to  the  above  are 
given  in  our  second  edition.) 

Northern  Italy  formerly  yielded  a  very  large  quantity  of  brim* 
stone,  especially  the  Romagna ;  but  many  of  the  beds  are  now 
exhausted,  and  the  production  is  slowly  receding,  from  23,274 
tons  in  1886  to  21,663  tons  in  1887  (details  in  the  Chem.  Zeit. 
xii.  p.  1659;  abstr.  J.  Soc.  Ch.  Ind.  1889,  p.  142).     The  whole 


OCCURRENCES  OF  SULPHUR.  21 

t>f  this  brimstone  is  used  for  inland  consumption,  as  a  remedy 
against  the  vinendisease. 

Salphur  containing  selenium  is  found  in  the  Lipari  Islands  and 
near  Naples,  but  not  in  quantity. 

In  many  other  parts  of  the  world  deposits  of  sulphur  have  been 
found,  and  have  been  sometimes  declared  to  be  very  important; 
but  bitherto  these  sulphur-mines  have  not  made  any  sensible 
impression  on  the  sulphur  trade,  of  which  Sicily  has  still  almost 
the  monopoly.  The  more  important  of  these  sulphur-mines  are 
the  following : — 

Andalusia  produces  sulphur,  some  of  which  is  refined  in 
Almeria. 

In  Germany  sulphur  has  been  found  at  Stassfurt  (Berl.  Ber. 
1890,  p.  192)  and  in  Upper  Silesia,  near  Ratibor,  where  beds  up 
to  20  ft.  thick  exist  (Chem.  Ind.  ii.  p.  136 ;  Fischer's  Jahresb. 
1882,  p.  223).  It  has  been  worked  by  extracting  it  from  the  ore 
by  means  of  carbon  disulphide. 

The  production  of.  sulphur  in  Germany,  as  indicated  by  the 
official  statistics,  does  not  distinguish  between  natural  sulphur 
and  that  which  is  recovered  in  the  Leblanc  process.  It  amounted 
in  1897  to  2317  tons,  in  1898  to  1954  tons,  in  1899  to  1663  tons. 

In  1899  the  importation  was  31,196  tons,  in  1900  40,689  tons. 
The  exportation  is  very  small. 

In  Austria,  at  Swoscowice  near  Cracow,  an  old  sulphur-mine 
exists  which  for  some  years  was  carried  on  with  great  vigour, 
the  sulphur  being  extracted  from  the  marl  by  means  of  carbon 
disulphide.  This  bed  is  now  practically  exhausted,  and  the  mine 
has  ceased  working  (Wagner's  Jahresb.  1878,  p.  333,  1879, 
p.  272;  Fischer's  Jahresb.  1885,  p.  204). 

Russia  possesses  considerable  stores  of  sulphur.  A  bed  of 
brimstone  has  been  found  by  GluschkofE  in  tlie  Astrachan 
Government,  on  the  east  bank  of  the  Baskuntschak  salt-sea ;  it 
is  a  mixture  of  «andy  rock  with  30  to  35  per  cent,  of  pure  sulphur 
(Fischer's  Jahresb.  1884,  p.  264).  In  West  Siberia  considerable 
beds  of  sulphur  are  said  to  exist.  In  the  Vistula  district  a 
sulphur-bed  is  being  worked  at  Czarki,  which  in  1883  yielded 
60,000  pud.  In  the  sandy  steppe  of  Karakum  a  large  number  of 
conical  hills  have  been  discovered  consisting  of  sulphury  rock  of 
50  per  cent.  (Chem.  Zeit.  1884,  p.  478).  In  the  north  of  the 
Caucasus,  in  the  Grodno  district,  sulphur   has  been   found  by 


22  RAW  MATERIALS  OF  MANUFACTURE. 

Baron  Heyking  (Chem.  Zeit.  1887,  p.  1620).  According  to 
Chem.  Ind.  1892,  p.  443,  the  sulphur  is  obtained  at  Tschirkat  in 
Daghestan  to  the  extent  of  300,000  pud  (at  40  lbs.)  per  annum ; 
the  selling  price  is  1'18  roubles  per  pud. 

According  to  Chem.  Zeit.  1894,  p.  2002,  a  large  bed  of  brim- 
stone has  been  found  in  Transcaspia,  60  versts  from  the  port  of 
Usun-Ada  on  the  Caspian  Sea,  only  2  versts  from  a  railway-line. 
The  bed  is  just  below  the  surface  of  the  ground  and  is  worked  by 
open  quarrying.  The  ore  contains  from  35  to  40  per  cent, 
sulphur,  and  costs  20  to  25  copeks  at  Usun-Ada.  If  the  results 
expected  were  realized,  Russia  would  become  entirely  independent 
of  Sicilian  sulphur.  Possibly  this  is  the  same  occurrence  which 
is  reported  in  Journ.  Soc.  Chem.  Ind.  1900,  p.  867,  as  ''  the 
richest  in  the  world,"  100  miles  from  Khiva,  extending  over 
23  square  miles. 

Chonski  (Chem.  Zeit.  1895,  Repert.  p.  411)  reports  on  the 
production  of  sulphur,  which,  he  says,  has  been  tried  in  several 
places  in  Russia,  but  has  been  everywhere  discontinued.  He 
enumerates  the  drawbacks  connected  with  the  various  methods  for 
extracting  sulphur  from  the  raw  ore.  This  paper  should  be 
consulted  by  those  who  consider  any  newly  discovered  vein  of 
sulphur-ore  as  being  equal  to  ready  money. 

Comp.  on  Russian  brimstone  also  Zsch.  angew.  Chem.  1897, 
p.  36 ;  Chem.  Ind.  1898,  p.  241 ;  Niedenfuhr,  Chem.  Zeit.  1897, 
No.  30;  Machalski,  Engin.  Min.  Journ.  Ixx.  p.  216;  Chem.  Trade 
Journal,  1900,  xxvii.  p.  220. 

Brimstone  is  got  near  Mossul  in  Mesopotamiay  near  Cairo,  and 
in  Tunis.  At  Djemsali  and  Ranga,  on  the  coast  of  the  Red  Sea, 
the  "  Compagnie  Soufriere  '*  is  said  to  get  300  tons  monthly. 

Very  large  quantities  of  sulphur  are  said  to  exist  in  Iceland, 
even  more  important  than  those  in  Sicily ;  the  deposits  at  Guld- 
bringe  Syssel,  in  the  south-west  of  Iceland,  were  some  time  ago  at 
work  with  satisfactory  results  (Chem.  News,  xl.  p.  31). 

Japan  possesses  veiy  large  stores  of  sulphur,  but  the  absence 
of  facilities  for  increasing  its  output  and  for  shipping  it  has 
hitherto  very  much  restricted  the  development  of  the  sulphur 
industiy  in  that  country.  Formerly  (comp.  J.  Soc.  Chem.  Ind. 
1890,  p.  344)  there  was  only  one  place  where  sulphur  was  worked 
on  any  scale,  namely  Atosanobori,  near  Kushiro,  on  the  south-east 
coast  of  the  island  in  which  the  port  of  Hakodate  is  situated. 


OCCURREXCES  OF  SULPHUR.  23 

The  Atoaanobori  mine  is  part  of  an  extinct  volcano^  whose  crater 
and  slopes  are  partially  covered  with  a  50-per-cent.  sulphur-ore. 
According  to  the  lowest  estimate  this  mine  contains  a  million  tons 
of  good  ore^  but  there  is  probably  five  times  as  much.  The  output 
is  at  present  about  9000  tons  per  annum ;  the  cost  of  the  sulphur 
free  on  board  at  Kushiro  is  about  SOs.  10d.y  but  it  has  hitherto 
been  shipped  from  Hakodate^  where  it  costs  £2  Ss,  2d.  per  ton, 
which  is  not  remunerative.  The  exportation  was  1541  tons  in 
1885,  4972  tons  in  1886,  7096  tons  in  1887,  3609  tons  in  1888, 
15,700  tons  in  1895.  The  shipments  generally  go  to  San 
Francisco. 

Apart  from  the  ordinary  yellow  sulphur,  which  sometimes  con^ 
tains  traces  of  selenium  and  tellurium,  there  occurs  in  Japan  an 
orange-red  variety,  containing  0*17  per  cent.  Te,  0*06  Se,  0*01 
As,  traces  of  molybdenum  ^and  earthy  matters  (Divers  and 
Shimidzu,  Chem.  News,  1883,  No.  1256). 

A  considerable  source  of  sulphur  has  recently  been  discovered  on 
the  volcanic  island  of  Etrof  u,  about  halfway  between  the  northern 
extremity  of  Japan  and  Kamschatka.  In  1900  already  10,000 
tons  sulphur  were  mined,  and  it  is  expected  to  reach  300  tons 
per  month  (Joum.  Soc.  Chem.  Ind.  1901,  p.  300). 

A  small  island  belonging  to  New  Zealand,  evidently  the  crater 
of  a  huge  submerged  volcano,  which  contains  large  deposits  of 
sulphur,  has  been  described  by  Mclvor  (Chem.  News,  1887,  Ivi. 
p.  251).  It  will  probably  be  very  soon  submerged  as  well. 
1692  tons  of  sulphur  were  produced  in  that  colony  in  1900. 

In  the  United  States  of  America  sulphur  has  been  found  in 
many  places,  particularly  at  Cove  Creek,  Millard  County,  South 
Utah  ;  at  Rabbit-Hole  Springs,  Humboldt  County,  Nevada ;  near 
Lake  Charles,  Louisiana  ;  in  Wyoming  and  other  Rocky  Mountain 
Territories  ;  in  Texas,  California,  and  so  forth.  Very  few  of  these 
occurrences  are  worked,  either  owing  to  the  smallness  of  the  stock 
or  to  the  diflSculties  of  carriage.  The  Rabbit- Hole  mines  have 
been  worked  off  and  on,  but  never  at  a  considerable  rate.  For  the 
purpose  of  working  the  best  deposit,  the  Cove  Creek  mine,  a  Com- 
pany (the  Dickert  and  Myers  Sulphur  Company)  was  formed 
with  a  capital  of  $2,000,000,  which  acquired  Dickert's  patents, 
mentioned  on  p.  18 ;  but  it  did  not  produce  more  than  about 
2000  tons  of  brimstone  in  1886,  and  2700  tons  in  1887,  so  that  it 
could  not  even  supply  all  the  needs  of  the  Pacific  coast,  which 


24 


KAW  MATERIALS  OF  MANUFACTURE. 


amount  to  4500  tons^  and  have  to  be  made  up  from  Sicily  and 
Japan  (details  in  the  '  Mineral  Resources  of  the  United  States,' 
Calendar  years  1885,  1886,  and  1887). 

A  very  large  deposit  of  sulphur  has  been  discovered  in  the 
Grand  Gulf  Basin,  near  Lake  Charles  City,  in  the  parish  of 
Calcasieu,  State  of  Louisiana.  Two  wells  have  been  bored  at 
different  localities,  which  struck  sulphur  at  a  depth  of  about 
^50  feet.  The  first  and  thickest  bed  of  sulphur  is  from  108  to 
112  feet  thick  ;  it  contains  near  the  top  62  per  cent.,  in  the  centre 
90  per  cent,  of  pure  sulphur.  One  of  the  wells  has  been  continued 
lower  down,  and  proved  the  existence  of  several  smaller  beds  of 
rich  brimstone-ore,  and  several  hundred  feet  of  gypsum  containing 
sulphur ;  in  the  other  well  no  gypsum,  but  calcareous  substance 
containing  sulphur  is  found.  The  working  presents  a  difBcnlty, 
as  there  are  several  hundred  feet,  of  quicksand  on  the  top  of 
the  brimstone  beds,  which  is  to  be  overcome  by  the  Frasch 
process  (p.  18). 

In  Lower  California,  not  far  from  the  mouth  of  the  Colorado 
River,  a  new  bed  of  sulphur  has  been  found.  The  crude  sulphur 
contains  70  to  80  per  cent,  pure  S  (Fischer's  Jahresb.  1897,  p.  420). 

According  to  the  volumes  of  ^  Mineral  Industry,^  the  production, 
imports,  and  consumption  of  sulphur  in  the  United  States  during 
the  years  1896  to  1900  have  been  as  follows  (in  long  tons)  : — 


Year. 


1891 
1892 
1893 
1894 
1895 
1896 
1897 
1898 
1899 
1900 


Productiou. 

Tons. 


1,071 
1,0^0 
1,200 
441 
1,(»50 
3,800 
1,690 
2,726 
1 ,5(i5 
4,630 


Crude. 


110,971 

100,938 

107,601 

124,467 

12.5,950 

145,318 

138,846 

159,790 

140,841 

166,457 


Importation. 

1 
1 

/ 

Consumption. 

\ 

Flowers. 

Refined.  ^ 

1 

Total. 

206 

10    i 

117,187 

118,208 

158 

26 

101,122 

102,752 

241 

1       41      , 

107,885 

109,090 

165 

41 

124,073 

r2,M  14 

581 

'     229 

128,410 

128,410 

665 

447 

146,430 

149.746 

319 

!      148 

139,313 

140,849 

507 

163 

160,460 

161.772 

336 

'      184 

141,361 

142,449 

628 

142 

167,328 

i 

171,418 

In  British  Columbia,  on  the  Skeena  River,  a  large  deposit  of 
sulphur  has  been  found,  and  it  was  expected  to  supply  the  Puget 
Sound  Country,  and  eventually  the  whole  Pacific  Coast,  from  this 
source  (Journ.  Soc.  Chem.  Ind.  1901,  p.  1040). 


SULPHUR  FROM  OTHER  MATERIALS.  25 

In  America  sulphur  is  found  also  in  many  other  places^  as  in 
the  volcanic  regions  of  Ecuador  and  Mexico,  at  Chilian  in  Cliili^ 
and  elsewhere. 

It  has  long  been  known  that  the  crater  of  the  Popocatepetl,  in 
Mexico^  contains  large  quantities  of  brimstone ;  and  a  railway  has 
been  projected  in  order  to  get  at  it.  An  annual  production  of 
50,000  tons  of  brimstone  was  expected  to  begin  with,  and  vitriol- 
works  were  to  be  erected  all  along  the  line  (Fischer^s  Jahresb. 
1884,  p.  265).  So  far  this  project  does  not  seem  to  have  been 
carried  out. 

On  the  island  of  Saba,  one  of  the  Antilles,  there  is  a  bed  ot 
brimstone,  yielding  on  an  average  45  per  cent,  of  sulphur,  which 
was  worked  for  some  time,  but  had  to  be  abandoned  as  not 
paying  the  expense  (Dingl.  Journ.  1886,  cclix.  p.  43). 

lu  Chili  brimstone  is  found  at  a  height  of  from  12,000  to 
13,000  feet  above  the  sea.  The  mines,  which  were  started  in 
September,  1900,  by  an  Iquique  Company,  are  54  miles  from  the 
nearest  railway  station.  The  product  is  said  to  be  of  very 
good  quality ;  it  is  used  in  the  provinces  of  Atacama  and  Tarapaca 
for  the  recovery  of  iodine  and  for  making  blasting-powder  for  the 
nitrate  works.  This  seems  to  be  the  Taltal  deposit  mentioned  in 
a  Consular  Report,  quoted  Journ.  Soc.  Chem.  Ind.  1901,  p.  1039. 
In  1901,  the  working  was  stopped  as  being  at  present  unremune- 
rative  (Zsch.  angew.  Ch.  1901,  p.  1243). 

In  Venezuela  large  beds  of  sulphur  have  been  found,  20  or  30 
miles  distant  from  the  coast,  with  which  they  are  to  be  connected 
by  a  wire-rope  line.  The  beds  are  to  be  worked  by  the  Deutsch- 
Venezolanische  Schwefelgruben  A.  G.,  at  Cologne. 

Sulphur  Manufactured  from  other  Materials. 

Free  sulphur  is  produced  in  large  quantities  in  the  manufacture 
of  coal-gas,  and  is  contained  in  the  spent  oxide  of  iron.  We  shall 
treat  of  this  later  on,  as  material  for  producing  sulphur  dioxide  ; 
in  this  place  we  mention  it  only  as  a  source  of  obtaining  free 
sulphur.  This  is  sometimes  done  by  extracting  it  with  carbon 
disulphide  ;  but  this  process  does  not  generally  seem  to  pay  (comp. 
Journ.  Soc.  Chem.  Ind.  1883,  p.  491).  Some  of  the  processes 
described  below  are  specially  intended  for  this  kind  of  material. 

Broadberry  (Gas  World,  1895,  xxiii.  p.  643)  extracts  the 
sulphur  from  spent  oxide  of  gas-works  by  means  of  benzol  at  a 


26  RAW  MATERIALS  OF  UANUFACTUBE. 

temperature  of  70°  or  80°  C,  employing  a  circulating-apparatus. 
1  gallon  of  hot  benzol  yields  on  cooling  2'5  to  2*75  lbs.  of  solid 
sulphur,  and  retains  0*25  lb.  in  solution^  which  is  obtained  in  dis- 
tillatioD.  From  an  experiment  with  20  lbs,,  he  calculates  a  profit 
of  £1  6s.  Sd.  per  ton  of  spent  oxide. 

The  sulphur  made  from  gas  oxide  is  mostly  of  a  dark  colour, 
owing  to  the  presence  of  a  very  small  quantity  of  tarry  substances, 
and  this  makes  it  very  difficult  to  sell,  so  that  it  is  nearly  always 
burned  without  extracting  it,  as  we  shall  see  infra,  No.  5. 

A  certain  quantity  of  sulphur  is  obtained  by  the  distillation  of 
pt/rites.  This,  however,  pays  in  very  few  places,  except  under 
special  circumstances — for  instance,  at  the  works  of  J,  D,  Starck 
in  Bohemia,  which  formerly  supplied  nearly  all  the  fuming  oil  of 
vitriol,  and  where  the  distillation  of  pyrites  is  practised  in  order 
to  obtain  a  material  for  the  manufacture  of  sulphate  of  iron.  Be- 
tween 1863  and  1872,  2440  tons  of  sulphur  were  thus  made. 
The  distillation  takes  place  in  earthenware  tubes  3  ft.  3  in.  long, 
5  in.  high,  and  5^  in.  wide,  quite  open  at  the  back,  and  in  front 
narrowed  to  an  opening  of  |  in.  diameter;  they  are  glazed  with 
common  salt ;  and  three  tiers  of  seven  tubes  each  are  placed  in 
each  furnace.  For  each  tube  there  is  a  small  receiver  of  sheet- 
iron  half  filled  with  water,  and  attached  to  the  tapering  end  of  the 
tube.  The  charge  of  pyrites  is  put  into  the  open  end  ;  a  slanting 
piece  of  sheet-iron  is  placed  in  front ;  and  the  opening  is  closed 
with  sand  or  pyrites  cinders,  as  shown  in  fig.  1. 


Here  only  one-third  of  the  sulphur  contained  in  the  pyrites  is 
gained ;  but  in  Sweden  half  (?)  of  the  sulphur  is  said  to  be  ob- 
tained in  a  furnace  built  similar  to  a  lime-kiln,  and  continued  at 


SULPHUR  FROM  PYRITES.  27 

the  top  in  a  wooden  chimney  serving  as  a  condensing-space.  The 
kiln,  having  been  first  made  red-hot,  is  charged  with  pyrites,  of 
which  one  portion  is  burned  whilst  the  other  portion  volatilizes 
and  is  condensed  at  the  top.  The  work  is  carried  on  continuously^ 
fresh  pyrites  being  from  time  to  time  introduced  through  an 
opening  near  the  top,  and  the  cinders  being  removed  at  the 
bottom. 

P.  W.  Hofmann  (Dingl.  Joum.  ccxx.  p.  232)  proposed  to  utilize 
the  sulphur  of  the  pyrites  smalls.  If  sulphur  dioxide  is  conducted 
over  red-hot  calcium  sulphide  (from  alkali- waste),  it  is  at  first 
completely  absorbed ;  afterwards  sulphur  distils  over,  and  the 
calcium  sulphide  is  transformed  into  sulphate.  Tiie  latter,  by 
conducting  ordinary  coal-gas  over  it  in  a  red-hot  state,  or  by 
mixing  it  with  coal  and  igniting,  is  reconverted  into  sulphide, 
which  can  be  used  over  again.  Hofmann  proposed  to  burn  the 
pyrites  smalls  at  the  mines,  to  obtain  their  sulphur  by  means  of 
calcium  sulphide  in  a  state  fit  for  sale,  to  treat  the  cinders  by  a 
process  to  be  described  in  the  13th  Chapter  for  zinc  chloride  and 
sodium  sulphate,  and  to  work  the  residue  for  pig-iron  in  a  blast- 
furnace. This  proposal  has  not  found  any  application  in  practice, 
and  is  not  likely  to  do  so,  since  the  burning  of  pyrites  dust  by  the 
shelf-furnace  is  quite  as  advantageous  for  acid-making  as  that  of 
lump  ore. 

Gerlach  (German  patent  229,  1877)  proposed  to  obtain  sulphur 
from  sulphur-ores,  and  especially  from  the  spent  oxides  of  gas- 
works, by  heating  them  in  iron  or  fireclay  retorts  whilst  at  the 
same  time  superheated  steam  is  passed  through.  The  sulphur  is 
said  to  distil  very  rapidly.  A  description  of  this  process,  with 
diagrams,  is  found  in  Wagner's  Jahresb.  1879,  p.  268.  It  was 
tried  in  Upper  Silesia  with  sulphur  marl,  but  did  not  auswer 
(Fischer's  Jahresb.  1882,  p.  234). 

O.  C.  D.  Ross  patented  a  process  in  every  way  similar  to 
Gerlach's  (E.  P.  No.  713,  1879) .  Other  processes  of  the  same 
kind  are  described  in  the  ^  Scientific  American,'  xxxix.  p.  276,  and 
in  the  '  Chemiker-Zeituug,'  1879,  p.  241,  by  Dubois  (E.  P. 
No.  13,108  of  1885  and  No.  7129  of  1886  ;  G.  P.  41,718:  the 
last  patent  describes  a  revolving  retort). 

According  to  a  French  patent  of  the  Societe  de  St.  Gobain 
(No.  107,820,  28th  April,  1875),  on  the  top  shelf  of  an  ordinary 
shelf-burner  for  pyrites  smalls  (see  Chapter  IV,)  a  fireclay  retort 


28  RAW  MATERIALS  OF  MANUFACTURE. 

is  to  be  placed,  in  which  the  pyrites  is  first  deprived,  by  distillation, 
of  a  portion  of  its  sulphur,  which  is  collected  in  the  well-known 
condensing-chambers  as  flowers  of  sulphur.  After  some  time  the 
partially  desulphurized  pyrites  is  let  down  to  the  next  lower  shelf, 
and  so  on  to  others  lower  down.  Here  the  remainder  of  the  sulphur 
burns,  and  the  gas  goes  into  acid-chambers,  whilst  its  heat  causes 
the  distillation  of  further  portions  of  pyrites  in  the  retort.  This 
process  does  not  answer  :  the  flowers  of  sulphur  obtained  is  very 
acid;  and  both  the  burner  and  the  chambers  work  very  badly.  A 
similar  process  has  been  again  patented  by  Labois  (E.  P.  No.  9761 
of  1884). 

Buisine  (Germ.  pat.  73223)  heats'  half-roasted  pyrites  with 
sulphuric  acid,  to  recover  sulphur,  ferrous  sulphate  being  ob- 
tained as  by-product.  According  to  pat.  79706,  the  pyrites  is  to 
be  distilled  in  closed  vessels  at  700°  C.  and  the  residue  treated  as 
above  with  sulphuric  acid.  The  residue,  consisting  of  sulphur  and 
ferrous  and  cupric  sulphate,  can  be  applied  as  it  is  to  vines  for 
.  certain  diseases  ;  or  else  it  is  extracted  with  water,  the  residue  is 
worked  for  sulphur,  and  the  solution,  by  treating  it  with  metallic 
iron,  yields  metallic  copper  and  ferrous  sulphate. 

Holloway's  process  (E.  P.  No.  500  and  1131, 1878)  at  one  time 
excited  much  attention.  He  blows  heated  air  through  melted  iron 
sulphide,  thus  decomposing  it  into  a  cupreous  matt  and  a  slag, 
together  with  free  sulphur,  which  distils  oflF  and  can  be  collected. 
The  principal  aim  of  this  process  was  the  concentration  of  poor 
copper-ores  in  countries  where  fuel  is  expensive.  It  has  been 
described  by  the  inventor  in  a  paper  read  before  the  Society  of 
Arts,  which  has  been  published  together  with  the  discussion 
following  the  reading  of  the  paper.  Bode  (Dingl.  Journ.  ccxxxii. 
p.  433)  has  criticised  it.  Dr.  Angus  Smith  (Alkali  Reports, 
1877-78,  p.  47)  expected  important  results  from  this  process, 
which  is  decidedly  very  interesting ;  but  it  has  found  no  practical 
application. 

Stickney  (Eng.  &  Miu.  Journ.  Ixv.  p.  674)  heats  pyrites  to  red 
heat  by  means  of  producer-gas.  There  is  an  escape  of  HoS  and 
SO2,  which  are  converted  into  free  sulphur  by  means  of  a  spray  of 
salt  solution  (comp.  Schaff^ner^s  and  Helbig's  process,  vol.  ii.  2nd 
edition  of  this  work,  p.  857) ;  the  reaction  is  to  be  promoted  by 
electric  sparks. 

Frohling,  Fleming,  and  Whitlock  (E.  P.  10,295,  1900)  intend 


SULPHUR  FROM  OTHER  SOURCES.  29 

to  obtain  practically  all  the  sulphur  from  FeSg  by  heating  the  ore 
in  a  retort  in  a  stream  of  carbon  dioxide  or  nitrogen  with  the 
addition  of  a  small  regulated  quantity  of  oxygen^  by  which  only 
the  iron  is  burnt  to  Vefi^,  the  sulphur  being  set  free. 

It  has  often  been  proposed  to  prepare  sulphur  by  y^a^^in^  gases 
containing  sulphur  dioxide  through  red-hot  coal.  A  special  appa- 
ratus for  this  purpose  has  been  proposed  by  Haenisch  and 
Schroeder  (E.  P.  6404,  1885).  They  pass  the  first  gases  through 
fire-clay  cylinders  filled  with  coke  and  heated  from  the  outside  by 
producer-gas  ;  the  products  of  combustion  travel  through  another 
cylinder,  filled  with  open  brick- work  and  heated  by  the  waste  fire-. 
gases  of  the  first  operation  ;  here  the  undecomposed  SO2,  the 
carbon  monoxide,  carbon  disulphide,  and  carbon  oxysulphide  act 
upon  one  another,  so  that,  if  the  current  has  been  properly 
regulated,  ultimately  only  CO2  and  S  are  formed.  Or  else  the 
SOo  is  at  once  treated  with  CO,  according  to  the  equation 

S02  +  2CO  =  2C02  +  S. 

This  process  has  been  tried  on  a  large  scale  at  Oberhausen 
(comp.  Chem.  Zeit.  1886,  p.  1039,  abstracted  in  J.  Soc.  Chem. 
Ind.  1886,  p.  534),  but  evidently  not  successfully. 

J.  and  F.  Weeren  obtain  the  SO2  for  this  purpose  by  calcining 
sulphates  with  silica  (G.  P.  38,041).  They  describe  a  special 
apparatus  for  this  reduction  and  the  reduction  of  the  SO2  by  in- 
candescent coke  to  S. 

Heinrici  (Zsch.  angew.  Ch.  1898,  p.  525)  employs  this  reaction 
for  the  purpose  of  utilizing  the  acid  tar  formed  in  the  purification 
of  mineral  oils.  By  heating  this  SO2  is  evolved,  which  is  reduced 
to  free  S  by  red-hot  coke. 

Sulphuretted  hydrogen  has  been  very  frequently  proposed  as  a 
material  for  the  production  of  free  sulphur,  which  has  become  an 
economical  possibility  through  the  Glaus  process.  We  cannot 
describe  this  industry  in  this  place  ;  it  is  fully  dealt  with  in  vol.  ii. 
of  the  2nd  edition  of  this  work,  page  891  et  seq.,  and  we  subjoin 
only  a  brief  notice  of  some  improvements  proposed  since  1896. 

CaruUa  (J.  Soc.  Chem.  Ind.  1897,  p.  980)  prefers  burning  H2S 
in  an  ordinary  pyrites-kitn,  in  lieu  of  the  Glaus  kiln,  as  the  yield 
is  much  larger. 

Baranoff  and  others  patent  (E.  P.  7269,  1898)  the  production  of 
S  from  H2S,  obtained  by  the  reduction  of  native  sulphates  and 


30 


RAW  MATERIALS  OF  MANUFACTURE. 


treatment  by  COg.  This  H2S  is  passed  over  red-hot  sulphates^ 
which  are  thereby  reduced  and  yield  free  S  and  SOg. 

Falaschkowski  (Russ.  pat.  5464  and  5477,  190L  ;  Chem.  Zg. 
1902,  p.  15)  describes  the  following  modifications  of  the  process  of 
Baranoif  and  Hildt  for  obtaining  S  and  SOo  from  sulphates. 
Instead  of  simply  mixing  the  sulphates  with  coke,  he  moulds  them 
into  briquettes  by  means  of  coal-tar,  &c.,  which  shortens  the  time  of 
reduction.  The  sulphide  is  decomposed  by  CO2  at  a  pressure  of 
2  or  3  atmospheres.  The  HgS  is  best  not  passed  at  once  through 
red-hot  sulphates,  but  first  through  a  solution  of  the  sulphides, 
which  forms  Ca(SH)2  and  NaHS.  The  former  is  converted  by 
eneans  of  Na2S04  into  NaHS,  which  with  CO3  gives  HgS  and 
NaHCOa.  Only  this  HgS  is  employed  for  being  oxidized  by 
sulphates  to  S  and  SO2. 

Davidson  and  the  United  Alkali  Co.  (E.  P.  17476,  1897,  and 
7088,  1898)  describe  improvements  in  the  subliming  of  sulphur. 

Albright  and  Hood  (E.  P.  11988,  1894)  purify  sulphur  by 
heating  it  for  some  time  just  below  its  boiling-point. 

The  tvorld's  production  of  sulphur  is  stated  as  follows  in  Min. 
Ind.  ix.  p.  611,  from  official  sources,  in  metric  tons  : — 


Country. 


1895. 


Austria 830 

France  4,213 

Hungary    ,         102 

Germany  2,061 

Greece   1,480 

Italy 370,766 

Japan     15,557 

Bussia    190 

Spain 2,231 

Sweden nil. 

United  States    1,676 


1896. 


643 

9,720 

i        138 

!      2,263 

1.540 

!  426,a53 

12,540 

437 

1.800 

77 

3,861 


1897. 


530 

10,723 

112 

2.317 

358 

496,658 

12,013 

574 

3,500 

nil. 

1,717 


1898. 


496 

9,818 

93 

1,954 

135 

502,351 

10,339 
? 

3!l00 

50 

2,770 


1899. 


.555 

11,744 

116 

1,663 

1,150 

563,697 

10.241 

? 

1,100 
nil. 
1,.590 


The  sulphur  produced  as  a  by-product  of  the  Leblanc  process 
by  the  Chance-Claus  process  in  Great  Britain  is  not  included. 
This  is  estimated  for  1898  at  31,000  tons. 


ANALYSIS  OF  SULPHUR.  31 

Technical  Analysis  of  Sulphur, 

The  first  quality  of  Sicilian  sulphur  (prima  Lercara  or  prima 
Licata)  is  o£  a  fine  amber  colour,  in  large  shining  pieces^  and  does 
not  contain  more  than  1  per  cent.  ash.  The  second  quality  (seconda 
vantaggiata)  is  still  fine  yellow,  but  not  so  shining,  with  ash  up  to 
2  per  cent.;  the  third  (terza  vantaggiata),  which  is  that  generally 
used  for  sulphuric-acid  making,  contains  up  to  5  per  cent,  ash 
and  is  coloured  brown,  partly  by  bituminous  substances,  partly  by 
amorphous  sulphur.  "  Zolfo  ventilato  '^  (manufactured  by  Walter 
aud  Trewhella  at  Naples,  Fischer's  Jahresb.  1901,  p.  406)  is 
sulphur,  finely  ground,  raised  by  a  chain  of  buckets  and  sifted  by  the 
action  of  a  current  of  cooled  furnace-gases  (which  produce  less 
danger  of  fire  than  air  would  do,  as  they  contain  less  oxygen) . 

The  ordinary  technical  assay  of  brimstone  is  performed  by  burn- 
ing a  weighed  quantity,  say  10  grams,  in  a  small  porcelain  capsule, 
and  estimating  the  quantity  of  ash  left  behind.  It  is,  however, 
advisable  to  estimate  also  the  moisture,  for  which  purpose,  in 
order  to  prevent  any  evaporation  during  grinding,  an  average 
sample  of  the  unground  or  merely  roughly-crushed  material, 
weighing  100  grams,  is  dried  at  100°  C.  for  some  hours  in  an 
oven  or  water-bath. 

Bituminous  substances  are  most  easily  recognized  by  the  colour 
of  the  sulphur  j  they  occur  chiefly  in  sulphur  made  from  spent 
oxide  of  gas-works,  which  is  sometimes  coloured  quite  black. 

Arsenic  sometimes  occurs  in  brimstone,  more  especially  in  that 
recovered  from  alkali-works,  always  in  the  shape  of  arsenious  sul- 
phide. On  extracting  the  brimstone  with  disulphide  of  carbon, 
the  As^Sa  remains  behind  aud  can  be  estimated.  Schaeppi  (Chem, 
Ind.  1881,  p.  409)  prefers  extracting  the  AsgSg  with  dilute 
ammonia  (as  described  by  the  German  Pharmacopoeia)  at  70P  or 
80°  C.  In  the  solution  the  sulphur  can  be  precipitated  with  silver 
nitrate  as  Ag^S,  which  is  filtered,  washed,  dissolved  in  hot  nitric 
acid,  and  estimated  as  chloride ;  6  molecules  of  AgCl  correspond 
to  1  of  A83S3.  It  is,  however,  more  expeditious  to  work  volume- 
trically.  The  ammoniacal  solution  of  arsenious  sulphide  is  exactly 
neutralized  with  pure  nitric  acid,  strongly  diluted  and  titrated  with 
decinormal  silver  nitrate,  till  a  drop  of  the  solution,  on  addition 
of  neutral  potassium  chromate,  produces  a  brown  colour.  When 
.employing  10  grams  of  sulphur  for  extraction  with  ammonia,  each 


32  RAW  MATERIALS  OF  MANUFACTURE. 

c.c.  of  decinormal  silver  solution  indicates  0*041  per  cent.  AS2S3. 
Sometimes  arsenic  occurs  in  recovered  sulphur  in  the  shape  of 
ferric  or  calcium  arsenite,  which  cannot  be  found  by  the  above 
process,  but  only  by  extracting  the  sulphur  with  carbon  disulphide 
and  digesting  the  residue  with  aqua  regia. 

A  qualitative  reaction  for  arsenic  consists  in  agitating  1  gram 
sulphur  with  15  drops  liquor  ammonia  and  2  c.c.  water  for  half  an 
hour,  filtering,  adding  to  the  filtrate  30  drops  of  hydrochloric  acid 
and  15  drops  solution  of  oxalic  acid,  placing  a  bright  piece  of  brass 
in  the  solution  and  heating  to  60"-100°  ;  in  the  presence  of  arsenic 
the  brass  is  stained  grey  or  black  (Hager,  Pharm.  Centr.  1884, 
pp.  263  &  443) . 

Selenium  is  discovered  by  deflagrating  the  sulphur  with  nitrate 
of  potash,  dissolving  in  hydrochloric  acid,  and  treating  with  SO2, 
which  precipitates  the  selenium  as  a  red  powder. 

Keed  (Chem.  Zeit.  1897,  Rep.  p.  252)  describes  the  American 
test  for  selenium.  Boil  05  gram  sulphur  with  a  solution  of 
0*5  gram  potassium  cyanide  in  5  c.c.  water,  filter  and  acidify  the 
filtrate  with  H CI ;  a  red  colour,  appearing  within  an  hour,  shows 
selenium.  Or  else  boil  1  gram  sulphur  with  a  solution  of  2  grams 
potassium  cyanide  for  an  hour,  add  another  0*5  gram  KCy  and 
boil  for  another  half-hour.  Of  course  any  iron  present  will  react 
with  the  sulphocyanide  formed. 

Macagno  (Chem.  News,  xliii.  p.  192)  proposed  the  direct  esti- 
mation of  sulphur  by  means  of  its  solubility  in  carbon  disulphide  *. 
Pfeiffer  (Zsch.  anorg.  Ch.  xv.  p.  194,  and  Lunge,  Chem.  techn. 
Untersuchungs  methoden,  i.  p.  240)  has  re-investigated  this  matter 
and  given  the  following  prescriptions  for  this  method : — Shake  a 
weighed  sample  of  powdered  sulphur  with  exactly  four  times  the 
quantity  of  pure  carbon  disulphide,  filter,  reduce  the  temperature 
to  15°  C,  and  ascertain  the  specific  gravity  of  the  solution.  The 
following  table  (abridged  from  the  original)  shows  the  number  of 
parts  of  sulphur  dissolved  by  100  parts  by  weight  of  CS2  at  15°  C, 
for  various  specific  gravities  found : — 

♦  F.  B.  Carpenter  (Journ.  Soc.  Chem.  Ind.  1902,  p.  832)  points  out  that  crude 
sulphui*  sometimes  contains  a  large  quantity  of  gypsum  which  interferes  with 
the  carhon-disulphide  treatment.  In  such  cases  the  calcium  sulphate  must  be 
previously  removed  by  boiling  with  hydrochloric  acid. 


ANALYSIS  OF  8ULPHUK. 


33 


Specific 

Sulphur 

Specific 

Sulphur 

Specific 

Sulphur 

graTity. 

diaaolved. 

gravity. 

dissolved. 

gravity. 

dissolved. 

1-2708 

0 

1-3087 

8-5 

13426 

17-0 

1-2731 

0-5 

1-3108 

9-0 

1-3445 

17-5 

1-2754 

10 

1-3129 

9-5 

1-3463 

18-0 

1-2779 

1-5 

1-3150 

10-0 

1-3481 

18-5 

1-2800 

20 

1-3170 

10-5       , 

1-3500 

190 

1-2833 

.7.5       1 

1-3190 

110 

1-3517 

19-5 

1-2^7 

30 

1-3211 

11-5 

1-3536 

20-0 

1-2870 

3-5 

1-3231 

120 

1-3553 

20-5 

1-2894 

40 

1-3251 

12-5 

1-3571 

21-0 

1-2916 

4-5 

1-3271 

130 

l-a587 

21-5 

1-2938 

50 

1-3-291 

13-5 

1-3605 

220 

1-2960 

5-5 

1-3311 

140 

1-3622 

22-5 

1-2982 

60       , 

1-3330 

14-5 

1-3640 

23-0 

1-3003 

6-5       ' 

1-3350 

150 

13()57 

23-5 

1-3024 

70 

1-3369 

15-5 

l-ii(>74 

24-0 

1-3045 

7-5 

1-3388 

160 

1  3692 

24-5 

1-3066 

80 

1-3408 

16-0 

1-37(K) 

25-0 

The  same  subject  is  again  treated  by  P.  Puchs  (Zsch.  angew.  Ch. 
1898,  p.  1189).  His  figures  are  slightly  different  from  those  of 
Pfeiffer;  but  the  latter^s  results  (which  were  obtained  in  my  own 
laboratory)  seem  to  me  the  most  accurate  obtainable. 

For  the  purpose  of  preventing  the  grape-disease  (the  Oidium)  the 
decree  of  fineness  of  ground  sulphur  is  very  important.  In  Prance 
this  is  ascertained  by  Chancel's  sulphurinieier,  shown  in  fig.  2  on  a 
scale  of  1 : 2.  This  is  a  glass  tube  sealed  at  the  bottom  and  closed 
at  the  top  by  a  ground-in  glass  stopper.  It  is  23  cm.  long  and 
15  mm.  wide,  and  divided  into  100  degrees  of  ^  c.c.  each,  beginning 
from  the  bottom  ;  the  100  degrees  occupy  a  space  of  100  mm. 

If  ground  sulphur  is  shaken  up  with  anhydrous  ether  it  forms, 
after  settling  down,  a  layer,  the  height  of  which  corresponds  to  the 
fineness  of  the  powder.  The  sulphur  to  be  tested  is  passed  through 
a  sieve  with  meshes  1  mm.  wide  ;  5  grams  of  it  are  put  in  the 
tube,  together  with  ether  of  17°*5  C,  or  very  nearly  that  tempera- 
ture, filling  half  the  tube.  The  tube  is  well  shaken  to  break  up 
all  small  lumps,  more  ether  is  poured  in  up  to  1  cm.  above  the 
degree  100,  the  tube  is  again  shaken  and  placed  in  a  vertical 
position.  When  the  layer  of  sulphur  ceases  to  subside,  its  height 
is  read  off  and  stated  as  "  degrees  Chancel.'^ 

Ordinary  ground  and  sifted  sulphur  shows  50°  to  55°  Chancel, 
finer  grades  70°  to  75°.     The  finest  grade  is  obtained  not  by 

VOL.  I.  n 


34 


RAW  MATERIALS  OF  MANUFACTURE. 


•^o 


sieving,  but  by  fanning— this  "  zolfo  ventilate  "  shows  90°  to  95 
Chancel  (Walter,  Chem.  Zeit.  1901,  p.  459 ;  supra,  p.  31).     For 
use  in  vineyards  the  sulphur  ought  to  show  at  least 
60°  Chancel ;  some  go  as  far  as  75°  Chancel.  1%  -• 

Analysis  of  refined  sulphur, — Sulphur  in  blocks 
or  rods  is  almost  always  practically  pure  ;  it  may  be 
tested  for  ashes,  arsenic,  and  selenium  as  above. 

Flowers  of  sulphur  is  never  quite  pure  unless 
specially  washed  ;  it  always  contains  some  acid, 
landa  (Fischer's  Jahresb.  1898,  p.  421)  found  up  to 
0*283  per  cent,  ashes  ;  the  average  of  30  samples  was 
0*063  per  cent.  He  also  tests  the  solubility  i n  boiling 
solution  of  caustic  soda  of  spec.  grav.  1*2.  This 
varied  from  88  per  cent,  (in  one  case  68  per  cent.) 
to  99*99  per  cent.,  average  98*04  per  cent. 


2.  Pyrites. 


^ITi 


-n 


1^ 


What  is  called  pyrites  or  iron-pyrites,  in  a  techni- 
cal sense,  is  hardly  ever  pure  iron  disulphide,  PeSo, 
but  either  a  mixture  of  this  with  gangue,  or  more 
frequently  at  the  same  time  with  other  sulphuretted 
ores,  as  shown  by  ftumerous  analyses.  The  iron  di- 
sulphide may  be  present  either  as  iron-pyrites  proper 
or  as  marcasite.  The  iron-pyrites  proper  crystallizes 
in  the  regular  system,  with  parallel  hemihedry, 
proved  even  on  the  faces  of  the  cube  by  striation 
(fig.  3). 

Besides  the  cube   (I),  the  octahedron,  a  (IT),  is 
frequently  found,  often  modified  by  the  pyritohedron, 
b  (III),  and,  if  both  are  equally  developed,  forming 
the  icosahedron  (II).     The  combined  forms  IV,  V, 
VI,  as  well  as  twin  crystals,  frequently  occur.     The 
crystals  are  often  well  developed ;  but  in  the  pyrites 
used  on  the  large  scale  they  are  mostly  quite  indistinct. 
The  colour  of  pure  pyrites  is  greyish  yellow,  and 
easily  distinguished  from  that  of  copper- pyrites.     The  microcrys- 
talline  pyrites  of  trade  often  shows  other  colours,  even  a  slate^ 
grey ;  the  powder  is  brownish  black.     Its  cleavage  parallel  to  the 
faces  of  the  cube  is  not  very  pronounced ;  the  fracture  is  con- 


FVHITEf.  35 

choidal  or  irr^ular.  Hardness  6  to  6^,  specific  gravity  4-83  to  5-2. 
Pure  FeS,  contains  46-67  per  cent,  of  iron  and  53'33  per  cent,  of 
sulphur. 

According  to  Meue,  the  pyrites  from  volcanic  formations  con- 
tains DO  water,  but  that  from  sedimentary  strata  both  water  and 

Fig.  3. 


clay.  Among  the  first  he  classes  tlie  yellow  octaliedral  pyrites, 
which  is  stable  in  the  air;  among  the  latter  the  grey  cubical 
pyrites,  which  is  easily  transformed  into  ferric  sulphate  (Compt. 
rend.  29th  April,  1867). 

Marcasite  crystallizes  in  the  rhombic  system,  in  rhombical 
prisms  wi  =  106°  2'  with  longitudinal  faces  /=100^  and  r,  and  the 
end  face  p  inclined  to  r  at  an  angle  of  158^  aff.     Tiiey  frequently 

d2 


S6  KAW  MATERIALS  OF  MANUFACTUKE. 

occur  in  twin  crystals,  partially  united  along  one  of  the  faces  m, 
also  in  triplets  aud  quadruplets,  &c.  (fig.  4),  in  fibrous,  bulbous,  &c. 
varieties ;  cleavage  indistinct ;  hard- 
ness 6  to  6-5  ;  specific  gravity  4-65  *"'?■  *■ 
to  488;  colour  grey  to  yellow  or 
greenish  yellow,  lighter  than  iron- 
pyrites    proper;    powder    greenish 
dark  grey.     Marcasite  ia  moat  fre- 
quently found  in  bituminous  slate 
and   coal,  and   decays   even   more 

quickly  than  pyrites,  with  the  formation  of  ferrous  sulphate  and 
basic  ferric  sulphate. 

Detailed  investigations  on  the  different  behaviour  of  pyrites  and 
marcasite  have  been  published  by  A,  P.  Brown  (Chem.  News, 
1895,  Ixxi.  p.  139,  and  following  numbers)  aud  by  Stokes  (Bulletin 
U.S.  Geol.  Surv.  No.  186,  1901). 

In  the  oiea  of  commerce  there  is  often  present,  mixed  with  FeSj, 
^magnetic  pyrites  (pyrrhotite)  of  the  formula  FejSg,  with  60'5  iron 
and  39'5  sulphur;  colour  between  brass-yellow  and  copper-red  ; 
hanlness  3"5  to  4'5 ;  specific  gravity  4'4  to  4*  7.  Pyrrhotite  occurs 
by  itself  in  large  quantities,  which  have  been  scarcely  utilized  up 
to  the  present. 

The  copper-pyrites  so  often  mixed  with  iron-pyritea  is  distin- 
guished from  it  by  its  colour,  yellow  as  brass,  sometimes  as  gold ; 
this  colour  modifies  that  of  the  iron-pyrites  according  to  the  degree 
of  admixture.  It  crystallizes  in  the  tetragonal  system,  but  in  the 
ores  which  concern  us  always  occurs  in  a  microcryatalline  form. 
Its  hardness  is  3'5  to  40,  specific  gravity  41  to4-3.  Pure  copper- 
pyrites  of  the  formula  FeCuSj  should  contain  3053  per  cent,  iron, 
34'58  per  cent,  copper,  and  34'88  per  cent,  sulphur;  but  the  ores 
serving  for  the  manufacture  of  sulphuric  acid  rarely  contain  beyond 
4  per  cent,  of  copper. 

The  first  application  of  pyrites  for  sulphuric -acid  making  is  gene- 
rally ascribed  to  a  Mr.  Hill,  of  Deptford,  who  in  1818  took  out  a 
patent  for  it  ♦.  In  France,  Clement- Desormes  seems  to  have  made 
the  first  proposals  and  experiraenta  in  that  way.  His  trials  did 
not,  however,  succeed,  because  he  believed  it  necessary  to  increase 
the  combustibility  of  pyrites  by  an  addition  of  coal.  This  is  both 
unnecessary,  with  properly  constructed  kilns,  and  very  injurious 
*  Sotol  attributes  this  honour  to  his  couatryuian,  d'Artiguaa,  in  1793. 


FIRST  APPLICATION  OP  PYRITK8,  37 

to  the  process,  from  the  carbonic  acid  getting  into  the  chambers. 

A  great  difficulty  was  experienced  in  lighting  the  kilns.     So  long 

as  it  was  attempted  to  do  this  from  below,  like  an  ordinary  fire, 

the  thing  would  not  work.     According  to  communications  from 

Mr.  Todd  (Government  Inspector  of  Alkali  Works),  a  workman 

of  his  father's  in  Cornwall,  in  1830,  accidentally  discovered  the 

way  of  lighting  the  kilns  from  the  top,  such  as  is  practised  to  this 

day.      Generally,   however,  the   principal  merit   of  introducing 

pyrites  is  ascribed  to  Messrs.  Perret  and  Son,  of  Chessy,  who  were 

led  to  it  by  the  necessity  of  desulphurizing  their  cupreous  pyrites 

previously  to  getting  the  copper,  and  of  condensing  the  gas  evolved. 

There  was  no  question  then  of  supplanting  the  Sicilian  sulphur 

generally.     Perret  and  Son,  with  the  greatest  care,  searched  into 

all  the  conditions  necessary  for  a  proper  combustion  of  the  ore ; 

and  to  them  the  honour  is  due  of  having  overcome  all  the  difficulties 

opposed  to  the  solution  of  this  problem,  and  of  having  rendered 

the  process  technically  useful.     Already  in  1833  they  had  burnt 

iron-pyrites  successfully  ;  and  in  a  patent  dated  November  20th, 

1835,  they  described  their  process,  to  which  their  partner,  Olivier, 

is  said  to  have  given  the  first  impulse.     In  1837,  Messrs.  Wehrle 

and  Braun,  in  Bohemia,  used  pyrites  for  generating  sulphurous 

acid   (Otto,  '  Lehrbuch  der  Chemie,'  4th  ed.  iii.  1,  p.  545) ;  but, 

according  to  Bauer  (/.  c.  p.  6),  I.  Brem  had  introduced  this  process 

into  Austria  (at  Lukawetz)  already  in  1833 — that  is,  at  the  same 

time  as  Perret. 

These  trials  at  making  sulphuric  acid  from  pyrites  possessed, 
however,  only  local  interest ;  and  probably  for  a  long  time  no 
general  attempt  to  do  away  with  Sicilian  brimstone  would  have 
been  made,  but  for  the  Neapolitan  Government,  in  1838,  being 
induced  to  grant  a  monopoly  for  the  exportation  of  Sicilian  sulphur 
to  the  Marseilles  firm  of  Taix  and  Co.  This  firm  at  once  raised 
the  price  of  brimstone  from  £6  to  £14  per  ton,  and  thus  would 
have  given  a  fatal  blow  to  the  manufacture  of  artificial  soda-ash, 
just  then  beginning  to  take  a  firm  hold,  if  no  other  source  of 
sulphur  had  been  known,  and  if  such  an  unnatural  measure 
could  have  been  carried  out  at  all.  But  the  attempt  came 
too  late — just  after  Perret  and  Son  had  proved  that  the  pyrites 
occurring  in  most  industrial  countries  could  be  used  for  vitriol- 
making  without  any  difficulty.  The  result  was  to  be  foreseen. 
Once  the  discovery  of  a  new  source  of  sulphur  had  become  a 


38  RAW  MATERIALS  Of  MANUFACTURE. 

matter  of  necessity^  there  were,  within  twelve  months  from  the 
rise  in  the  price  of  brimstone,  fifteen  patents  taken  out  in  England 
for  burning  pyrites  for  the  purpose  of  making  sulphurous  acid, 
and  even  a  larger  number  for  making  sulphur  from  pyrites, 
gypsum,  &c. 

According  to  Muspratt^s  ^ Chemistry^  (vol.  ii.  p.  1023),  Dr. 
Thomas  Thomson  was  the  first  in  England  to  point  to  pyrites  in 
this  crisis ;  but  most  probably  many  others  at  the  same  time 
turned  to  it.  So  much  is  proved — that  Thomas  Farmer,  of  Lon- 
don, was  the  first  in  England  who  employed  pyrites  on  a  large 
scale  (in  1839)  for  the  manufacture  of  sulphuric  acid  (Hofmann, 
'  Beport  by  the  Juries,  International  Exhibition,  1862,  Class  II. 
Section  A/  p.  12). 

Mr.  E.  K.  Muspratt  states  that  his  father,  in  1839  and  1840, 
used  large  quantities  of  Wicklow  and  Welsh  pyrites  at  Liverpool 
and  Newton,  the  cupreous  cinders  being  sent  to  the  Sutton  Copper 
Company  at  St.  Helens. 

In  Germany  the  Oker  works,  at  the  Rammelsberg,  near  Goslar, 
seem  to  have  been  the  first  who  calcined  the  local  ore  in  such  a 
way  as  to  convert  the  sulphurous  acid  given  off  into  sulphuric  acid 
in  acid-chambers;  and  other  smelting- works,  such  as  those  at 
Freiberg,  followed  their  example.  In  these  cases  the  reasons 
were,  not  only  that  at  a  comparatively  small  expense  sulphuric 
acid  could  be  obtained  as  a  by-product  from  the  sulphurous  acid 
otherwise  lost,  but  also  that  the  acid  fumes  destroyed  the  vege- 
tation of  a  large  district  round  the  works,  and  that  means  had  to 
be  taken  for  preventing  this,  apart  from  any  consideration  of 
profit. 

The  Sicilian  brimstone  monopoly  certainly  did  not  last  long ; 
diplomatic  pressure  on  the  part  of  England  soon  led  to  its 
abolition ;  and  with  the  lowering  of  the  price  of  brimstone  most 
works  at  first  returned  to  its  employment.  But  the  ice  was  now 
broken  ;  the  conviction  had  been  gained  that  it  was  possible  to 
make  acid  without  Sicilian  brimstone  ;  the  owners  of  pyrites- 
mines  took  pains  to  advance  the  use  of  pyrites  by  low  prices; 
and  thus,  in  the  course  of  the  next  twenty  years,  brimstone  was 
gradually,  but  steadily,  driven  from  its  place  in  sulphuric-acid 
making,  in  proportion  as,  on  the  one  hand,  it  became  dearer 
from  the  causes  above  mentioned  (disease  of  the  vines  &c.),  and  as 


f 


FIRST  EMPLOYMENT  OF  PYRITES.  39 

more  pyrites-mines  were  opened  out.  In  1852  brimstone  was  no 
longer  used  in  Lancashire,  but  on  the  Tyne  7580  tons  of  it  were 
still  burned. 

The  decisive  point  in  favour  of  the  use  of  pyrites  was  this^  that 
continually  increasing  quantities  of  cupreous  pyrites  came  into  the 
market^  from  Spain  especiaUy  (first  in  1859),  but  also  from  other 
countries.  These  had  at  any  rate  to  be  burnt  and  their  sulphur 
expelled  before  they  could  be  worked  for  copper.  Already  with 
Perret  and  Son  this  had  been  the  stimulus  for  their  efforts ;  but 
this  has  been  done  on  a  much  more  colossal  scale  in  consequence 
of  the  opening  out  of  the  cupreous-pyrites  mines  in  the  south  of 
Spain^  in  Portugal,  and  in  Norway.  In  England  iron-pyrites 
is  now  all  but  out  of  the  fields  and  has  been  supplanted  by 
cupreous  pyrites.  This  has  been  the  case  to  a  less  extent  in 
France  and  Germany^  because  they  possess  mines  of  rich  iron- 
pyrites,  which  in  England  are  not  numerous ;  but  even  in  those 
countries  more  cupreous  pyrites  is  now  used.  In  1867  pyrites 
had  almost  entirely  supplanted  brimstone  in  France  as  a  raw 
material  for  acid-making  in  the  large  industrial  centres  ('  Rapport 
du  Jury  International^  Expos.  Univ.  de  1867/  vol.  vii.  p.  19). 
In  Germany  this  state  was  brought  about  somewhat  later,  but 
quite  as  completely.  Only  during  the  feverish  years  1871  to  1873, 
when  the  price  of  pyrites  had  risen  very  high,  a  few  factories  in 
Hanover,  in  Hamburg,  and  Stettin  temporarily  returned  to  the  use 
of  brimstone  (Hasenclever,  /.  c.  p.  155) ;  but  with  lower  prices  of 
pyrites  this  was  given  up  again.  Spanish  pyrites  began  to  be  used 
in  (iermany  in  1877. 

Tims,  starting  from  tlie  use  of  iron-pyrites,  that  of  cupreous 
pyrites  has  followed ;  and  to  this  was  added  the  employment  of 
other  sulphurous  ores  and  of  the  intermediate  products  of  smelting 
— for  instance,  copper-regulus  {''  coarse  metal '')  at  Mansfield  and 
Swansea.  The  first  chambers  working  with  SO3  from  the  metal- 
lurgical treatment  of  copper  and  lead  ores  were  started  at  Oker  in 
1859,  at  Freiberg  in  1861.  The  Freiberg  works  employ  for  this 
purpose  even  poor  lead-matts  with  about  22  per  cent,  of  sulphur, 
which  formerly  was  thought  impossible  (Bode,  '  Beitriige  zur 
Theorie  und  Praxis  der  Schwefelsiiurefabrikation,'  1872,  p.  1). 
We  shall  further  on  describe  the  application  of  other  sulphur^ores 
apart  from  pyrites  proper. 


40 


RAW  MATERIALS  OF  MANUFACTURE. 


The  principal  sources  of  pyrites  will  now  be  mentioned  without 
separating  the  cupreous  from  the  non-cupreous,  because  no  strict 
limit  can  be  drawn.  Some  kinds  of  pyrites  contain  so  little  copper 
(below  1  per  cent.)  that  it  cannot  be  utilized  ;  and  these  go  with 
the  totally  non-cupreous  ores. 

Great  Britain  possesses  several  deposits  of  pyrites,  but  none  of 
very  great  importance.  In  Cornwall  and  Devonshire  pyrites  of 
the  following  composition  is  found  : — 


rattinson. 

Sulphur  27-00 

Iron 22-69 

Copper     2-00 

Lead    trace 

Zinc 1-23 

Lime    0-22 

Carbonate  of  Lime      

Magnesia 0*12 

Arsenic    032 

Insoluble  (silica) . . ,  45*60 

Oxygen  as  FcgO;;  . ,  0*  1 3 

Moisture 0*64 


Clapham  (8  analyses). 

24-013-34-880 

27-076-60-676 

0-400-  4-600 

0-       -  7-446 

0-       -  9-086 

Gypsum     0*       -  0-596 

0-       -  3-579 

0-       -  1-160 
2000-38-676 


99-95 


Cleveland  pyrites  (from  the  north  of:  Yorkshire)  is  only  used  in  a 
local  factory ;  in  1874, 500  tons  of  it  were  obtained.  Composition 
(according  to  Pattinson^s  analysis)  : — 

Iron  disulphide 52*12 

(corresponding  to  27'  18  sulphur) . 

Iron  protoxide 11-92 

Alumina    8*10 

Lime ,  0*27 

Magnesia  TOO 

Carbonic  acid    2-40 

Insoluble  in  acid  11*12 

Water    ../. 12-80 


99-79 


PYRITES  IN  GREAT  BRITAIN. 


41 


In  Ireland  there  are  large  beds  of  pyrites,  especially  in  the 
county  of  Wickloir ;  and  up  to  about  1862  this  Irish  ore  supplied 
a  very  large  portion  of  the  pyrites  used  in  England.  In  1860 
still  40,000  tons  of  it  were  imported  into  the  Tyne  River ;  but  in 
1863  the  importation  had  fallen  to  4000  tons,  and  has  long  since 
ceased  entirely.  The  same  has  been  the  case  in  Lancashire  j  and 
only  a  few  works  in  Ireland  itself  burn  this  kind  of  pyrites.  It  is 
found  in  the  county  of  Wicklow  in  beds  from  6  to  50  feet  in 
thickness,  which  overlie  siliceous  clay-slate.  The  beds  go  down 
to  depths  of  80  to  100  fathoms.  The  bulk  of  the  ore  contains 
only  30  to  35  per  cent,  of  sulphur.  A  small  quantity  only 
of  richer  ore  (analyses  a,  b,  c)  has  been  found  in  the  valley  of 
Ovoca.  The  Irish  ore  is  too  hard  and  slaty  and  does  not  bum 
well ;  it  requires  a  great  heat,  and  consequently  deep  kilns.  It 
nearly  always  contains  copper,  but  rarely  suflScient  to  pay  for 
extracting  it,  from  which  standpoint  the  following  analyses  must 
be  judged : — 


Pattinson. 
a. 

Clapham. 

b. 

r. 

d. 

e. 

Sulphur 

..    44-20 

40-410 

42-128 

37-975 

34-()76 

Iron   

..    40o2 

32-222 

a'l-ooo 

34-650 

42-400 

Copper  

..      0-90 

4-133 

2-400 

2-400 

1-333 

Lead  

..       1-50 

2-963 

1-600 

1-080 

1-593 

Zinc    

..      3-51 

•  •  ■ 

•  •  • 

•  ■  • 

•  •  • 

Arsenic  

..      0-33 

•  •  ■ 

0-602 

0-40(» 

0-183 

Lime  

..      0-24 

•  •  ■ 

•  •  • 

•  •  • 

•  ■  • 

Inifoluble   

8-80 

17-676 

18-676 

22-500 

20-000 

Moisture    

..      0K)9 

•  •  • 

•  ■  ■ 

•  •• 

•  •  ■ 

Oxygen  as  Fe-^O, 

..      0-25 

•  •  • 

•  ■• 

■  •  ■ 

•  •  • 

100-34 


97-404 


100-406 


99-005 


100-185 


In  JVales  (in  the  Cae  Coch  Mine)  pyrites  is  found  entirely  free 
from  arsenic^  according  to  Drink  water  (Journ.  Soc.  Chem.  Ind. 
1885,  p.  533).  It  contains  48*3  per  cent,  of  sulphur,  and  is  used 
for  manufacturing  very  pure  oil  of  vitriol. 

A  certain  quantity  of  pyrites  is  picked  from  coals,  and  is  known 
as  coal'brasses.  If  quite  free  from  coal,  they  are  very  rich — 
according  to  R.  D.  Thompson  (in  Richardson  &  Watts's  '  Chemical 
Technology,'  vol.  i.  pt.  iii.  p.  15),  53*55  sulphur,  45*07  iron,  0*70 
manganese,  0*80  silica;  but  practically  they  cannot  be  obtained 


42  RAW  MATERIALS  OF  MANUFACTURE. 

in  this  state^  and  the  carbonaceous  matter  adhering  to  them  causes 
very  much  trouble  in  the  vitriol  chambers.  Their  principal  use 
in  acid-making  is  for  lighting  the  burners,  or  for  getting  up  their 
heat  if  it  has  gone  down.  Mr.  G.  E.  Davis  informs  me  that  coal- 
brasses  with  44  per  cent.  S  and  some  carbon  can  be  burnt  in 
ordinary  pyrites-kilns,  and,  if  proper  arrangements  are  made,  yield 
perfectly  clear  acid  from  the  Glover  tower.  Apart  from  this  they 
are  worked  up  by  weathering  for  copperas  and  Venetian  red,  and 
this  is  probably  the  way  in  which  most  of  the  quantity  obtained 
in  England  (10,000  tons  in  1874)  is  consumed. 

The  total  production  of  pyrites  in  the  United  Kingdom  was 
25,401  tons  in  1882,  27,829  tons  in  1886;  in  1887,  22,079  tons; 
in  1888,  23,507  tons  ;  in  1889, 17,719  tons;  in  1890,  16,018  tons ; 
1895,  9193  tons; ^1896,  10,177  tons;  1897,  10,752  tons;  1898, 
12,302  tons;  1899,  12,426  tons;  1900,  12,484  tons. 

The  importations  of  foreign  pi/rites  into  Great  Britain  during  the 
years  1862  to  1887  are  quoted  in  our  second  edition,  vol.  i.  p.  32. 
Here  we  shall  quote  (from  the  volumes  of  ^  Mineral  Industry ') 
the  importations  of  pyrites  (iron  and  cupreous)  into  Great  Britain 
since  the  year  1888.  (The  tons  are  metrical  tons  at  1000  kil8.= 
0-9812  English  ton.) 

Year.  Pyrites  imported.         '  Year.  Pyrites  imported. 

Tons.  Tons. 


1888 629,056 

1889 654,872 

1890 667,625 


1895 591,782 

1896 598,480 

1897 633,009 


1891 662,297         1898 665,544 

1892 614,238     I    1899 712,393 


1893 622,63i     i    1900 752,605 

1894 625,968     | 

The  most  important  German  pyrites-bed  is  that  of  Meggen  in 
the  Siegen  district,  in  Westphalia,  3  miles  from  the  Altenhunden 
station  on  the  Ruhr-Sieg  railway.  This  bed  occurs  along  with 
heavy  spar  in  the  so-called  "  Kramenzel;^^  it  is  known  for  a  length 
of  2000  fathoms,  and  its  thickness  changes  from  ^  to  3  fathoms 
(Wagner^s  '  Jahresbericht,'  1865,  p.  221).  The  same  authority 
states  it  to  be  *'grey  iron-pyrites,"  quite  uncrystalline,  free  from 
arsenic  [?] .     The  mass  of  ore  above  the  bottom  of  the  valley  is 


PYRITES  IN  GERMANY.  43 

estimated  at  4J  million  tons ;  how  far  the  ore  descends  below  the 
bottom  of  the  valley  is  as  yet  unknown. 

The  ore  has  not  an  attractive  outward  appearance ;  its  colour 
is  slate-grey ;  but  it  burns  very  well  in  the  kilns^  and  it  would  be 
even  more  valuable  if  the  zinc  contained  in  it  did  not  prevent  its 
burning  completely.  Older  analyses  of  it  are  given  iu  our  2nd 
edition^  vol.  i.  p.  35.  Here  I  quote  the  most  recent  analyses 
made  at  the  Rhenania  Chemical  works^  as  furnished  to  mc  by 
Dr.  R.  Hasenclever  in  1902  : — 


a, 

Gangue... 1202 

Sulphur 41-94 

Iron   34-92 

Zinc  7-56 

Lead  038 

Lime 0*50 

Arsenic trace 


b. 

Average. 

12-96 

120 

43-42 

400-43-0 

35-56 

35-0 

5-81 

7-0 

not  estim. 

0-3-0-5 

ij 

0-1-0-5 

005 

trace-005 

97-32  97-80 

The  average  represents  12  per  cent,  gangue,  75  per  cent,  iron- 
pyrites  (FeS2),  10*5  per  cent,  zinc-blende  (ZnS),  together  97*5. 

Jurisch  (Schwefelsaure-fabrikation^  p.  14  et  seq.)  quotes  a 
number  of  analyses  of  Westphalian  pyrites,  by  F.  Quincke,  for 
the  year  1892.  In  these  the  sulphur  varied  from  41  to  46-75 
per  cent.,  iron  from  2955  to  36*16  per  cent.,  zinc  from  8*2  to 
19-41  per  cent.  (I  exclude  two  samples  containing  27*58  and 
4205  per  cent,  zinc,  which  are  more  correctly  classed  as  blende 
than  as  pyrites),  lead  from  0-3  to  1*7  per  cent.,  arsenic  from  01  to 
0-2  per  cent.,  besides  silica,  alumina,  lime,  magnesia,  manganese, 
alkalies,  and  small  quantities  of  other  substances. 

The  same  source  quotes  analyses  of  pyrites  from  Bensberg 
(46'86  per  cent.  S),  Aachen  (46*0  per  cent.),  Rammelsberg 
(44-65  to  48-4  per  cent.),  Freiberg  (52-20  per  cent.). 

The  following  is  a  complete  analysis  by  Fresenius  of  ore  from 
the  Philippine  pit  belonging  to  the  Sicilia  Mining  Company  at 
Meggen,  made  in  1898  : — 


44  RAW  MATERIALS  OF  MANUFACTURE. 

Iron    34-89 

Zinc 8-38 

Manganese    0"155 

Cobalt  and  Nickel    0024 

Lead  0*298 

Alumina    trace 

Lime 1  '41 

Magnesia   0*75 

Sulphur     44*55 

Arsenic 0*07 

Carbon  dioxide 1*90 

Phosphorus  peroxide    trace 

Gangue 5*83 

Oxygen  as  sulphate^  thiosulphate^  &c.^ 

and  traces  of  other  substances     1*  743 


100,000 


There  are  smaller  beds  of  pyrites  in  several  other  places  in 
Germany,  such  as  those  near  Goslar,  near  Schwelm  in  West- 
phalia, near  Merzdorf  in  Silesia,  &c.  Their  production  is  only 
small  compared  with  that  of  the  Meggen  pyrites.  The  pyrites  of 
the  Rammelsberg  in  the  Harz,  according  to  Mene,  contains  48*4 
per  cent,  of  sulphur  (probably  only  picked  lumps).  The  cupreous 
pyrites  of  the  same  place  is  stated  by  Hilgenfeld  to  contain : — 

Copper  12-22 

Lead  2*43 

Iron    39-10 

Zinc,  Manganese,  Cobalt,  Nickel   1*23 

Arsenic 018 

Antimony 0'16 

Sulphur 44'65 

Selenium,  Thallium,  Indium,  Bismuth traces 

99-97 

The  bed  of  Schwelm  in  Westphalia,  in  the  Devonian  formation, 
has  a  thickness  of  from  10  to  33  feet,  over  a  surface  of  nearly 
150  acres,  and  is  covered  by  rich  iron-ore;  the  pyrites  itself 
consists  of  two-thirds  powder  mixed  with  well-crystallized  pieces. 


PYRITES  IN  GERMANY  AND  AUSTRIA.  45 

The  ore  contains  about  40  per  cent,  sulphur^  and  more  or  less 
clay,  which  is  removed  by  washing ;  after  this  it  is  sold  to  the 
vitriol-makers,  who  like  it  on  account  of  its  freedom  from  arsenic 
(Dingl.  Journ.  ccxxviii.  p.  283) ;  Hjelt,  however,  found  more 
arsenic  in  it  than  in  Meggen  pyrites. 

On  the  island  of  Wollin  a  pyrites-bed  is  found  in  a  bed  of  marl 
belonging  to  the  chalk  formation. 

A  great  drawback  to  the  German  ores  is  their  proportion  of 
zinc,  which  retains  a  considerable  quantity  of  sulphur  in  the 
state  of  sulphate.  In  Silesia  14  per  cent,  of  zinc  is  allowed  as 
a  maximum;  upwards  of  this  for  each  per  cent,  of  zinc  the  same 
quantity  of  sulphur  is  deducted  from  the  invoice  (Kosmann,  in 
Fischer's  Jahresb.  1886,  p.  268). 

The  production  of  German  pyrites  during  the  years  1853  to 
1886  is  quoted  in  the  second  edition  of  this  work,  vol.  i.  p.  38; 
that  between  1891  and  1897  by  Hasenclever,  Chem.  Ind.  1899, 
p.  25. 

The  maximum  production  in  1874  was  143,476  tons ;  the 
average  of  the  last  years  is  about  130,000  tons.  The  production 
was  133,302  tons  in  1897,  136,849  tons  in  1898,  144,602  tons  in 
1899.  Hasenclever  estimates  that  about  65,000  tons  was  con- 
sumed in  the  manufacture  of  wood  pulp.  The  importation  of 
foreign  (chiefly  Spanish)  pyrites  into  Germany  increased  from 
238,643  tons  in  1891  to  357,017  tons  in  1897,  all  of  this  for 
sulphuric  acid.  In  1898  it  was  376,817  tons,  in  1899  437,732 
tons,  in  1900  457,679  tons. 

The  exportation  is  small :  in  1898  19,219  tons,  in  1899  16,985 
tons,  in  1900  24,936  tons. 

Austria-Hungary  possesses  large  beds  of  pyrites  at  Schemnitz 
and  Schmolnitz  in  Hungary,  in  Styria,  and  Tirol.  The  pyrites  from 
Schemnitz  contains  on  an  average  47  to  48  per  cent.  S,  39  to  40 
per  cent.  Fe,  0*58  per  cent.  Cu,  1*5  to  2  per  cent.  Zn,  besides  lead, 
silver  (81  grams  per  ton),  and  gold  (2*2  grams  per  ton).  Schmol- 
nitz ore  contains  44  to  48  per  cent.  S,  0*4  to  06  per  cent.  Cu, 
2  to  3  per  cent.  Zn.  Jurisch  (from  whose  *  Schwefelsaure- 
fabrikation,'  p.  18,  the  above  is  taken)  quotes  an  analysis  of 
Schmolnitz  pyrites  with  48*89  per  cent.  S,  0'32  per  cent.  Cu, 
0'14  per  cent.  As;  70,000  or  80,000  tons  of  this  pyrites  are 
obtained  per  annum. 

In  Tirol  pyrites  is  found  testing  40*5  to  41*3  per  cent.  S. 

In  Styria  (Riedl,  Zeitschr.  f.  d.  chem.  Grossgewerbe,  ii.  p.  567), 


46 


RAW  MATERIALS  OF  MANUFACTURE. 


in  the  Saun  valley,  a  number  of  beds  of  very  pure  but  easily  decom- 
posable pyrites  occur  in  the  clay  porphyry^  with  a  percentage  of 
48  to  52  of  sulphur.  It  is  used  in  the  chemical  works  at  Hrastnigg^ 
and  in  Bohemia.  The  production  is  about  3000  tons  per  annum 
(Fischer,  Jahresb.  1886,  p.  255). 

In  Switzerland,  in  the  Canton  of  Wallis,  a  pyrites  is  obtained 
which  does  not  seem  to  have  found  any  technical  application 
as  yet.  Its  composition,  according  to  an  analysis  made  in  my 
laboratory,  is : — 

(of  this  0*05  as  lead 
sulphate  in  the  in- 
soluble residue). 


Sulphur     .... 

50-46 

Iron   

44'55 

Lead 

0-37 

Lime 

1-13 

Maffnesia  .... 

Oil 

Carbonic  acid 

1-01 

Silica,   Iron 
Alumina  . 
Moisture   . . . . 

, ,, , 

peroxide, 

•  •••••••••a 

} 

. . . 

1-70 
0-40 

(insoluble). 


99  73 


In  Poland  pyrites  occurs  together  with  blende,  containing  some 
thallium  (Antiporo,  Fischer's  Jahresb.  1897,  p.  421). 

lu  Belgium  a  rich  pyrites  is  met  with,  the  great  friability  and 
softness  of  which  do  not  tell  in  its  favour.  The  following  are 
analyses  of  this  pyrites : — 


0. 


Sulphur 42-80 


5ITic  1 


36-70 
7-23 


0-92 
0'4(> 


Iron 

Ferric  oxide 

Oxygen  in  ferric 
oxide... 

Leud 

Zinc  

Arsenic 0*20 

Thallium  

Alumina    trace 

Silica     8-8(> 

Carbonic  acid   

Calcium  carbonate .      0*84 

Lime 

Water  I'-IG 


b. 
35-50 
38-60 

4-24 


c. 
46-20 

40:)0 

2-20 


0(ii> 
5-26 
031 


14-90 


trace 


0-5(> 


0-41 
0-22 
0-41 


d. 
40-01 

39-68 

0-32 

0-37 

1-80 

trat^e 

trace 


9-10        12-23 


042 


025 
025 


e. 
50W 
43-61 

0-18 

1-75 
trace 


2-85 
0-73 


45-60 
38-52 

6-0O 


0-92 
0-10 


trace 


9-00 


Oil 


0-36 


99  U       10002        lK)-46        9991       10014        9959 


PYRITES  IN  BELGIUM  AND  FRANCE.  47 

{a,  b,  and  c  bv  Clapham  in  Richardson  and  Watts's  '  Chemical 
Technology/  vol.  i.  part  iii.  p.  14 ;  d,  pyrites  from  llodieux  near 
Spa ;  e,  from  Santon's  pit  on  the  Meuse^  both  by  Pattinson,  /.  c. ; 
f,  by  MacCuUoch^  Chem.  News,  xxvii.  p.  125.) 

The  Belgian  pyrites  is  usually  only  got  as  a  by-product  in 
obtaining  lead-  and  zinc-ores  in  the  provinces  of  Liege  and 
Namur ;  it  is  either  microcrystalline  or  crystalline  or  in  bulbous 
pieces  with  a  concentrically  fibrous  structure.  Its  quality  is 
uneven.     It  is  mostly  used  locally  and  in  the  north  of  France. 

In  I860  as  much  as  42,513  tons  of  pyrites  was  got,  but  this  was 
the  maximum  attained.  In  1879  still  15,577  tons  were  procured, 
but  in  1880  only  7913  tons,  and  in  1881  2965  tons.  The  pro- 
duction  remained  about  2000  or  3000  tons  for  a  number  of  years, 
but  since  1898  it  has  been  altogether  insignificant. 

In  France  the  principal  deposits  of  pyrites  are  those  of  the 
Rhone  (Chessy  and  Sain-Bel)  and  of  the  South  (Gard  and  Arduch). 
The  Rhone  beds  exist  on  both  banks  of  the  Brevenne,  a  tributary 
of  the  Saone,  on  a  widtii  of  4  or  5  miles.  The  bed  on  the  left  bank 
is  that  of  Chessy,  about  6  miles  long  and  several  yards  thick. 
This  pyrites  is  bright  yellow,  very  crystalline  and  friable.  When 
first  got  it  contained  4  or  5  per  cent,  of  copper ;  but  the  cupreous 
vein  has  run  out,  and  the  non-cupreous  ore  on  this  side  has  nearly 
ceased  to  be  worked.  The  beds  on  the  right  bank  are  those  of 
Sain-Bel  or  Sourcieux.  The  northern  part  furnishes  a  more  com- 
pact ore  than  that  from  Chessy.  Most  of  it  is  non-cupreous,  but 
there  is  also  a  vein  with  4  or  5  per  cent,  copper ;  the  gangue  is 
mostly  sulphate  of  baryta.  Much  more  important  is  the  southern 
part  of  this  bed,  the  "  masse  de  Bibost.''  The  ore  is  here  very 
rich  in  sulphur,  green  with  yellow  reflexion,  and  very  friable,  so 
that  there  is  almost  as  much  smalls  as  lumps ;  the  gangue  is  almost 
entirely  siliceous.  The  beds  in  the  South  of  France  are  more 
numerous,  but  much  less  important.  The  most  considerable  mine 
is  that  of  Saint-Julien-de-Valgalgues^  in  the  Dc'partement  du 
Gard;  there  is  another  mine  at  Soyons,  in  the  Ardeche.  The 
other  French  mines  are  of  little  importance.  A  detailed  descrip- 
tion of  the  French  pyrites-mines  has  been  given  by  Girard  and 
Morin  (Compt.  rend.  1875,  Ixxxi.  p.  190;  Annales  de  Chimie 
et  de  Physique,  [5]  vii.  p.  229) ;  from  this  paper  the  following 
analyses  are  extracted,  which  seem  more  trustworthy  than  those 


48 


RAW  MATERIALS  OP  MANUFACTURE. 


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PYRITES  IN  FRANCE.  49 

• 

by  ilene,  given  in  the  1st  edition  of  this  book^  p.  92,  from  the 
Monit.  Scient.  1867,  p.  410. 

These  analyses  may  be  summed  up  as  follows : — ^The  pyrites  from 
the  Rhone  and  Sain-Bel,  on  an  average,  contains  46  to  48  per 
cent,  of  sulphur  and  10  to  12  per  cent,  of  gangue,  consisting  of 
clay,  sand,  and  barytes.  In  the  southern  part  of  the  district 
of  Sain-Bel  the  percentage  of  sulphur  rises  to  50  or  53,  and  the 
gangue  is  inconsiderable  and  free  from  barytes ;  arsenic  is  not 
present  in  quantities  sufficient  for  determination.  In  the  district 
of  St.  Julien  (Le  Card)  pyrites  is  not  found  in  the  clay-slate,  as 
at  Sain-Bel,  but  in  the  Lias  or  Trias  ;  the  sulphur  varies  from  40 
to  45  per  cent. ;  the  gangue  is  calcareous,  and  varies  from  3  to  6 
per  cent. ;  arsenic  is  present  up  to  O'l  per  cent.,  sometimes  also 
fluorspar  in  quantities  sufficient  for  estimation.  The  pyrites 
from  Ardeche  contains  from  45  to  50  per  cent,  of  sulphur ;  the 
gangue  is  clay,  free  from  lime ;  arsenic  occurs  up  to  0*3  percent.: 
fluorspar  sometimes  occurs  in  injurious  quantities ;  the  hydro- 
fluoric acid  given  off  from  it  in  one  case  destroyed  the  glass 
apparatus  for  spreading  the  nitric  acid,  and  the  latter  thus  got 
to  the  chamber-bottom  and  corroded  it. 

In  1874  there  were  used  in  France  178,400  tons,  of  the  value 
of  £240,000.  Of  this  the  beds  of  Sain-Bel,  which  supply  two- 
thirds  of  the  French  factories,  contributed  120,000  tons,  those 
of  St.  Julien  (in  the  department  Gard)  24,600  tons,  those  of 
Le  Soulier  (Gard)  6000  tons,  those  of  Soyons  (Ardeche)  900  tons. 
Girard  and  Morin  give  twenty-three  analyses  of  French  and  five 
of  foreign  pyrites  used  in  France. 

According  to  Scheurer-Kestner  (Wurst,  Diet,  de  Chimie,  ii. 
p.  138)  the  pyrites  from  Chessy  and  Sain-Bel  contains  45  to  48  per 
cent,  of  sulphur  with  very  little  arsenic  and  selenium,  that  from 
Chessy  also  1  or  2  per  cent,  of  copper  and  zinc.  The  copper  is 
obtained  from  the  cinders,  at  least  at  the  Chessy  works,  by  allowing 
them  to  lie  for  a  time  and  moistening  them :  the  liquid  running  oS 
contains  copper  and  zinc  sulphates ;  and  the  copper  is  got  from 
it  by  cementation.  Nearly  all  French  works^  as  well  as  those 
in  Alsace  and  Switzerland,  obtain  their  ore  from  those  two 
pits ;  only  the  works  at  Gard  and  Marseilles  get  it  from  Alais, 
where  the  pyrites  contains  38  to  42  per  cent,  of  sulphur  ;  a  few 
factories  in  the  north  of  France  use  Belgian  pyrites,  those  in  the 
south  use  Spanish  pyrites. 

VOL.  I.  E 


50 


RAW  MATERIALS  OF  MANUFACTURE. 


The  production  of  pyrites  in  France  was  : — 


1891. 

243,030  tons. 

1896. 

295,325  tons 

1892. 

226,804    „ 

1897. 

298,571     „ 

1893. 

227,288    „ 

1898. 

306,002    „ 

1894. 

278,452    „ 

1899. 

313,087     „ 

1895. 

248,934    „ 

France  imported  and  exported  pyrites  as  follows  : — 

1890.  Imported  39,552  tons.      Exported  15,907  tons. 

1891.  „         45,457     „  „         12,120     „ 

Italy  possesses  beds  of  pyrites  in  several  places.  Those 
occurring  in  the  province  of  Bergamo,  tested  in  Vienna  (Wag- 
ner's Jahresb.  1879,  p.  272),  are  composed  as  follows : — 


Iron 

Copper     

Zinc 

Lead 

Silver    .' 

Sulphur   

Arsenic 

Alumina  

Lime 

Magnesia     

Silica    

COj,  O  and  H^O  (by  diff.) 


Redolta 
quarry. 


lOO-OO 


Fasseyra 

quarry. 


trace 

41-72 

trace 

trace 

■  •  • 

•  «  • 

39'32 

44-'36 

0-53 

014 

2'37 

1-28 

5-89 

0-88 

0-66 

0-39 

7-16 

9-68 

7-78 

l*5.i 

10000 


S.  Guiseppe 
pit. 


48-35 
007 
018 


30-97 

•  ■  ■ 

1-86 
1-70 
014 
10-45 
6-28 


100-00 


Vallantica 
pit. 


36-79 
1-69 

•  •  • 

trace 
0014 

41-56 
0-18 
1-25 
0-37 
010 

16-40 
1-646 


100-00 


In  the  Val  d^Aosta  there  are  several  mines,  some  of  which 
contain  a  strougly  arsenical  pyrites. 

Those  at  Brosso,  near  Ivrea,  belonging  to  Messrs.  Sclopis  &  Co., 
yield  pyrites  containing  very  little  arsenic  :  present  output  about 
20,000  tons  per  annum.  One  quality  contains  48  or  49  per  cent, 
of  sulphur  and  0*2  of  arsenic,  the  other  nearly  50  of  sulphur  and 
only  traces  of  arsenic.  It  is  too  explosive  for  burning  in  lumps, 
but  excellent  for  burning  as  smalls.  Another  mine  is  at 
Pr^  St.  Didier  in  the  same  valley.  This  Aosta  pyrites  mostly 
requires  special  contrivances  for  getting  rid  of  the  arsenic  in 
burning ;  the  cinders  are  worked  for  copper,  silver,  and  gold. 


PYRITES  IN  ITALY,  SWEDEN,  AND  NORWAY.  51 

Pyrites  in  quantity  is  also  found  at  Agordo  (Cadore),  Sestri 
Levante,  and  of  very  good  quality  in  Sicily.  The  whole  of  the 
24  Italian  sulphuric-acid  works  burn  pyrites,  partly  imported 
from  Spain  (Caudiani,  Chem.  Ind.  1895,  p.  153) ;  none  of  them 
bum  brimstone. 

The  production  of  pyrites  in  Italy  was  : — 

1897  57,383  tons. 

1898  66,120     „ 

1899  75,308     „ 

Swedish  pyrites,  from  Fahlun,  varies  between  43  and  48  per 
cent,  of  sulphur.  This  ore  is  obtained  as  a  by-product  in  the 
getting  of  copper-ores,  and  is  said  to  exist  in  enormous  quantity ; 
but,  owing  to  the  diflSculty  of  transit,  its  exportation  does  not  pay. 
It  is  said  to  burn  well. 

Pattinson.         Browell  and  Marreco. 

Sulphur    43-70  38*05 

Iron  3901  42  80 

Copper 0-60  1*50 

Lead 0-12 

Zinc  2-57 

Lime 0*85 

Magnesia 0*69 

Arsenic trace 

Insoluble 11-66  12-16 

Oxygen,  as  Fe A 0-22     fjS)^'^^ 

Water   0-20 


99-62  100-00 

In  Norway  there  exist,  very  lai'ge  beds  of  pyrites,  both  free 
from  and  containing  copper.  Of  the  many  pits  formerly  worked 
there,  all  those  had  to  stop  which  produce  ores  with  from  35  to 
40  per  cent,  of  sulphur.  The  richer  ores,  even  those  free  from 
copper,  have  maintained  their  position  to  some  extent,  because  they 
bum  well,  are  easily  lighted,  keep  the  heat  well,  do  not  "  scar,''  &c. 
They  are  mostly  hard  and  difficult  to  break.  The  most  consider- 
able pits  are  those  of  Ytteroen,  which  export  vid  Drontheim;  they 
supply  6000  to  8000  tons  per  annum.     A  large  mass  of  cupreous 

£2 


52  RAW  MATERIALS  OF  MANUFACTURE. 

pyrites,  with  45  per  cent,  of  sulphur  and  3  of  copper,  at  Vigsnaes, 
was  worked  by  an  Antwerp  Company,  but  is  now  exhausted. 
Norwegian  pyrites  contains  very  little  arsenic.  Other  pits  exist 
thirty  miles  from  Drontheim,  on  the  Hardanger  Fjord,  near 
Bergen,  &c.  The  Norwegian  pyrites  is  more  in  favour  as  a 
sulphur-ore  (excepting  its  difficult  breakage)  than  as  a  copper-ore ; 
its  cinders  do  not  very  well  suit  the  copper-works. 

Analyses  of  Norwegian  Pyrites. 

Faltinson.  MacCuUoch. 


/^ 


Ytteroen  ore.     Drontheim  ore.  I.  II. 

Sulphur 44-50  5060  46-15  38-17 

Iron    39-22  44*62  4420  82-80 

Copper    1-80  trace  120  110 

Zinc 1-18                     1'34  210  2-32 

Lead    trace 

Lime    2-10  trace 

Calcium  carbonate ...  2'55  11*90 

Magnesia 0*01  trace 

Magnesium  carbonate ...  ...  1*08 

Carbonic  acid 1*65                      ...  ...  ... 

Arsenic    ...  ...  trace 

Insoluble OOS                     315  3-20  1220 

Oxygen,  as  Fe.^O.,  0*45 

Moi.sture     ....'... 0-17                     020  040  0-25 

100-16  99-91  99-60  99*82 

The  following  information  is  due  to  Mr.  Knudsen^  manager  of 
the  Sulitjelma  mine  (through  Dr.  Hasenclever).  Norway  exported 
in  1901  about  90,000  tons  pyrites  from  the  following  pits : — 

Sulitjelma,  near  Bodoe  . . .  35-36,000  tons  with  45  p.c.  sulphur. 

Killingdal   25,000  „        43-44  p.c.     „ 

Roros,  nearTrondhjera...      15,000  „        43-44    „      „ 

Bossmo  „  ...      15,000  „        48-50   „       „ 

By  far  the  largest  mine  is  the  first-mentioned,  which  is  expected 
to  yield  an  additional  20,000  or  25,000  tons  in  1902  and  is 
reckoned  to  last  for  centuries  to  come.  It  contains  very  little 
arsenic.  Much  ore,  richer  in  copper  and  poorer  in  sulphur,  is 
also  smelted  on  the  spot.  The  ore  from  Killingdal  and  Roros 
is  also  cupreous ;  that  from  Bossmo  is  free  from  copper,  with 


PYRITES  IN  SPAIN  AND  PORTUGAL.  53 

traces  of  arsenic.  The  following  mines  are  not  yet  worked  for 
want  of  railway  communication  : — Foldal,  Vaarteigen,  and  Nudal. 
They  test  43  or  44  per  cent.  S,  and  at  most  2*5  per  cent.  Cu,  and 
might  yield  from  60,000  to  90,000  tons  per  annum. 

Spain  and  Portugal  possess  the  largest  known  beds  of  pyrites. 
Much  of  it  is  cupreous,  and  all  of  it  is  distinguished  by  its  very 
good  behaviour  in  burners ;  so  that  the  burners  have  been  built 
very  much  lower  for  it,  and  much  labour  is  saved.  This  pyrites 
has  only  been  worked  again  since  1855  ;  but  the  Romans,  and 
before  them  the  Phoenicians  and  Carthaginians,  knew  it  very 
well,  as  is  shown  by  many  traces.  The  bed,  however,  was  at  that 
time  only  worked  where  it  was  richest  in  copper.  According  to 
Schonichen  (Dingl.  Journ.  clxx.  p.  448)  all  the  beds  are  within  a 
belt  of  five  leagues  width,  reaching,  parallel  to  the  Sierra  Morena, 
from  the  western  frontier  of  the  province  of  Seville,  across  the 
hilly  country  situated  to  the  south  of  this,  right  through  Portugal 
to  the  Atlantic  Ocean — a  distance  of  30  leagues.  The  prevailing 
rocks  in  that  country  are  clay- slate  and  crystalline  slates;  but 
parallel  to  the  granitic  tract  of  the  Sierra  Morena  felsite-porphyry 
and  quartzite  have  broken  through  the  slate,  and  only  in  the 
neighbourhood  of  such  dykes  are  the  pyrites-beds  found.  Their 
shape  is  that  of  large  lenticular  pockets  in  the  metamorphic  clay- 
slate,  from  20  to  36  fathoms  thick,  and  extending  to  a  length  of 
170  to  260  fathoms.  The  whole  bed  is  filled  with  pure  pyrites, 
without  any  visible  gangue.  The  ore  is  in  a  few  places  found 
at  only  1  or  2  fathoms  below  the  surface,  undecomposed,  and 
in  a  sandy  state,  so  that  it  can  be  got  by  daylight  work.  In  other 
places  the  zone  of  decomposition  reaches  from  10  to  50  fathoms 
downwards.  The  percentage  of  copper  varies  from  2^  to  40 ;  but 
ores  with  more  than  10  per  cent,  of  copper  are  only  contained  in 
small  vertical  zones  within  the  large  masses.  Only  these  "  black  '^ 
ores  were  the  object  of  the  mining-operations  on  the  part  of  the 
Phoenicians  and  Romans.  The  quantity  of  pyrites  existing  there 
is  almost  inexhaustible,  and  can  certainly  supply  the  requirements 
of  mankind,  both  of  copper  and  of  sulphur,  for  thousands  of  years 
to  come. 

Special  highways,  and  latterly  also  railways,  have  been  made,  in 
order  to  facilitate  the  communication  with  the  ports  of  Huelva, 
San  Lucar  du  Guadiana,  and  Pomaron ;  but  a  great  deal  of  the 
ore  is  still  conveyed  for  some  distance  on  mule-back. 


54  RAW  MATERIALS  OF  MANUFACTURE. 

Of  the  many  companies  which  had  been  formed  for  working 
this  ore  most  have  ceased  to  exist ;  and  only  four  or  five  remain, 
all  of  them  in  English  and  French  hands.  The  smallest  of 
these  is  the  Buitron  Pyrites  Company,  which  works  the  mines 
of  Buitron  and  Poderosa.  The  Tharsis  Sulphur  and  Copper 
Company  possesses  much  more  extensive  mines,  a  railway  of  its 
own,  a  wharf  at  Huelva,  and  also  a  number  of  works  in  England 
and  Scotland  for  the  wet  extraction  of  the  copper  from  the  cinders 
returned  to  them.  The  Tharsis  ore  is  very  good,  but  very  soft, 
and  makes  much  dust  in  breaking.  The  San-Domingo  mine  lies 
in  Portuguese  territory  ;  its  ore  is  known  as  Mason's  ore,  and  is 
considered  superior  to  all  others^  so  that  it  commands  a  better 
price.  The  last,  but  largest,  of  these  companies  is  the  Rio-Tinto 
Company,  which  has  thrown  such  large  quantities  of  pyrites  into 
the  English  market  that,  from  1875  to  1876,  prices  receded  by 
more  than  one-third.  Its  ore  is  also  of  excellent  quality.  The 
mines  of  Carpio  and  Lagunazo,  in  the  province  of  Huelva,  are 
not  yet  worked  for  exportation. 

The  Spanish  (and  Portuguese)  pyrites  never  contains  less  than 
46,  and  up  to  50  per  cent,  of  sulphur,  besides  3  to  4^  per  cent, 
of  copper,  which,  however,  by  most  of  the  English  buyers,  is  not 
bought,  but  returned  in  kind  to  the  seller  in  the  shape  of  cinders 
from  the  pyrites-burners.  The  value  of  the  copper  (if  bought)  is 
still  fixed  by  the  so-called  "  Cornish  assay  " — that  is,  a  process  of 
dry  assaying  known  only  to  a  few  assayers  living  at  Redruth  and 
other  places  in  Cornwall,  the  great  inaccuracy  of  which  is  per- 
fectly well  known  to  all  parties  concerned  :  it  shows,  for  instance, 
only  2  per  cent,  if  4  per  cent,  is  actually  present ;  and  from  this 
diflference  the  buyer  must  pay  the  cost  of  extracting  the  copper 
and  his  own  profit,  since  the  price  to  be  paid  for  the  copper  in  the 
ore  by  Cornish  assay  is  sometimes  higher  than  the  value  of  a  similar 
quantity  of  copper  metal.  This  remarkably  irrational  system  has 
not  hitherto  been  done  awav  with  for  sales. 

In  Germanv  also  in  1877  a  number  of  manufactui*ers  united 

r 

in  working  Spanish  pyrites  (especially  Rio-Tinto  ore),  and  in 
delivering  all  their  cinders  to  the  Duisburg  copper-works.  The 
Oker  works  also  use  similar  ores,  which  they  work  up  themselves 
for  copper. 

The  ore  of  the  three  principal  companies  is  very  similar  in 
composition ;  its  analysis  is  as  follows : — 


SPANISH  PYRITES.  55 

Ciaudet         MacCuUoch 
Pattinson.  (San  Domingo  (San  Bomingo 

t * s  ore).  ore). 

Sulphur 4800        49*60        4460        49-30  49O0  4980 

Iron    40-74  4288  38-70  41-41  43-65  4288 

CJopper    3-42  2-26  380  581  3-20                 226 

I/ead   0-82  0*52  0-58  066  OOa 

Zinc trace  0*10  0*30  trace  0-35                 0-10 

Idme  0-21  0-18  0*14  014  0-10                 018 

MagnesiA    0*08  trace  trace  trace 

ThaUinm trace  trace  trace  trace 

Araenic   0-21  0-28  026  031  047                 028 

Injoluble    5-67  294  1110  2-00  0-63                 2*94 

Oiygen  (aa  Fe^Oa)  0-09  015  0*23  0*25  1*07 

Moisture 091  0-95  0-17  0-05  070                 095 

100-15        99-86        99-88        99-93         10000  9939 

The  following  analyses  represent  the  average  quality  : — 

Bio  Tinto.  S.  Domingo. 

Cumenge.  Caron.  ^^^  Pattinson.  Bartlett.  5]^^"^ 

Sulphur 48-00  607  4900'  49-90  4980  4750' 

Iron    4000  41-3  43-55  41-41  43-55  41-92 

Copper    3-42  35  320  246  8-20  421 

Lead    0*82  ...  0-93  0-98  0-93  1-52 

Zinc trace  ...  0-35  044  035  022 

Araenic   0-21  ...  047  055  047  038 

Jarisch  (Schwefelsaure-fabrikation,  p.  30  et  seq,)  quotes  further 
analyses.  In  1879  the  sulphur  in  Rio-Tinto  ore  averaged  48*55 
per  cent.,  varying  between  48-18  and  48*77  per  cent.  S. 

A  new  pyrites-mine  has  been  opened  in  Spain^  called  St.  Mardy 
Tinto  Santarossa.  Its  product  has  been  found  by  Lunge  and 
Banziger  (Zeitsch.  angew.  Chem.  1896^  p.  421)  to  contain  0*85 
per  cent,  moisture,  5*20  insoluble,  43*87  sulphur,  42"  12  iron, 
1*09  arsenic,  2*15  antimony,  3*17  copper. 

Some  kinds  of  Spanish  pyrites  are  in  bad  repute  with  the 
manufactnrers  as  '^ explosive"  or  '^detonating/'  because  they 
decrepitate  in  the  kilns  shortly  after  lighting  with  loud  detona- 
tions, and  thereby  make  so  much  fine  powder  that  the  burners 
are  stopped  up  and  "scars''  are  formed.  The  reason  of  this 
detonating  property  is  probably  to  be  sought  in  the  presence  of 
hydrated  silicates  (zeolites)  in  the  ore  *. 

*  The  explosive  pyrites  from  Goshen  Copper  Mine,  near  Scull  Harbour, 
County  Cork,  is  said  to  contain  confined  carbon  dioxide  and  water  (Blount. 
J.  Soc.  Chem.  Ind.  1885,  p.  074). 


56  RAW  MATERIALS  OF  MANUFACTURE. 

According  to  Hjelt  the  average  percentage  of  arsenic  in  Spanish 
ores  is  0*91. 

Pyrites  with  very  little  or  no  copper  is  also  found  in  Spain. 
One  of  the  best  descriptions  is  that  of  the  Agnas  Teuidas  mine, 
containing  iron  4660  per  cent.,  sulphur  53' 15  per  cent.,  silica 
0*20  per  cent.,  arsenic,  copper,  selenium,  silver  and  gold  traces. 
It  is  sold  both  in  the  state  of  lumps  and  smalls.  It  burns  A'ery 
easily  down  to  1*0  or  05  per  cent,  of  sulphur,  so  that  the  cinders, 
which  contain  685  per  cent,  of  metallic  iron,  and  no  copper, 
phosphorus,  Jead,  or  zinc,  are  very  valuable  for  blast-furnaces. 
The  annual  sales  have  exceeded  200,000  tons,  but  recently  very 
little  has  come  into  the  market  owing  to  an  accident  at  the  mine. 

H.  J.  Davis  of  New  York,  one  of  the  principal  importers  of 
pyrites  to  the  U.S.,  gives  the  following  analyses  of  very  good, 
hard  Spanish  ores  containing  but  little  copper  : — 

Araceua.  Balmacca.  San  Tolmo. 

S  51-77  50-19             46-40 

Fe     45-53  45-61             40*11 

Cu    0-29  0-20               1-90 

Si     l'9D  300             11-27 

As    ?  ?                none 

The  production  of  iron-pyrites  (non-cupreous)  in  Spain,  accord- 
ing to  '  United  States  Mineral  Resources '  for  1900,  p.  826,  was 
as  follows  1 — 


1891. 

279,161  tons. 

1896. 

98,393  tons  (?). 

1892. 

435,906  „ 

1897. 

217,545  „ 

1893. 

393,453  „ 

1898. 

255,896  „ 

1894. 

511,769  „ 

1899. 

316,212  „ 

1895. 

480,255  „ 

• 

The  production  of  cupreous  pyrites  and  its  exportation  by  the 
three  principal  firms  in  Spain  and  Portugal  was,  according  to 
the  same  authority,  p.  186 : — 

1.  Rio  Tin  to  Company. 

1898.  Production  1,465,380  tons  (2,852  p.c.  Cu). 

1899.  „  1,649,841     „    (2,719   „      „  ). 

1900.  „  1,894,504     „    (2,744   „      „  ). 
Exportation  in  1900 :  704,803  tons. 


PYRITES  IN  NORTH  AMERICA.  57 

2.  Tharsis  Sulphur  &  Copper  Co. 

1899.  Production  572,854;  exportation  222,475  tons. 

1900.  „  468,738)  „  220,019     „ 

3.  Mason  &  Barry,  Ltd.     Exported  : 

1899.  339,298  tons. 

1900.  394,740     „ 

Enormous  quantities  of  cupreous  pyrites  are  roasted  and  worked 
for  copper  in  Spain,  without  utilizing  the  sulphur,  as  is  apparent 
from  the  above  figures. 

The  United  States  of  North  America  are  very  rich  in  pyrites. 
The  principal  mines  worked  at  present  are  the  following : — 

In  New  Hampshire :  the  Milan  mines,  Coos  County.  The  ore 
is  of  excellent  quality,  and  is  now  sorted  into  two  grades,  of  the 
following  composition : — 

No.  1.  No.  '2, 

Sulphur    46-0  350 

Copper 3-7  50 

Iron 40-0  305 

Silica    6-2  25*5 

Zinc 4-0  8-0 

Arsenic 0  0 

No.  1  is  in  special  favour,  but  No.  2  burns  very  well  and  is 
readily  bought.  Smelting-works  exist  for  extracting  the  copper 
and  silver. 

New  York  :  2000  tons  were  raised  at  Hermon,  County 
St,  Lawrence ;  sulphur  contents,  38*0  per  cent.  Another  mine 
at  Ulster  County,  with  39  per  cent,  ore,  was  worked  till  stopped 
bv  an  inrush  of  water. 

Massachusetts :  the  mines  of  the  Davis  Company,  at  Charle- 
mont  (Mass.),  are  about  130  miles  from  !New  York,  in  the 
centre  of  a  network  of  railways.  The  ore  contains  485  per  cent, 
sulphur,  no  trace  of  arsenic,  antimony,  or  cobalt,  little  or  no  zinc, 
lead,  or  calcium,  1*5  copper,  45*3  iron,  and  less  than  3  per  cent, 
of  silica.  It  is  granular,  easily  broken  by  hand,  and  burns  down 
to  3  per  cent,  of  sulphur.  In  1884,  about  30,000  tons  were  got; 
it  was  burned  in  four  works. 

Virginia:  Arminius  Copper  Mines  Company  and  Sulphur  Mines 
Company,  both  in  Louisa  County.    The  ore  contains  49*5  per  cent. 


58 


RAW  MATERIALS  OF  MANUFACTURE. 


sulphur,  0*5  copper,  43*5  iron,  6*4  silica,  &c.  Annual  output, 
13,000  tons  (in  1885). 

Georgia:  Dallas  mine,  Paulding  County.  The  ore  contains: 
sulphur  40  per  cent.,  copper  2'75  (sometimes  up  to  11  per  cent.), 
silica  8  per  cent. 

The  absence  of  arsenic  in  most  American  pyrites  (as  far  as  it  is 
now  worked)  is  a  remarkable  feature. 

K.  F.  Stahl  (Zsch.  f.  angew.  Chem.  1893,  p.  54)  quotes  analyses 
of  American  pyrites.  No.  1  is  from  Tallapoosa  Mine,  Georgia, 
1882 ;  No.  2  from  Rogers  Mine,  Paulding  Co.,  Dallas,  Ga. ;  No.  3 
from  Sulphur  Mines  Co.  of  Virginia,  Louisa  Co.,  1884 ;  No.  4, 
Peru  Zinc  Co.,  La  Salle,  111. ;  No.  5  from  Dodgeville,  Wis. ; 
No.  6,  from  the  same  mine  as  No.  3,  1891 ;  No.  7,  Davis  Sulphur 
Ore  Co.,  Franklin  Co.,  Mass.,  1891. 


1. 

2.              3.             4.             5. 

6. 

7.           ; 

Water    

451 

31 
30 
01 
2-9 
? 

—       1      2-9 
37-6         371 
40-6         41-5 

5-2           O-fl 

50-2     1    43-7 

1-3 

40-6 

37-3 

10 

1-9 

10-5 
iraoe 

0-8      t 

Sulphur 

42*4 

Irou   

354 

Copper  

1"4 

Ziiie   

4-5 

0-01 

9-5 

? 

0-8 

1-4 

5-5 

Cadmium  

Insoluble  

Arsenic 

? 

14-7           - 
002          — 

? 

51 

trace     i 

1 

We  quote  from  the  volumes  of  '  Mineral  Industry '  the  pro- 
duction, imports,  and  consumption  of  pyrites  in  the  United  States, 
not  counting  the  auriferous  pyrites  used  for  the  manufacture  of 
sulphuric  acid  in  Canada,  expressed  in  long  tons  of  2,240  lbs. : — 


Year. 

Production. 

Imports. 

1 
Consumption. 

1891  

100,319 
106,250 

95,000 
107,462 

81,000 
109,282 
133,368 
191,160 
178,408 
201,317 

130,000 
210,000 
194,000 
146,023 
190,436 
199,678 
259,546 
171,879 
310,008 
329,449 

i         239.319 

1892  

316,250 

289,000 

1         253.485 

1         271,436 

1         308,960 

392,914 

363,039 

488,416 

'         530.766 

1893  

1894  

1895  

1896  

1897  

1898  

1899  

1900  

1 

Most   of  the  American  pyrites,  including  the  Newfoundland 


PYRITES  IN  CANADA^  NEWFOUNDLAND^  AND  AUSTRALIA. 


59 


ore^  is  granular  and  more  fit  for  fines'  burners  thau  for  lump- 
burners. 

In  Canada  there  are  two  mines :  the  Albert  mine  and  the 
Crown  mine.  They  supplied  the  first  pyrites  used  in  the  United 
States  for  making  oil  of  vitriol.  Sulphur  40*0  per  cent.,  iron  350, 
copper  4'0,  silica  20*0.     Output : 

1891.  60,474  tons.         1894.  36,185  tons.         1897.  34,471  tons. 

1892.  53,372    „  1895.  30,534    „  1898.  24,721 

1893.  52,270    „  1896.  30,103    „  1899.  35,742 


}> 


>> 


In  Newfoundland,  on  Piney's  Island,  there  is  a  very  large  bed 
of  pyrites,  accessible  by  a  shaft  60  feet  deep.  The  bed  is  72  feet 
-wide,  and  28  feet  of  it  contains  3  or  4  per  cent,  copper.  This  ore 
is  veiy  easy  to  roast ;  an  analysis  of  the  non-cupreous  ore  showed 
Cu0b7,  S  51-16,  Fe  48-35,  SiO^  013,  CaO  022,  As  002;  no 
Sb,  Pb,  Zn,  Bi  (Eng.  Min.  Joum.  1892,  p.  467). 

In  South  Australia  pyrites  is  found  with  48* 7  per  cent.  S  and 
2-8  per  cent.  Cu  (Mene,  Mon.  Sc.  1867,  p.  411 ). 

The  World^s  production  of  iron-pyrites  (in  metric  tons)  is 
stated  in  Min.  Ind.  ix.  p.  615,  from  official  sources  (I  cannot 
explain  the  difference  between  these  and  the  other  "  official  '^ 
figures  given  in  various  places  supra)  : — 


■  ■  ""~ 

" 

1 

i8'j6.  : 

1897. 

1898. 

1899. 

2,560 

1,828 

147 

283 

2,000 

3,670 

240 

430 

30,586 

35,299 

29,228 

25,117  j 

282,064 

303,448 

310,972 

318,832 

129.168 

133,302 

136,849 

144,623 

52,697 

44,454 

58,079 

79,519  1 

45,728 

58,320 

67,191 

76,538 

27,712 

33,316 

33,100 

31,500 

60,rj07 

9i,484 

89,763 

90,00()  1 

200,000 

210,265 

248,218 

275,(x>8  i 

11,550 

19,380  . 

20,000 

25.(KJ0 

100,000 

217,545  ; 

2<50,016 

319,285  1 

1,<X)9 

517  1 

386 

150  1 

10,178 

10,753 

12,302 

12.426 

117,782 

128,468 
1,295,049 

1H219 

181,263 

1,073,.541 

1,460,710 

1,580,624  ; 

1895. 

Belgium     3,510 

Sosnia   

Canada 31,024 

France  253.416 

Germany  127,03(5 

Hungary   69,195 

Italy  38,586 

Newfoundland 34,879 

Norway     61,994 

Portugal  (r«) 200,000 

Buasia  11,042 

Spain  (6)   60/J67 

Sweden 221 

Great  Britain   9,193 

United  States   107,371 

TotalB 1,007,734 


(a)  For  Portugal  the  output  for  1895  and  1896  is  roughly  estimated.  For  this 
country  only  pyrites  with  less  than  1  per  cent,  copper  is  included. 

(6)  For  Spain  the  cupreous  pyrites,  from  which  copper  is  extracted,  is  not 
included,  oomp.  p.  57. 


60 


RAW  MATERIALS  OF  MANUFACTURE. 


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PRICES  OF  PYRITES  ;    POOR  AND  RICH  ORE. 


61 


Prices  obtained  in  the  Liverpool  district  for  pyrites,  when  sold 
for  sulphur  only : — 


Prices  per 
Year.  unit  of  sulphur. 

1861  10-85rf. 

1862  9-625 

1863  8 

1865  •  9 

Jan.  1866  9i 

Mar.  1866 1102 

Jan.  1868  1004 

June  1868 9^ 

Oct.  1868  8 

Jan.  1869  7 

June  1869 8 


Year. 

1870  

1871  

1872  

1873  

1876  

1877  

1878  

Jan.  1879  to 
Dec.  1884 
1885  to 
1887 


} 


} 


Prices  per 
unit  of  sulphur. 

6irf. 

-i 

/  ■>-> 

7i 

4 

^ 

H 

H 

3  to  34 


(E.  K.  Muspratt  in  J.  Soc.  Chera.  Ind.  1886,  p.  406.) 

Jurisch  (Schwefelsaure-fabrikation  p.  58)  quotes  the  prices  of 
pyrites  in  Germany  from  1853  to  1892 ;  but  this  is  of  very  little 
use,  as  there  is  nothing  said  about  the  percentage  of  sulphur. 
Previous  to  1883  the  price  was  always  above  10  marks  per  ton,, 
from  1884  to  1892  it  ranged  about  7^  marks  per  ton.  Only  one 
definite  statement  is  made,  viz.  that  100  kil.  of  sulphur  actually 
burned  from  Rio  Tinto,  deducting  the  drawback  for  copper,  in 
1881  cost  4-65  to  5-10  marks  (?). 

In  1900,  the  ordinary  price  of  German  pyrites  was  12  marks 
per  ton  at  the  mine ;  for  large  contracts  probably  less. 


Proportional  value  of  poor  and  rich  Pyrites. 

It  is  no  matter  of  surprise  that  the  rich  and  at  the  same  time 
well-burning  Spanish  ores,  and  those  ores  similar  to  them  else- 
where, where  they  could  be  imported,  have  driven  the  poor  ores 
out  of  the  field.  An  ore  of  35  per  cent.,  like  that  from  Wicklow, 
even  for  the  same  weight  of  sulphur,  has  much  less  value  than  a 
45-per-cent.  ore.  The  wages  for  breaking  and  burning  the  ore  in 
both  cases  must  be  ruled  by  the  gross  weight  of  the  ore,  and  con- 
sequently for  equal  weights  of  sulphur  come  to  much  more  with 
poor  than  with  rich  pyrites;  moreover,  under  conditions  otherwise 
equal,  the  unburnt  sulphur  in  the  cinders  is  the  same  by  weight. 
If,  for  instance,  5  percent,  of  sulphur  are  left  in  the  cinders. 


62  RAW  MATERIALS  OF  MANUFACTURE. 

this  amounts  with  35-per-cent.  ore  to.!l  =  |;  with  45-per-cent.  ore 

to  only  75= i;   *he  proportion  to  be  kept  in  view  is  accordingly 

not  85  :  45  =  7  :  9,  but  30  :  40=3  :  4.  Furthermore,  the  same 
holds  good  of  cost  of  plant  and  repairs  and  of  wages,  and,  lastly, 
since  the  poor  ores  generally  contain  no  copper,  also  of  the  cost 
of  removing  the  cinders. 

Therefore,  unless  the  burning  is  nothing  but  a  preparation  for 
the  metallurgical  treatment,  where  the  sulphur  is  quite  of  secondary 
importance,  the  ores  poor  in  sulphur  are  always  avoided  as  much 
as  possible. 

Analysis  of  Pyrites. 

In  the  analysis  of  pyrites  for  technical  purposes,  in  the  first 
instance  their  percentage  of  sulphur  is  taken  into  account ;  and  it 
is  therefore  mostly  the  custom  to  estimate  only  this  and,  perhaps, 
also  the  moisture.  If  the  ore  has  afterwards  to  yield  copper,  this 
must  of  course  also  be  considered ;  but  where  the  copper,  as  is 
mostly  the  case,  is  not  bought  by  the  vitriol-maker,  but  the  cinders 
are  returned  to  the  seller,  the  estimation  of  copper  is  generally 
omitted  in  the  chemical  works  as  unnecessarv.  This  restriction 
to  the  estimation  of  sulphur  ought,  however,  only  to  take  place 
with  pyrites  from  well-known  localities,  whose  general  composition 
and  properties  are  well  known,  and  where  the  salient  point  is  only 
the  percentage  of  the  most  important  constituent,  viz.  the  sulphur. 
Each  cargo,  even  each  portion  of  a  cargo  going  to  a  separate 
buyer,  is  sampled  in  the  presence  of  both  the  buyer's  and  seller's 
agents,  according  to  well-understood  rules  :  the  sample  is  broken 
up.  reduced,  and  sealed  up  in  bottles,  which  are  sent  to  an 
analytical  chemist  (generally  mentioned  in  the  contract  note) ; 
this  chemist's  certificate  rules  the  price  to  be  paid  for  the  pyrites 
down  to  i  per  cent.  If,  for  instance,  a  sale  has  been  made  at  6d, 
per  ^'  unit,"  this  means  that  for  each  per  cent,  of  sulphur  found 
the  sum  of  6d.  per  ton  is  paid;  thus  for  48;^^  per  cent,  of  sulphur 
48ix6rf.  =  245.  lirf.  per  ton.  The  ton  is  generally  calculated 
=  21  cwt. ;  that  is  to  say,  the  buyer  receives  an  allowance  in 
weight  of  5  per  cent. 

The  first  treatment  of  the  pyrites  in  analyses,  in  the  majority 
of  cases,  is  by  the  wet  way,  by  fuming  nitric  acid  or  aqua  regia ;  but 
the  prescriptions  differ  in  details.     The  decomposition  was  formerlv 


ANALYSIS  OF  FYRIT£S.  63 

frequently  made^  irom  Fresenius's  prescription,  by  means  of  red 
filming  nitric  acid,  which  it  is  sometimes  difficult  to  obtain  free 
from  sulphuric  acid,  and  which  is  unpleasant  to  handle.  In  lieu 
of  this  sometimes  chlorate  of  potash  along  with  hydrochloric  acid, 
or,  still  better,  with  nitric  acid  of  1*36  sp.  gr.,  have  been  used. 
The  author  has  always  found  the  best,  safest,  and  cheapest  way  to 
be  that  by  aqua  regia,  made  from  1  part  of  fuming  hydrochloric 
acid  and  3  or  4  parts  of  nitric  acid  of  1*36  to  1*4  sp.  gr.,  and  this 
mixture  is  now  used  in  most  places.  The  mineral  is  converted 
into  an  impalpable  powder  and  passed  through  the  finest  silk 
gauze  ;  the  triturating  ought  to  be  done  first  in  a  steel  mortar  or 
by  wrapping  it  up  in  paper  and  smashing  with  a  hammer,  and 
then  in  an  agate  mortar,  no/  in  a  porcelain  or  Wedgwood  mortar. 
The  powder  is  treated  with  about  50  parts  of  aqua  regia  ;  if  no 
reaction  takes  place  at  once,  it  should  be  gently  heated  on  a 
water-bath  till  the  reaction  sets  in  ;  but  then  the  beaker  should 
be  removed  instantly  from  the  water-bath,  and  only  replaced  when 
the  reaction  slackens  :  thus  the  decomposition  is  generally  complete 
in  10  minutes.  The  operation  should  be  performed  in  a  large 
beaker,  or,  still  better,  in  an  Erlenmeyer's  flask  covered  by  a 
funnel  or  a  watchglass,  lest  any  loss  should  take  place  by  spurting; 
and  the  work  must  be  done  in  a  draught-place,  on  account  of  the 
mass  of  acid  vapours  given  off.  If  the  decomposition  should  not  be 
perfect  after  heating  some  time,  some  more  aqua  regia  has  to  be 
added  and  the  heating  continued ;  but  mostly  this  will  be  caused 
by  the  powder  not  being  sufficiently  fine,  and  the  analysis  in  this 
case  cannot  easily  be  finished.  In  this  way  of  decomposing  the 
ore,  which  is  both  quick  and  safe,  the  disagreeable  separation  of 
sulphur  happens  very  rarely.  If  it  does,  the  sulphur  is  oxidized 
by  cautiously  adding  a  little  chlorate  of  potash. 

The  residue  from  the  solution  will  contain  silica  and  silicates, 
perhaps  a  little  lead  or  barium,  both  as  sulphates.  Although  their 
sulphur  is  thus  not  estimated,  no  harm  is  done,  as  it  is  anyhow 
valueless  to  the  manufacturer.  Lead  sulphate  is  pretty  soluble  in 
concentrated  acids,  but  it  is  almost  entirely  precipitated  again  by 
the  immediately  following  treatment. 

At  all  events  the  whole  of  the  nitric  acid  present  must  be 
destroyed  or  removed,  because  the  estimation  of  sulphuric  acid 
by  barium  chloride  in  the  presence  of  nitric  acid  or  its  salts  gives 
results  much  in  excess  of  the  truth.      Tlie  whole  is  therefore 


64  RAW  MATERIALS  OF  MANUFACTURE. 

evaporated  to  dryness  on  the  water-bath*  with  an  excess  of 
hydrochloric  acid^  by  which  at  the  same  time  all  silicic  acid 
dissolved  is  made  insoluble.  The  mass  is  again  moistened  with 
strong  hydrochloric  acid;  and  if  on  gently  heating  no  yellow 
vapour  and  no  smell  of  nitrous  products  are  perceived,  it  is  diluted 
with  hot  water  and  the  solution  filtered  from  the  residue.  Care 
must  be  taken  not  to  employ  too  much  hydrochloric  acid,  as 
barium  sulphate  is  not  quite  insoluble  in  hot  concentrated  acids ; 
on  the  other  hand,  enough  acid  must  be  present  to  dissolve  all 
salts  of  iron,  which  cannot  be  doubtful  if  the  colour  and  behaviour 
of  the  residue  are  observed. 

Some  chemists  prefer  to  the  aqua  regia  above  described  a 
solution  of  bromine  in  hydrochloric  acid ;  but  I  have  not  found 
this  to  answer  very  well.  Drown  (Chem.  News,  xliii.  p.  89)  heats 
the  pyrites  with  a  solution  of  caustic  soda  of  spec.  grav.  1*25,  adds 
cautiously  bromine  in  excess,  acidulates  with  hydrochloric  acid, 
and  evaporates  to  dryness. 

Noaillon  (Zsch.  angew.  Ch.  1897,  p.  351)  employs  a  mixture  ot 
sodium  chlorate  and  nitric  acid  for  decomposing  the  pyrites,  in 
order  to  avoid  loss  of  sulphuric  acid  when  drying  the  resulting 
mass.  (Such  a  loss  never  occurs  when  working  according  to  my 
prescription.) 

Where  the  utmost  accuracy  is  not  desired  the  solution  may 
now  be  at  once  treated  with  barium  chloride,  as  follows  : — 

The  clear  solution  is  brought  to  full  boiling ;  and  to  it  during 
boiling  a  hot  solution  of  barium  chloride  is  slowly  added.  Lest 
too  great  an  excess  of  this  be  used,  it  is  preferable  to  use  a 
measured  quantity  of  a  concentrated  solution  of  known  strength, 
but  more  than  sufficient  for  precipitating  all  the  sulphuric  acid 
present.  It  is  best  to  pour  the  hot  solution  of  barium  chloride 
rather  slowly  into  the  boiling  solution  of  sulphate,  with  constant 
stirring,  but  it  is  quite  unnecessary  to  do  this  drop  by  drop  as 
prescribed  by  Gladding  (Chem.  News,  Ixxx.  p.  181) ;  comp. 
Lunge,  Zsch.  ang.  Chem.  1895,  p.  69,  and  Journ.  Amer.  Chem. 
Soc,  March  1895.  If  the  process  is  carried  out  as  described 
here,  the  barium  sulphate  settles  down  completely  in  a  few 
seconds,  leaving  a  perfectly  clear   liquid,  and    nothing    of   the 

♦  The  last  evaporation  may  be  hastened  by  employing  a  saud-bath  or  asbestos 
cardboard,  taking  Ctire  to  remove  the  vessel  at  the  moment  when  the  mass  has 
become  drv. 


PRECIPITATION  OF  BABIUM  SULPHATE. 


65 


Fig,  5. 


precipitate  passes  through  the  filter.  It  is  quite  unnecessary  to 
allow  a  long  time  for  the  settling.  If  the  operation  is  carried  on 
as  described^  the  filtrate  never  becomes  cloudy  afterwards ;  on  the 
other  hand,  the  work  ia  greatly  expedited  by  filtering  the  liquid 
in  the  boiling-liot  state,  say  15  or  20  minutes  after  precipitation. 
A  Bunsen's  filter-pump  acts  rather  too  strongly  in 
this  case ;  but  it  is  very  useful  to  employ  a  simple 
contrivance  indicated  many  years  ago  by  Piccard, 
which  does  excellent  service  in  other  analytical 
operations^  viz.^  a  glass  tube  attached  to  the  funnel 
by  means  of  an  elastic  joint,  with  a  loop  causing 
a  continuous  jet  of  liquid  to  issue  at  the  bottom 
(fig.  5).  The  straight  part  below  the  loop  may 
be  8  or  10  inches  long ;  the  filter  must  be  pressed 
tight  to  the  sides  of  the  funnel  to  prevent  any  air 
being  sucked  in.  When  this  contrivance  is  used, 
which  does  not  act  so  violently  as  a  Bunsen  pump, 
the  liquid,  so  long  as  there  is  not  too  much 
precipitate  in  the  filter,  runs  through  in  a  con- 
tinuous jet. 

At  first  only  the  clear  liquid  is  poured  off  as 
completely  as  possible  from  the  dense  granular 
precipitate;  this  is  covered  with  boiling  water, 
acidulated  with  a  few  drops  of  hydrochloric  acid  ; 
the  liquid  is  boiled  for  a  few  moments,  and  can 
be  decanted  in  about  two  minutes'  time.  This 
operation  is  again  repeated  twice  or  three  times, 
but  without  adding  any  more  hydrochloric  acid  ; 
the  precipitate  is  washed  onto  the  filter,  and  after 
very  little  washing  the  filtrate  will  be  found  per- 
fectlv  neutral  and  free  from  dissolved  matters. 
The  filter  is  dried,  the  precipitate  taken  out,  and 
the  filter  burnt,  preferably  in  a  platinum  crucible 
laid  on  its  side ;  then  the  precipitate  is  put  in  and  ^^ 

Ignited,  not  too  strongly :  and  for  each  100  parts  of  barium 
sulphate  found  13' 733  parts  of  sulphur  are  calculated.  The 
ignited  barium  sulphate  must  not  cake  together;  on  moistening, 
it  should  not  give  an  alkaline  reaction;  and  on  heating  with 
dilute  hydrochloric  acid  and  filtering,  no  barium  salt  ought  to  be 
found  in  the  solution. 

VOL,  I.  F 


66  .     RAW  MATERIALS  OF  MANUFACTURE. 

It  generally  happens^  even .  if  the  solution  before  precipitation 
was  rather  strongly  acid^  that  t^e  precipitate  is  stained  yellowish 
by  precipitated  ferric  oxide  or  basic  ferric  sulphate,  which  cannot 
be  removed  even  by  boiling  with  dilute  hydrochloric  acid. 

Although  this  proves  the  presence  of  a  foreign  substance  in  the 
barium  sulphate^  which  ought  to  make  the  result  too  high^  yet  it 
is  found  in  practice  that  the  results  are  always  too  low.  The 
cause  of  this  apparent  anomaly  has  been  studied  by  Jannasch  and 
Richards  (Journ.  f.  prakt.  Chem.  [2]  xxxiv.  p.  321),  who  found 
that  in  the  presence  of  iron  a  barium-ferric  sulphate  is  precipitated, 
which  on  ignition  slowly  loses  a  portion  of  its  sulphuric  acid.  If 
the  ignition  is  carried  on  very  persistently,  the  error  thus  pro- 
duced may  amount  to  a  full  per  cent,  of  sulphur  or  upwards ; 
but  I  have  shown,  in  the  paper  quoted  below,  that  with  the 
ordinary  mode  of  ignition  it  does  not  exceed  018  per  cent. ; 
hence  the  above-described  method  is  always  available  where 
perfect  accuracy  is  not  required  and  a  speedy  completion  of 
the  test  is  a  consideration.  Westmoreland  (J.  Soc.  Chem.  Ind. 
1887,  p.  84)  even  contends  that  its  results  entirely  agree  with 
those  obtained  by  my  new  method  (an  opinion  to  which  I  must 
demur). 

Where,  however,  the  greatest  possible  accuracy  and  freedom 

from  error  is  required  (and  this  is  the  case  when  testing  an  average 

sample  of  pyrites  representing  a  whole  cargo,  or  a  large  portion 

of  such),  it  is  necessary  to  remove  the  disturbing  influence  of 

the  iron.     This  can  be  done  in  two  different  ways,  by  the  dry  and 

by  the  wet  method.     The  dry  method  is  that  recommended  by 

Fresenius  (Zeitsch.  f .  anal.  Chemie,  xvi.  p.  335) .     He  prescribes 

to  decompose  the  pyrites  by  fluxing  it  with  20  parts  of  a  mixture 

of  2  parts  of  dry  sodium  carbonate  entirely  free  from  sulphate, 

and  1  part  of  potassium  nitrate,  passing  carbonic  acid  into  the 

solution  for  the  precipitation  of  lead,  boiling  the  residue  with  a 

solution  of  sodium  carbouate  and  then  with  water,  acidulating  with 

hydrochloric  acid,  and  repeatedly  evaporating  for  the  expulsion  of 

nitric  acid^  after  which  the  process  is  carried  on  as  usual,  the 

precipitation  taking  place  by  barium  chloride.     This  process  is 

much  more  troublesome  and  tedious  than  that  to  be  described 

below,  which  employs  the  wet  method.    Another  objection  to  it  is 

that  it  estimates  not  merely  the  sulphur  of  the  iron  and  copper 

sulphides,  but  also  that  of  galena  and  of  barium  sulphate,  which 


REMOVAL  OF  IRON  IN  TESTING  PYRITES.  G7 

are  entirely  useless  to  th^  manufacturer  of  sulphuric  acid^. 
Moreover,  the  platinum  crucibles  are  strongly  acted  upon,  and  coal- 
gas  cannot  very  well  be  employed  in  the  operation  of  decomposing 
the  pyrites,  as  its  sulphur  would  cause  an  error  in  the  test.  Hence 
it  is  advisable  to  use  spirit-lamps  of  a  special  shape,  calculated 
to  yield  the  necessary  heat.  [The  use  of  spirit-lamps  can  be 
practically  avoided  by  placing  the  crucible  in  a  round  hole  made 
in  a  piece  of  asbestos  cardboard,  in  which  case  the  products  of 
the  combustion  of  coal-gas  are  carried  off  sideways.] 

Hayes  (*  American  Chemist,'  v.  p.  271)  describes  a  method  of 
decomposing  pyrites  with  alcoholic  soda  and  lime,  the  advantages 
of  which  are  in  no  way  evident. 

Fahlberg  and  lies  (Ber.  d.  deutsch.  chem.  Ges.  xi.  p.  1187) 
recommend  fluxing  the  sulphur-ore  with  caustic  potash  (25  grams 
to  0*1  gram  of  S)  in  a  silver  crucible  for  15  to  20  minutes,  lixivia- 
ting the  mass,  oxidizing  the  lower  oxides  of  sulphur  by  bromine- 
water,  and  precipitating  by  barium  chloride. 

Clark  (J.  Soc.  Chem.  Ind.  1885,  p.  329)  heats  the  pyrites  with 
a  mixture  of  sodium  carbonate  and  magnesia  to  a  dark-red  heat ; 
the  resulting  mass  is  lixiviated  with  water  whilst  passing  in 
carbonic  acid,  and  the  sulphuric  acid  estimated  in  the  usual  way. 
J.  Pattison  {ibid,  p.  724)  shows  that  this  method  gives  exactly  the 
same  result  as  mine  (of  course,  only  in  cases  where  barium 
sulphate  and  galena  are  absent,  which  militates  against  Clark's 
process). 

Looking  at  the  great  desirability  of  retaining  the  decomposition 
of  pyrites  in  the  wei  way,  I  have  worked  out  a  method  for  doing  so 
without  incurring  the  error  caused  by  the  presence  of  iron.  This 
method  was  first  described  in  the  Zeitsch.  f.  anal.  Chemie,  1880, 
p.  419,  and  has  been  very  generally  accepted  for  the  assaying  of 
pyrites  between  buyer  and  seller.  Objections  made  to  the  accuracy 
of  that  process  by  Jannasch  and  Richards  (Joum.  f.  prakt.  Chem. 
[2]  xxxix.  p.  321)  have  been  withdrawn  by  them  {ibid,  xl. 
p.  326),  and  have  been  completely  refuted  by  experiments  made 
in  my  laboratory  by  two  independent  investigators  (Zeitsch.  f. 
angew.  Chemie,  1889,  p.  473).  The  process,  as  it  will  now  be 
described,  may  hence  be  regarded  as  the  most  accurate  known  for 
the  estimation  of  sulphur  in  pyrites,  where  it  is  desirable  nol 

*  Concerning  the  action  of  nitric  acid  on  lead  sulphate,  see  my  experiments 
detailed  in  J.  Soc.  Chem.  Ind.  1887,  p.  96. 

f2 


68  RAW  MATERIALS  OF  MANUFACTURE. 

to  include  galena  and  heavy -spar^  and  it  is  at  the  same  time  very 
easy  and  speedy  of  execution^  if  the  following  directions  are 
accurately  observed. 

About  0*5  grm.  of  pyrites  is  heated  with  about  10  c.  c.  of  a 
mixture  of  3  vols,  nitric  acid-  (spec.  grav.  1*4)  and  1  vol.  strong 
hydrochloric  acid,  both  ascertained   to  be  absolutely  free  from 
sulphuric  acid.    The  operation  is  performed  as  described  above, 
in  such  manner  that  no  loss  by  spurting  takes  place.    The  mixture 
is  heated  up  now  and  then^  till  the  decomposition  is  complete^  and 
is  then  evaporated  to  dryness  in  a  water-bath.     Now  add  5  c.  c. 
hydrochloric  acid^  evaporate  once  more  (no  nitrous  fumes  ought 
to  escape  now)^  add  1  c.  c.  concentrated  hydrochloric  acid  and 
100  c.  c.  hot  water;  pass  through  a  small  filter  and  wash  with  hot 
water.     The  insoluble  residue  may  be  dried,  ignited,  and  weighed. 
It  may  contain^  besides  silicic  acid  and  silicates,  the  sulphates  of 
barium,  lead,  and  even  calcium,  whose  sulphur,  as  being  useless, 
is  purposely  neglected.     (If  this  residue  is  not  to  be  estimated,  it 
need  not  be  filtered  oflp,  and  the  next  step,  the  elimination  of  the 
iron,  may  be  taken  without  removing  the  silica,  &c.)     The  filtrate 
and  washings  are  saturated  with  ammonia,  avoiding  a  very  large 
excess  of  it ;  the  mixture  is  kept  at  a  moderately  warm  tempe- 
rature for  about  10  minutes  (at  the  expiration  of  which  time  it 
ought  still  to  smell  of  ammonia  very  distinctly,  not  merely  faintly), 
and  the  precipitated  ferric  hydrate  is  filtered  off  while  the  liquid 
is  still  hot.      For  this  purpose  funnels  must  be  used,  made  at  an 
angle  of  exactly  60°,  whose  tube  is  not  too  wide  and  is  completely 
filled  by  the  liquid  running  through;    or   else  a  Piccard's  tube 
(comp.  above,  p.  65),  or  a  filter-pump  is  employed.     The  filtering- 
paper  must  be  sufficiently  dense,  but  should  act  rapidly ;  the  filter 
must  be  adapted  to  the  funnel  so  that  no  air-channel  is  left  be- 
tween paper  and  glass.     The  hot  liquid  is  first  decanted  from  tlie 
ferric  hydrate,  and  the  latter  is  then  washed  onto  the  filter  with 
boiling  water.     The  washing  is  continued  with  hot  water  in  such 
manner  that  each  time  the  whole  precipitate  is  thoroughly  churned 
up  and  no  channels  are  formed  in  the  mass.     When  acting  on 
these  instructions,  the  whole  operation  can  be  performed  in  from 
half  to  one  hour,  and  no  trace  of  sulphuric  acid  is  retained  in  the 
precipitate.     The  total  bulk  of  the  filtrate  and  washings  need  not 
exceed  200  or  250  c.  c,  which  saves  concentrating  the  liquid  b}' 
evaporation.     The  end  of  the  washing  is  indicated  by  the  fact  that 


REMOVAL  OF  IRON  IN  TESTING  PYRITES.  69 

1  c.  c.^  on  adding  barium  chloride^  shows  no  opalescence  even 
after  a  few  minutes.  (It  is,  however,  best  in  important  cases  to 
test  the  iron  precipitate  for  sulphur  by  drying  it,  detaching  it  as 
well  as  possible  from  the  filter,  fluxing  with  pure  sodium  carbonate, 
dissolving  in  hot  water,  acidulating  and  adding  BaCla.) 

The  clear  liquid,  which  now  contains  all  the  sulphuric  acid 
combined  with  ammonia,  is  acidulated  with  pure  hydrochloric 
acid  in  very  slight  excess,  heated  to  boiling,  the  burner  removed, 
and  20  c.  c.  of  a  10-per-cent.  solution  of  barium  chloride,  pre- 
viously heated,  is  slowly  poured  in.  This  quantity,  which  suffices 
in  any  case  for  0*5  gram  pyrites,  is  roughly  measured  oflP  in  a  test- 
in  be  provided  with  a  mark,  and  is  heated  in  the  same  tube.  After 
precipitation,  the  liquid  is  left  to  stand  for  half  an  hour,  when  the 
precipitate  should  be  completely  settled.  The  clear  portion  is  now 
decanted,  and  the  washing  continued  by  decantation  with  boiling 
water,  as  mentioned  on  p.  65,  where  the  mode  of  igniting  the 
precipitate  is  also  described.  The  ignited  precipitate  should  be  a 
perfectly  white  and  loose  powder,  one  part  of  which  is  equal  to 
013733  sulphur. 

The  accuracy  of  this  method  and  its  complete  accordance 
(in  the  case  of  pure  ores)  with  the  fusion  method  of  Fresenius 
have  been  proved  by  Pattinson  (Joum.  Soc.  Chem.  Ind.  1890, 
p.  21),  who  points  out  how  much  more  convenient  is  the  former 
than  the  latter. 

Kiister  and  Thiel  (Zsch.  anorg.  Ch.  xix.  p.  97)  erroneously 
assume  that  the  ferric  hydrate  cannot  easily  be  washed  by  my 
method  so  as  to  remove  all  sulphate  (which  is  refuted  by  hundreds 
of  students  who  have  carried  out  this  method  in  my  laboratory, 
and  thousands  of  chemists  elsewhere).  They  therefore  propose  to 
precipitate  the  barium  sulphate  without  filtering  off  the  ferric 
hydrate  and  to  remove  the  latter  subsequently  by  several  hours' 
digestion  with  hydrochloric  acid ;  or  else  to  prevent  the  preci- 
pitation of  ferric  salts  along  with  the  barium  sulphate  by  the 
addition  of  a  large  quantity  of  ammonium  oxalate.  Both  methods 
take  much  more  time  than  mine,  without  any  gain  in  accuracy, 
•as  I  have  shown  in  Zsch.  anorg.  Ch.  ix.  p.  454,  and  again 
xxi.  p.  194.  This  is  confirmed  by  Herting  (Zsch.  angew.  Ch. 
1899,  p.  274). 

According  to  Heidenreich  (Zsch.  anorg.  Ch.  xx.  p.  233)  the 
contamination  of  barium  sulphate  by  iron  salts  can  be  avoided  by 


70  RAW  MATERIALS  OP  MANUFACTURE. 

reducing  the  ferric  sulphate  to  ferrous  sulphate  by  means  of  zinc 
and  preventing  the  access  of  air  and  light  during  the  precipitation. 
Herting  and  Lehnardt  (Chem.  Zeit.  1899,  No.  75)  effect  the  same 
purpose  much  more  quickly  by  employing  stannous  chloride  in 
lieu  of  zinc. 

Noaillon  (Zsch.  angew.  Ch.  1897,  p.  351)  proposes  to  avoid  the 
filtration  of  the  ferric  hydrate  by  diluting  the  liquid  to  a  certain 
mark,  filtering,  and  employing  a  portion  of  the  filtrate  for  the 
precipitation  with  barium  chloride  ;  but  this  method  introduces 
more  than  one  error  and  must  be  rejected. 

Sodium  peroxide  is  proposed  for  the  decomposition  of  pyrites  by 
Hempel,  Hohnel  (Arch.  Pharm.  1894,  p.  222),  and  Glaser  (Chem. 
Zeit.  1894,  p.  1448). 

In  lieu  of  the  estimation  of  sulphuric  acid  by  weight,  some 
chemists  prefer  titration  by  means  of  a  standard  solution  of 
barium  chloride.  This  was  first  proposed  by  Wildenstein  (Zeitsch. 
f.  anal.  Chemie,  i.  p.  432),  and  afterwards,  especially  for  the 
analysis  of  pyrites,  by  Teschemacher  and  Smith  (Chem.  News, 
xxiv.  pp,  61,  66  ;  comp.  also  Glendinning  and  Edger,  ib.  p.  140). 
Although  this  process,  notwithstanding  some  assertions  to  the 
contrary,  is  most  certainly  no  more  accurate  than  the  gravimetric 
process,  and  in  most  hands  is  less  so,  and  is  not  used  by  many 
chemists  in  important  cases,  we  shall  take  this  opportunity  of 
describing  the  estimation  of  sulphates  by  titration  with  barium 
chloride  in  its  simplest  form,  such  as  is  used  at  some  works  in 
testing  black-ash,  &c.  ;  it  is  also  used  sometimes  in  testing  pyrites, 
blende,  burnt-ore,  &c.  for  purposes  where  no  great  accuracy  is 
required. 

The  liquid  is  brought  to .  the  boil  in  a  porcelain  dish,  barium- 
chloride  solution  is  added  from  a  burette ;  from  time  to  time  a 
few  drops  are  taken  out  with  a  glass  tube,  passed  through  a 
miniature  filter  onto  a  glass  plate  resting  on  a  black  background, 
upon  which  a  number  of  drops  both  of  dilute  sulphuric  acid  and  of 
barium  chloride  have  been  put.  If  the  filtrate  still  gives  a 
cloudiness  with  a  barium-chloride  drop,  easily  visible  on  the  black 
ground,  the  little  filter  is  thrown  back  into  the  dish,  more  barium- 
chloride  solution  is  added  from  the  burette,  another  test  is  made, 
and  so  forth.  The  end  is  attained  when  a  filtered,  drop  gives  an 
extremely  slight  cloudiness  both  with  a  drop  of  barium  chloride 
and  with  one  of  sulphuric  acid.     The  work  is  very  much  expedited 


ESTJUATION  OF  SULPHATES  BY  TITRATION.  71 

by  the  following  contrivance,  proposed  by  Wildensteio  and  shown 
ID  fig.  6.  The  acidulated  solution  is  poured  into  a  vessel,  A,  made 
of  a  bottle  by  removing  the  bottom,  or  a  small  tubulated  jar, 
through  whose  cork  posses  a  bent  tube  B,  provided  at  the  lower 
end  with  the  pinchcock  /,  at  the  upper  end  with  a  bent-down  funnel 
/.  The  latter  (which  must  be  bell-shaped)  is  closed  by  two  disks 
of  filtering-paper  and  a  piece  of  linen  gauze  tied  over  all ;  and  the 
liquid  must  cover  the  whole  tube.  This  arrangement  permits  of 
withdrawing  at  will  small  filtered  samples  of  a  few  drops  each, 

Fig.  0. 


which  ai'e  run  into  a  test-tube  and  tried  with  a  drop  of  barium- 
chloride  solution.  It  must,  of  course,  not  be  omitted  first  to  run 
a  few  c.  c.  out  of  the  tube  B  and  back  into  the  jar  A  before  taking 
the  sample  for  testing ;  and  the  contents  of  the  test-tube  must  be 
always  put  back  into  A,  not  to  waste  too  much  substance.  If  by 
accident  the  point  of  finishing  the  reaction  has  been  overstepped, 
one  or  more  c.  c.  of  titrated  sulphuric  acid  are  put  in  and  are 
afterwards  deducted  from  the  result. 

C.  and  J.  Beringer  effect  the  titration  by  barium  chloride  after 
addition  of  sodium  acetate  and  acetic  acid  (Chem.  News,  lix. 
p.  41). 

Various  other  volumetric  methods  for  the  estimation  of  sul- 
phates, by  Carl  Alohr,  Ad.  Clemm,  Wildenstein  (2nd  method], 
Schwarz,  and  Fappenheim,  are  described  in  the  treatises  of  Fresenius 
and  Mohr  ;  but  they  are  more  complicated  and  not  more  accurate 
than  the  direct  titration  with  barium  chloride  as  just  described. 
We,  therefore,  mention  only  one  method  of  this  kind.  This  is  the 
method  proposed  by  Wilsing  (Chcm.  Iiul.  1886,  p.  25),  a  slight 


72  RAW  MATERIALS  OF  MANUFACTURE. 

but  apparently  useful  modiHeation  of  those  just  mentioued.  He 
precipitates  a  neutral  solution  of  the  sulphate  or  solution  con- 
taining such^  boiling  in  a  porcelain  dish^  with  a  4-per-cent. 
barium-chloride  solution  of  known  strength ;  he  then  adds  a  few 
drops  of  an  alcoholic  solution  of  phenolphthalein  and  a  2-per- 
cent, solution  of  sodium  carbonate :  as  soon  as  the  last  part  of 
barium  chloride  has  been  precipitated  as  carbonate  the  colour 
turns  red^  so  that  the  soda  used  is  a  measure  for  the  sulphate 
originally  present.  If  the  solution  to  be  tested  is  either  acid  or 
alkaline^  it  must  be  made  neutral  by  sodium  carbonate  or  hydro- 
chloric acid^  phenolphthalein  being  used  as  indicator  here  as  well. 
L.  W.  Andrews  (Amer.  Chem.  J.  1889,  p.  567,  &  Chem.  Zeit. 
1889,  Rep.  p.  39)  proposes  the  following  method  for  estimating 
sulphuric  acid  combined  with  bases  : — The  solution  is  diluted  till 
it  contains  no  more  than  2  per  cent.  SO3,  is  almost  neutralized 
and  brought  to  a  boiling  heat.  !Now  a  solution  of  pure  barium 
chromate  in  hydrochloric  acid  is  added,  and  then  ammonia,  the 
excess  of  which  is  removed  by  boiling.  The  solution  is  filtered 
while  hot  and  is  washed  at  once.  Now  a  quantity  of  chromic 
acid,  equivalent  to  the  sulphuric  acid  originally  present,  will  he  in 
solution  ;  this  is  estimated  by  adding  potassium  iodide  and  strong 
hydrochloric  acid,  and  titrating  with  decinormal  thiosulphate- 
solution  (1  c.c.  =  12*85  mg.  I  =  2'662  mg.  SO3).  It  is  claimed 
that  this  operation  is  more  quickly  performed  than  the  gravimetric 
process,  and  is  at  least  as  accurate ;  but  both  of  these  assertions 
are  doubtful. 

Similar  methods  are  described  by  Renter  (Chem.  Zeit.  1898, 
p.  357)  and  Marboutin  and  Moulinie  (Chem.  Cbl.  1898,  i. 
p.  218) . 

Several  methods  have  been  proposed  for  estimating  the  available 
sulphur  of  sulphur-ores — that  is,  that  portion  of  it  which  passes 
into  the  chambers  in  the  shape  of  SOg  and  SO3.  Thus  W.  G. 
Mixter  (Amer.  Chem.  J.  ii.  p.  396)  burns  the  pyrites  in  a  current 
of  oxygen,  and  passes  the  vapours  into  bromine-water  containing 
some  hydrochloric  acid  and  an  excess  of  bromine.  A  similar 
process  is  recommended  by  Zulkowsky  (Wagner's  Jahresb.  1881, 
p.  160),  both  for  testing  pyrites  and  spent  oxides  of  gas-works. 
The  latter  is  always  contaminated  with  sawdust,  tarry  matters,  and 
variable  quantities  of  lime,  which  retains  part  of  the  sulphur  in 
burning,  whence  an  estimation  of  the  total  sulphur  is  quite  useless 


ESTIMATION  OP  AVAttABLB  gULPHUK.  73 

for  practical  purposes.  The  process  takes  place  in  a  combustion- 
tube  (fig.  7),  3  feet  long,  narrowed  at  a,  aod  dravn  out  at  tbe  end 
iato  a  long  tube,  not  too  thin,  and  bent  downwards.  Between  a 
snd  b  there  is  a  layer  of  platinized  asbestos  (see  below),  8  to  10 
inches  long,  and  at  a  distance  of  3  or  4  inches  from  this  a  porcelain 

Fig.  7. 


boat  with  about  0'4  grm,  of  spent  oxide  or  pyrites.  The  end  of 
the  tube  at  k  is  connected  with  an  oxygen  gas-bolder.  The  absorp- 
tion of  tbe  vapours  takes  place  in  tbe  two  3-bull)  tubes  c  and  d 
(5|  inches  high)  and  the  tube  e,  filled  with  glass-wool.  The 
absorbing-liquid  is  made  by  dissolving  180  grama  caustic  potash 
(purified  with  alcohol  from  sulphate)  in  water,  adding  100  grams 
bromine,  taking  care  to  keep  tbe  mixture  cool,  and  diluting  to 
1000  c.  c.  30  c.  c.  of  this  suffice  for  estimating  0'5  grm.  sulphur. 
The  tube  e  ought  also  to  be  moistened  with  it.  First  heat  the 
portion  of  tbe  tube  between  a  and  b,  passing  moist  oxygen  through 
it  at  the  same  time ;  then  heat  the  boat  from  the  right  to  tbe  left ; 
lastly  the  tube,  up  to  the  place  /.  The  current  of  gas  must  l>e 
much  stronger  than  for  an  organic  analysis,  lest  any  sulphur  should 
escape  unbumt,  but  not  strong  enough  to  draw  off  any  SOi  uu- 
absorbed.  So  long  as  any  dew  appears  at  h,  it  must  be  driven  into 
the  receiver  with  a  fiunsen  burner.  When  this  ceases  (usually  in 
about  an  hour),  the  experiment  is  finished.  The  receivers  are  then 
taken  off,  washed  out,  and  the  acid  remaining  in  h  is  recovered  by 
aspunting  water  several  times  through  it.  All  the  liquids  are 
united,  supersaturated  with  hydrochloric  acid  in  order  to  de- 
compose the  potassium  hypobromite,  heated,  concentrated  if 
necessary,  and  the  sulphuric  acid  is  precipitated  by  barium 
chloride  in  tbe  usnal  manner  (or,  more  conveniently,  the  receivers 


74  RAW  MATERIALS  OF  MANUFACTURE. 

are  charged  with  hydrogen  peroxides  free  from  sulphuric  acid  and 
are  retitrated  after  the  end  of  the  operation). 

Jannasch  (Journ.  f.  prakt.  Ch.  [2]  xl.  p.  237)  heats  pyrites  in 
a  mixture  of  air  or  oxygen  and  nitric-acid  vapours  ;  the  vapours 
of  SO2  and  SOg  are  absorbed  in  bromine- water.  [It  must  not  be 
forgotten  that  in  the  presence  of  nitric  acid  the  barium  sulphate 
is  never  free  from  nitrate^  and  that  hence  all  nitric  acid  must  be 
removed  previously.  I  would,  therefore,  propose  to  use  in  that 
class  of  processes  hydrogen  peroxide  as  an  absorbent,  which  is  very 
efficient  and  requires  no  special  precautions;  in  this  case  the 
acids  absorbed  can  be  estimated  by  titration  with  the  standard 
alkali.] 

Graeger  (Dingl.  Journ.  ccxli.  p.  53 ;  Fischer's  Jahresb.  1881, 
p.  161)  beats  pyrites  with  reduced  metallic  iron,  decomposes  the 
FeS  formed  by  dilute  hydrochloric  acid,  and  titrates  the  H^S 
evolved  by  passing  it  into  a  solution  of  iodine.  This  method  has 
been  again  proposed  by  Treadwell  (Berl.  Ber.  xxiv.  p.  1937,  and 
xxiv.  p.  2377)  and  by  Eliasberg  (Zsch.  anal.  Ch.  1899,  p.  240), 
but  it  does  not  seem  to  be  practically  employed. 

Expeditious  assays  of  pyrites  have  been  proposed  in  many  ways, 
but  none  of  them  is  sufficiently  accurate  to  be  employed  for  esti- 
mating the  sulphur  in  fresh  pyrites,  and  some  of  them  are  not 
even  accurate  enough  for  testing  the  sulphur  remaining  in  burnt- 
ore  (pyrites  cinders). 

The  so-called  mechanical  pi/rites  assay  of  Anthon  (Dingl.  Journ. 
clxi.  p.  115)  is  too  rough  and  unreliable  even  for  very  simple  pur- 
poses.    (Comp.  1st  ed.  of  this  work,  i.  p.  108.) 

In  the  Freiberg  works  1  gram  of  finely  ground  pyrites  is  mixed 
with  2  grams  sodium  carbonate  and  2  grams  saltpetre  :  the  mixture 
is  fluxed  in  a  small  iron  dish  in  a  red-hot  muffle-furnace,  dissolved 
in  hot  water  and  filtered  into  a  beaker  in  which  there  is  hydro- 
chloric acid  by  saturating  the  soda  in  excess.  Then  the  filtrate  is 
brought  to  boiling,  and  the  sulphuric  acid  estimated  by  a  standard 
solution  of  barium  chloride,  preferably  by  Wildenstein's  method 
(supra,  p.  70).  Liebig  (Post's  Tech.  chem.  Analyse,  2nd  ed.  i, 
p.  677)  recommends  this  method  as  a  quick  and  easy  one,  where 
no  great  accuracy  is  required. 

In  the  method  of  Pelouze  (Compt.  Bend.  liii.  p.  685 ;  Ann.  de 
Chim.  et  de  Phys.  [3]  Ixiii.  p.  415)  the  finely  powdered  pyrites 
is  mixed  with  chlorate  of  potash,  common  salt,  and  an  exactly 


TESTING  PYRITES  CINDERS  FOR  SULPHUR.  75 

weighed  quantity  of  sodium  carbonate^  and  ignited^  which  can  be 
done  in  an  iron  spoon.  The  fluxed  mass  is  dissolved  in  water^ 
filtered  J  the  residue  washed^  and  the  soda  not  converted  into  sul- 
phate estimated  alkalimetrically.  This  process  continued  to  be 
recommended  in  French  treatises  till  very  recently^  although  its 
inaccuracy  was  established  and  the  sources  of  error  partly  demon- 
strated by  many  chemists,  such  as  Barreswil^  Bottomley^  Bocheroff^ 
Lunge^  and  especially  Kolb  ('  Notes  sur  PEssai  des  Pyrites  de 
Fer ').  Kolb  found  the  sources  of  error  on  the  one  hand  in  the 
formation  of  sodium  silicate^  on  the  other  hand  in  the  decompo- 
sition of  potassium  chlorate  in  the  presence  of  ferric  oxide  into 
chlorine^  oxygen^. and  caustic  potash.  New  experiments  made  in 
my  laboratory  by  Mr.  Rey  have  equally  proved  the  method 
to  be  wrong,  even  if  the  "constant  error '^  of  1  to  1^  per  cent., 
admitted  by  Pelouze,  is  taken  into  account.  A  principal  objection 
is  the  difficulty  of  evading  the  mechanical  loss  by  spurting  iu  the 
fluxing  process. 

This  fault  is  avoided  in  the  plan  proposed  by  Kolb  (J.  pharm. 
Chim.  [4]  X.  p.  401),  which,  however,  is  only  intended  for  testing 
burnt-ore.  Kolb  mixes  5  or  10  grams  of  this  with  5  grams  pure 
sodium  carbonate  and  50  grams  cupric  oxide,  heats  about  15 
minutes  in  an  iron  capsule  to  a  dark-red  heat,  with  stirring,  lixi- 
viates the  melted  mass,  and  estimates  the  unconsumed  soda  volu- 
metrically.  The  trials  made  in  the  autboi*^s  laboratory  showed 
that  there  is  no  spurting,  but  that  the  heating  must  not  be  pro- 
longed too  much,  in  order  to  avoid  the  formation  of  silicates.  The 
lixiviation  of  the  large  bulk  of  cupric  and  ferric  oxide  is  tedious, 
and  the  method  is  somewhat  costly,  as  it  requires  50  grams  of 
cupric  oxide  for  each  test,  nor  are  the  results  very  satisfactory 
(see  below) . 

A  much  better  method  for  testing  burnt-ore  was  2)roposed  by 
J.  Watson  (J.  Soc.  Chem.  Ind.  1888,  p.  305).  2  or  3  grams  of 
pyrites  cinders  are  mixed  with  1  or  2  grams  of  sodium  bicarbonate 
of  known  titre  ;  the  mixture  is  heated  in  a  nickel,  porcelain,  or 
platinum  crucible  by  means  of  a  small  Bunsen  flame  for  5  or  10 
minutes^  stirred  up,  heated  once  more  for  15  minutes  with  a  some- 
what stronger  flame,  treated  with  hot  water,  filtered  and  washed. 
The  solution  is  titrated  with  hydrochloric  acid  and  methyl-orange ; 
the  loss  of  titre  in  comparison  with  the  original  one  is  equal  to  the 
sulphate  formed.      The  escaping   carbonic  acid  keeps  the  ^lass 


76  RAW  MATERIALS  Of  MANUFACTURE. 

porous  ;  there  is  no  spurting,  and  the  lixiyiation  of  the  small  bulk 
of  the  mixture  is  easy  and  expeditious. 

Experiments  made  iu  my  laboratory  (Zeits.  f.  ang.  Chem. 
1892,  p.  447)  showed  that  Watson's  method  yielded  results 
closely  agreeing  with  those  obtained  by  accurate  gravimetrical 
methods,  whilst  the  method  of  Pelouze,  even  with  burnt-ore, 
yielded  too  low  results,  and  that  of  Kolb  was  not  more  reliable. 
But  it  was  found  that  special  precautions  must  be  observed  in 
order  to  yield  accurate  results.  3-200  grams  of  the  finely  ground 
samples  are  mixed  with  2*000  grams  sodium  bicarbonate  (of  known 
alkalimetrical  titre),  and  heated  in  a  nickel  or  iron  crucible;  a 
platinum  crucible  easily  leads  to  over-heating.  The  heating  is 
continued  for  10  or  15  minutes  with  a  very  small  flame,  then 
another  15  minutes  with  a  strong  flame,  but  without  fusing  the 
mass.  The  crucible  must  be  kept  covered  and  the  mass  must  n(»t 
be  stirred ;  it  should  in  the  end  be  red-hot,  and  after  cooling  black 
and  porous.  It  is  boiled  in  a  porcelain  dish  with  water,  adding  the 
same  volume  oE  neutral  solution  of  sodium  chloride.  This  is 
an  essential  improvement,  as  without  this  addition  some  oxide 
of  iron  invariably  passes  through  the  filter,  and  makes  the 
following  titration  by  methyl-orange  almost  impossible.  The 
filtered  solution  is  titrated  with  standard  acid.  The  ditference 
between  the  original  titre  of  bicarbonate  and  that  now  found 
shows  the  sulphur,  1  c.  cm.  normal  acid  indicating  0'5  per  cent.  S. 
In  the  presence  of  a  somewhat  considerable  quantity  of  zinc  this 
method  does  not  answer. 

Magnetic  pyrites  {pyrrhotite),  FcjSg,  is  sometimes  present, 
especially  in  some  kinds  of  American  pyrites.  As  that  ore  yields 
its  sulphur  very  imperfectly  in  ordinary  pyrites-kilns,  its  estimation 
may  become  important.  Cone  (Journ.  Amer.  Chem.  Soc.  xviii. 
p.  404)  effects  this  by  grinding  the  ore  so  that  all  passes  through 
a  60-mesh  sieve  (not  more  finely  !),  spreading  the  powder  on  a 
sheet  of  glazed  paper,  applying  a  magnet  to  this,  removing  the 
mechanically  adhering  pyrites  by  gently  knocking  the  magnet  and 
separately  brushing  off  the  pyrrhotite  after  putting  on  the  anchor. 
This  is  repeated  five  or  six  times,  and  the  sulphur  estimated  in  the 
separated  portions. 

Marcasite  and  pyrites  can  be  distinguished  by  the  easier  de- 
composition of  the  former  when  boiling  with  a  solution  of  ferric 
salt.     This  behaviour  has  been  studied  in  detail  by  H.  N.  Stokes 


OTHER  CONSTITUEirrs  OF  PYRITES.  11 

(Bulletin  U.S.  Greol.  Surv.  No.  186) ;  but  it  is  of  no  practical 
importance  for  technical  analysis. 

Estimation  of  other  constituents  of  Pyrites, — Usually  it  is 
snfficient  to  estimate  the  sulphur  in  a  pyrites  whose  nature  is 
otherwise  known.  If^  howeyer^  the  pyrites  is  of  unknown  compo- 
sition^ its  value  for  acid-making  can  only  be  estimated  by  a  com- 
plete determination  of  all  its  constituents  according  to  the  rules 
of  mineral-analysis.  If  it  contains^  for  instance,  calcium  carbonate, 
this  on  burning  will  retain  its  equivalent  of  sulphuric  acid  equal 
to  0*32  per  cent.  S  for  each  per  cent.  CaCOg ;  if  calcium  sulphate 
is  present  from  the  first,  its  sulphuric  acid  has  to  be  deducted 
from  the  whole  quantity  of  sulphur  found.  If  lead  has  been  found, 
an  equivalent  of  sulphur  must  be  considered  as  practically  lost ; 
and  the  same  is  the  case  with  zinc, — because  the  sulphates  of  both 
metals  are  hardly  or  not  at  all  decomposed  at  the  temperature  of 
a  pyrites-burner.  In  France  half  of  the  S  combined  with  Zn  is 
considered  as  lost,  =  0*245  p.  c.  S  per  1  p.  c.  Zn  (for  copper 
they  reckon  0*505  p.  c.  S  per  1  p.  c.  Cu  as  lost).  Frequently 
arsenic  will  also  have  to  be  sought  for ;  and  even  silica  may 
be  of  importance — firstly,  because  in  the  presence  of  much 
silica  "  explosive  '^  properties  of  the  pyrites  must  be  feared  (see 
p.  55}^  and  secondly,  in  the  case  of  cupreous  pyrites,  because 
silica  lessens  the  value  of  the  cinders.  Even  silver  and  ffold 
are  sometimes  sought  for  (comp.  Chem.  News,  xxvi.  p.  63, 
xxxiv.  pp.  94,  132,  152,  172)  ;  but  it  cannot  be  said  that  the 
quantities  found  have  any  influence  on  the  commercial  value  of 
pyrites. 

It  is  not  our  object  here  to  treat  of  the  estimation  of  all 
these  substances,  nor  that  of  the  copper  which,  in  the  majority 
of  cases,  represents  a  large  portion  of  the  value  of  pyrites  *.  We 
make  an  exception  only  with  arsenic,  because  special  methods  for 
estimating  this  in  pyrites  have  been  worked  out  which  are  not 
found  in  the  ordinary  text-books. 

The  process  employed  at  Freiberg  is  that  used  by  Reich, 
and  is  as  follows : — Digest  about  0'5  gram  of  finely  pulverized 
pyrites  in  a  porcelain  crucible,  covered  with  a  watch-glass,  with 

*  For  these  substances,  see  Lunge  and  Hurter^s '  Alkali-Maker's  Handbook ' ; 
also  a  very  extensive  paper  by  Westmoreland,  J.  Soc.  Cbem.  Ind.  1886,  p.  31, 
aod  criticisnis  on  the  same,  p.  277 ;  and  Lunge's  Ghemisch-Technische  Unter- 
Buchungsmethoden,'  i.  p.  250  et  seq. 


I 


78  HAW  MATERIALS  OF  MANUFACTURE. 

concentrated  nitric  acid  at  a  gentle  heat^  until  the  residue  assume9 
a  lighter  colour  and  the  separated  sulphur  has  turned  a  pure 
yellow.  After  decomposition^  heat  the  crucible  on  a  sand-bath  to 
get  rid  of  the  excess  of  acid^  but  not  to  dryness.  Add  4  grams 
of  sodium  carbonate,  dry  completely  on  the  sand-bath,  add  4 
grams  of  potassium  nitrate,  and  heat  the  mass  until  the  contents 
of  the  crucible  have  been  in  quiet  fusion  for  ten  minutes.  Extract 
the  cooled  mass  with  hot  water  and  filter;  the  filtrate  contains  all 
the  arsenic  as  sodium  arseniate.  Acidify  with  a  little  nitric  acid, 
keep  for  two  hours  on  a  sand-bath  to  get  rid  of  the  carbon  dioxide, 
add  a  sufficient  quantity  of  a  solution  of  silver  nitrate,  and 
neutralize  carefully  with  dilute  ammonia.  The  reddish-brown 
precipitate  of  silver  arseniate  is  filtered,  washed,  dried,  taken  oflF 
the  filter  as  well  as  possible,  the  filter  is  incinerated  in  a  muffle,  the 
precipitate  put  to  it,  a  sufficient  quantity  of  assay  lead  is  added,  and 
the  silver  estimated  by  cupellation.  100  parts  of  silver  correspond 
to  23' 15  of  arsenic. 

Leroy  M.  McCay  has  modified  and  greatly  simplified  this  method 
(Chem.  News,  xlviii.  p.  7)  by  estimating  the  excess  of  silver  used 
by  Volhard's  method.  Later  on  (Amer.  Chem.  J.  viii.  no.  2)  the 
same  author  recommends  as  preferable  another  plan,  namely  dis- 
solving the  AggAsOi  in  dilute  ammonia,  and  either  estimating  the 
silver  by  Volhard's  volumetric  method  (precipitation  with  ammo- 
nium thiocyanate),  or  evaporating,  drying,  and  weighing  the  total 
in  a  thin  platinum  dish.  If  the  arsenic  is  to  be  precipitated  as 
pentasulpliide,  which  is  otherwise  a  tedious  operation,  McCay 
recommends  (Amer.  Chem.  J.  ix.  no.  3,  and  x.  no.  6)  to  place  the 
solution  in  a  flask  with  a  well-fitting  stopper,  acidify  with  HCl, 
and  dilute  with  freshly  boiled  water  till  the  flask  is  nearly  full, 
pass  in  H2S  to  saturation,  insert  and  fasten  down  the  stopper,  and 
place  the  whole  in  a  water-bath  for  an  hour.  At  the  end  of  that 
time  all  the  arsenic  will  be  precipitated  as  pentasulphide,  As^S^, 
containing  no  free  sulphur. 

Clark  (J.  Soc.  Chem.  Ind.  1887,  p.  352)  recommends  the 
following  method  as  especially  adapted  for  estimating  very  small 
quantities  of  arsenic  in  pyrites  rich  in  sulphur : — Mix  3  grams  of 
pyrites  in  a  platinum  crucible  with  four  times  as  much  of  a  mixture 
of  calcined  magnesia  and  sodium  hydrate,  heat  for  about  10 
minutes  over  a  moderately  low  Bunsen  flame,  extract  the  shrunk 
mass  with  boiling  water,  acidify  the  solution  with  hydrochloric 


ZINC-BLENDE.  79 

acid  (which  evolyes  mach  H2S)^  boil  for  a  few  minutes^  and 
saturate  with  H2S^  when  all  the  arsenic  will  be  thrown  down  as 
aulphide;  wash  the  precipitate^  extract  the  sulphide  of  arsenic 
with  ammonia,  evaporate  the  solution  to  d]7ness,  dissolve  in 
strong  nitric  acid,  and  estimate  the  As  as  ammonio-arseniate  of 
magnesia^  or  else  by  silver  solution  as  above  described.  Or  else 
the  calcined  mixture,  after  neutralizing  it  with  HCl,  as  above 
mentioned,  is  reduced  by  cuprous  chloride,  and  the  liquid  is  slowly 
distilled  into  water,  repeating  this  operation  twice  with  strong 
HCl,  which  will  cause  all  the  arsenic  to  pass  over  as  AsCI^;  which 
can  be  either  precipitated  by  H2S  or  titrated  by  iodine.  Clark 
points  out  the  necessity  of  carefully  testing  all  the  reagents 
employed  for  arsenic,  of  which  he  had  found  as  much  as  0*02  per 
cent,  even  in  commercial  caustic  soda. 

Nahnsen's  process  (Chem.  Zeit.  xi,  p.  692  ;  abstr.  J.  Soc.  Chem. 
Ind.  1887,  p.  564)  does  not  offer  any  special  advantage.  The 
process  described  in  detail  by  H.  Fresenius  (Zeitsch.  f.  anal. 
Cliemie,  1888,  p.  34)  is  no  doubt  very  accurate,  but  lengthy  and 
troublesome. 

Blattner  and  Brasseur  (Z.  angew.  Ch.  1898,  p.  262)  give  exact 
instructions  for  estimating  arsenic  in  pyrites,  both  in  the  wet  and 
dry  methods. 

3.    ZiNC-BLENDE. 

This  mineral  is  now  the  principal  zinc-ore.  Previously  to 
reducing  the  zinc,  the  blende  must  be  roasted  in  order  to  convert 
it  into  ZnO,  and  this  process  was  formerly  carried  out  without 
taking  any  care  to  deal  with  the  enormous  quantities  of  SOg 
formed.  Sanitary  legislation  at  last  interfered  with  this  procedure, 
which  of  course  laid  waste  all  the  country  round  the  zinc- works, 
and  compelled  measures  for  dealing  with  the  noxious  gases.  Part 
of  this  is  used  for  the  production  of  liquid  sulphur  dioxide  (comp. 
Chap.  IV.) ;  most  of  it,  however,  serves  for  the  manufacture  of 
sulphuric  acid,  so  that  blende  has  now  become  one  of  the  more 
important  raw  materials  for  this  purpose.  The  historical  develop- 
ment of  this  industry  will  be  related  in  Chap.  IV. 

Blende  occurs  in  large  quantities  for  instance  in  Silesia,  West- 
phalia, Rhineland,  Saxony,  Austria,  Belgium,  Wales,  the  Isle  of 
Man,  Spain,  Italy,  France,  the  United  States,  in  nearly  all  of 


80  RAW  MATERIALS  OF  MANUFACTURE. 

which  localities  it  is  utilized  for  the  manufacture  of  sulphuric 
acid. 

Pure  blende^  ZnS,  contains  32*9  per  cent.  S,  and  67*1  per  cent. 
Zn.  The  commercial  ore  is^  of  course^  always  impure.  We  quote 
the  following  analyses^  by  Minor  (Chem.  Zeit.  1889,  p.  1602)^  of 
Rhenish  blende : — 

S 30-24  27-94  22-11  21-05 

ZnasZnS 2273  27-17  3446  31-16 

Zn  in  other  combination  .. .  503  475  5-83  6*65 

Fe  15-98  1312  206  2-33 

Gangue  (by  diff.)  21-02  27*02  35-54  88-84 

Drasche  analyzed  a  blende  from  Carinthia :  ZnS  68*41  per  cent., 
PbS  4-55  ;  FeS,  205 ;  ZnCOj  240 ;  CaCOg  893 ;  MgCOg  1062 ; 
AljOa  0-63  ;  gangue  (principally  quartz)  2-32  per  cent. 

Pennsylvanian  blende,  according  to  P.  A.  Genth  : — Sulphur 
32-69  to  33-06  per  cent.,  Zinc  6647,  Iron 038,  Cobalt  034. 

Jurisch  (Schwefelsaurefabrikation,  p.  61)  quotes  analyses  of 
various  descriptions  of  blende,  burnt  by  the  Chemische  Fabrik, 
Bhenania,  with  sulphur  contents  varying  from  18-40  to  32*20,  and 
zinc  from  14-90  to  50*22  per  cent. 

Haenisch  and  Schroeder  (Chem.  Ind.  1884,  p.  118)  quote  the 
contents  of  Silesian  blende =23  to  37  per  cent.  S,  also  an  inferior 
blende  =8  to  21  per  cent.  S. 

Blende  frequently  contains  cadmium  and  mercury.  The  latter 
occurs  in  Rhenish  blende  only  =002  per  cent.,  but  in  Spanish 
(Aviles  in  Asturia)  =0135  per  cent. 

According  to  direct  information  from  the  Rhenania  Chemical 
Works  at  Stolberg,  the  sulphur  contents  in  the  blende  roasted 
there  ranges  between  20  and  30  per  cent. ;  on  the  average  25  to 
28  per  cent.  Iron  does  not  do  any  harm,  but  lime  retains  its 
equivalent  of  S  as  CaSO^.  Lead  affects  the  duration  of  the 
roasting-floors  ;  it  is  partially  volatilized  with  a  little  silver,  and 
reappears  in  the  flue-dust,  the  towers,  and  chambers.  Mercury  and 
fluorine  are  also  volatilized  and  act  very  injuriously  on  the  plati- 
num vessels  used  for  concentration.  Recently  the  sulphuric  acid 
factories  refuse  blende  containing  fluorides.  Arsenic  generally 
occurs  in  blende  in  such  extremely  slight  quantities  that  the  acid 
made  from  it  may  be  considered  as  technically  pure. 

The  production  of   blende  in  Prussia  in   1890   amounted   to 


OTHER  METALLIC  SULPHIDES.  81 

362^464  tons;    Belgium  in  1889  to  12,376  tons;   France  and 
Algiers  in  1887  to  13,800  tons ;  Spain  in  1885  to  2,488  tons. 

Analyses  of  Zinc-blende. — The  sulphur  is  estimated  by  the  wet 
method  as  described  p.  62.  In  the  cinders  from  blende  the  same 
method  must  be  eiQployed  since  the  dry  methods,  e.  g.  Watson- 
Lunge's  (p.  75),  give  quite  wrong  results.  Details  respecting  this 
and  the  other  constituents  of  zinc-blende  are  found  in  Lunge 
and  Hurter's  'Alkali-Maker's  Handbook '  and  Lunge's  '  Chemisch- 
technische  Untersuchungsmethoden.' 

4.  Otheb  Metallic  Sulphides. 

Pyrites  proper  has  hardly  any  other  application  than  that  for 
sulphuric-acid  making,  and  it  is  obtained  almost  exclusively  for  this 
purpose.  In  the  case  of  cupreous  pyrites  the  sulphur  constitutes 
only  a  portion,  but  a  very  considerable  one,  of  its  value.  The 
working  of  poor  copper- ores  would  not  pay,  apart  from  the 
noxious  effect  of  the  gas  produced  in  calcining  the  ore,  unless  the 
price  of  the  ore  were  very  moderate ;  and  this  is  only  possible  by 
the  acid-makers  paying  on  their  part  for  the  ore,  which  they  can 
well  afford,  as  most  kinds  of  cupreous  pyrites  behave  very  well 
in  the  burners,  and  yield  quite  as  much  acid  in  proportion  to 
their  percentage  of  copper  as  the  non-cupreous  ores.  The  case 
of  zinc-blende  is  now  similar  to  that  of  cupreous  pyrites. 

The  case  is  different  with  most  other  sulphuretted  ores  occurring 
in  smelting-operations,  such  as  galena,  the  many  mixed  ores  con- 
taining blende  and  galena,  besides  iron-  and  copper-pyrites,  the 
richer  copper-pyntes  themselves,  and,  lastly,  the  intermediate  pro- 
ducts, "  coarse  metal/'  "  matte/'  &c.  These,  for  their  metallurgical 
utilization,  equally  require  a  calcination  evolving  sulphur  dioxide ; 
but  the  matter  is  very  different  here  from  what  it  is  with  a  good 
pyrites,  whether  it  be  pure  iron -pyrites  or  containing  a  few  per  cent, 
of  copper.  On  the  whole,  all  those  ores  and  metallurgical  products 
are  much  poorer  in  sulphur  than  ordinary  good  pyrites ;  and  for 
this  reason  they  are  less  easily  calcined  in  such  a  manner  as  to 
allow  of  utilizing  the  gas,  because  the  evolution  of  heat  by  the  com- 
bustion of  their  own  sulphur  is  not  sufBcient  to  maintain  the  process 
energetically.  An  external  stimulus  was  required  before  smelting- 
works  would  seriously  attempt  to  utilize  the  sulphur  dioxide 
contained  in  the  gas  from  calcining  the  ores ;  and  this  proved  to  be 

VOL.  I.  O 


82  RAW  MATERIALS  OF  MANUFACTURE. 

■ 

the  damage  and  nuisance  caused  by  the  noxiotts  vapours  all  round  the 
works.  The  claims  for  damages^  the  law-suits,  and  the  measures 
taken  by  the  authorities  at  last  made  it  impossible  in  many  places 
for  the  works  to  go  on  in  the  old  way ;  and  although  it  appeared  at 
first  as  if  the  sulphurous  acid  could  not  be  condensed  at  all  in  this 
case,  or  only  at  a  loss,  practice  has  now  succeeded  in  fulfilling  the 
task  in  most  (but  not  in  all)  cases,  principally  by  the  construction 
of  improved  burners,  which  will  be  described  in  the  fourth  Chapter. 
It  would  undoubtedly  be  too  much  to  say  that  the  task  had 
been  solved  in  all  its  parts;  the  success  has  mostly  been  only 
partial.  In  many  cases  where  an  ore  could  not  possibly  have 
been  calcined  so  as  to  utilize  the  gas,  mixing  of  it  with  others 
has  been  resorted  to.  Thus  the  Halsbriicke  works,  near  Freiberg, 
roast  galena  and  blende  along  with  pyrites  ;  and  in  1870  they  made 
8000  tons  of  sulphuric  acid  from  the  gas. 

In  reference  to  the  sulphur  dioxide  escaping  as  noxious  vapour, 
Leplay  (comp.  Percy,  ^  Metallurgy,'  1862,  i.  p.  337)  mentions  that  in 
South  Wales  annually  46,000  tons  of  sulphur  escaped  into  the  air  as 
sulphur  dioxide,  along  with  arsenic,  fluorine,  lead,  and  zinc  com- 
pounds, in  spite  of  the  condensing-chambers.  In  fact  the  country 
round  Swansea  was  stripped  of  all  vegetation.  At  Fi'eiberg  the  works 
in  1864  paid  upwards  oi£2750  damages  on  account  of  their  vapours, 
in  1870,  after  better  condensation  had  been  eflfected,  onlv  .€239. 
It  should  not  be  forgotten  that  sulphur  dioxide  occurs  in  very 
large  quantity,  although  in  a  much  more  dilute  state,  in  all  coal- 
smoke,  and  consequently  in  the  atmosphere  and  the  rain-water 
of  all  large  towns,  and  that  the  most  perfect  *'  smoke-combustion^' 
cannot  do  away  with  this.  Much  more  injurious  than  the  vapours 
escaping  through  high  chimneys,  which  are  soon  diluted  with  air, 
is  the  smoke  from  brick-works,  coke-ovens,  and  other  fires  which 
emit  their  smoke  at  a  low  height  above  the  ground.  Mr.  Fletcher 
has  calculated  that  at  St.  Helens  the  acids  escaping  amounted  : 

From  fire-gases    to  800  tons  per  week. 

„     copper- works „  380         „         „ 

„     glass-works „  180         „         „ 

„     alkali- works    „     25         „         „ 

Similar  calculations  have  been  made  by  Mr.  Hasenclever  (Chem. 
Industrie,  1879,  p.  225),  who  has  given  strong  proof  of  the  damao-e 
done  by  coal-smoke  alone. 


ACID-GASES  IN  SMOKE.  83 

According  to  the  28th  Alkali  Report  (for  the  year  1891),  p.  19,  the 
quantity  of  acid  gas  which  escapes  into  the  air  at  St.  Helens,  cal- 
culating HCl  as  its  equivalent  of  sulphur  acids,  is  as  follows  : — 

Tons  sulphur 
per  annum. 

From  Copper  and  Lead  smelting  works 1 1 ,480  ^ 

Glass-works 7,500  V  19,313 

Polishing-powder  works 333  J 

Coal  burnt  (1^  per  cent,  of  1,040,000) 15,600 

Chance-Claus  process ...  620 

Sulphuric-acid  chambers    173^       ^^^ 

„     Alkali-works    402j       ^^^ 


Total 36,108 

This  is  the  equivalent  of  72,216  tons  80^  or  110,586  H2SO4, 
of  which  the  alkali-works  contribute  only  1^  per  cent.  Since  all 
this  is  given  off  from  an  area  of  about  3  square  miles,  each  square 
mile  at  St.  Helens  receives  the  equivalent  of  12,036  tons  of  sulphur, 
against  11  tons  in  summer  or  44  tons  in  winter  on  a  square  mile 
in  London. 

In  Chapter  IV.  we  shall  deal  with  the  various  attempts  at 
utilizing,  or  at  least  rendering  innocuous,  the  acid  gases  given  out 
in  calcining  ores,  and  we  shall  here  enumerate  only  the  various 
classes  of  ores  or  waste  substances  coming  under  the  head  of 
causing  "  noxious  vapours,^'  such  as  might  serve  for  the  manu- 
facture of  sulphuric  acid  (apart  from  zinc-blende,  comp.  p.  79). 

Copper-pyrites  and  mixtures  of  this  with  blende,  galena,  &c.  are 
roasted  in  several  places  in  kilns  so  as  to  utilize  the  SO2  in  acid- 
chambers — at  Chessy  near  Lyons,  at  Oker  in  the  Harz,  at  Manz- 
field,  at  Swansea.  At  the  Altenau  silver-works  near  Clausthal,  in 
1872,  228  tons  of  vitriol  of  106°  Tw.  were  made  from  copper- 
pyrites  (and  314  tons  from  lead-matte,  Wagner's  ^  Jahresb.'  1874, 
p.  276).  At  Freiberg  the  Mulden  and  Halsbriicke  works  proceed 
in  the  same  way ;  but  they  only  utilize  ores  and  products  pretty 
rich  in  sulphur  for  vitriol-making. 

The  following  particulars  respecting  the  materials  burned  at 
the  Government  works  at  Oker  in  1901  have  been  communicated  to 
me  from  an  official  source.     The  ores  are  : — 

g2 


84 


KAW  MATERIALS  OF  MANUFACTURE. 


Lumps. 
Tons. 

Cop[)er-ores  No.  1 1 ,205 

2 4,095 

3 1,417 

Mixed  ores 7.916 

Pyritic  lead-ore 805 

Copper-matte 6,288 

Lead-matte 3.377 

*'  Spurotein  *'  (rcguliis)  ...... 


25,103 


Total. 

Tons. 

Ton8. 

895 

2,100 

88 

4,183, 

73 

1,49a 

3,770 

11,686. 

&4 

869. 

•  •• 

6,288 

•  •  • 

3.377- 

1,620 

1,620. 

6,510 

31,613. 

Composition  of  these  materials  : — 


Copper-ore. 


1. 


Cii  17-70 

Fe  23()0 

Zn  I     950 

Pb  3-70 

S 32-00 


o 


9-70 

475 

30  40 

33-50 

5-80  , 

4-90 

2-4(J 

1-75 

3600 

40  50 

Aiixed 
ore. 

• 

lead- 
ore. 

uopi^r- 

uiaite. 

460 

1-05 

30-47 

12-40 

24-.50 

24-40 

21-50 

15-.')0 

8-75 

1005 

6-75 

5-80 

24-tKJ 

34-00 

18-70 

.,*  Kesulua. 
matte.       ® 


18-20 
21-70; 
15  00  I 
710 
1700 


64-,38 
8-93 
1-34 
2-95 

20-70 


The  production  of  acid  at  Oker  is  per  annum  21,000  tons. 
50°  B.,  in  5  sets  of  chambers  of  19,656  cub.  mtrs.  capacity,  t.  e. 
1068*38  kg.  acid  of  5°  B.,  per  1  cb.  m.  chamber-space.  The  kiln-, 
gases  have  4  to  5  per  cent.  SO2. 

Traces  of  Hg,  Tl,  Cd,  and  Se  have  been  found  both  in  the  ores 
and  in  the  products  obtained  therefrom. 

Apart  from  pure  pyrites,  the  "  ordinary  ores ''  are  best  adapted; 
for  vitriol-making,  because  they  contain  their  sulphur  mostly 
as  FeS2;  the  "mixed  ores''  are  less  favourable,  on  account  of 
their  galena,  and  the  rich  copper-ores  on  account  of  their  large 
percentage  of  copper.  Of  the  lead-ores  only  those  anaply  permeated, 
by  pyrites  are  fit  for  vitriol-making.  The  sulphur  in  the  ores 
worked  at  Oker  varies  from  20  to  40  per  cent. ;  on  an  average  it 
is  30  per  cent. ;  but  it  must  be  noticed  that  the  sulphur  of  the 
galena  is  altogether  unavailable  for  vitriol-making.  The  case  is. 
not  much  better  when  copper-pyrites  predominates,  because  this, 
furnishes  too  poor  a  gas,  and,  moreover,  decrepitatqs  and  fall?  to. 


SPENT  OXIDE  OF  GAS-WORKS.  85 

powder  in  roasting.  If  no  more  than  35  per  cent,  of  copper- 
pyrites  is  mixed  with  iron-pyrites,  it  does  no  harm.  Blende  behaves 
in  a  similar  way,  but  rather  more  favourably ;  ores  containing  35 
per  cent,  blende  along  with  25  per  cent,  pyrites  yield  gas  quite 
adapted  for  vitriol-making.  * 

The  first  sulphuric-acid  works  at  Oker  were  erected  in  1841 ;' 
there  is  now  one  of  the  largest  acid  works  in  Germany,  viz.  14  sets 
of  chambers  with  a  capacity  of  800,000  cubic  feet. 

Galena  is  probably  nowhere  worked  in  such  a  way  as  to  extract 
its  sulphur  in  the  shape  of  sulphuric  acid.  The  purest  galena  con- 
tains only  13'4  per  cent,  of  sulphur;  it  is  transformed  into  lead 
sulphate  on  roasting,  and  only  in  the  strongest  white  heat  gives  off 
a  portion  of  its  sulphur  as  SO2;  moreover  the  metallurgical  pro- 
cesses to  which  it  is  subject  are  of  such  a  nature  that  only  poor 
gas  can  be  produced  from  it.  This  subject  has  been  discussed  by 
Bode  in  his  '  Beitrage  zur  Theorie  und  Praxis  der  Schwefelsaure- 
fabrikation,'  1872,  pp.  32  &  63 ;  his  conclusion  is  that  even  mix- 
tures of  galena  and  pyrites  cannot  be  roasted  in  kilns  for  vitriol- 
making  if  they  contain  more  than  18  to  20  per  cent,  of  galena. 

^'Coarse  metal '^  of  copper- smelting  is  roasted  for  vitriol  at 
Mansfeld.  A  product  containing  34  per  cent.  Cu,  28  per  cent. 
Fe,  and  28  per  cent.  S,  according  to  Bode,  yields  gas  with  5^  per 
cent,  by  volume  of  SOo,  and  at  a  sufficiently  high  temperature  to 
work  with  the  Glover  tower.  In  most  cases,  up  to  the  present, 
coarse  metal  cannot  be  roasted  so  as  to  utilize  the  SOo. 

Lead-matte  is  used  for  vitriol-making — for  instance,  at  Freiberg 
and  in  the  Lower  Harz ;  it  is  there  roasted  in  large  kilns  of  12^ 
tons  capacity.  The  matte  loses  half  its  sulphur,  aud  yields  gas  with 
4  to  6  per  cent,  of  SO2 ;  the  temperature,  according  to  Bode,  is 
high  enough  for  the  Glover  tower.  In  the  Upper  Harz  the 
utilization  of  its  sulphur  in  metallurgy  has  in  general  not  been 
found  practicable. 

5.  By-products  op  other  Manufactures. 

{Spent  oxide  of  gas-works,  soda-waste,  ammonia-works,  ifc.) 

The^pent  oxides  from  the  purification  of  gas  by  hydrated  ferric 
oxide  are  in  many  places  used  for  vitriol-making.  This  sulphur 
originally  also  comes  from  pyrites,  viz.  from  that  contained  in  the 


86  RAW  MATERIALS  OF  MANUFACTURE. 

coal^  which  appears  in  the  gas  mostly  as  sulphuretted  hydrogen. 
Most  works  remove  it  from  the  gas  by  a  mixture  of  hydrated  iron 
oxide  and  sawdust.  In  this  case  sulphide  of  iron  and  sulphur  are 
formed^  according  to  the  equation 

2Fe(bH)3  +  3H2S=2FeS  +  S  +  6H20; 

and  when  the  mass^  having  become  inactive,  is  exposed  to  the  air,  it 
again  passes  over  into  ferric  hydroxide,  more  sulphur  being  preci- 
pitated^ thus : 

2FeS  +  03  +  3H20=2Fe(OH)a  +  S2. 

The  hydroxide  thus  reproduced  and  mixed  with  sulphur  is  again 
used  in  the  purifiers,  and  is  regenerated  about  30  or  40  times 
before  the  sulphur  has  accumulated  therein  to  such  an  extent  that 
the  mixture  does  not  work  any  longer ;  it  is  then  replaced  by  fresh 
oxide,  and  the  spent  ore  is  passed  over  to  vitriol- makers. 

Phipson  states  the  composition  of  such  a  mass  to  be : — 

Water 14  per  cent. 

Sulphur  60         „ 

Organic  substance  insoluble  in  alcohol.       3         „ 

Organic  substance  soluble  in  alcohol 
(calcium  ferrocyanide  and  sulpho- 
cyanide,  ammonium  sulphocyanide, 
ammonium  chloride,  hydrocarbons).       1*5      „ 

Clay  and  sand 8         „ 

Calcium  carbonate,  ferric  oxide,  &c....     13*5      „ 

If  the  oxide  contains  considerable  quantities  of  cyanides,  it  may 
cause  great  trouble  in  the  manufacture  of  sulphuric  acid  (31st 
Alkali  Report,  p.  89). 

Hot  water  extracts  the  ferrocyanides  and  sulphocyanides,  along 
with  ammonium  chloride;  the  solution  can  be  evaporated  to  dryness, 
and  the  residue  separated  by  alcohol  into  insoluble  calcium  ferro- 
cyanide and  soluble  sulphocyanide  and  chloride. 

According  to  the  analyses  of  Davis  (^  Chemical  News,'  xxix. 
1874,  p.  30),  three  samples  of  spent  oxides  contained : — 


SPENT  OXIDE  OF  OAS-WOKKS. 


87 


I. 

Sulphur  .'..;■/.'....    &4-376 

Ferric  hydroxide 14*421 

Insoluble ,..^»,...„     iV0i}2 

Moisture 2*079 

Liiue(a8Ca8)  2399 

Sawdust 2470 

Calcium  carbonate 

Ammonium  sulphocjanide  2*662 

Ammonium  chloride 1    ,,^/.- 

Ammonium  cyanide J 

Ammonium  ferrocyanide 

Prussian  blue    trace 


II. 

III. 

62-3r>8 

67-956 

17112 

15-3;i5 

r»-099 

8-301 

5-387 

3*900 

1-776 

1-002 

5135 

300(> 

1-324 

1102 

100*064 


l*66;j 
0-366 

100*220 


trace 


100-605 


These  samples  seem  to  have  been  taken  from  precipitated  iron 
hydroxide,  to  judge  from  further  analyses  by  Davis  (Chem.  News, 
xxxvi.  p.  189),  in  which  also  tarry  substances  are  taken  into  account. 

Residues  proceeding  from 


P  recipitated 
Fe(0H)3. 

Ferric  hydroxide  17*74-19*36 

Sawdust 1-98-  472 

Calcium  carbonate 0-    -  1-04 

Ammonium  sulphocjanide  ...       1*99-  2-74 

Ammonium  ferrocyanide trace 

Tarry  matters 0*72-  1*22 

Sulphur  62-44-67-18 

Insoluble  in  dilute  HCl 3-6(>-  5-47 

Prussian  blue 

Calcium  sulphate   

Ammonium  sulphate 

Moislu re  ( by  difference)   , . . . . .      4-72-  5  76 


Bog-iron- 
ore. 
15-96-26-42 
1  14-  3-72 
0*     -  1-73 
0-94-  1-93 
trace-  021 
0-92-  1-14 
48-76-57*44 
9-74-11-42 
trace-  0-17 


Copperas. 
504-  6-84 
1-(M-  3-24 
0- 

l-t>8-  3*41 
0-27-  0  64 
0-72-  118 
48-76-55-74 
7-82-12-68 
trace-  1-74 

trace-  1*43 

12*78-16'72 

7*22-10-82      7-98-  9-22 


Bad 

oxides. 

8-72-20-40 

2-16-  9-76 

0*    -10-36 

1*18-  4*72 

trace-  0*44 

0*55-  im 

32*42-42-16 

12*12-20-71 

trace-  064 

0-     -  3-23 

0-     -  114 

7*49-3;i-41 


From  these  analyses  it  can  be  seen,  first,  that  it  is  decidedly  best 
to  extract  the  mass  at  first  with  water,  in  order  to  remove  the  am- 
monia compounds,  which  are  in  themselves  valuable,  and  which,  if 
they  get  into  the  chambers,  destroy  a  good  deal  of  nitre  (their  value 
is  certainly  greatly  lessened  by  the  sulphocyanide) ;  secondly,  that 
sometimes  a  considerable  quantity  of  calcium  carbonate  is  present, 
whicji  may  get  into  it  at  the  gas-works  by  lime  being  added,  on 
purpose  or  by  mistake,  and  which,  of  course,  retains  an  equivalent 
quantity  of  sulphur  in  the  shape  of  gypsum.  In  fact  a  sample  of 
the  residue  left  after  burning  contained 


88  RAW  MATERIALS  OP  MANUFACTURE. 

Insoluble 33-386 

Ferric  oxide    52-399 

Calcium  sulphate    13"315 

Sulphur  0-200 

These  impurities  (which  cause  a  loss  by  retaining  sulphuric  acid) 
aud  the  sulphates  present  from  the  first  (which  are  not  available) 
must  be  allowed  for  in  analyzing.  This,  according  to  Davis,  was 
formerly  done  by  extracting  the  sulphur  by  means  of  carbon 
bisulphide,  evaporating  the  solution,  and  weighing  off  the  sulphur  ; 
but  as  the  presence  of  tarry  matters  causes  an  error,  Davis  now 
makes  the  analysis  by  burning  the  sulphur  in  a  current  of  air  in  a 
combustion- tube  of  Bohemian  glass,  conducting  the  SO3  formed 
into  an  absorbing-apparatus  filled  with  iodine  solution,  and  reti- 
trating  the  unaffected  iodine  by  a  solution  of  sodium  thiosulphate 
(Chem.  News,  xxxvi.  p.  190 ;  comp.  also  Zulkowsky's  process,  p.  72) . 

The  burning  of  this  gas-sulphur  is  usually  done  in  shelf-furnaces 
similar  to  those  used  for  pyrites-smalls.  They  will  be  described  in 
detail  in  the  fourth  Chapter.  Already  in  1861,  at  Barking  Creek,  on 
the  Thames,  2180  tons  of  this  material  were  used  ;  but  much  larger 
quantities  might  have  been  got,  since,  according  to  A.  W.  Hofmann 
('  Report,'  1862,  p.  15),  even  at  that  time  at  least  10,000  tons  of 
sulphur  were  contained  in  the  London  gas.  Much  of  the  acid 
made  from  spent  oxide  is  sold  as  "  brimstone  acid.'' 

In  France  also,  at  that  time,  the  sulphur  from  gas-works  was 
used  on  a  large  scale.  The  factory  at  Aubervilliers,  belonging  to 
the  Society  of  St.-Gobain,  used  no  other ;  Messrs.  Seybel  and  Co.  at 
Liesing,  near  Vienna,  and  Kunheim  and  Co.  at  Berlin  (Wagner's 
Jahresb.  1864,  p.  153  5  Hasenclever,  /.  c.  p.  167)  do  the  same. 

The  rational  treatment  of  spent  oxides  for  the  purpose  of  obtain- 
ing ammonium  salts,  ferrocyanides,  and  sulphocyanides  is  described 
in  Lunge's  '  Coal-Tar  and  Ammonia,'  3rd  edition,  p.  716. 

The  sulphur  contained  in  alkaluwaste,  in  the  shape  of  calcium 
sulphide,  has  been  frequently  proposed  for  the  manufacture  of 
sulphuric  acid,  nearly  always  after  having  been  first  converted  into 
sulphuretted  hydrogen.  The  only  successful  process  in  this  line 
(the  Chance  process  of  treating  alkali-waste)  belongs  to  the  domain 
of  alkali-manufacture,  and  cannot  be  treated  in  this  volume. 
Only  the  contrivances  for  burning  the  hydrogen  sulphide  will  be 
described  in  the  fourth  Chapter. 

Borntrager    (G.  P.  15,757)    proposes  decomposing  the  yellow 


SULPHURETTED  HYDROGEN.  89 

liquors  from  alkali-waste  by  meaDS  of  ferric  oxide  (ground  damp 
pyrites  cinders)^  to  filter  the  sulphur  and  ferric  sulphide  which  is 
thus  precipitated,  and  burn  it  after  drying  in  ordinary  shelf- 
burners.  [Oxide  of  iron  in  this  state  is  a  very  inferior  reagent 
for  removing  the  sulphur  from  yellow  liquors  and  the  like.] 

An  anonymous  inventor  has  proposed  to  absorb  the  sulphuretted 
hydrogen  in  hydrated  ferric  oxide  suspended  in  water,  filter,  press 
the  residue,  dry  it,  and  bum  it  on  shelf-burners.  Wyss  (Bull.  Soc. 
ind.  Mulh.  1890,  p.  281)  has  shown  that  this  process  is  neither 
novel  nor  in  any  way  promising  of  success. 

The  sulphuretted  hydrogen  given  off  in  the  manufacture  of  sulphate 
of  ammonia  (comp.  Lungers  'Coal-Tar  and  Ammonia,'  3rd  ed. 
p.  857)  is  sometimes  used  for  the  manufacture  of  sulphuric  acid. 
Here  the  HoS  is  not  merely  diluted  with  a  large  quantity  of  inert 
gases,  but  is  also  of  very  unequal  concentration,  which  formerly 
rendered  the  manufacture  of  sulphuric  acid  from  this  source  an 
unprofitable  process.  The  same  can  be  said  of  most  other  eases  in 
which  HgS  is  given  off  as  a  by-product. 

The  utilization  of  the  HjS  from  sulphate-of-ammonia  works  for 
the  manufacture  of  sulphuric  acid  has,  however,  been  greatly 
improved  and  is  now  no  longer  a  rare  exception,  but  is  practised 
in  a  good  many  English  works.  If  the  gas  is  properly  introduced 
into  the  burner  (comp.  Chapter  IV.),  the  consumption  of  nitre  is 
not  excessive,  and  it  is  even  possible  to  increase  the  heat  by  this 
means,  if  the  spent  oxides  should  not  suffice  for  this  purpose.  The 
action  of  the  large  quantity  of  carbon  dioxide  accompanying  the 
HjS  in  the  case  of  sulphate-of-ammonia  works  would  seem  to 
consist  only  in  requiring  a  certain  amount  of  chamber-space, 
contrary  to  the  opinion  reported  in  Chapter  VIII. 

Sulphur  dioxide,  formed  in  many  manufacturing  operations  as  a 
disagreeable  by-product,  apart  from  those  already  described,  is 
sometimes  proposed  to  be  converted  directly  or  indirectly  into 
sulphuric  acid.  The  special  cases  in  which  this  has  been  attempted 
will  be  treated  in  the  next  Chapter. 

6.  Nitrate  op  Soda,  NOgNa  (commonly  called  ''  Mere  '^). 

i  (NajO)  =  31-05  36-49  per  cent, 

i  (NA)    =  5401.  63-51      „ 


8509  100-00 

Hardness  1*5  to  2;  spec.  grav.  2*09  to  2*39.     In  the  pure  state, 


90 


RAW  MATERIALS  OF  MANUFACTURE. 


and  in  large  crystals,  it  is  colourless^  transparent^  and  brilliant  as 
glass  ;  in  small  crystals  it  is  white  and  opaque.  The  crystals  are 
rhombohedra  with  angles  of  106°  SO'  and  73°  SO'.  It  has  a 
cooling,  bitter  taste.  Heated  to  a  certain  temperature  it  melts ; 
at  a  red-heat  it  is  decomposed  into  sodium  nitrite  and  oxygen  gas. 
The  fusing-point  is  316°-319°  C.  (Carnelley,  J.  Chem.  Soc.  1878, 
ii.  p.  277).  Mixed  with  coal,  deflagrates  on  heating.  It  attracts 
moisture  from  the  air  (especially  if  not  quite  free  from  chlorides), 
and  readily  dissolves  in  water,  with  a  considerable  lowering  of  the 
temperature. 

1  part  of  sodium  nitrate,  according  to  Marx,  requires  for  solu- 
tion 1-58  part  of  water  at  -6°,  1-25  at  0°,  0*46  at  +119°  C. 
According  to  Kopp,  1  part  of  sodium  nitrate  at  18°*5  C.  requires 
1*14  of  water,  or  100  parts  of  water  dissolve  87"72  parts  of  the 
salt.  In  the  presence  of  sodium  chloride  its  solubility  is  consider- 
ably less. 


Specific  Gravity  of  the  Solutions  of  Sodium  Nitrate  at  20"  C. 


Parts  of  salt 

Specific 

Parts  of  salt 

Specitic 

in  100  water. 

L'rftvitv. 

1                   V 

111  100  water. 

gravity. 

1 

10065 

21 

1-1498 

2 

10131 

22 

11578 

3 

1-0197 

23 

1-1659 

4 

102f)A 

24 

1-1740 

o 

1-0332 

25 

1182> 

6 

10399 

26 

1-1904 

7 

1-0408 

27 

,       1-1987 

8 

10537 

28 

1-2070 

9 

l-OGUO 

29 

1-2154 

10 

1  0676 

30 

1-2239 

11 

10746 

31 

1-2325 

12 

1-0817 

32 

1-2^12 

13 

10889 

33 

1-2500 

U 

1  0962 

31 

1-2589 

15 

1-1035 

35 

1-2679 

1() 

1-1109 

3() 

1-2770 

17 

11184 

37 

1-2863 

18 

11260 

38 

1-2958 

1!) 

1-1338 

39 

1-3055 

20 

1-1418 

40 

1-3155 

OCCURRENCE  OF  NITRATE  OF  SODA. 


91 


Parts  of  salt 

Specific 

Parts  of  salt 

Specific 

ill  100  water. 

gravity. 

in  100  water. 

giavity 

41 

1-3255 

46 

1-3761 

42 

1-3355 

47 

1-3861. 

43 

1  -3456 

48 

1-3968 

44 

1-3557 

49 

14^74 

45 

1-3659 

50 

1-4180 

Kiti*ate  of  soda  occurs  iu  many  places  iu  small  quantities;  but 
the  only  large  beds  which  supply  the  world  with  this  article  are 
situated  in  a  region  of  the  west  coast  of  South  America,  formerly 
belonging  to  Peru  and  now  to. Chili.  This  occurrence,  and  the 
industry  founded  thereon,  have  been  described  in  various  commu- 
nications by  Langbein  (Wagner^s  Jahresb.  1871,  p.  300  ;  1872, 
p.  290;  1879,  p.  390)  ;  also  by  W.  E.  Billinghurst,  of  whose  book 
(written  in  Spanish)  Darapsky  gives  an  extract  in  the  '  Chem. 
Zeit/  xi.  p.  752  (J.  Soc.  Chem.  Ind.  1887,  p.  545).  Comp.  also 
Buchanan  {ibid.  1893,  p.  128)  and  Behrend  (Zschr.  deutsch.  Ingen. 
1899,  p.  1199;  Fischer's  Jahresb.  1899,  p.  406). 

The  nitre-beds  are  principally  situated  in  the  province  ot 
Tarapaca,  between  68°  15'  and  78°  18'  longitude,  and  19°  12'  and 
21°  18'  30",  latitude  ;  they  also  occur  somewhat  south,  especially 
near  Antofagasta  and  Taltal.  They  were  discovered  in  1821  by 
Mariano  de  Rivero,  and  have  been  worked  since  1830.  The  nitre 
zone  is  situated  at  an  altitude  of  3600  feet  above  the  sea-level. 

The  total  area  of  the  nitre-bearing  strata  is  estimated  by  Billing- 
hurst at  21,212  estacas  (about  150,000  acres),  and  the  yield 
obtainable  therefrom  =  1980  millions  of  Spanish  cwts.  The  nitre- 
bearing  rock,  called  caliche,  is  found  in  layers  of  from  10  inches 
to  5  feet  in  depth,  which  rarely  crop  out  at  the  surface.  The  over- 
lying rock,  called  costra,  is  18  inches  to  7  feet  thick,  and  consists 
principally  of  a  hard  conglomerate  of  sand,  felspar,  phosphates, 
and  other  minerals. 

The  composition  of  the  caliche  varies;  it  contains  from  48 
to  75per  cent,  of  sodium  nitrate,  20  to  43  per  cent,  of  sodium 
chloride,  and  varying  quantities  of  sodium  sulphate,  calcium  sul- 
phate; potassium  nitrate,  potassium  iodate,  magnesium  chloride, 
also  insoluble  earthy  portions  and  organic  substance  (guano).  It 
is  first  broken  by  a  stone-breaking  machine,  and  then  put  into  the 
dissolvers.  These  are  partly  open  square  tanks,  preferably,  how- 
ever, closed  egg-shaped  boilers  with  two  manholes—one  on  the 


92  KAW  MATGRIALS  OF  MANUFACTURE. 

r 

top  for  filling  in  the  caliche,  another  at  the  bottom  for  emptying 
the  residue.  The  mass  rests  on  a  perforated  bottom.  The  boilers 
are  filled  entirely  with  the  broken  rock,  and  half  with  mother- 
liquor,  and  were  formerly  always  heated  by  direct  steam  injected 
below  the  false  bottom.  After  1|  to  2^  hours  the  liquid,  then 
sufficiently  saturated  with  nitre,  is  run  into  settlers ;  from  these 
it  flows,  after  several  hours,  into  a  second  settler,  where,  by  half 
an  hour's  rest,  it  allows  some  still-suspended  common  salt  to  sub- 
side, and  then  runs  into  shallow  coolers.  The  residue  from  the 
dissolvers^  which  still  contains  15  to  35  per  cent,  of  sodium 
nitrate,  is  either  emptied  at  once  or  boiled  again  with  fresh  water. 
The  crystals,  separated  in  the  coolers  after  draining  off  the  mother- 
liquors,  are  spread  in  layers  of  12  to  18  inches  thickness  on  a  large 
surface  exposed  to  draught,  and  dried  with  frequent  stirring.  The 
total  cost  of  sodium  nitrate,  up  to  its  reaching  European  ports,  in 
1871,  amounted  to  £S  ISs.  per  ton,  which  left  a  good  margin 
for  profit  at  the  average  price  of  .£12  (it  has  reached  £16  and  more). 
At  present  both  the  producing  and  selling  prices  are  much  lower. 

The  above-described  system  of  dissolving  by  open  steam  was 
afterwards  abandoned  for  closed  steam-coils  or  similarly-acting 
apparatus;  at  the  same  time  air  heated  to  120^-150°  C.  is  forced 
through  the  liquid  by  means  of  injectors,  in  order  to  hasten  the 
evaporation.  This  produces  both  stronger  and  purer  liquors,  the 
quantity  of  sodium  chloride  being  the  same  in  the  stronger  as 
in  the  weaker  liquor. 

The  composition  of  the  crude  nitre-earth  is  shown  by  the  fol- 
lowing analyses : — 

Caliche.  Costra. 

^ ^ ^ 

a.  h.  c.  d.  c. 

Sodium  nitrate 70-62  (50-97  51-50  49-05  18-60 

Sodium  iodate  1*90  0*73 

Sodium  iodide  ...  traces  traces 

Sodium  chloride  2239  leS.)  2208  29-95  33«80 

Sodium  sulphate 1 80  4-5<i  899  902  16-64 

Potassium  chloride ...  855  4*57  2*44 

Magnesium  chloride ...  043  125  1-62 

Magnesium  bulphate  0*51  5*88 

Calcium  sulphate 0*87  l"3l  ...  ••• 

Calcium  carbonate ...  0*12  015  0*09 

Silica  and  ferric  oxide ...  090  2-80  3'00 

Insoluble  0-92  406  6-00  318  2010 

Moisture   0*99  5*64  ...  ...  ... 

10000     10000 


NITRATE  OF  SODA  AND  POTASH.  9S 

The  analyses  a  and  b  {a  white,  b  brown  caliche)  are  by  Machattic 
(Chem.  News,  xxxi.  p.  263) .  They  are  somewhat  suspicious,  both 
on  account  of  the  total  absence  of  potassium  salts  and  of  the 
extremely  improbably  high  percentage  of  sodium  iodate.  This  is 
all  the  more  noticeable  as  Machattie  at  the  same  time  states  the 
average  percentage  of  iodine  in  five  samples  of  mother-liquor  to  be 
=056,  equal  to  0*873  per  cent,  of  sodium  iodate,  which  may  be 
nearer  the  truth.  The  analyses  c,  rf,  and  e  are  by  V.  L^Olivier 
(Compt.  Rend.,  26th  October,  1875). 

The  iodine  contained  in  the  mother-liquors  is  now  recovered  to 
a  great  extent,  and  forms  one  of  the  principal  sources  of  this 
article. 

Another  bed  of  nitrate  of  soda  has  been  found  in  the  South- 
American  State  of  Colombia  (Journ.  Soc.  Chem.  Ind.  1894, 
p.  1001).  It  is  about  100  kilometres  distant  from  San  Juan  de 
la  Cienaga,  and  had  been  proved  up  to  that  time  for  a  surface  of 
75  square  kilometres.  It  has  a  thickness  of  from  30  centimetres 
to  3  metres,  and  averages  11  to  12  per  cent.  NaNOy,  together 
with  calcium  carbonate,  calcium  sulphate,  and  silicates.  The 
recoverable  nitre  is  estimated  to  exceed  7  million  tons,  but  none 
of  it  is  as  yet  in  the  trade.  Another  bed  has  been  discovered  in 
Texas  ;  this  is  stated  to  contain  98  per  cent,  pure  nitrate  (Chem. 
Ind.  1902,  p.  265). 

A  deposit  of  potassium  nitrate  has  been  found  near  Cochabamba, 
in  Bolivia  (Sacc,  Compt.  Rend.  xcix.  p.  84).  This  deposit, 
reported  to  be  enormous,  but  not  yet  worked,  consists  of  60  "70 
per  cent,  potassium  nitrate,  30" 70  borax,  a  little  salt  and  water, 
8"60  organic  substances.  On  dissolving  the  saline  mixture  in  hot 
water  and  cooling,  pure  potassium  nitrate  crystallizes  out. 

The  consumption  of  nitrate  of  soda  during  the  years  1898  to 
1901  has  been  as  follows : — 

1898.  1899.  1900.  1901. 

Tons.  Tons.  Tons.  Tons. 

Continent  of  Europe  (chiefly 

Germany)  904,500  981,000  1,026,000  l.Oyc.OOO 

United  Kingdom  132,500  121,000  126,000  118.000 

United  States     125,000  133,000  170,0(X)  192,(H)0 

Other  countries     10,000  25,000  28,000  18,0(H> 

Total...     1,178,000        1,200,000        1,350,000        1,304,000- 
Price  on  31  st  Dec,  per  cwt.  ...  7^*.  0</.  8*\  tW.  Jls. 


94  RAW  MATERIALS  OF  MANUFACTURE. 

(Statistics  of  previous  years  are  given  in  the  first  two  editions  of 
this  book,  pp.  80  and  81.) 

When  emptying  nitrate  of  soda  from  the  bags  a  certain  quan- 
tity of  the  salt,  which  is  always  damp,  remains  adhering  to  them ; 
this  not  only  causes  loss,  but  renders  them  useless,  and  even  pro- 
duces a  danger  of  fire.  It  is  therefore  well  to  lixiviate  the  bags  with 
hot  water  and  to, dry  them.  The  solution  is  evaporated  to  a  small 
bulk  and  crystallized.  The  mother-liquor  from  this  operation  is 
always  very  rich  in  chlorides,  which  seems  to  show  that  the  deli- 
quescence of  sodium  nitrate  is  not  a  property  of  the  pure  salt,  but 
is  owing  to  the  magnesium  and  calcium  chloride  contained  in  it, 
since  the  dampest  salt  will  adhere  to  the  bags.  The  washed  and 
dried  bags  should  not  be  stored  in  quantity,  as  they  are  still  very 
inflammable. 

Composition  of  Commercial  Nitrate  of  Soda. — R.  Wagner 
(Jahresb.  1869,  p.  248)  found  in  commercial  nitrate  of  soda  : — 

Sodium  nitrate    9103 

„      nitrite    0*31 

„      chloride 1*52 

Potassium  chloride 0  64 

Sodium  sulphate     0*92 

„      iodate 0-29 

Magnesium  chloride  0*93 

Boric  acid    traces 

Moisture 1*36 


10000 


The  nitrate  of  soda  imported  into  England,  as  used  by  vitriol- 
makers,  is  much  purer  than  the  above  sample.  The  English  sellers 
mostly  guarantee  a  maximum  of  5  per  cent.  "  refraction  '^  (that  is, 
the  total  percentage  of  all  foreign  constituents,  inclusive  of  water) , 
frequently,  however,  4  or  even  3^  per  cent,  refraction.  English 
vitriol-makers  would,  indeed,  altogether  refuse  nitrate  containing 
upwards  of  3  per  cent,  of  chlorides,  like  that  analyzed  by  Wagner, 
1  per  cent,  being  the  maximum  allowed.  The  muriatic  acid  gene- 
rated from  them,  of  course,  gives,  with  nitric  acid,  free  chlorine 
and  its  compounds  with  nitrogen  oxides,  and  causes  a  loss  of  the 
latter.     The  average  composition  of  nitrate  for  chemical  works  is 


COMPOSITION  OP  COMMERCIAL  NITRATE  OP  SODA.  95 

96  sodium  nitrate  (including  nitrate,  iodate,  &c.), 
0'5  chlorides  (calculated  as  NaCl), 
0*75  sulphates  (calculated  as  NaSO^), 
2"  75  moisture. 

Gilbert  (Zsch.  f.  angew.  Chem.  1893,  p.  495)  pointed  out  that 
the  Chilian  nitre  always  contains,  and  always  has  contained, 
some  potassium  nitrate.  He  states  that  the  percentage  of  KNO^^ 
rarely  exceeds  5  per  cent.,  and  the  deficiency  of  nitrogen  caused 
thereby  is  more  than  compensated  by  the  value  of  the  potassium 
for  agricultural  purposes.  The  old  method  of  testing  for 
"  refraction  "  is  obstinately  adhered  to  by  the  producers,  and  is 
preferred  by  Gilbert  to  the  direct  guarantee  of  15*57  per  cent, 
nitrogen  demanded  by  the  agricultural  control-stations.  Jones 
(loc.  cit.  p.  698)  mentions  that  he  had  met  with  nitre  containing 
much  more  potash  ;  but  this  nitre,  which  is  recovered  from  the 
bilge-water  of  the  carrying  vessels,  occurs  only  quite  exceptionally 
(comp.  below).  Most  suphuric-acid  manufacturers  do  not  share 
Gilbert's  opinion  :  see  below. 

An  impurity  formerly  entirely  overlooked  in  commercial  nitrate 
of  soda  consists  in  perchiorate  and  perhaps  also  chlorate  of 
sodium. 

Beckurts  (Arch.  d.  Pharm.  ccxxiv.  p.  323  ;  Fischer's  Jahresb. 
1886,  p.  305)  found  in  all  descriptions  of  commercial  nitre  small 
quantities  of  chlorates  and  perchlorates,  and  this  has  been  con- 
firmed from  all  sides.  A  large  number  of  methods  have  been 
devised  for  estimating  the  perchiorate  (comp.  Lunge's  Chem.- 
techn.  Uutersuchuugsmethoden,  i.  p.  283  et  seq,),  all  of  which 
are  practically  founded  upon  converting  the  perchiorate  into 
chloride,  preferably  by  fusing  the  nitrate  with  lime  or  sodium 
carbonate  and  manganese  peroxide,  estimating  the  chloride  in  the 
ordinary  way,  and  deducting  the  chloride  previously  existing  in 
the  nitrate. 

In  order  to  manufacture  nitrate  of  soda  free  from  perchiorate, 
which  does  not  occur  in  the  first  crystallization,  but  accumulates  in 
the  mother-liquors,  and  after  using  these  three  or  four  times  over 
contaminates  the  nitrate  crystals  up  to  1  per  cent.,  H.  Foelsch 
&  Co.  (G.  P.  125,206)  cools  down  the  impure  mother-liquors  to 
0°C.,  1  cub.  metre  of  which  then  furnishes  160  kil.  of  a  mixture 


9G  RAW  MATERIALS  OF  MANUFACTURE. 

of  salts,  containing  150  NaNOg  and  NaClOj.  The  new  mother- 
liquor,  when  employed  for  redissolving  crude  nitre,  at  first 
furnishes  nitrate  free  from  perchlorate. 


Analysis  of  Nitrate  of  Soda. 

In  the  laboratories  working  for  the  importers  of  nitrate  of  soda 
the  value  of  nitrate  is  mostly  only  estimated  indirectly,  viz.  the 
"  refraction.'^  10  grams  are  well  dried  in  a  porcelain  capsule, 
weighed  again,  dissolved,  the  residue  (if  any)  is  estimated,  the 
liquid  dissolved  to  a  certain  volume,  and  in  separate  portions  of  the 
liquid  the  chloride  and  sulphate  are  estimated  in  the  usual  way. 
The  sum  total  of  moisture,  insoluble  residue,  sodium  chloride, 
and  sodium  sulphate  is  called  the  *'  refraction,^'  and  it  is  assumed 
that  the  remainder  is  real  sodium  nitrate.  This  may,  however, 
lead  to  very  erroneous  results,  where,  for  instance,  the  nitre 
contains  some  potassium  nitrate.  A  case  in  point  has  been 
described  by  me  in  ^  Chem.  Ind.'  1883,  p.  369,  where  an  error 
amounting  to  2  per  cent,  was  caused  in  this  way.  Perchlorate 
causes  also  errors;  and  altogether  it  stands  to  reason  that  the 
consumer  of  nitrate  receives  justice  only  by  a  real  determination 
of  the  nitric  acid  contained  in  (or,  more  properly  speaking,  to  be 
evolved  from)  a  sample  of  nitrate.  On  the  other  hand,  the  interests 
of  the  importers  and  dealers  in  nitrate  are  quite  the  opposite. 
According  to  Fischer's  Jahresb.  1899,  p.  407,  the  Hamburg  im- 
porters insist  upon  the  ''  indirect "  (f.  e.  altogether  deceptive) 
analysis,  and  want  the  perchlorate  to  be  counted  as  nitrate. 

The  direct  analysis,  i.  e.  the  estimation  of  the  NaNO^  (or  its 
equivalent  of  KNOa),  can  be  carried  out  in  many  ways,  a  complete 
enumeration  of  which  is  found  in  my  '  Chemisch-technische 
Untersuchungsmethoden,'  i.  p.  273  et  seq.  Among  these,  those 
mostly  used  are  the  Schloesing-Grandeau  and  the  Ulsch  methods 
(comp.  below,  in  the  section  on  Nitric  Acid),  but  at  sulphuric-acid 
works  the  method  nearly  always  employed  is  the  '^  nitrometer' 
method/'  which  is  carried  out  as  follows  * : — 

Dissolve  a  good-sized  sample,  say  20  to  30  grams,  of  the  nitrate 

*  The  nitrometer  in  its  use  for  the  analysis  of  nitrous  vitriol  will  be  described 
in  Chap.  III. 


ANALYSIS  or  NITRATE  OF  SODA. 


97 


in  twice  its  weight  of  water,  employing  a  flask  of  known  contents 
and  heating  very  gently.  Weigh  out  a  quantity  corresponding  to 
about  0-4  gram  NaNOg  in  an  ordinary  weighing-glass  or  in  a  tube 
with  stopcock,  as  employed  for  testing  fuming  sulphuric  acid 
(fig.  8).  Run  its  contents  into  a  nitrometer,  either  a  "bulb- 
nitrometer,''  as  shown  in  fig.  9,  or,  preferably,  the  nou-graduated 

Fifr.  8. 


Fig.  9. 


agitating-vessel  connected  with  a  Lunge's  gas-volumeter,  to  be 
described  in  the  next  Chapter.  In  the  latter  case  no  observation 
of  temperature  and  barometric  pressure  nor  any  reduction  tables 
are  required.  Do  not  rinse  the  weighing-tube  (which  would 
dilute  the  liquid  too  much),  but  weigh  it  back  as  it  is.     Decompose 


VOL.  I. 


98  RAW  MATERIALS  OF  MANUFACTURE. 

the  solution  within  the  nitrometer  with  a  sufficient  quantity  of 
strong  sulphuric  acid  and  mercury,  and  measure  the  nitric  oxide 
given  oflE  as  will  be  described  in  the  next  Chapter,  where  also  a 
table  for  reducing  the  readings  to  NaNOg  will  be  given. 

7.  Nitric  Acid,  NOgH.* 

This  may  be  called  one  of  the  raw  materials  of  vitriol- making, 
although  a  manufactured  product  itself^  in  those  works  using  it 
in  lieu  of  solid  nitrate  of  soda. 

Nitric  acid  proper  (the  monohydrate)  has  the  equivalent  6305 
(0  =  16),  and  may  be  said  to  contain,  as  formerly  expressed, 
85*71  nitric  anhydride  (NgOa)  and  14'29  water.  Its  specific 
gravity  is  1*54  at  20°,  or  1*55  at  15°.  It  is  colourless  if  perfectly 
pure;  but  the  strongest  acid  of  commerce  is  always  coloured 
yellow,  or  even  red,  by  a  partial  decomposition  into  oxygen  and 
nitrogen  peroxide,  N2O4  (hyponitric  acid) .  Its  boiling-point  is 
86°  C.  On  boiling  an  acid  containing  a  little  water,  at  first 
strong  acid  distils  over,  till  the  boiling-point  of  the  remainder  has 
reached  126°,  at  which  point  the  thermometer  remains  stationary, 
and  an  acid  of  constant  composition  for  any  certain  pressure  distils 
over.  Exactly  the  same  point  is  reached  from  the  opposite  side 
by  distilling  more  dilute  acids,  in  which  case  water  distils  over, 
and  the  remaining  acid  becomes  more  and  more  concentrated,  till 
the  above  stationary  point  is  reached.  The  acid  at  that  point  has 
nearly  the  composition  2NO3H  +  3H2O  (corresponding  to  6ON2O5 
and  4OH2O)  and  a  specific  gravity  of  1'42. 

The  following  table  shows  the  boiling-points  of  nitric  acid  of 
various  strengths : — 


Spec.  gray. 

Boiling-point. 

1    Spec.  grav. 

Boiling-point. 

115 

104°  C. 

1--13 

123°  C. 

1-20 

108 

1         1-48 

115 

1-30 

113 

1-50 

99 

1-35 

117 

!         1-52 

86 

1-40 

119 

*  Some  interesting  notes  on  the  early  history  of  manufacturing  nitric  acid  in 
England  are  contained  in  Guttmann's  paper,  Journ.  Soc.  Chem.  Ind.  1901,  p.  7. 
The  cost  of  producing  200  lbs.  of  acid  spec.  grav.  1'375  in  1771  was  £8  2s.  2d. 
without  labour.    See  also  W.  P.  Reid's  notes,  ibid.  p.  8. 


SPECIFIC  GRAVITIES  OF  NITAIC  ACID, 


99 


For  the  percentage  of  nitric  acid  for  different  specific  gravities, 
Kolb  (Ball.  Soe.  Ind.  de  Mulhouse,  1866^  p.  412)  has  given  a 
table  which  is  now  rendered  obsolete  by  the  more  accurate  table 
derived  from  the  experiments  of  Longe  and  Rey  (Zsch.  angew.  Ch. 
1891,  p.  165) .  The  specific  gravities  are  taken  at  15°  C,  referred  to 
water  of  4P  and  reduced  to  the  vacuum.  They  refer  to  chemically 
pure  nitric  acid;  commercial  acid,  containing  nitrous  acid,  &c., 
contains  less  real  HNOg  at  the  same  specific  gravity. 


Specific 
graTities 

Degrees 

100  parU  by  weight 
contain 

1 

1  litre  contains  kilog. 

,                                              1 

at?^° 

Twacld. 

ii 

4°- 

N,0,. 

HNO3. 

NA- 

HNO,.      1 

1000 

0 

0-08 

010 

0001 

0001        ' 

1005 

1 

0-85       i          1-00 

0008 

0010       . 

1010 

2 

1-62                 1-90 

0-016 

0-019 

i         1-015 

3 

2-39 

280 

0-024 

00-28       1 

1020 

4 

3-17 

3-70 

0033 

0038       ' 

1-025 

5 

3-94 

4-60 

0O40 

0047 

1030 

6 

4-71 

5-50 

0049 

0057 

1035 

7 

5-47 

6-38 

0057 

0066 

1-040 

8 

6-22 

7-26 

0064 

0075 

1045 

9 

6-97 

813 

0073 

0085 

1-050 

10 

7-71 

8-99 

0081 

0094 

1055 

11 

8-43 

9-84 

0-089 

0104 

1-060 

12 

9-15 

10-68 

0-097 

0-113 

i         1065 

13 

9-87 

11-51 

0105 

0123 

1070 

14 

10-57 

12  3:} 

0-113 

0132 

^         1075 

15 

11-27 

1315 

0-121 

0-141 

1080 

16 

\\m 

13-95 

0-129 

0151 

1-085 

17 

12m 

14-74 

0-137 

0160       ; 

1090 

18 

13-31 

15-53 

0-145 

0169       ; 

'         1095 

19 

1399 

16-32 

,        0-153 

0179       ! 

1100 

20 

14-67 

1711 

j        0161 

0-188 

1105 

21 

15-34 

17-89 

0170 

0198 

l-llO 

22 

16-00 

1867 

0-177 

0-207 

1115 

23 

16-67               19-45 

0-186 

0-217 

1120 

24 

17-34 

20  23 

0195 

0-227 

1-125 

25 

1800 

2100 

0-202 

0236 

1-130 

26 

18-66       !        21-77 

0-211 

0-246       \ 

'         1135 

27 

19-32       '        22-54 

0  219 

0256       \ 

M40 

28 

19-98               23-31 

0-228 

026(5 

1         1-145 

29 

20-(^       '        24-08 

0-237 

0-276       i 

1-150 

30 

21-29       \        24-84 

0-245 

0-286 

1155 

31 

2194               25-60 

0-2r>4 

0-296 

1160 

32 

22-(M)                2rr3<) 

0-262 

0-306 

M65 

33 

23-25               2712 

0-271 

0316 

1170 

34 

23-90                27-88 

0279 

0  32r> 

1175 

35 

24-54                28-63 

0-288 

0-336       i 

1180 

36 

25-18                2938 

0-297 

0347 

1-185 

37 

25-83                3013 

0-306 

0  357 

1 

E 

0 

100 


RAW  MATERIALS  OF  MANUFACTURE. 


Table  (continued). 


1 

Specific 
giiiTities 

1 

Degrees 

100  i>arte  bj  weight 
contain 

1 
1' 

1  litre  contains  kilog. 

atl^° 

Twadd. 



1 

1 

10. 

;       Sfi,.             HXO3. 

1 

1190 

38 

26-47               30-88 

1        0-315               0-367 

1195 

39 

2710               31-62 

'        0-324               0-378 

1-200 

40 

27-74                32-36 

0-333       i        0-388 

1-205 

41 

283(5                33-09 

0-342               0-399 

1-210 

42 

28-99       ;        33-82 

!        0-351                0-409 

1-215 

43 

29-61        ,        34-55 

0-3(>0               0-4-20 

1-2:^0 

44 

30-24                35-28 

0369               0-430 

1225 

45 

3088                3(v03 

0378                0-441 

1-230 

46 

31-53               36-78 

0-387                0-452 

1-235 

47 

3217               37-53 

0-397               0-463 

1-240 

48 

1        32-82               38-29 

0-407               0475 

1-245 

49 

33-47               3905 

0417                0486 

1-250 

60 

3413               39-82 

0-427               0-498 

1         1-255 

51 

34-78                40-58 

0-437               0-509 

'        1 2()0 

52 

35-44                41-34 

0-447               0-521        ; 

1-2(55 

53 

3609                4210 

0-457               0-533 

1-270 

54 

3(;-75                4287 

1        0-467               0-544 

1-275 

55 

37-41                43-64 

0-477               0-566       ■ 

1-280 

56 

3807                44-41 

0-487                0-508 

1-285 

57 

38-73                4518 

0-498                0-581 

1-290 

58 

39-39                45-95 

0-508       '        0593 

1-295 

59 

4005                4(»-72 

0-519                0(505 

1-300 

00 

4071               47-49 

0-529                0617        1 

1305 

01 

41-37       ;        48-26 

0-540               0-630       ' 

1-310 

62 

4206 

4907       ' 

0-551        !        0-643       1 

1-315 

63 

4276 

49-89       1 

0562           '     0-656        ' 

1-320 

64 

43-47 

50-71 

0-573                0(569 

1-325 

65 

44-17 

51-53 

0-585                0083 

l-33(> 

66 

44-89 

52  37 

0-597               0-697 

1-335 

67 

45-62 

53-22 

0-(MX)               0-710 

1-340 

68 

4r.-35 

54-07 

0621 

0-725 

1-345 

(i9 

47  08 

54-93 

0(53;5 

0-739 

1-350 

70 

47-82 

55-79 

!        0-(>45 

0-753       1 

1-355 

71 

48-57 

56-66 

0-658 

0-768       ! 

1-3G0       . 

72 

49-35 

57-57 

0671        \        0-783 

1-305 

73 

5013 

58-48 

0(584                0-798 

1-370 

74 

50-91 

59-39 

0-698                0-814 

1-375 

75 

51  (59                60  30 

0-71 1                0  829 

l-3^<0 

76        1 

52-52                61-27 

0-725                084(5 

1-385       ; 

77 

53-35       !        62-24 

0-739       ,        0-8(52 

1-390 

78 

54-20                63-23 

0-753                0879 

1-395 

79 

55-07                &4  25     J 

0-7(58 

0-896 

1-400 

80 

5597                65-30 

o-7as 

0-914 

1-405 

81 

5()92               66-40 

0-8(X> 

09;53 

1-410 

82 

5786       '        67-50       , 

0-816 

0-952 

1-415 

83 

58-83       j        68-63 

0-832 

0-9J1 

1-420 

84 

59-83       '        69-80 

0-849 

0-991 

1425 

85 

60-84       ;        70-98 

0-8(57 

1011 

1-430 

m 

61-86               72-17       ' 

0-885 

1-032 

1-435 

87 

62-91               73-39 

0-903 

1053       ! 

1-440       , 

88 

6401               74^ 

1 

0-921 

1075       1 

SPECIFIC  GRAVITIES  OF  NITRIC  ACID. 


101 


Table  (continued). 


Specific 
grarities 

Degrees 

100  parts  by  weight, 
contain 

1 

1  litre  contains  kilog. 

at  ^P- 

Twadd. 

40- 

N,0,. 

HNOj. 

NjO,.       1      HNO3. 

1-445 

89 

65-13 

75-98 

0941        ,        1098 

1450 

90 

66-24       1        77-28 

0-961        1        1-121 

i         1 455 

91 

67-^8               78-60 

0-981                1144 

1-460 

92 

(i8-56               79-JI8 

1001                1  168 

1-465 

93 

(;9-79       ,        81-42 

1023               1-193 

'         1-470 

94 

7106               82-90 

1-(H5               1-219 

1-475 

95 

72-39                84-45 

1-068 

1-246 

1-480 

96 

73-76               86a') 

1092 

1274 

1-485 

97 

7518               87  70 

1116               1-302 

1-490 

98 

7680               89-60 

1-144                1-335 

1-495 

99 

78-52               9160 

1174                1-369 

1-500 

100 

80-65               94-09 

1-210               1-411 

1501 

— 

8109               94-60 

1-217 

1-420 

1-502 

— 

81-50               9508 

l-:>>4 

1-428 

1-503 

— 

81-91        ;        95-.55       i 

1-231                1-436 

1-504 

— 

82-29               96-00 

1-238 

1-444 

1-505 

101 

82-63               96-39 

1-244 

1-451 

1-506 

— 

82-94               9676       | 

1249 

1-457 

1-507 

83-26               97-13 

1-255 

1-464 

1-508 

~^ 

83-58               97-50 

i-2<;o 

1-470 

1509 

83-87               97-84 

1-265 

1-476 

1-510 

102 

8409               9810 

1-270 

1-481 

1-511 

84-28                98-32        i 

1-274 

1486 

1-512 

84-46               98-53 

1-277 

1-490 

1-513 

84-63               98-73 

1-280 

1-494 

'         1-514 

— 

84-78               98-90 

1-283 

1-497 

1-515 

103 

84-92               J»9  07 

1-287 

1-501 

1-516 

— 

ar04               99-21 

1-1^89 

1-504 

1-517 

85-15               99-34 

1-292 

1-507 

1-518 

— 

8^3-26               99-46 

1-294 

1-510 

1-519 

__ 

85-35               99-57 

1-296 

1-512 

1-520 

104 

85-44 

9967        1 

1-299 

1 

1-515 

Correction  of  the  observed  specific  gravities  for  temperatures 

a  Uttle  above  or  below  15°  C. 


With  spec.  grav.  between  1*000 — 1 

1-021—1 

1041—1 

1071—1 

1-101-1 

1131—1 


9} 

)* 
if 
)f 


7f 


i> 


'> 


») 


}> 


)i 


Add  for  -1°C. 
Deduct  for  +1°C. 

•020  00001 

•040  00002 

•070  0-0003 

•100  00004 

•130  0-0005 

•160  0-0006 


102 


RAW  MATERIALS  OF  MANUFACTURE. 


Correction  of  the  observed  specific  gravities  (continued). 


With  spec.  grav. 

between 

1-161— 1-200 

0-0007 

1-201— 1-245 

00008 

1-246-1-280 

00009 

1-281     1-310 

00010 

1-311—1-350 

0-0011 

1-351     1-365 

00012 

1-366     1-400 

00013 

1-401—1-435 

0  0014 

1-436— 1-490 

0  0015 

1-491— 1-500 

0-0016 

1-501     1-520 

0-0017 

Loring  Jackson  and  Wing,  and  a  little  later  on  R.  Hirsch 
(Chem.  Zeit.  1888,  p.  911),  have  shown  that  the  presence  of 
lower  oxides  of  nitrogen  in  nitric  acid  has  a  considerable  influence 
on  its  specific  gravity.  Thus  the  first  runnings  from  a  distillation 
possessed  a  specific  gravity  =1*62,  but  contained  12  percent, 
by  weight  of  HNO2.  Hirsch  assumes  (without  strict  proof)  that 
each  per  cent,  of  HNO2  raises  the  specific  gravity  by  0  01.  If 
this  is  correct,  an  acid  of  sp.  grav.  1*44,  but  containing  1  per 
cent.  HNO2,  really  contains  only  99  per  cent,  of  HNOj,  of  spec, 
grav,  1*43.  Now  100  grams  of  pure  acid  of  1*44  are  =  74'4 
grams  HNO3,  but  99  grams  of  1"43  only  =710;  hence  the  1  per 
cent,  of  HNO2  present  makes  a  difterence  of  3*4  per  cent,  of  HNOg 
in  the  real  strength^  compared  with  the  apparent  strength  as  taken 
from  the  specific-gravity  tables. 

This  subject  has  been  more  accurately  investigated  by  Lunge 

and  Marchlewski.     From  their  paper  (Zsch.  f.  angew.  Ch.  1892, 

p.  10)  I  give  the  following  table,  showing  this  influence  in  the 

150 

case  of  nitric  acid  of  spec.  grav.  1*4960  (at  —75-)  : — 

4^ 


PROPERTIES  OF  NITRIC  ACID. 


103 


If  A      1 

per  cent. 

Alteration  of 

per  (jent. 

1 
Alteration  of   , 

spec.  grav.  by 
N,0, 

spec.  grav.  by 

I         0-25 

0-00050 

6*55 

004475 

0-50 

0-00075        , 

70{) 

0-04650 

075        ! 

000150        1 

7-25 

004720 

I-OO 

0-00300 

750 

005000        ' 

i         1-25 

0-00475 

775 

005165 

1         1-50 

000675 

8-00 

005325        ' 

t         175 

000775 

8-25 

005500 

(         200        ; 

0-01050 

8-50 

0-05660 

2-25 

001250 

8-75 

0058-25 

2-50 

0-01425 

900 

006'-)00 

2-75 

001625 

9-25 

006160 

300 

0-01800 

9-50 

0-06325 

325 

001985 

9-75 

0  06500 

3oO       • 

002165 

10-00 

006ii00 

3-75 

002350 

10-25 

006815 

4-00 

002525 

10-50 

006976 

4-25 

002690 

10  75 

0-07135 

'         4-50 

002875 

1100 

007300 

4*75 

0  03050 

11-25 

007450 

500 

0-03225 

11-50 

007600 

1         5-25 

003365 

1175 

0-07750 

'         5-50 

003600 

12-00 

0078nO 

575 

003775 

1225 

008050 

;        600 

003950 

12-50 

0-08200 

6-25 

0-04175 

12-75 

0-083r>() 

6-50 

0(>i300 

Saposehnikoff  (Chem.  Centralbl.  190Q,  ii.  p.  708,  and  1901,  ii. 
p.  1330)  has  studied  the  conditions  of  equilibrium  between  HNOj^, 
HNO2,  and  NO,  i.  e.  the  formation  of  HNO.,  and  NO  from  HNO2, 
and  the  reduction  of  HNO«  by  NO  to  HNOo. 

The  oxidizing  properties  of  nitric  acid  are  well  known  and  can- 
not be  described  in  detail  here ;  but  it  should  be  mentioned  that 
an  acid  containing  the  lower  oxides  of  nitrogen,  such  as  the  '^  red 
fuming  nitric  acid/^  has  even  more  strongljr oxidizing  properties 
than  the  pure  acid,  and  this  helps  to  explain  some  points  in  the 
theory  of  the  formation  of  sulphuric  acid,  as  we  shall  see  in  a 
subsequent  chapter. 

Manufacture  of  Nitric  Acid. — This  acid  has  been  known  since 
the  times  of  Geber,  in  the  eighth  century;  and  Raymundus 
Lullus  in  1225  taught  how  to  prepare  it  by  distilling  a  mixture  of 
clay  and  saltpetre.  Now-a-days  it  is  always  made  by  distilling 
nitrate  of  soda  with  sulphuric  acid,  an  excess  of  the  latter  acid 
beyond  the  theoretical  quantity  being  used  in  practice.     By  the 


104  RAW  MATERIALS  OF  MANUFACTURE. 

equation :  2NaN0jj  +  H2SO4 = 2HN08 + Na2S04,  in  theory  85  parts 
of  NaNOg  require  49  parts  of  SO4H2,  and  yield  BSNOaH  along  with 
71Na2S04 ;  this  comes  to  the  same  as  57*6  parts  of  SO4HS,  or, 
say,  60  parts  of  ordinary  strong  oil  of  vitriol  (with  95  per  cent,  of 
SO4H2)  to  100  parts  of  95-per-cent.  nitrate.  If  these  proportions 
are  used,  a  portion  of  the  nitric  acid  is  always  decomposed  inio  O 
and  N2O4,  and  red  fuming  acid  is  obtained.  This  arises  from  the 
fact  that  the  above  equation  is  only  realized  at  a  high  temperature, 
whilst  at  less  elevated  temperatures  sodium  bisulphate  is  formed  : 
NaNOj  +  H2SO4 = HNO3 = NaH SO4.  Moreover,  the  presence  of 
strong  sulphuric  acid,  owing  to  its  attraction  for  the  elements  of 
water,  has  a  tendency  to  split  up  some  HNO3  into  H2O  and  N2O5, 
the  latter  compound  being  at  once  decomposed  into  N2O4  and  O. 
To  avoid  the  loss  involved  in  this  operation,  generally  more  dilute 
nitric  is  produced  by  employing  weaker  sulphuric  acid,  say  of 
14<y*-148°  Tw.,  and  more  than  the  theoretical  quantity  of  it,  gene- 
rally from  20  to  30  per  cent,  in  excess  of  the  simple  equivalent. 
In  this  case  the  admixture  of  a  certain  quantity  of  sodium  bi- 
sulphate makes  the  residue  of  distillation  much  more  easily  fusible 
and  facilitates  its  removal  from  the  retorts.  When  the  acid  is  made 
at  factories  where  salt  is  decomposed,  even  more  sulphuric  acid 
than  the  above  is  generally  employed,  as  the  excess  is  not  lost,  the 
residual  "  cylinder-cake  "  or  '*  nitre-cake  "  being  regularly  mixed 
with  the  salt  to  be  decomposed  in  the  sulphate-pans ;  in  this  case 
as  much  sulphuric  acid  is  saved  as  corresponds  to  the  bisulphate 
contained  in  the  cylinder-cake. 

Nitric  acid  was  formerly  made  in  glass  retorts,  which  are  prac- 
tically obsolete  now,  cast-iron  retorts  being  universally  employed. 
The  retorts  belong  mainly  to  two  different  types — horizontal 
cylinders,  charged  sideways,  and  pots  or  stills,  charged  from 
the  top. 

The  ordinary  type  of  French  cylinder  apparatus,  used  in  many 
places  outside  of  France  as  well,  is  represented  in  figs.  10  and  11 
on  a  scale  of  1 :  25. 

The  ends  of  the  cylinders  are  here  exposed  to  the  air  and  con- 
sist of  cast-iron  disks,  1^  inch  thick,  cemented  into  the  rebates 
cast  on  to  the  ends  of  the  cylinder  by  the  usual  rust  cement  (100 
iron  filings,  5  flowers  of  sulphur,  5  sal-ammoniac),  or  by  a  mixture 
of  this  with  ground  fire-bricks  and  the  like.  At  all  events  the 
back  end  is   fixed  in  this  way,  and  is  provided  with  a  pipe  for 


BAW  MATERIALS  OF  MANUFACTURE. 
Fig.  11. 


taking  away  tbe  vapours  ;  the  other  end  is  made  to  take  off  and' 
serves  for  charging  the  nitre  and  discharging  the  residue.  A  hole 
and  S-shaped  funnel  in  the  man-lid  allow  of  running  in  the  sul- 
phuric acid.  These  cylinder-ends  cause  a  good  deal  of  cooling,and 
consequently  a  loss  of  fuel,  which  can  be  avoided  to  a  great 
extent  if  they  are  not  made  of  iron  but  of  a  single  stone  flag  each ; 
the  charging  end  also  remains  fixed  in  this  case,  the  nitre  being 
charged  through  a  small  general  opening  in  it,  and  the  residue 
being  run  off  in  a  liquid  state  through  a  pipe  generally  closed  by  a 
ground-in  iron  stopper.  A  little  more  sulphuric  acid  is  employed' 
in  this  case,  so  as  to  obtain  a  very  fluid  mass  at  the  end.  If 
sulphuric  acid  of  144°  Tw,  is  employed,  the  receivers  will  contain' 
nitric  acid  of  77°  to  82°  Tw.;  if  weaker  acid  is  desired,  a  little 
water  is  put  into  the  receivers.  The  strongest  acid,  of  100°  Tw,„ 
can  only  be  made  from  strong  I'itriol  and  dried  nitrate. 


CYLINDERS  FOR  NITRIC  ACID.  107 

At  first  the  cjliaders  are  fired  rather  strongly;  but  as  soon  as 
the  first  receivers  get  warm  the  fire  is  slackened,  and  during  18 
hours  is  kept  so  that  of  eight  receivers  only  the  firsffive  are  warm 
to  the  touch.  If  the  heat  gets  up  too  high,  the  coutents  of  the 
retort  may  boil  over,  and  far  more  ruddy  vapours  will  be  formed. 
The  end  of  the  reaction  is  known  by  the  cooling  of  the  receivers ; 
then  the  fire  is  increased  again  for  a  little  time,  and  at  last  is 
allowed  to  go  down. 

In  regular  work,  there  are  some  red  vapours  at  first,  but  much 
less  with  rather  weaker  acid  (say  135°  Tw.)  than  with  stronger 
acid.  At  the  end  the  red  or  yellow  vapours  appear  again  and  last 
np  to  the  finish. 

The  cylinders  are  sometimes  cast  so  that  their  upper  half  can  be 
protected  against  the  attack  of  the  acid  by  lining  it  with  acid-proof 
bricks  (see  fig.  12) ;  but  some  believe  that  this  does  more  harm 

Fig.  1-2. 


than  good,  as  the  upper  part  of  the  metal  cylinder  is  all  the  less 
acted  upon  by  the  nitric  acid  the  hotter  it  becomes. 

A  more  perfect  form  of  cylinders  is  that  employed  at  the 
Griesheim  works,  aud  shown  in  full  detail  iu  figs.  13  to  16  with 
all  the  measurements  marked  in  centimetres  *. 

These  retorts  work  off  8  cwt.  of  nitre  per  24  hours,  with  an 
expenditure  of  2i  cwt.  of  coal  or  very  little  more,  inclusive  of  the 
time  of  filling  and  emptying.  In  case  of  need,  25  per  cent,  more 
can  be  charged,  without  fear  of  boiling  over,  with  careful  work. 

•  These  fipires  are  taken  from  HaussermaQn's  article  "  Nitric  Acid, '  in 
Huepratt-Bunte'B  Enc,  d.  Teclin.  Chemie,  4tU  ed.  vii,  p.  051  et  »eq.  Some  notes 
from  thiB  article  are  also  given  in  tbe  following  piiges. 


RAW  UATERIALB  OF  UANTTPACTITHE. 


GRIKSHEIM  RSTORT8  POK  NITRIC  ACID. 


109 


III 


I  ii 
III 
III 
III 


o 
o 

> 

•*^ 

G 
O 


P 

o 


o 

c 
.2 

'■+3 
u 


RAW  MATERIALS  OF  MANUFACTURE. 

Fig.  10. 


tjectional  plan. 
Such  boiliug  over  occurs  more  easily  with  stroug  sulpliuric  acid 
(of  1'84  spec,  grav.)  than  with  weaker  acid  (140°  Tw.).  The  setting 
is  so  arranged  that  the  tire-gases  entirely  surround  the  cylindrical 
part,  and  the  ends  are  made  of  sandstone  slabs,  cemented  and 
kept  in  their  places  by  iron  bars  pressing  against  them  on  the 
flutside.  In  this  kind  of  apparatus  no  corrosion  takes  place, 
wherefore  the  arrangement  shown  in  fig,  12  (p.  107)  is  quite 
unnecessary.  The  exit  opening  continues  into  a  glass  tube, 
forming  connection  with  the  condensing-apparatus.  The  arrange- 
ment for  running  off  the  nitre-cake  is  made  quite  clear  in  fig.  13. 
The  objection  sometimes  made  to  cylindrical  retorts,  that  they 
do  not  easily  permit  the  manufacture  of  the  strongest  nitric  aciil, 
is  refuted  by  the  experience  of  many  years  at  the  various  works 
belonging  to  the  Grieaheim  Company. 


Vol.  I.  Sidiihuric  Aad. 


STILLS  FOR  NITRIC  ACID.  Ill 

The  other  class  of  retorts,  taking  the  shape  of  pots  or  stills,  is 
either  entirely  surrounded  by  the  fire^  or  with  its  top  exposed  to 
the  air.  The  former  kiiid,  as  employed  in  France  for  very  strong 
nitric  acid,  is  shown  in  fig.  17.  It  consists  of  cast-iron  pots  of 
from  4  to  5  feet  diameter  and  equal  height,  and  a  metal  thickness 
of  1 J  to  2  inches  (rather  thicker  at  the  bottom).  There  is  a  wide 
neck  a  at  the  top,  closed  by  a  lid,  fastened  on  with  a  suitable 
cement,  e.ff.  a  mixture  of  clay  and  gypsum.  There  is  a  tube  b 
for  carrying  away  the  gas,  either  coming  out  perpendicularly  at 
the  top,  as  shown  here,  or  bending  away  horizontally,  as  in  a 
laboratory  retort ;  this  tube  should  be  lined  with  an  earthenware 
tube  as  far  as  it  is  at  all  liable  to  cool  down  below  the  point 
where  the  metal  can  be  acted  upon  by  nitric  acid.  Another 
tube  c  serves  for  introducing  the  sulphuric  acid  ;  this  is  preferable 
to  running  it  in  through  the  neck  a,  after  charging  the  nitre. 
Sometimes  there  is  no  pipe  provided  for  running  out  the  liquid 
residue,  but  it  is  better  to  have  one,  as  shown  at  d,  and  to  protect 
this  tube  against  the  direct  action  of  the  fire  by  a  fire-proof 
covering.  Where  this  is  not  provided,  the  liquid  residue  must 
be  ladled  out  through  a  at  the  close  of  the  operation,  which  is  a 
disagreeable  proceeding.  The  pot  is  set  in  a  furnace  so  that 
it  is  altogether  surrounded  by  the  fire,  even  at  the  top,  to  which 
access  is  afforded  for  charging  by  lifting  off  a  fire-clay  slab,  or 
a  metal  plate  filled  with  ashes,  as  shown  at  e.  By  this  means  a 
saving  of  fuel  is  effected,  and  the  equal  heating  of  the  retort 
causes  it  to  stand  the  action  of  the  nitric  acid  very  well.  A 
pot  5  feet  wide  and  5  feet  high  takes  a  charge  of  9  cwt.  of  nitre, 
and  requires  from  16  to  18  hours  to  work  this  off,  including 
the  time  for  charging  and  emptying.  Of  this  time,  one  hour 
may  be  reckoned  for  charging  and  making  the  joints,  six  hours 
for  the  first  stage,  where  red  fumes  appear,  about  as  much  for 
the  second  stage,  where  the  vapours  are  almost  colourless,  and 
four  or  five  hours  for  the  last  stage,  where  the  temperature  has  to 
be  raised  much  higher,  the  yellow  and  red  vapours  appear  again 
and  more  water  comes  over  with  the  acid. 

That  kind  of  pot  where  the  top  (with  the  small  hole)  is  exposed 
to  the  air  is  shown  on  a  scale  of  1 :  60  in  fig.  18.  It  forms  part 
of  the  Valentiner  vacuum  system  to  be  described  below.  The  pot, 
for  a  charge  of  a  ton  of  nitre,  is  composed  of  two  parts.  The 
outlet-pipe  for  the  nitre-cake  runs  almost  horizontally,  so  that  it 


112  KAW  UlTEKIALS  OF  MANUFACTURE. 

is  easily  cleaned.      The   gas-pipe   first  eaters  a  amall   receiver, 
destined  to  keep  back  any  froth  caiTied  over.     Such  a  vacuum 


retort  is  finished  in   12  hours,  with  about  4  cwt.  of  coal  per  tou 
of  nitre. 


4  rOU  MTKIC  ACID. 


114  RAW  HATEBIALS  OP  UANUPACTUBE. 

Figs.  19,  20,  and  21,  from  drawings  which  I  owe  to  the 
kindness  of  Mr.  H.  H.  Niedenfiihr,  show  the  kind  of  still 
employed  by  Mr.  O.  Guttmaun  in  couDexioii  with  his  coudensiiig- 
plant,  but  of  course  applicable  in  every  other  case.  The  drawings 
are  to  scale  and  are  clear  enough  without  further  explanations. 
The  brick  setting,  as  arranged  by  Mr.  Niedenfuhr,  has  had  an 


excellent  effect,  and  admits  of  huishiug  a  charge  of  13  cwt.  in 
24  boura  with  only  17  per  cent,  of  coal.  The  internal  flanges 
have  the  effect  of  diverting  the  contents  of  the  pot,  when 
frothing,  towards  the  centre,  and  of  preventing  any  acid  con- 
densing from  running  down  the  sides.  These  retorts  have  been 
found  specially  useful  for  making  a  maximum  of  strong  acid. 

Usually  it  is  preferred  to  cast  such  conical  pots  in  one  piece 
(like  caustic-soila  pots),  and  to  set  them  so  that  the  cover  projects 
over  the  brickwork.     In  order  to  kee|)  the  cover  sufficiently  hot,  it  is 


KETOKTS  FOB  XlTKIt  ACIU.  115 

covered  by  a  layer  of  ashes  or  by  bricks ;  the  drying  of  the  nitre 
Id  this  case  is  equally  performed  by  the  waste  heat  of  the  fire,  but 
in  a  separate  place  at  the  end  of  the  retort-bench. 

At  some  works  they  use  large  semicylindrical  trougha  of  cast 
metal  with  broad  flanges  aad  a  vertical  rim  all  round,  in  order  to 
cover  them  by  a  brick  arch  or  a  stone  slab.     At  others  they  employ 

FiK-  21. 


lai^c  pots  with  rounded  bottom,  lying  on  their  side :  the  open 
end,  which  forms  part  of  the  front  of  the  furnaces,  being  closed 
by  a  stone  slab.  Neither  of  these  forms  has  found  very  much 
favour  elsewhere. 

Prentice  (Engi.  pat.  6960,  1893)  carries  on  the  process  in  a 
continuous  manner.  The  nitre  is  mixed  with  sulphuric  acid 
outside  the  retort,  preferably  in  a  kind  of  mortar-mill  (according 
to  patent  No.  8902,  1893,  a  lai'ge  excess  of  sulphuric  acid  should 
be  employed  and  the  residue  subsequently  used  for  the  manu- 


116  KAW  MATERIALS  OF  MANUFACTURE. 

facture  ot  superphosphate) .     The  mud  thus  produced  is  conveyed 
iuto  a  heated  chamber  in  which  the  nitrate  dissolves  in  the  sul- 
phuric acid^  but  no  nitric  acid  is  as  yet  split  off  [?]  ;  here  chlorine 
and  nitrogen  tetroxide  are  liberated  and  escape  into  a  condensing- 
apparatus.     Owing  to  this  the  nitric  acid  is  later  on  free  from 
volatile  impurities  [?].      The   mixture  is  now  charged  into  the 
retort^  which  has  an  oblong  section  and  is  divided  into  a  number 
of  separate  chambers  by  partitions  stai*ting  from  the  cover  and 
not  reaching  entirely  to  the  bottom.     Above  each  chamber  the 
cover  is  provided  with  a  head  and  vapour-pipe.     The  retort  is 
heated  from  below,  and  the  fire-gas  subsequently  travels  round  the 
sides.     The  mixture  coming  from  the  heating-chamber  enters  the 
first  chamber  of  the  retort,  where  it  begins  to  boil  and  gives  off  a 
large  quantity  of  strong  nitric  acid  mixed  with  a  little  nitrogen 
tetroxide.    The  mixture  now,  without  ceasing  to  boil,  flows  on  from 
chamber  to  chamber,  giving  oft'  pure  nitric  acid,  which  gets  weaker 
and  weaker  in  the  following  chambers.     In  the  last  chamber,  placed 
immediately  above  the  fire,  the  temperature  is  highest ;  here  the 
last  nitric  acid  is  driven  off,  together  with  much  water  and  a  little 
sulphuric  acid,  and  the  nitre-cake  is  drawn  off,  free  from  the  nitrate. 
By  this  method  §  of  the  fuel  and  f  of  the  condensing-plant  [?J 
can  be  saved.     A  still  producing  4  tons  per  week  weighs  less  than 
two  tons. — A  communication  by  Prentice  in  the  ^  Journal  of  the 
Society  of  Chemical  Industry,^  1894,  p.  323,  gives  nothing  new. 
In  discussing  it  doubts  were  expressed  as  to  whether  that  process 
is  applicable  at  such  works  where  the  residue  cannot  be  utilized 
for  the  manufacture  of   superphosphate,  as  it  contains  a  large 
excess  of  acid.     Indeed,  this  extra  quantity  of  acid  required  for 
working  that  otherwise  very  ingenious  process  has  made  it  an 
economical  failure. 

Uebel  (patents  of  the  Chemische  Fabrik  Ehenania,  E.  P.  27240, 
1 898,  and  3305, 1901)  proceeds  in  a  novel  way  for  the  manufacture 
of  nitric  acid.  The  nitre-cake,  running  out  at  a  high  temperature 
from  the  retorts,  is  mixed  with  sulphuric  acid  of  about  1*71  spec, 
grav,  in  such  proportions  that  a  '^  polysulphate  '*  is  formed,  the 
water  being  evaporated  by  the  heat  remaining  in  the  nitre-cake. 
This  polysulphate,  of  a  composition =NaH3(S04)  2,  serves  instead 
of  fresh  sulphuric  acid  for  manufacturing  the  next  batch  of  nitric 
acid,  in  which  case  the  latter  is  obtained  of  the  highest  strength, 
just    as    if    the    strongest   sulphuric   acid   had    been    employed. 


uebel's  process  for  nitric  acid,  117 

Of  course  the  fresh  nitre-cake  formed  from  the  second  operation 
amounts  to  much  more  than  that  from  the  first ;  therefore  a  portion 
of  it  is  set  aside  in  the  ordinary  manner^  and  the  remainder  is  again 
employed  for  making  nitric  acid.  The  practical  work  carried  out 
with  this  process  has  led  to  the  construction  of  a  new  and  original 
style  of  retorts,  which  may  be  very  usefully  adopted  even  when 
nitrate  of  soda  is  to  be  decomposed  in  the  ordinary  way  by 
sulphuric  acid,  not  by  "  polysulphate.'' 

The  principal  advantages  of  the  new  process  are :  that  the 
alternate  heating  and  cooling  of  the  apparatus  is  avoided,  which 
produces  a  saving  in  fuel  and  prolonged  duration  of  the  plant ; 
that  there  is  not  the  same  inequality  of  the  nitric  acid  as  is  pro- 
duced during  the  period  of  working  oflF  a  retort  on  the  old  system ; 
that  a  much  smaller  and  consequently  much  cheaper  plant  and 
only  half  of  the  ordinary  ground-space  are  required  for  the  same 
output,  both  for  distillation  and  condensation  (the  Uebel  plant 
may  be  combined  with  any  of  the  systems  of  condensation  to  be 
described  below)  ;  that  there  is  less  labour -required ;  and  that  the 
strongest  acid  can  be  made  by  means  of  ordinary  sulphuric  acid 
140°  Tw.,  as  its  water  is  evaporated  free  of  expense  in  the  formation 
of  the  polysulphate — ^'  waste-acid  '^  from  nitrating  processes  being 
equally  fit  for  employment. 

The  Uebel  process  is  illustrated  in  figs.  22  to  24.  Two  parallel 
retorts  A,  A'  (consisting  of  a  cast-iron  bottom  piece  and  a  stone  or 
stoneware  cover)  are  alternately  charged  with  nitrate  of  soda  and 
the  requisite  quantity  of  liquid  '^  polysulphate''  (or  else,  if  there 
is  a  sufficient  quantity  of  strong  acid  at  disposal,  e.g.  where 
manufacturing  by  contact  processes,  directly  with  such  acid).  The 
heating  is  performed  by  the  waste  fire-gases  of  the  lower  retort  B, 
a  temperature  of  170°  to  200°  C.  being  thus  attained  in  A  and  A'. 
When  most  of  the  nitric  acid  has  beeu  expelled,  the  contents  of 
A  and  A'  are  let  down  into  retort  B,  where  the  last  portion 
of  nitric  acid  is  liberated,  at  a  temperature  of  about  300°  C.  The 
contents  of  B  have,  of  course,  been  previously  run  out,  but  never 
completely,  leaving  always  a  stock  of  hot  liquid  "  bisulphate  "  in 
the  retort.  The  bisulphate  (nitre-cake)  is  run  from  B  into  the 
cast-iron  pan  C,  where  it  is  mixed  with  previously  heated  sulphuric 
acid  of  about  140°  Tw.  (or  with  waste  acid  from  nitrating  pro- 
cesses of  equal  strength)  in  the  proportion  of  forming  a  tetrasul- 
phate,  H2SO4,  NaHSOi.     In  consequence  of  the  high  temperature 


KfiVi  MATERIALS  OF  MANDFACTfKK. 

Fig.  -22. 


UEBEL^S  PROCESS  FOR  XITRIC  ACID. 


119 


of  the  liquid  nitre-cake,  the  water  present  in  the  fresh  sulphuric 
acid  is  evaporated  (together  with  any  nitric  acid  present  in  waste 
acids,  if  such  are  employed)  and  is  carried  away  by  a  pipe,  or  a 
vapour  hood,  not  shown  in  the  drawing.  Half  of  the  ''  poly- 
sulphate  "  formed  in  C  is  employed  for  a  fresh  operation  in  A,  A', 


%m.. 


wp.. 


"t^-^t-i— 


Scale  1 : 8(i. 


\  0,5  0 

I  i  1 1  I  I  ' '  ■ '  t 


ftm 


the  other  half  beiug  at  disposal  for  any  outside  utilization  in  lieu 
of  highly  concentrated  acid.  If  such  utilization  is  not  possible, 
half  of  the  nitre-cake  is  run  out  from  C  before  adding  fresh 
sulphuric  acid  and  only  the  other  half  is  employed  for  making 
^'  polysulphate,"  the  unemployed  half  being  utilized  in  the  manner 
followed  in  other  cases. 

(An  English  patent  by  Claes,  No.  1072,  1900,  describes  the 
manufacture  of  such  ^^  polysulphates  '^  from  nitre-cake  and  sul- 
phuric acid  as  a  commercial  article.) 

The  flame  of  the  hearth  F  first  heats  retort  B,  which  is  pro- 
tected by  an  arch,  and  then,  according  to  the  position  of  the 
damper,  either  A  or  A',  v^v^  are  valves  for  discharging  the 
contents  of  A,  A'  into  B  ;  v'^  another  valve  for  discharging  B  into 
C,  placed  high  enough  to  leave  a  stock  of  liquid  nitre-cake  in  B. 

After  heating-up,  A  is  charged  with  8  cwt.  nitrate  of  soda, 
previously  dried  on  the  shallow  basins  T,  T'  on  the  top  of  the 
furnace.  The  charging  is  performed  through  manholes  H,  H^ 
which  are  afterwards  closed  by  covers  and  kept  tight  by  nitrate 


120  RAW  MATERIALS  OF  MANUPACTURB. 

of  soda  heaped  upon  them.  Then  fused  polysulphate  is  gradually 
run  in  through  a  swan-neck  pipe  from  the  tilting-box  K,  pre- 
viously lifted  to  the  top  of  the  furnace.  This  polysulphate  will 
be  at  a  temperature  of  about  120°  or  130°,  and  must  therefore 
be  gradually  introduced  within  from  half  an  hour  to  an  hour,  so 
as  to  avoid  a  tumultuous  evolution  of  nitric  acid.  Of  course,  in 
lieu  of  this,  fresh  acid  can  be  employed,  as  stated  above.  During 
the  introduction  of  the  hot  polysulphate  damper  z  is  closed  and 
z'  is  opened ;  when  finished,  z  is  opened  so  that  the  fire-gases  play 
upon  A.  When  the  temperature  has  risen  to  about  170°,  nearly 
all  HNO3  has  been  driven  out;  the  thin,  liquid  melt  contains  a 
little  nitrate  and  all  the  water  introduced  with  the  nitrate  and  the 
polysulphate  or  fresh  acid.  It  is  now  slowly  run  through  valve  v 
into  retort  B,  where  it  meets  with  a  stock  of  hot  bisulphate. 
Here,  without  the  frothing  taking  place  in  the  old,  directly  fired,- 
retorts,  the  last  nitric  acid  and  the  water  is  drawn  off  within  a 
very  short  time.  The  contents  of  B  remain  there  until  the  con- 
tents of  A'  (which  has  been  charged  and  worked  in  the  mean- 
time) are  ready  to  be  run  oflF,  which  takes  from  3^  to  4  hours. 
Then  B  is  discharged  into  C,  where  fresh  acid  is  run  in  as  before 
described,  so  that  room  is  made  in  B  for  receiving  the  contents  of 
A'.  A  in  the  meantime  has  been  left  empty  for  an  hour,  damper 
z  being  closed,  in  order  to  cool  down.  Now  the  polysulphate  is 
run  out  of  C  into  the  tilting-box  K,  which  is  hoisted  up  to  serve 
as  before.  Thus  a  charge  of  8  cwt.  of  nitrate  can  be  worked  oft* 
in  each  of  the  retorts  A  and  A'  every  four  hours. 

A  good  cement  for  permanent  joints  against  nitric  acid  in  the 
retorts  consists  of  10  parts  powdered  volvic  lava,  7  iron  filings,  7 
powdered  brimstone,  7  fire-clay,  10  ground  fire-bricks,  moistened 
with  as  little  water  as  possible.  If  carefully  stemmed  into  the 
joint,  it  becomes  very  hard. 

Cement  for  the  earthenware  pipes,  &c.,  in  the  condensing- 
apparatus  can  be  made  from  5  parts  hot  linseed-oil,  2  parts 
brimstone,  2  parts  india-rubber  scraps,  and  enough  sulphate  of 
baryta  to  produce  a  thick  paste  which  is  employed  in  the  hot  state. 

The  most  universally  employed  cement  for  nitric  acid  (and  other 
acids)  is  asbestos  cement,  Guttmann  gives  the  following  pre- 
scription for  preparing  it: — 1  part  silicate  of  soda  is  dissolved  in 
19  parts  water  [or,  which  is  preferable,  the  usual  33  percent, 
solution  is  diluted  with  8  times  its  volume  of  water]  and  asbestos 
liowder  is  kneaded  with  it  in  small  quantities  at  a  time,  until  a 


Vi^POURS  FROM  NITRK-ACID  RETORTS.  121 

toagh  paste  is  obtained.  Should  a  cement  be  required  whidi  will 
become  very  hard^  a  little  finely  powdered  barium  sulphate  is  mixed 
with  it ;  but  this  is  not  desirable  where  pipes  have  to  be  changed^ 
as  the  cement  cannot  be  removed  without  risk  of  damaging  the 
pottery.  If  too  little  water  is  used  from  the  first,  the  water 
absorbed  by  the  cement  will  cause  it  to  swell  and  to  burst  the 
sockets.  The  cement  is  applied  in  small  bits,  and  tightly  pressed  in 
by  means  of  a  piece  of  wood  with  a  blunt-ended  tool.  The  sur- 
face is  flattened  and  moistened  with  some  silicate  of  soda  solution. 
If  the  putty  in  the  sockets  shrinks,  about  §  incli  of  it  is  raked  out 
and  fresh  cement  put  in. 

Asbestos  cement  must  never  be  treated  with  pure  water  to 
begin  with,  but  with  acid  or  acid  fumes,  in  order  to  ensure  its 
setting  by  the  separation  of  silica. 

The  gases  and  vapours  evolved  during  the  working  of  the  retorts, 
apart  from  the  vapour  of  nitric  acid  itself,  consist  of  aqueous 
vapour,  nitrogen  peroxide,  hydrogen  chloride  (which  is,  however, 
almost  entirely  converted  into  the  following  gases),  chlorine, 
nitrosyl  chloride,  and  a  little  iodine.  HCl  and  the  gases  derived 
from  it  (NOCl  and  CI)  are  principally  formed  at  the  commencement, 
through  the  decomposition  of  sodium  chloride  ;  but  towards  the 
end  they  appear  again  owing  to  the  decomposition  of  perchlorate. 
All  of  these  impurities  are  dissolved  by  cold  nitric  acid,  and  hence 
occur  in  ordinary,  "  unbleached  "  nitric  acid. 

Volney  (Journ.  Amer.  Chem.  Soc.  1891,  xiii.  p.  246)  showed 
that  the  frothing  in  the  ordinary  nitric-acid  process  takes  place 
only  in  the  last  stage,  when  the  strong  acid  has  passed  over  and 
when  the  last  portion  of  the  nitre  is  suddenly  acted  upon,  with 
formation  of  weaker  acid.  At  this  period  practically  only 
NaHSOl  is  ^^  the  retort  besides  NaNOg. 

Later  on  (ibid.  1901,  p.  489)  Volney  returned  to  this  subject, 
with  the  following  results.  During  the  first  period  of  the  process, 
when  the  temperature  of  the  retort  is  not  above  100°,  the  com- 
pound NaHa  (804)3  is  formed,  which  Volney  calls  '^  trisulphate  ^^ 
(it  is  really  a  tetrasulphate  and  identical  with  UebeFs  ^'  poly- 
sulphate,''  p.  117),  by  the  reaction  : 

NaNO3"f2H2SOj=NaH3(SO.02  +  HNO3. 

The  second  period  sets  in  at  100°  and  ends  at  121°  ;  here  the 
principal  reaction  is : 

NaN03  +  NaH3(S04)2=2NaHS04+ HNO,. 


122  RAW  MATERIALS  OF  MANUFACTURE. 

During  the  first  period  pure  nitric  acid^  boiliug  between  81^  and 
88°,  distils  over.  During  the  second  period  the  HNOs  begins  to 
decompose  into  lower  oxides  and  HgO,  so  that  more  dilute  acid 
must  now  be  formed. 

Later  again  (Journ.  Soc.  Chem.  Ind.  1891,  p.  544;  comp.  also 
Journ.  Amer.  Chem.  Soc.  1902,  p.  226),  Volney  states  that  the 
first  phase,  where  acid  of  77°-90°  boiling-point  comes  over,  takes 
place  at  a  temperature  of  97^-122° ;  the  second  phase,  where  acid 
ofspec.  grav.  1*505,  boiling  at  94°-100°,  comes  over,  requires  a 
temperature  in  the  retort  of  130°-165°.  Above  this  the  decom- 
position of  HNO3  sets  in  and  yellow  acid  comes  over.  All  this 
refers  to  working  under  ordinary  pressures.  When,  however, 
working  at  reduced  pressure  on  the  Valentiner  system  (originally 
proposed  by  me,  comp.  infra),  say  at  300  mm.,  the  first  stage 
runs  from  55^-100°,  the  boiling-point  of  the  strongest  acid  at  that 
pressure  being  only  45°-75° ;  the  second  stage,  where  the  poly- 
sulphate  acts  upon  more  nitrate,  begins  at  100^  and  is  finished 
at  120°,  instead  of  at  165°  at  ordinary  pressure. 

[In  considering  Volney's  results,  we  must  not  overlook  that 
they  were  obtained  in  glass  vessels  on  a  small  scale.  On  the 
manufacturing  scale,  and  working  in  iron  vessels,  higher  tempera- 
tures cannot  be  avoided  and  the  formation  o£  nitrous  vapours  is 
proportionately  increased.  The  frothing  at  the  last  stage  of  the 
distillation  is  generally  ascribed  to  the  partial  decomposition  of 
sodium  bisulphate  into  pyrosulphate  and  water:  2NaHS04= 
NagSA  +  HjO.] 

In  a  subsequent  paper  (Journ.  Soc.  Chem.  Ind.  1901,  p.  1189) 
Volney  gives  the  results  of  working  at  a  much  stronger  vacuum, 
viz.,  110  mm.  absolute  pressure.  During  the  first  phase,  at  about 
74°,  free  sulphuric  acid  acted  on  the  nitrate  \  during  the  second 
phase,  at  about  85°,  the  polysulphate  did  the  principal  action. 
The  outside  temperature  rose  to  140°.  The  distilling  nitric 
monohydrate  boiled  at  30°.  With  concentrated  sulphuric  acid 
there  is  a  great  amount  of  frothing,  which  does  not  take  place  with 
acid  of  60°  B.  When  working  with  such  acid  at  ordinary 
pressure,  the  greatest  portion  of  the  nitric  acid  distils  at  about 
118°  without  frothing;  at  a  pressure  of  110  mm.  at  74°,  with 
slight  frothing.  In  both  cases  the  remaining  salt-cake  consisted 
of  sodium  bisulphate  and  water  of  crystallization.  The  nitric  acid 
produced  showed   in  both  cases   1*38  spec.  grav.  at  21°  C. ;    to 


CONDENSATION  OF  NITRIC  ACI1>.        *  123 

produce  stronger  acid^  it  must  be  redistilled  with  concentrated 
sulphuric  acid. 

The  condensation  of  nitric  acid  is^  properly  speakings  only  a 
cooling-process,  but  it  is  preferably  carried  on  in  such  manner 
that^  in  the  first  instance,  stronger  and  weaker  acid,  coming  over 
at  different  stages,  are  separately  collected,  and  that,  if  possible, 
the  above-mentioned  impurities  (p.  121)  are  kept  out  of  the  acid 
and  are  separately  treated.  For  many  years,  which  now  appears 
strange  to  us,  in  this  distilling  and  condensing  process  only  air- 
cooling  was  employed,  and  it  is  only  during  the  last  ten  or  fifteen 
years  that  the  much  more  efficient  system  of  water-cooling,  which 
is  so  universal  in  other  distilling  processes,  has  been  applied  for 
nitric  acid,  and  that  with  complete  success. 

The  old  condensing-plant  for  nitric  acid  consisted  entirely  of  a 
series  of  earthenware  receivers  (Woulfe's  bottles),  combined  in 
sets  of  six  to  twenty  and  more,  according  to  the  size  of  the  retort. 
Sometimes  two  or  even  more  of  these  jars  are  superposed  over  one 
another,  in  order  to  increase  the  cooling-surface.  According  to 
the  strength  of  acid  intended  to  be  made,  they  are  either  left 
empty  or  charged  with  a  little  water,  as  already  mentioned. 
Sometimes  they  are  cooled  on  the  outside  with  water ;  but  generally 
this  is  not  the  case.  Each  of  the  jars  is  provided  with  a  bottom 
tap  for  running  off  the  condensed  acid;  that  from  the  first  two 
receivers  is  more  impure  than  that  of  the  others,  as  it  contains  a 
little  sulphuric  acid  and  iron  carried  over  from  the  retort.  The 
acid  becomes  weaker  the  further  the  receivers  are  from  the  retort. 
Since  the  receivers  now  and  then  crack  with  the  heat,  it  is 
advisable  to  put  them  on  stoneware  saucers  provided  with  a  spout, 
for  collecting  the  acid  running  out. 

The  cement  used  for  joining  the  receivers  with  the  pipes,  &c., 
has  been  described  on  p.  120. 

This  style  of  condensing-plant  is  still  found  at  many,  especially 
smaller,  works ;  but  it  must  be  considered  quite  out  of  date,  as  its 
cooling  action  is  too  imperfect,  as  the  great  number  of  joints  is 
troublesome  to  keep  tight,  as  the  receivers,  on  breaking,  cause  great 
loss  and  danger  to  health  and  life,  and  as  there  is  always  some  loss 
of  uncondensed  vapours. 

A  minor  improvement,  which  can  be  made,  consists  in  inter- 
posing between  the  retorts  and  the  receivers  a  somewhat  long 
glass  tube,  or  rather  a  number  of  air-cooled  glass  pipes  of  slightly 


124 


RAW  MATERIALS  OP  MANUFACTURE. 


conical  shape,  as  shown  in  fig.  25,    with   sufficient  fall  for  the 
condensed  acids  not  to  stop  in  the  tubes  and  run  out  of  the  joints. 


Fig.  26. 


With  a  length  of  from  10  to  13  feet  (the  longer  the  better)  the 
cooling  by  air  is  already  very  efficient.  The  single  tubes  are  put 
loosely  together,  without  any  cement. 

Gobel  proposed  (Dingl.  Journ.  ccxx.  p.  241),  to  my  knowledge 
for  the  first  time,  the  system  of  cooling  such  pipes  by  water, 
employing  a  long  glass  tube  placed  in  a  trough.  This  plan  must 
have  led  to  frequent  breakages  and  was  probably  soon  abandoned 
for  that  reason,  but  in  principle  it  was  perfectly  correct. 

Much  more  durable,  as  well  as  efficient,  are  water-cooled 
stoneware  cooling-worms,  which  do  away  with  the  necessity  of 
employing  a  large  number  of  receivers. 
These  coils  or  worms  were  first  manu- 
factured by  Messrs.  Doulton  &  Watts,  of 
Lambeth,  as  shown  in  fig.  26,  but  are  now 
made  by  many  other  English  and  German 
firms,  in  various  shapes,  and  are  compara- 
tively very  durable;  good  worms  stand  300 
operations  and  upwards.  They  admit  of 
fractionating  the  products,  but  are  mostly 
employed  when  acid  of  medium  strength 
(up  to  82°  T\v. )  is  to  be  made. 

It  is  nowadays  considered  indispensable  to  employ  some 
contrivance  for  depriving  the  gas  issuing  from  the  condensers  of 
not  condensable  oxides  (NOo  and  NO) .  Where  the  acid  is  made 
at  a  sulphuricacid  factory,  we  may  employ  a  small  Gay-Lussac 
absorbing-tower,  consisting  of  a  stack  of  stoneware  pipes  filled 
with  coke  and  continually  fed  with  sulphuric  acid  of  144°  to  152° 
Tw.  The  gas  enters  at  the  bottom  and  issues  at  the  top,  and 
thereby  gives  up  all  its  nitrous  and  hyponitric  acid  to  the  vitriol, 
which  arrives  at  the  bottom  as  a  more  or  less  rich  "  nitrous 
vitriol,^'  and  can  be  employed  in  the  manufacture  of  sulphuric 
acid.  For  a  ton  of  nitre  from  3i  to  4  cwt.  of  vitriol  are  required  ; 
and  nitrogen  acids  corresponding  to  3  to  5  per  cent,  of  nitric  acid 


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CONDKNSATION  OF  MTKIC  ACID.  12'J 

of  1"33  spec.  grav.    are   absorbed   by    the   same^   more   or  less, 
according  to  the  percentage  of  chlorides  in  the  nitre. 

For  such  manufactures  of  nitric  acid  as  are  not  in  connexion 
with  sulphuric-acid  works,  the  coke-tower  can  be  fed  with  water. 
If  care  is  taken  that  an  excess  of  air  is  always  present,  not 
merely  the  last  remnant  of  nitric  acid  is  condensed,  but  the  lower 
nitrogen  oxides  are  likewise  converted  into  nitric  acid  and  thus 
saved. 

Farpreferable  to  coke-towers  for  both  the  just-mentioned  purposes 
are  the  "  plate-towers  "  constructed  by  the  Author,  in  conjunction 
with  L.  Rohrmann,  and  frequently  called  "  Lunge  towers.*'     These 
will  be  described  in  detail  further  on  (in  Chapter  YI.; ;  in  this 
place  we  will  only  point  out  that  the  use  of  coke  is  irrational, 
because  it  destroys  nitric  acid,  converting  it  into   nitrous  acids 
and  lower  oxides.     The  plate-towers,  of  which  hundi*eds  are  in  use 
at  nitric-acid  works,  explosive  works,  &c.,  for  the  above-mentioned 
purpose,  are  made  of  the  best  fire-  and  acid-resisting  stoneware, 
and,  as  will  be  seen  hereafter,  they  are  so  constructed  as  to  ofler 
the  most  intimate  possible  contact  between  the  gases  and  liquids. 
Fig.  27  shows  the  arrangement  as  suj^plied  by  the  Krauschwitzer 
Thonwaarenfabrik  near  Muskau,  Germany,  for  the  condensation 
of  the  last  fumes,  or  the  recovery  of  nitric  acid  from  lower  oxides. 
A  B  C  is  the  stoneware  shell  of  the  tower,  D  the  cover  with 
distributing  arrangement,  E  the  plates,  F  the  anmiUir  bearers, 
G  drawing-off  tap  with  hydraulic  lute,  H  exit-tube,  J  sight  for 
observing  the  condensation,  K  recfeiver,  M  injector  for  drawing- 
air  through  the  neck  N,  in  connexion  with  the  last  receiver  O. 

Figs.  28  &  29  show  how  a  cooling- worm  can  be  combined  with 
other  pieces  to  form  a  complete  condensing-apparutus.  The 
vapours,  coming  from  two  retorts  charged  with  6  cwt.  of  nitrate 
of  soda  each,  first  pass  through  receivers  a  a  for  impure  acid 
carried  over,  which  is  run  oft*  into  the  carboy  b,  then  through  the 
cooling- worms  c  c,  discharging  their  contents  of  j>ui'c  acid  into 
carboys  d  rf,  then  into  a  collecting-receiver  e  and  into  a  '^  plate- 
tower  ^*  /  for  recovering  nitric  acid  from  N2O4,  and  finally  into  a 
last  receiver  g  and  injector  h.  The  pots  i  i,  equally  discharging 
their  vapours  into  e,  serve  for  refining  (bleaching)  the  yellow 
nitric  acid  (see  below). 

Such   apparatus   is    especially    needed    for    recoveiing    huge 
quantities  of  nitrogen  oxides,  given  oft*  in  the  treatment  of  wunIc 


KAW  MATKHI.^I^  or  MANrFACTURE. 


[ 


receiver^  is  run  into  V3  or  V4,  according  to  its  strength,  that 
condensing  in  receiver  ff  always  into  V^. 

The  refining  or  bleaching  of  nitric  acid  consists  in  drivin*^  off 
the  lower  oxides,  so  that  the  acid  becomes  colourless.  This  can 
be  done  by  long  heating  in  a  water-bath,  which  is  a  tedious  opera- 
tion—much more  quickly  if  a  current  of  air  is  blown  throu^^h  the 
gently  heated  acid  ;  the  air  along  with  the  gas  contained  in  it  is 
conducted  through  a  small  coke-tower,  or,  preferably,  a  small 
''plate-tower^'  (see  above),  fed  with   water,  where  dilute  nitric 


To  fa<x  p.^127.]  Pol.  I.  S„lp\wie  Add. 


CONDENSATION  OF  NITRIC  ACID.  127 

uitratiiig   acids  from  the  manufacture  of  nitroglycerine^  nitro- 
cellulose^ aniline^  &c.y  and  reconverting  them  into  nitric  acid. 

For  such  purposes  it  is  sometimes  necessary  to  combine  several 
plate-towers  in  sets,  one  tower  being  placed  higher  than  the  others 
and  delivering  its  weak  acid  to  those  lower  ones,  to  be  got  up  to 
strength  (Rohrmann  &  Niedenfuhr,  E.  P.  29746,  1897). 

The  weak  acid  can  also  be  pumped  back  to  be  used  over  and 
over  again,  till  it  has  got  up  to  the  maximum  strength  (1*38  or 
1'40  spec.  grav.).  Figs.  30  aod  31  show  a  complete  nitric-acid 
regeneration  plant,  as  employed  after  long  experience  by  H.  H. 
Niedenfuhr.  Pipe  a  (6  inches  wide)  comes  from  the  denitrator  ; 
it  is  preferably  rather  long,  say  40  feet,  so  as  to  cool  the  gases 
which  pass  through  receiver  b  into  the  first  tower  Ri ;  glass  tube 
c  admits  of  watching  the  process.  R^  is  filled  with  34  LuQge 
plates.  The  second  tower  Rg  contains  30  Lunge  plates  and  above 
them  2  feet  of  stoneware  balls.  The  connecting-pipe  between  the 
towers  contains  a  "  KirchhoflF  pipe  '^  d,  which  admits  of  mixing  air 
with  the  gases  in  case  of  need.  Pipe  e  takes  the  gases  away  from 
R2,  through  the  regulating  '*  sight ''/ into  receiver^,  and  through 
h  into  the  chimney.  V^,  V2  are  cisterns  for  feeding  the  towers ; 
Vj  in  the  beginning  receives  a  little  water,  V^  is  entirely  filled 
with  water.  As  soon  as  the  denitrator  has  been  started,  water  is 
run  down  from  Vi  into  R^  drop  by  drop,  and  from  Vj  into  R2  ^^  & 
strong  jet,  sufficient  for  absorbing  all  nitrous  products.  The  liquid 
from  R2  is  collected  in  V^,  and  is  pumped  back  by  the  "Plath^' 
pump  P  (to  be  described  later  on)  into  Vi  and  Vj.  With  this  weak 
acid  Ri  is  later  on  fed  to  such  an  extent  that  the  acid  recovered 
here  comes  out  with  the  desired  strength  and  runs  into.  V3.  On 
the  other  hand,  R3  is  always  fed  up  to  the  extent  of  completely 
recovering  the  last  traces  of  nitric  acid.  If  the  weak  acid  from 
V4  does  not  suffice  for  that  purpose,  it  is  made  up  with  water, 
preferably  at  a  temperature  of  50°  C*  The  acid  condensing  in 
receiver  b  is  run  into  V3  or  V4,  according  to  its  strength,  that 
condensing  in  receiver  g  always  into  V^. 

The  refining  or  bleaching  of  nitric  acid  consists  in  driving  off 
the  lower  oxides,  so  that  the  acid  becomes  colourless.  This  can 
be  done  by  long  heating  in  a  water-bath,  which  is  a  tedious  opera- 
tion— much  more  quickly  if  a  current  of  air  is  blown  through  the 
gently  heated  acid  ;  the  air  along  with  the  gas  contained  in  it  is 
conducted  through  a  small  coke-tower,  or,  preferably,  a  small 
'*  plate-tower '^  (see  above),  fed  with   water,  where  dilute  nitric 


OKIESBEIM  PROCESS  FOR  NITRIC  ACID.  1^9 

acid  is  contained.      This  refining  is,  of  course,  unnecessary  for 
nitric  acid  used  in  the  manufacture  of  sulphuric  acid. 

Hirsch  (G.  P.  46,096)  runs  the  impure  acid  through  a  stoneware 
worm,  placed  in  water  of  80°  C.  Air  is  blown  in  at  the  bottom, 
and  the  feed  of  nitric  acid  is  so  regulated  that  it  runs  out  at  the 
bottom  at  a  temperature  of  60^  C.  and  sufficiently  bleached.  It 
runs  through  a  second  worm  placed  in  cold  water,  and  can  then 
be  put  into  the  carboys.  The  nitrous  gases  escaping  at  the  top 
are  treated  in  the  usual  manner.  One  worm  can  purify  several 
tons  of  acid  per  diem.  The  same  process  may  also  serve  for 
treating  the  waste  acid  of  nitroglycerine  and  nitrobenzene  works ; 
in  this  case  air  heated  to  150°  C.  or  steam  is  blown  in  at  the 
bottom,  and  the  feed  of  acid  is  so  regulated  that  it  issues,  at  a  tem- 
perature of  140°  C,  as  comparatively  pure  sulphuric  acid. 

The  French  Government  gunpowder  works  have  employed  such 
worms  for  a  long  time  for  this  purpose.  An  ordinary  size  of  worm 
furnishes  2  cwt.  acid  per  hour,  with  less  than  0*3  per  cent.  N2O4 
and  practically  free  from  chlorine. 

The  Griesheim  process  does  away  with  the  necessity  of  bleaching 
the  nitric  acid,  as  it  is  produced  at  once  in  a  pure  state.  (A 
similar  result  is  aimed  at  by  the  apparatus  of  Guttmann  in  its 
recent  form  and  by  that  of  Valentiner,  to  be  described  later  on.) 

The  Chemische  Fabrik  Griesheim  (Germ.  pat.  59,099)  places 
behind  the  retort  a  reflux-cooler,  consisting  of  aRohrmann  stone- 
ware worm  contained  in  a  water-tub  kept  at  about  60°  C.  by  the 
heat  of  the  operation  itself.  The  acid  vapours  ascending  in  this 
cooler  are  partially  condensed  there ;  in  consequence  of  the  high 
temperature  the  lower  nitrogen  oxides  (together  with  the  chlorine) 
escape  in  the  state  of  vapour,  and  are  condensed  by  air  and  water 
in  a  "  Lunge  tower  '^  (plate-column)  to  weak  nitric  acid.  The  acid 
condensing  in  the  worm  flows  into  a  receiver,  kept  at  80°  C,  and 
is  therefore  perfectly  pure,  no  '*  bleaching  '^  being  required.  Air 
is  advantageously  introduced  into  the  receiver. 

This  system  is  illustrated  in  fig.  32.  We  notice  that  the 
receiver,  into  which  the  acid  flows  back  from  the  reflux-cooler,  is 
provided  with  a  glass  pipe  reaching  down  to  the  bottom,  through 
which  air  is  introduced,  which  aids  in  driving  ofi^  N3O4  and 
chlorine,  &c.,  and  also  somewhat  cools  the  acid.  The  strong  and 
pure  acid  from  this  receiver  is  from  time  to  time  run  off  into 
a  lower  receiver^  not  shown  in  the  figure,  where  it  cools  down 

VOL.  I.  K 


180  BAW  MATERIALS  OP  MANUFACTURE. 

sufficiently  for  being  withdrawn  into  carboya;  the  vapours  rising 
here  are  also  paBse<l  into  the  condensing-apparatus.  The  vapours 
issuing  from  the  top  of  the  worm  are  passed  through  a  few 
receivers  and  ultimately  iiito  the  plate-tower. 

In  practice  the  temperatiiVe  of  the  water  in  the  worm-tub  rises 
to  40°  or  50°  C.  in  the  case  of  slow  distillation,  and  60°  in  that  of 
rapid  distillation ;  there  is  always  some  fresh  water  run  iu,  care 
being  taken  not  to  cool  too  much. 

Tip.  n-J. 


This  apparatus  is  generally  combined  with  the  retorts  shown  on 
p.  107.  Each  chaise  of  400  kil.  nitrate  of  soda  (undried)  with 
450  kil.  sulphuric  acid  (95  per  cent.  HJSO4)  yields  first  two  litres 
of  impure  acid,  which  is  run  off  separately,  then  240  or  250  kit. 
acid  of  48°  Baume  =91  per  cent.  HNOa,  with  less  than  1  per 
cent.  NjOj,  usually  only  0"5  per  cent.  N^Oi,  and  no  chlorine  at 
all ;  then  60  or  65  kil.  acid  of  43°  to  44°  Baume,  perfectly  clear, 
aud  8  kils.  of  25°  to  30°  Baume  impure  acid  from  the  tower. 


guttmann's  condensing-affaratus.  131 

When  working  with  dried  nitrate^  the  first  250  kil.  of  acid  show 
49°B.=93  per  cent.  NHO3.  The  weaker  acid  (42°  B.)  can  be 
put  back  into  the  retort  and  recovered  as  strong  acid  in  the  next 
distillation.     The  nitre-cake  tests  aboat  30  per  cent.  '^  iree'^  SO]. 

The  Griesheim  system  has  been  working  for  many  yeaiB  at  a 
number  of  factories  with  perfect  satisfaction. 

The  same  principle  as  that  followed  in  the  Griesheim  condensing- 
plant  is  the  foundation  of  the  patents  of  Skoglund  (G.  P.  104^357 
and  105,704),  where  first  strong  acid  is  condensed  in  a  stoneware 
apparatus  and  the  weak,  impure  acid  in  a  lead  condenser  [?]. 
Piatt  (E.  P.  9133,  1901)  describes  an  improvement  of  the  same 
system. 

G.  Guttmann  (E.  P.  8915,  1890)  has  constructed  a  nitric-acid 
condensing-apparatus  on  the  principle  of  building  it  up  entirely 
of  perpendicular  pipes^  so  arranged  that  the  gases  travel  upwards 
and  downwards  and  the  acid  is  run  off  at  the  bottom,  as  it 
is  liquefied,  by  means  of  hydraulically  sealed  branch-pipes,  into 
a  common  reservoir.  The  pipes  are  8  feet  long  and  have  thin 
walls  {^  inch  thick)  ;  they  perform  the  condensation  incom- 
parably  better  than  ordinary  receivers,  even  when  merely  cooled 
by  air,  but  in  this  case  there  must  be  a  considerable  number  of 
such  8-feet  pipes,  say  15  or  20,  to  finish  off  a  charge  of  12  cwt. 
in  a  shift  of  10  or  11  hours.  The  last  pipe  is  connected  with  a 
*'  Lunge  tower  "  (plate-tower,  comp.  p.  125),  fed  with  water,  in 
order  to  retain  the  uncoiidensed  oxides,  in  the  shape  of  weak 
nitric  acid,  amounting  to  about  5  to  7  per  cent,  of  the  total  acid. 
The  Guttmann  system  is  especially  suitable  for  the  manufacture 
of  strong  nitric  acid,  of  course  by  means  of  dried  nitrate  and  strong 
sulphuric  acid. 

The  former  shape  of  Guttmann^s  system  is  shown  in  our  second 
edition,  pp.  890  and  891.  Many  plants  have  been  erected  on  that 
principle  with  great  success.  Later  on,  Guttmann  improved  his 
system  in  various  ways.  He  fixed  an  injector,  fed  with  com- 
pressed air,  immediately  behind  the  exit-tube  from  the  still,  where 
the  whole  of  the  vapours  are  still  uncondensed.  They  are  thus 
rapidly  drawn  away  from  the  retort  and  mixed  with  hot  air.  It  is 
contended  that  in  this  way  nitric  acid  with  not  more  than  0*7  per 
cent.  NcOj  and  at  a  concentration  of  97  per  cent,  can  be  made 
during  the  whole  of  the  process.  The  acid  is  as  nearly  colouriess 
as  can  be  desired.     [If  all  the  acid  is  97  per  cent.,  what  becomes 

k2 


132  RAW  MATERIALS  OF  MANUFACTURE. 

of  the  water  contained  in  the  sulphuric  acid^  unless  this  is  of 
equal  strength?     Comp.  also  Volney^  p.  121.] 

Another  improvement  of  Guttmann's  is  the  substitution  of  water- 
cooling  for  air-coolings  which  admits  of  a  considerable  saving  in 
pipes.  There  are  only  six  of  these,  one  exposed  to  the  air  and  the 
other  five  contained  in  a  water-tank^  through  the  bottom  of  which 
they  pass  water-tight  by  means  of  rubber  rings.  Guttmann  states 
that  here  all  the  acid  can  be  obtained  with  96  per  cent.  HNOs, 
and  slightly  over  1  per  cent.  N^O^ ;  this  increase  of  NjO^  is  caused 
by  the  greater  rapidity  of  the  cooling,  which  does  not  leave  so  much 
time  for  the  oxidation  of  NOg  by  the  air.  Otherwise  the  con- 
densing battery  is  similar  to  the  first,  inclusive  of  the  plate-tower. 

A  recent  patent  of  Guttmann's  is  E.  P.  18,189,  1897.  In  his 
English  patent  No.  13,694,  of  1901,  he  describes  an  arrangement 
for  condensing  nitric  acid  at  a  comparatively  high  temperature, 
when  it  is  less  liable  to  absorb  nitrous  gases. 

Figs.  33,  34,  35  show  a  Guttmann  plant  with  the  most  recent 
improvements,  as  designed  by  H.  H.  Niedenfuhr  and  supplied  by 
the  Krauschwitz  pottery.  The  drawings  are  to  scale  and  explain 
themselves.  Each  retort,  with  its  set  of  cooling-pipes  &c.,  decom- 
poses from  12  to  14  cwt.  of  nitrate  of  soda  in  a  working  day  of 
12  or  14  hours ;  with  somewhat  larger  retorts,  the  cooling.battery 
can  be  driven  up  to  20  cwt.  nitrate  per  day. 

Hart  (Engl.  pat.  17,289,  1894)  uses  an  apparatus  consisting  of 
a  series  of  superposed  glass  tubes,  slightly  inclined  to  the  hori. 
zontal,  which  starts  from  an  upright  stand-pipe  and  ends  in  another 
upright  pipe.  The  pipes  are  cooled  by  squirting  water  upon  them 
or  otherwise.  The  vapours  pass  simultaneously  through  all  the 
inclined  pipes.  As  the  water  squirted  on  to  the  glass  tubes 
evaporates,  its  cooling-action  is  very  strong.  Hart  asserts  that 
by  his  method  the  distillation  is  efiected  in  half  the  usual  time, 
with  very  little  fuel  and  slight  formation  of  N2O4.  There  are 
15  tubes  to  each  condenser,  about  an  inch  wide  and  six  feet  long^ 
for  a  retort  working  off  1000  lbs.  of  sodium  nitrate  in  8  hours. 
This  system  has  been  introduced  with  great  success  in  a  number 
of  American  and  English  works. 

Dieterle  and  Rohrmann  (G.  P.  85,240)  promote  the  evolution 
of  gases  in  the  nitric-acid  retort  by  the  introduction  of  some  inert 
gas,  which  must  certainly  be  au  obstacle  to  condensation.  Their 
object  is  more  rationally  attained  by  the  application  of  a  vacuum,  as 
proposed  by  Valentiuer  (see  also  Guttmann's  injectors,  p.  131). 


GUTTMANN  8  C0NDENSIX6-APPARATUS. 


133 


134 


Raw  materials  of  xianufacture. 


Valentiner  (Eng.  pat.  610, 1892,  and  19,192,  1895;  figs.  36  and 
37)  manufactures  nitric  acid  in  a  vacuum.  The  retort  in  which 
the  sodium  nitrate  is  decomposed  with  sulphuric  acid  is  connected 
with  a  cooling-worm,  and  this  is  connected  with  a  receiver,  from 
which,  with  the  interposition  of  a  Woulfe^s  bottle,  the  air  is 
aspirated  by  an  air-pump.  In  this  way  the  most  highly  con. 
centrated  pure  nitric  acid  can  be  obtained.  Perfectly  pure  nitric 
monohydrate,  produced  by  this  process,  is  now  found  in  commerce. 

Fig.  :34. 


Section  A-B. 


[Before  Valentiner  (whose  patent  dates  Sept.  8, 1891),  I  had  shown 
that  this  can  be  done  by  distilling  in  vacuo,  Zsch.  f.  angew.  Ch. 
1891,  p.  167,  published  March  15,  1891.] 

Hallwell  (Chem.  Zeit.  1895,  p.  118)  gives  some  details  of  the 
practical  application  of  Valentiner^s  process.  The  cast-iron  retort 
holds  16  cwt.  of  nitrate  of  soda  and  is  nearly  globular  in  form 
(it  is  shown  in  fig.  18,  p.  112).     It  is  not  heated  directly  by  the 


JjtTHQS  :     ^ 


valestixer's  system  for  nitric  acid. 


135 


CD 
CO 


SI£ 


Ix 


tu 


136  RAW  MATERIALS  OF  MANUFACTURE. 

flame^  but  is  surrounded  by  hot  gases.  At  the  top  there  are  necks 
for  the  acid  vapour,  for  charging  the  nitrate,  for  letting  in  air,  for  a 
thermometer  (in  a  pipe  closed  at  the  bottom),  and  for  introducing 
sulphuric  acid.  The  8-inch  wide  neck  which  carries  away  the 
acid  vapours  is  continued  into  a  glass  cylinder,  through  which 
the  inside  can  be  observed,  then  into  an  earthenware  bend,  con- 
nected  with  an  earthenware  worm  of  2.J-inch  bore  and  50  square 
feet  cooling-surface^  ending  in  a  three-way  cock.  Then  follow 
two  earthenware  receivers  of  60  gallons  capacity  each,  with  outlet- 
cocks  at  the  bottom,  a  receiver  of  18  gallons,  a  smaller  earthenware 
worm  (2^ -inch  bore  and  25  square  feet  cooling-surface),  a  60-gallon 
receiver  and  five  18-gallon  receivers,  all  of  which  are  provided  with 
outlet-cocks  at  the  bottom  and  air-cocks  at  the  top.  The  second 
small  receiver  behind  the  second  worm  is  charged  with  water,  the 
fourth  with  sulphuric  acid;  in  these  the  inlet-pipes  are  deep  enough 
to  dip  into  the  liquid.  The  last  receiver  is  connected  with  the 
air-pump.  The  two  large  receivers  behind  the  first  worm  take 
most  of  the  condensed  acid  and  are  alternately  put  into  series  by 
means  of  the  three-way  cock ;  thus  the  acid  can  be  drawn  off 
without  interrupting  the  work.  The  joints  are  all  made  by  mclans 
of  flanges  provided  with  rills  and  a  cement  made  of  silicate  of  soda 
and  asbestos  (comp.  p.  120).  The  vacuum  helps  to  keep  the  joints 
tight,  and  they  stand  very  M'ell. 

When  the  nitrate  has  been  charged,  all  necks  are  closed,  the 
air-pump  is  started^  and  by  opening  a  tap  in  the  connecting-pipe 
sulphuric  acid  is  drawn  in  from  a  store-tank.  Much  gas  is  given 
off  at  once ;  first  of  all  nitrosvl  chloride,  which  mostlv  travels  as 
far  as  the  receivers  behind  the  second  worm.  When  the  vacuum 
has  gone  up  to  500  millimetres  of  mercury,  the  fire  is  started  and 
the  thermometer  rises  to  80°,  which  tem|)erature  is  kept  up  during 
the  principal  phase.  The  vacuum  is  kept  at  650  or  670  millim. 
In  the  end  the  temperature  must  be  raised  to  120^^  or  at  most 
130°.  When  no  more  acid  distils  over,  the  air-pump  is  stopped, 
and  the  temperature  is  raised  to  170°  or  175°,  in  order  to  render 
the  nitre-cake  more  liquid. 

Through  this  low  temperature  the  decomposition  of  the  nitric 
acid  and  the  reducing-action  of  the  iron  are  brought  to  a  minimum. 
Therefore  the  yield  is  almost  equal  to  theory,  and  that  mostly  in 
the  shape  of  strong  acid.  With  undried  nitre  and  sulphuric  acid 
of  142°  Tw.  the  yield,  according  to  Hallwell,  is  95*7  per  cent,  of 


valentiner's  process  for  nitric  acid.  137 

the  theoretical,  in  the  shape  of  acid  of  90J°Tw.  (.78  per  cent.  HNO3) , 
and  3*8  per  cent,  impure  acid  of  21^°  Tw.,  together  99*5  per  cent. 
With  undried  nitrate  and  sulphuric  acid  of  160°  Tw.  the  yield  is 
99  per  cent,  nitric  acid  of  93^°  Tw.  (81  per  cent.  HNOg),  and 
08  per  cent,  as  dilute  acid,  together  99*8  per  cent.  The  weak 
acid  is  left  in  the  receivers  till  it  has  risen  to  66°  Tw.  With 
dry  nitrate  and  sulphuric  acid  168°  Tw.,  real  nitric  monohydrate 
can  be  obtained.  The  usual  strength,  100°  Tw.,  contains  pnly 
O'OJ?  per  cent.  NgOg  and  no  chlorine  at  all,  against  0*95  to  192 
per  cent.  N2O8  in  the  ordinary  100°  acid. 

Hall  well  states  that  while  in  other  processes  charges  of  6  to 
8cwt.  nitrate  require  from  15  to  20  hours  to  be  worked  off,  here  a 
16  cwt.  charge  takes  only  7  or  8  hours,  and  two  charges  are  easily 
made  in  24  hours,  which  means  four  or  five  times  the  usual  quantity. 
The  consumption  of  coal  is  8  or  9  parts  for  firing  and  6  or  7  parts 
for  the  vacuum,  together  14  or  16  parts  to  103  nitrate,  against  32  to 
35  parts  in  the  old  process.  There  is  also  no  steam  or  compressed 
air  needed  for  refining  the  acid.  The  durability  of  the  retorts  is 
greater  than  in  the  old  process,  and  the  earthenware  vessels  do  not 
suffer  at  all.  The  temperature  of  the  first  receivers  is  only  35°  to 
42°,  the  back  receivers  are  cold ;  they  never  crack,  nor  do  they 
collapse  through  the  atmospheric  pressure,  as  they  are  made  rather 
thick- walled  and  nearly  globular  in  shape.  Any  cracks  in  the 
pipes  or  bad  places  in  the  receivers  are  cured  by  putting  on  asbestos 
paper  soaked  in  silicate  of  soda  solution.  If  too  much  frothing 
is  observed  through  the  glass  cylinder,  this  is  at  once  remedied 
by  opening  the  air-cock.  The  total  length  of  the  apparatus  is 
only  40  feet,  the  width  of  the  furnace  17  feet,  that  of  the  con- 
densing.plant  5  feet.  Large  apparatus  holding  from  50  to  60  cwt. 
is  to  be  constructed.  The  sanitary  drawbacks  of  the  ordinary 
nitric  acid  manufacture  are  absent  when  working  with  a  vacuum. 

The  action  of  the  acid  gases  escaping  from  the  condensation 
(especially  NOCl)  upon  the  air-pump  must  be  prevented  by 
charging  the  last  receiver  with  milk  of  lime,  which  should,  of 
course,  be  renewed  from  time  to  time. 

Further  communications  on  the  Valentiner  process  have  been 
made  by  Franke  (Chem.  Zeit.  1897,  p.  511).  For  each  ton  of 
nitrate  decomposed  there  should  be  about  87  cubic  feet  condensing- 
space.  The  retorts  should  bs  entirely  surrounded  by  the  fire,  or 
their  upper  part  and  the  branch-pipe  should  be  protected  by  an 


138  HAW  MATERIALS  OF  MANUFACTURE. 

acid-proof  liDing.  With  sufficient  condensing-space  and  good 
cooling,  and  if  the  formation  of  NoOj  is  prevented,  the  yield  should 
be  almost  the  theoretical,  since  only  part  of  the  chlorides  can 
escape.  The  nitre-cake  is  free  from  nitrogen  compounds,  and  the 
first  receiver,  which  is  filled  with  water,  is  not  changed  even  after 
several  operations.  The  temperature  during  the  distillation  itself 
is  hardly  100°  C,  but  later  on  it  must  rise  to  175°,  to  make  the 
nitre-cake  sufficiently  liquid.  The  hot  vapours  then  formed  may 
decompose  some  of  the  condensed  acid,  unless  they  are  very  well 
cooled  immediately  behind  the  retort.  Theoretically  1000  kil. 
96  per  cent,  nitrate  of  soda,  with  2  per  cent,  water,  treated  with 
1000  kil.  94  per  cent,  sulphuric  acid,  should  furnish  796'5  kil. 
nitric  acid  of  spec.  grav.  1-486  (89"3  per  cent.  HNOa)  ;  from  1000 
kil.  96  per  cent,  nitrate,  previously  dried,  771*5  kil.  nitric  acid 
spec.  grav.  1*497  (92*2  per  cent.  HNO3)  should  be  obtained,  and 
practically  the  yield  need  not  be  much  less.  But  with  con- 
centrated acid  there  is  much  frothing,  through  the  production  of 
N2O4,  because  the  acid  does  not  at  once  penetrate  through  the 
nitrate;  this  is  avoided  by  employing  more  sulphuric  acid,  or 
by  introducing  liquid  nitric  acid  into  the  retort.  Valentiiier 
has  recently  recommended  the  preparation  of  stronger  nitric  acid 
by  redistilling  the  weak  acid  in  the  vacuum  with  concentrated 
sulphuric  acid ;  but  this  double  distillation  costs  decidedly  more 
acid,  coals,  and  wages  in  comparison  with  the  direct  distillation. 
Comp.  also  the  same  author  in  Zsch.  angew.  Ch.  1899,  p.  269. 
Bergmann  (ibid.  1900,  p.  1003)  also  re^xirts  favourably  on  this 
process,  but  finds  it  necessary  to  pass  the  gases  through  milk  of 
lime  before  they  reach  the  pump,  in  order  to  retain  the  nitrosyl 
chloride.  He  consumes  5  cwt.  coals  for  a  charge  of  16  cwt. 
nitrate. 

The  manufacture  of  nitric  acid  bv  means  of  a  vacuum  has  also 
been  patented  by  Dreyfus  (E.  P.  13,826,  1895),  who  mentions  a 
temperature  of  170°-190'^. 

In  spite  of  the  disadvantage  that  a  double  distillation  is  required 
in  order  to  obtain  very  strong  nitric  acid,  the  Valentiner  system 
has  been  introduced  in  many  factories.  Owing  to  the  low  tempe- 
rature, the  material  of  the  apparatus  is  more  durable,  the  product 
is  pure,  and  the  yield  almost  equal  to  theory.  In  the  latter 
respect,  as  Guttmann  remarks,  the  results  in  all  well-conducted 
factories  are  about  the  same.  100  parts  real  NaMOs  ought  to 
yield  74*13  parts  real  HNO3;  but  of  course  any  NO2  contained  in 


VARIOUS  SYSTEMS  FOR  NITRIC  ACID.  139 

the  acid  must  be  deducted  from  tbis^  and  at  least  5  per  cent,  is 
necessarily  obtained  as  weak  acid  (tower  acid) . 

The  Valentiuer  system  has  been  represented  as  decidedly 
inferior  to  Guttmann's  by  some  observations  made  in  a  scientific 
publication  in  1901,  but  has  been  quite  as  strongly  defended  from 
the  other  side.  We  can  here  only  give  the  respective  references  : 
Zsch.  fur  angew.  Chemie,  1901,  pp.  413,  495,  571,  658,  and  731. 

Compare  also  Volney's  results  on  the  smaller  scale  when  dis- 
tilling in  a  vacuum,  p.  121, 

The  principal  choice  of  a  condensing  system  nowadays  seems 
to  lie  between  the  systems  of  Griesheim,  Guttmann,  and  Valen- 
tiner.  Their  results  (allowance  being  made  for  the  exaggerations 
of  interested  parties)  seem  to  be  so  nearly  alike,  that  it  becomes 
very  much  a  question  of  first  cost  of  the  apparatus,  which  we  can- 
not treat  of  here,  since  patent  licences  play  a  considerable  part  in 
.this  case. 

Concentration  of  Nitric  Acid, —  (Comp.  Valentiner's  process, 
p.  138).  Colin  (French  pat.  211,045)  prepares  fuming  nitric  acid 
of  spec.  grav.  1*5  by  distilling  nitric  acid  of  1*4  with  sulphuric  acid 
of  1*84  in  enamelled  cast-iron  retorts,  and  employing  a  glass  three- 
way  cock  for  separating  the  distillates.  [This  apparatus  docs  not 
appear  to  be  practicable.] 

Erouard  (Germ.  pat.  62,714)  also  concentrates  dilute  nitric 
acid,  or  waste  acids  from  nitrating  processes,  by  adding  strong 
sulphuric  acid,  or  a  solution  of  CaClj  or  MgCl2  [!],  and  distilling 
the  mixture  in  a  vessel  in  which  it  travels  in  a  zigzag  direction. 

H.  A.  Frasch  (Germ.  pat.  82,578)  prepares  highly  concentrated 
nitric  acid  by  passing  the  vapours  from  the  nitric-acid  retort 
through  a  tower  heated  above  the  boiling-point  of  the  acid,  in 
which  hot  concentrated  sulphuric  acid  is  descending,  or  in  >vhicli 
other  dehydrating  substances,  such  as  anhydrous  sulphate  of  soda 
or  burnt  pi aster-of -Paris,  act  upon  the  mixed  vapours. 

The  Verein  Chemischer  Fabriken  in  Mannheim  (G.  P.  85,042) 
places  between  the  still  and  the  condenser  a  dephlegmator,  from 
which  the  dilute  acid  condensed  there  runs  back  into  the  still. 
This  dephlegmator  is  kept  at  a  temperature  of  85*^  C,  so  that  the 
concentrated  acid  can  pass  on. 

The  fixed  residue  from  the  manufacture  of  nitric  acid  (called 
''nitre-cake/'  or,  in  the  workmen's  language,  '^ sally  nixon,''  a 
corruption  of  "  sal  enixum  ")  is  practically  a  mixture  of  neutral 
arid  acid  sodium  sulphate.     It  generally  contains  from  25  to  30 


140  RAW  MATERIALS  OF  MANUFACT^JRE. 

per  cent,  '^free  aeid^'  (i,  e.  bisulphate  acid)  calculated  as  SOs,  J^nd 
only  traces  of  nitrate.  We  shall  treat  of  it  in  detail  in  Vol.  II., 
and  here  only  remark  that  most  of  it  is  worked  up  with  com- 
mon salt  into  ordinary  salt-cake  and  hydrochloric  acid ;  part  of 
it  is  also  used  up  directly  for  glass-making,  but  no  doubt  not  to 
great  advantage.  Kirkman  (£.  P.  5703,  1889)  employs  it  as  an 
absorbent  for  ammonia,  in  which  case  a  profitable  utilization  of 
NagSOj  will  be  very  difficult. 

Giles,  Roberts,  and  Boake  (Engl.  pat.  11,979,  1890)  convert 
ordinary  nitre-cake  by  addition  of  sulphuric  acid  into  '^penta- 
sulphate,''  Na^O,  SSOg,  SHgO,  which  can  be  packed  in  iron 
drums  [?]  or  ordinary  casks  and  usefully  employed  for  certain 
purposes  (comp.  Uebel's  *^  polysulphate,*'  p.  117). 

The  cost  of  manufacturing  nitric  acid  at  a  Continental  factory 
(some  years  ago)  was  as  follows,  and  can  be  easily  reduced  to 
current  English  prices : — 

1.  For  acid  of  3&^  Baume  (=sp.  gr.  l-334or  SOper  cent.  NO3H). 

£    s.     d. 
4  charges  of  4  cwt.  each  nitrate  of  soda,  at  16^....     12  16     O 

16  cwt.  sulphuric  acid  144^  Tw.,  at  3^ 2     8    O 

10  cwt.  lignite  (very  inferior  quality),  at  9rf 0     7     6 

2  men,  at  3^ * 0     6     0 

Interest  and  writing  off  the  plant    0     8     0 

General  expenses 0     16 

Packages,  &c 1  16     0 

Yield  :  21  cwt.  acid  at  36^  Baume 19     3     0 

Cost  of  1  cwt.  acid  at  36°  Baume 0  18     3 

2.  For  acid  ofoO""  Baume  {^sp.  gr.  1-532=93  per  cent.  NOgH). 

£    s.    d. 
6  cwt.  of  nitrate  of  soda  (dry),  at  19^ 5  14     0 

6  cwt.  sulphuric  acid  168°  Tw.,  at  5^.  6r/ 113  0 

6  cwt.  lignite,  at  9rf. 0     4  6 

Wages — 2  men 0     6  0 

Sundries  and  general  expenses 0  12  0 

Smallstores  0  11  0 

Yield :  3  cwt.  2  qrs.  10  lb.  acid 9     0     6 

Deduct  value  of  5  cwt.  nitre-cake    0  15     0 

8     5     6 
Cost  of  1  cwt.  of  acid  50'' Baume    2     6    0 


WASTE  ACIDS  FROM  NITRATING  PROCESSES.  141 

The  cost  price  at  a  French  works  is  stated  by  Sorel,  for  100  kil. 
of  acid  of  36°  Baume^  made  in  large  cylinders  : — 

francs. 

Supervision  (^  of  the  foreman^s  wages) 0*59 

Wages  of  workmen 113 

76-33  kil.  nitre  at  27  frs 20*69 

83-95  kil.  acid  60°  B.  at  2-25  frs 1*89 

36  kil.  coal  at  2-15  frs 077 

Lighting    0*27 

Kepairs 2*55 

General  expenses 0*65 


28-54 
Deduct  88-54  kil.  nitre-cake  at  2*25  frs.    ...       1-99 


Cost  of  100  kil.  nitric  acid  36°  B 26-55 

Utilization  of  waste  acids  from  nitrating  processes. — ^Enormous 
quantities  of  nitric  acid,  always  mixed  with  strong  sulphuric  acid, 
are  consumed  in  the  manufacture  of  nitrobenzene,  nitrotoluene, 
and  other  aromatic  compounds  required  in  the  manufacture  of 
colouring-matters,  as  well  as  in  that  of  nitroglycerine,  nitrocellulose, 
and  other  substances  serving  as  explosives.  The  waste  acids  formed 
in  the  first  class  of  processes  contain  but  little  nitric  acid,  generally 
only  about  1  per  cent.,  with  about  \  per  cent,  of  nitrobenzene  &c. 
They  may  be  used  directly  in  the  Glover  tower,  where  the  nitric 
acid  is  utilized  as  well  as  the  sulphuric  acid.  Special  processes  for 
denitrating  these  acids  are  rarely  employed,  least  of  all  with  a  view 
of  recovering  the  nitric  acid,  which  does  not  pay  for  the  trouble  and 
expense. 

The  case  is  entirely  different  with  the  waste  acids  from  the 
manufacture  of  explosives.  These  contain  much  more  nitric  acid 
than  those  from  the  manufacture  of  nitrobenzene.  Nitroglycerine 
waste  acid  contains  about  10  per  cent.  HNO3,  70  H3SO4,  20  HgO; 
gun-cotton  acid  11  or  12  HNO3,  80  H2SO4,  8  HjO.  These  acids, 
if  it  is  not  possible  to  consume  them  in  a  Glover  tower,  can  be 
used  for  replacing  part  of  the  sulphuric  acid  in  the  nitric-acid 
manufacture;  or  else  they  are  denitrated  by  steam,  producing 
dilute  sulphuric  acid  (which  is  concentrated  by  evaporation  and 
used  over  again)  and  nitric  acid,  together  with  lower  nitrogen 


142  RAW  MATERIALS  OF  MANUFACTUREt 

oxides.  By  passing  the  vapours  mixed  with  air  through  some 
receivers  and  then  through  a ''  Lunge  tower/'  the  nitrogen  oxides 
are  also  converted  into  nitric  acid^  the  total  being  recovered  as 
nitric  acid  of  70**  or  even  80°  Tw.  (comp.  pp.  125  &  127). 

A  detailed  description  of  the  denitrating  process  is  found  in 
O.  Guttmann^s  'Manufacture  of  Explosives'  (London^  1895), 
vol.  ii.  p.  177. 

The  denitration  is  altogether  similar  in  this  case  to  the  process 
to  be  described  in  Chapter  VI.  in  connection  with  the  recovery  of 
nitre  in  the  lead-chamber  process.  The  best  kind  of  apparatus  is 
a  column  of  Volvic  lava^  made  in  one  piece  and  packed  with  bits 
of  flint  or  quartz.  Steam  is  injected  to  such  an  extent  that  the 
outflowing  denitrated  sulphuric  acid  has  a  specific  gravity  of  about 
1'635;  it  is  often  strongly  coloured.  The  vapours  are  passed, 
together  with  air,  injected  or  aspirated  by  suction,  through  a 
number  of  receivers,  say  6  or  8,  or  else  a  small  Guttmann  battery, 
and  then  into  a  Lunge  tower  fed  with  a  very  thin  stream  of  water, 
followed  again  by  a  few  receivers. 

"Where  very  large  quantities  of  nitrous  vapours  have  to  be  re- 
generated, whether  it  be  from  waste  acids  of  the  just-mentioned 
kind  or  from  other  chemical  processes,  it  is  best  to  combine  several 
plate-towers,  one  of  which  may  be  placed  above  the  others  so  as 
to  feed  them  with  the  weak  acid  produced  therein.  Thus  all 
the  recovered  nitric  acid  can  be  brought  up  to  spec.  grav.  1'38. 
The  Krauschwitzer  Thonwaarenfabrik,  Muskau  (Silesia),  furnishes 
this  kind  of  plant.  A  very  complete  apparatus  for  this  purpose 
has  been  arranged  by  Niedenfuhr,  as  described  and  illustrated 
supra^  p.  127. 

Where  sulphuric  anhydride  is  made,  these  waste  acids  can  b^ 
brought  up  to  strength  by  means  of  SO3  and  used  over  again. 

Various  Processes  for  the  Manvfacture  of  Nitric  Add. 

Glock  (G.  P.  110,254)  heats  nitrate  in  a  pan  provided  with 
stirring-gear  to  120°-150°  and  runs  in  the  equivalent  quantity  of 
sulphuric  acid,  previously  heated  to  100^-130°,  in  a  thin  jet.  The 
end  of  the  decomposition  is  facilitated  by  steam  or  a  thin  jet  of 
water.  At  last  air  is  blown  through,  whereupon  the  solid,  pul- 
verulent neutral  sodium  sulphate  is  ladled  out.     Or  else  the  nitrate 


VAIIIOUS  PROCESSES  FOR  NITRIC  ACID.  143 

is  from  the  first  heated  to  250°  C.     [This  process  looks  extremely 
impracticable.] 

Manufacture  of  Nitric  Acid  ivithout  Sulphuric  Acid, — Campbell 
.&  Walker  (E.  P.  9782,  1894)  grind  nitre-cake  with  nitrate  of  soda 
and  charge  the  mixture  into  retorts  provided  with  a  mechanical 
agitator. 

Garroway  (E.  P.  6777,  1899;  Journ.  Soc.  Chem.  Ind.  1901^ 
p.  1191)  mixes  ordinary  acid  uitre-cake  with  sodium  nitrate,  heats 
the  mixture  in  a  retort,  and  blows  a  spray  of  weak  nitric  acid 
by  means  of  compressed  air  over  the  mixture.  The  nitrogen 
oxides^  mixed  with  steam  and  air,  are  regenerated  by  condensing-^ 
tubes  and  towers  into  nitric.acid  (see  pp.  125  &  127).  '  It  is  alleged 
that  ultimately  a  96-per-cent.  acid  can  be  produced  [?  this  cer- 
tainly cannot  be  done  by  any  ordinary  regenerating  process] .  The 
residue  is  neutral  salt-cake,  testing  9836  per  cent.  This  process 
is  stated  to  have  been  worked  for  three  years  at  Glasgow. 

Garroway  (E.  P.  2466,  1895)  also  prepares  nitric  acid  by  heat-^ 
ing  a  mixture  of  nitrate  of  soda  and  ferrous  sulphate  or  alum, 
obtaining  sulphate  of  soda  and  oxide  of  iron  or  alumina. 
He  also  patents  the  decomposition  of  sodium  nitrate  by  silica 
(E.  P.  2489,  1896). 

Very  interesting  are  the  processes  intended  for  decomposing 
nitrate  of  soda  in  such  manner  that,  besides  nitric  acid,  caustic 
soda  is  formed .  Theoretically  these  processes  are  enormously  supe- 
rior to  the  ordinary  process ;  there  is  no  waste  of  sulphuric  acid  and 
no  production  of  nitre-cake,  which  is  a  product  of  very  low  value, 
but  the  soda  is  brought  into  its  most  valuable  form,  as  caustic  or 
carbonate.  But  not  one  of  these  processes  has  come  into  regular  use. 
They  all  suffer  from  the  drawback  that  the  temperature  of  decom- 
position is  too  high,  which  necessitates  special  shapes  of  retorts 
and  great  wear  and  tear  of  these,  and  that  some  of  the  nitric  acid 
(often  a  very  considerable  proportion)  is  reduced  to  lower  oxides. 
These  can  be  reconverted  into  nitric  acid  by  means  of  intimate 
contact  with  air  or  water,  in  *'  plate-columns  ^'  (Lunge  towers)  or 
otherwise ;  but  this  cannot  be  done  without  a  perceptible  loss,  and 
it  never  leads  to  the  production  of  very  strong  nitric  acid,  such  as 
is  required  for  the  manufacture  of  explosives  and  many  other 
purposes. 

We  therefore  only  refer  to  the  enumeration  of  these  processes 


144  »AW  MATERIALS  OF  MANUFACTURE. 

in  vol.  iii.  (2nd  edition)  p.  254  et  seq.,  and  briefly  qaote  the  more 
recent  additions  to  the  subject. 

A  special  retort  for  the  Lunge  and  Lyte  process  (decomposition 
of  NaNOs  by  Fe20g)  has  been  constructed  and  patented  (G.  P. 
90^654).  It  consists  of  a  revolving  cylinder  placed  in  a  sloping 
position,  with  inner  projections  and  contrivances  for  feeding  and 
exhausting  without  stopping  the  process.  A  full  description  of 
the  whole  process  has  been  given  by  J.  L.  F.  Vogel  in  the  Eng.  & 
Min.  Journ.  1900,  p.  408, 

Main,  Stevenston,  and  McDonald  (E.  P.  23,819,  1895)  heat 
sodium  nitrate  with  manganese  oxides.  Garroway  (G.  P.  79,699) 
employs  lime  and  superheated  steam.  Vogt  (E.  P.  22,018, 1891) 
heats  with  lime,  ferric  or  manganese  oxides  in  a  current  of  super- 
heated steam  and  carbon  dioxide. 

Darling  and  Forrest  (E.  P.  5808, 1894)  propose  obtaining  nitric 
acid  by  the  electrolysis  of  fused  alkaline  nitrates,  together  with 
metallic  potassium  or  sodium.  Patent  no.  13,171,  1895,  extends 
this  process  to  the  production  of  nitrous  fumes  (together  with 
sodium  oxide)  for  the  manufacture  of  sulphuric  acid. 

Siemens  and  Halske  (Oerm.  pat.  15,103)  suggest  utilizing 
the  well-known  formation  of  nitric  acid  by  the  direct  union  of 
oxygen  and  nitrogen  under  the  influence  of  the  silent  electrical 
discharge.  This  reaction,  which  under  ordinary  circumstances  is 
much  too  slow,  is  to  be  promoted  by  adding  ammonia-gas,  which 
causes  an  abundant  formation  and  separation  of  solid  ammonium 
nitrate. 

McDougall  also  employs  electricity  (E.  P.  4643,  1899). 

Crookes  (Elect.  World,  xxxiii.  p.  319;  Fischer's  Jahresb.  1898, 
p.  307)  shows  that  by  means  of  induction- sparks  74  grams  NaNO^ 
are  formed  by  one  kilowatt-hour,  or  1  ton  of  nitrate  by  14,000  kilo- 
watt-hours. This  would  at  present  cost  £25  with  the  best  steam- 
engines  and  dynamos  working  day  and  night,  and  is  therefore  out 
of  the  question,  but  it  might  be  done  by  very  cheap  water-power. 

W.  Ostwald  (B.  P.  no.  898,  1902)  improves  the  well-known 
formation  of  nitric  acid  from  ammonia,  under  the  influence  of 
platinum,  by  passing  that  gas,  with  more  or  less  its  volume  of 
atmospheric  air,  at  a  red-heat  over  smooth  platinum,  coated  with 
&  layer  of  spongy  or  black  platinum.  The  smooth  platinum  causes 
the  ammonia  to  be  burnt  into  nitric  acid,  with  practically  no  for- 
mation of  free  nitrogen.     The  finely  divided  platinum  accelerates 


TRANSPORTATION  AND  PUMPING  OP  NITRIC  ACID.  145 

both  reactions^  the  second  one  more  than  the  first.  By  moderate 
use  of  the  finely  divided  platinum  with  the  smooth  platinum,  the 
operation  can  be  so  performed  that  the  reaction  takes  place  rapidly, 
but  without  any  great  formation  of  free  nitrogen.  The  same 
effect  is  produced  by  iridium,  rhodium,  palladium,  the  peroxides 
of  lead  and  manganese,  the  oxides  of  silver,  copper,  iron 
chromium,  nickel,  and  cobalt. 

Statistics  concerning  nitric  acid  are  very  difficult  to  obtain.  For 
the  year  1 894  the  well-known  firm  Gehe  &  Co.,  of  Dresden,  reckon 
that  the  productign  of  nitric  acid  in  Germany  was  54,000  tons,  for 
which  40,000  tons  nitrate  of  soda  were  consumed.  In  the  United 
States,  in  190i),  27,890  tons  nitric  acid  of  various  strengths  were 
made  (U.S.  Census  Bulletin,  No.  210). 

Transportation  of  Nitric  Acid. — Nitric  acid  is  usually  sent  out  in 
glass  carboys  or  earthenware  jars.  Strong  acid,  when  kept  in 
tightly  closed  vessels,  may  give  off  a  dangerous  amount  of  vapours, 
especially  in  the  sunshine  or  under  similar  conditions.  Guttmann 
recommends  covering  the  carboys  loosely  with  earthenware  or 
glass  cups  fitting  over  the  necks,  also  making  the  straw  in  which 
the  carboys  are  packed  incombustible  by  dipping  it  in  a  solution 
of  zinc  chloride  or  nitre-cake  [which  will  very  quickly  corrode  it; 
neutral  sodium  sulphate  is  decidedly  preferable  I],  and  to  lime- 
wash  the  top  of  the  carboys  exposed  to  sunlight ;  also  to  store  the 
carboys  in  an  excavated  chamber,  where  a  breakage  will  not  cause 
much  damage,  21s  the  place  can  be  swamped  with  water.  Some- 
times fires  are  caused  by  nitric  acid  from  a  broken  carboy  inflam- 
ing the  straw  ;  in  which  case  the  poisonous  vapours  are  exceedingly 
dangerous  to  inhale  (comp.  Chap.  VI.) . 

Strong  nitric  acid  can  be  kept  and  treated  in  cast-iron  or 
wrought-iron  or  leaden  vessels,  but,  of  course,  any  dilution  caused 
by  the  moisture  of  air  or  otherwise  will  cause  a  violent  action. 
Aluminium  resists  nitric  acid  even  in  a  somewhat  more  dilute  state. 

Protection  against  accidents  caused  by  fumes  of  Nitric  and 
Nitrous  Acid.  —  In  the  sixth  Chapter  we  shall  treat  of  this 
subject  in  connection  with  Gay-Lussac  and  Glover  towers. 
I  will  here  only  allude  to  the  official  rules  published  by  the 
"  Berufsgenossenschaft  fiir  chemische  Industrie,''  Fischer's 
Jahresb.  L899,  p.  411,  and  the  report  oy  Duisberg,  Zsch.  {.  angew. 
Ch.  1897,  p.  492. 

Pumping  of  Nitric  Acid. — For  this  purpose  Paul  Kestner,  of 

VOL.  I. 


s 


RAW  MATERIALS  OF  UANSFAC^URE. 
Fig.  88. 


ANALYSIS  OF  NITRIC  ACID.  147 

Lille^  has  constructed  special  ''pulsometers^'  entirely  of  stoneware, 
one  form  of  which  is  shown  in  fig.  38 — exhibiting  the  cylinder  A, 
the  float  B,  the  air-valve  C^  and  the  delivery-pipe  D.  All 
flanges  are  made  tight  by  thin  sheet  asbestos^  the  faces  being  ground 
and  polished.  The  working  of  this  ^'  pulsometer  ^'  is  exactly  like 
that  of  the  cast-iron  pulsometer  described  in  Chap.  YI. 

Another  automatic  and  continuous  pulsometer  has  been  con- 
structed by  Plath^  and  is  sold  by  the  Vereinigte  Thonwaarenwerke, 
Charlottenburg  (fig.  39) .  It  also  consists  entirely  of  stoneware^ 
including  the  valves.  The  acid  enters  through  valve  a,  the  hollow 
ball  of  which  is  weighted  so  that  it  just  sinks  in  the  liquid^ 
and  is  therefore  easily  raised  by  the  inflowing  liquid.  When 
the  vessel  is  full^  the  acid  gets  up  to  the  other  valve,  the  ball  of 
which,  by  is  so  light  that  it  even  floats  upon  water.  It  is,  of  course, 
raised  by  the  acid  and  shuts  ofF  the  upper  air-way  c.  The  com- 
pressed air  now  enters  through  d  and  forces  the  acid  up  into  the 
rising-main  e,  and  thus  into  the  upper  store<tank.  As  soon  as  the 
vessel  is  empty,  the  ball  b  descends,  being  aided  by  the  short 
column  of  liquid  in  c.  The  compressed  air  cannot  now  enter  the 
vessel,  and,  as  there  is  now  no  counter  pressure,  the  ball  a  is  again 
raised  and  the  acid  flows  in  from  the  lower  tank,  the  air  escaping 
through  e.  This  action  continues  so  long  as  there  is  acid  in  the 
lower  store-tank  and  compressed  air  in  d.  Balls  a  and  b  are 
accurately  ground  as  usual  for  pumps  &c.  A  new  model  made  by 
the  same  firm  prevents  any  escape  of  compressed  air  during  the 
charging. 

Schartler  (Zsch.  angew.  Ch.  1901,  p.  729)  describes  apparatus 
constructed  by  O.  Guttmann  from  stoneware  for  the  purpose  of 
raising  acids,  viz.,  first  an  injector  for  working  with  steam  or  com- 
pressed air,  and,  secondly,  a  constantly  acting  acid-egg. 

Analysis  of  Nitric  Acid, — Nitric  acid  is  frequently  merely  tested 
by  the  hydrometer,  but  this  is  quite  illusory,  owing  to  the  influence 
of  the  nitrogen  peroxide  (p.  102).  When  tested  by  titration  it 
should  be  noticed  that  methyl-orange  is  destroyed  by  nitrous  acid ; 
but  this  can  be  overcome  by  adding  the  indicator  only  towards 
the  end  of  the  titration  (comp.  Chap.  III.,  where  the  indicators 
are  more  specially  treated).  When  titrating  with  caustic  soda, 
this  indicates  ail  acids :  HNOs,  NjO^  (which  reacts  =  HNOj  + 
HNO2),  HsS04,  &c.  At  least  a  permanganate  titration  should  be 
made  as  well,  in  order  to  estimate  Ns04« 

l2 


148  BAW  MATERIALS  OF  MANUFACTURE. 

The  impurities  contained  in  commercial  nitric  acid  are  as 
follows — chhrincy  sulphuric  acid,  fixed  residue,  iron :  all  found  and 
estimated  by  well-known  methods.  Nitrous  acid  or  nitrogen 
tetroxide  is  best  estimated  by  means  of  potassium  permanganate^ 
running  the  acid  from  a  burette  into  the  warm  diluted  solution  of 
permanganate,  as  will  be  described  in  the  next  Chapter.  (The 
influence  of  NO^H  on  the  specific  gravity  of  nitric  acid  has  been 
noticed  above.)  Iodine  is  recognized  by  boiling  1  c.c.  in  order  to 
remove  the  lower  nitrogen  oxides  and  to  oxidize  all  iodine  into 
iodic  acid,  diluting  with  5  c.c.  previously  boiled  water,  and  adding 
a  few  drops  of  a  solution  of  potassium  iodide  and  starch,  made 
with  water  free  from  air.  A  blue  colour  shows  the  presence  of 
iodine  in  the  original  acid,  according  to  the  reaction 

HI08  +  5KI  +  2H,0=  5KOH-f-6I. 

This  test,  according  to  Beckurts  (Fischer's  Jahresb,  1886,  p.  305), 
is  much  more  delicate  than  the  ordinary  one  of  reducing  the  iodate 
by  zinc  and  extracting  the  iodine  set  free  by  carbon  bisulphide ; 
but  Beckurts^s  test  would,  of  course^  lead  to  serious  errors  unless  a 
check  test  was  made  with  the  iodide  of  potassium  employed,  which 
might  itself  contain  some  iodate. 


SULPHUR  DIOXIDE.  149 


CHAPTER  III. 

THE  PROPEllTIES  ANI)  ANALYSIS  OF  THE  TECHNICALLY 
EMPLOYED  OXIDES  AND  ACIDS  OF  SULPHUR. 

Sulphur  Dioxide,  SOg.     (Sulphurous  Anhydride;  erroneously 

designated  Sulphurous  Acid.) 

Sulphur  dioxide  is  at  the  ordinary  temperature  and  pressure  a 
colourless  gas  of  suffocating  smell,  neither  supporting  combustion 
nor  combustible  itself  directly.  Even  when  greatly  diluted  with 
air  it  has  a  very  injurious  action  upon  plants  and  animals  (comp. 
further  on,  p.  154). 

Sulphur  dioxide  contains  50  per  cent,  by  weight  of  sulphur  and 
60  per  cent,  oxygen.  Its  specific  gravity  has  been  found  by  various 
observers =2*222  to  2*247  (air  =  l);  calculated  from  the  mole- 
cular weight  =2*216.  A  litre  of  the  gas  at  0°  C.  and  760  millim. 
pressure  weighs  2*8608  grams.  Its  coefiScient  of  dilatation  is  not 
exactly  equal  to  that  of  air,  but  rather  larger,  especially  at  lower 
temperatures,  namely  for  each  1°  C,  according  to  Amagat : — - 

Between    0°  and  10^ 0004233 

10°    „    20°     0004005 

At           50°     0*003846 

100°     0*003757 


if 
» 


150°     0*003718 

200°     0-003695 

250°     0*003685 


Its  specific  heat,  compared  with  its  equal  weight  of  water  is 
=0*1544;  compared  with  its  equal  weight  of  air =0*3414.  Mathias 
(Compt.  Rend.  cxix.p.404)  gives  it  as  between  —20°  and  + 130°  C: 

0*31 712  +  0*0003507/  +  0000006762  /«. 

The  density  of  saturated  vapour  of  SO2  (that  is,  in  contact  with 


150  PROPKRTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUK. 

liquid  SOj)  at  various  temperatures  (water  of  0°=1)  is,  according 
to  Cailletet  and  Matbias  (Compt.  Rend.  civ.  p.  1536) : — 


At    7-3  C. 

...  0-0()621 

„  16-5 

...  000858 

„  24-7 

...  00112 

„  37-5 

...  0-01fi9 

„  45-4 

.    0-0218 

„  58-2 

...  00310 

,.  78-7 

...  0-0464 

..  910 

...  00626 

At 

100-6  C. 

...  0-0786 

123 

...  0-1840 

130 

...  0-1607 

135 

..  0-1888 

144 

...  0-2195 

152-5 

...  0-3426 

154-9 

...  0-1017 

„    156     critical  point. 

The  heat  of  formation  of  one  molecule  of  SO3  (  =  64)  from 
ordinary  (rhombical)  sulphur  is  =71,080  cal.  (Thomsen),  or  69,260 
cal.  (Berthelot). 

By  moderate  cooling  sulphur  dioxide  can  be  condensed  to  a 
liquid,  even  without  application  of  pressure.  Liquid  SO2  is  a 
colourless  mobile  fluid,  of  about  the  same  refractive  power  as 
water,  boiling  at  —10°  C. ;  but  on  drawing  it  ofl^  at  the  ordinary 
temperature  from  a  reservoir  it  remains  liquid  for  some  time,  the 
evaporation  cooling  it  down  below  its  boiling-point.  Its  latent 
heat  at  0°  is  912,  at  10°  88-7,  at  20°  84-7,  at  30°  805. 

Its  vapour-tension  is  :  — 


At    0   C.  =  0'53  atmosphere  overpres?ure. 


10°       =  1-26 


„   20°       =  2-24  atmospheres  „ 

„  30-       =  3-51 
„  40°       =5-15 


}9  » 


The  specific  gravity  of  liquid  sulphur  dioxide  at  various  tem- 
peratures has  been  accurately  determined  by  A.  Lange  (Zsch. 
angew.  Ch.  1899,  p.  275)  as  follows : — 


Tempeniliire. 

Specific  pravity. 

Temperature. 

Specific  gi'Hvity. 

-20'^  C. 

1-4846 

+  20°  C. 

1-3831 

-10° 

1-4601 

25° 

1-3695 

-  5° 

1-4476 

30° 

1-3556 

0° 

1-4350 

35° 

1-3441 

+   5° 

1-4223 

40° 

1-3264 

10° 

1-4095 

50° 

1-2957 

15° 

1-3964 

60° 

1-2633 

SULPHUR  DIOXIDE.  151 

He  found  that  absolutely  anhydrous  liquid  SO3  does  not  aot 
upon  iron  up  to  100°  C.  Technical  sulphur  dioxide  has  a  slight 
action^  owing  to  the  presence  of  a  little  water.  The  temperature 
at  which  this  takes  place  increases  with  the  purity  of  the  acid, 
e.g.  it  is  70°  with  ^cid  containing  07  per  cent.  H2O.  Since  liquid 
SO2  cannot  dissolve  more  than  1  per  cent,  water,  even  the  most 
impure  product  cannot  act  on  the  iron  vessels  in  which  it  is 
transported  at  ordinary  temperatures.  The  mixture  of  ferrous 
sulphite  and  thiosulphate  formed  acts  as  a  protecting  crust.  lu 
ice-machines  where  SO2  is  the  active  agent,  and  where  the  tem- 
perature in  the  pumps  may  rise  considerably,  only  absolutely 
anhydrous  SOg  should  be  employed.  (Comp.,  on  this  subject,  also 
Zsch.  angew.  Ch.  1899,  pp.  300  &  595.) 

Sulphur  dioxide  is  produced  by  burning  brimstone,  and  by 
heating  (roasting)  many  metallic  sulphides,  in  the  presence  of  air; 
by  the  action  of  strong  mineral  acids,  both  on  its  own  salts,  the 
sulphites,  and  on  the  thiosulphates  and  all  polythiouic  acids ;  by 
heating  sulphuric  anhydride  with  sulphur,  or  by  heating  oil 
of  vitriol  with  brimstone,  coal,  organic  substances,  or  several 
metals;  by  strongly  heating  the  vapour  of  sulphuric  anhydride, 
or  sulphuric  acid,  with  simultaneous  formation  of  oxygen  and 
water  respectively ;  and  by  igniting  many  sulphates,  whereby  the 
sulphuric  anhydride  first  liberated  at  once  splits  up  into  sulphur 
dioxide  and  oxygen. 

Thus  sulphur  dioxide  is  produced  from  sulphuric  acid  or 
anhydride  in  many  ways  by  reductive  processes.  On  the  other 
hand,  the  sulphur  dioxide  passes  over,  even  more  easily,  into  sul- 
phuric acid  by  oxidation  processes;  and  it  is  accordingly  one  of  the 
most  frequent  and  potent  reducing  agents.  Under  certain  condi- 
tions, by  the  action  of  light,  of  the  electric  current,  or  of  a  very 
high  temperature  and  pressure  combined,  the  sulphur  dioxide  splits 
up  into  sulphur  and  sulphuric  anhydride.  In  the  presence  of  oxygen 
(for  instance,  that  of  atmospheric  air),  or  of  bodies  easily  parting 
with  their  oxygen  (such  as  the  higher  oxides  of  nitrogen,  of  man- 
ganese, of  lead),  sulphuric  acid  or  its  salts  are  formed.  A  very  im- 
portant reaction  is  that  between  SO2  and  sulphuretted  hydrogen, 
HjS.  When  completely  dry  the  two  gases  do  not  seem  to  act 
upon  each  other.  Even  in  the  presence  of  moisture  no  action 
takes  place  if  the  temperature  is  above  400° C.  (E.  Mulder).  At 
the  ordinary  temperature  water  and  sulphur  are  produced,  but  at 


152  PROPERTIES  OP  OXIDES  AND  ACIDS  OF  SULPHUR. 

the  same  time  also  pentathionie  acid^  according  to  the  equation 

5  SO2  +  5  HjS  =  S5O6H2  H-  4  H2O  +  5  S. 

This  action  occurs  simultaneously  with  the  simple  reaction, 

« 

S02  +  2H2S  =  2H30  +  S3, 

one  or  the  other  of  these  prevailing,  according  to  the  proportion  of 
the  two  gases  in  the  mixture. 

With  water,  sulphur  dioxide  does  not  form  sulphurous  acid  proper, 
SOgHg,  but  only,  under  certain  conditions,  a  solid  compound  with 
much  more  water  (9,  11,  or  15  HgO  to  SOj),  which  has  not  yet 
been  definitively  investigated.  Sulphur  dioxide  dissolves  pretty 
freely  in  water;  and  this  solution  behaves  in  every  way  as  if  it 
contained  the  real  acid  SO3H2 ;  but  constantly,  even  at  the  ordinary 
temperature,  the  dioxide  (SO2)  evaporates  from  it.  One  volume 
of  water  absorbs,  under  760  millim.  pressure  and  at  0°,  nearly  80 
volumes  SO2.  The  coefficient  of  absorption,  according  to  Bunsen 
and  Schonfeld,  at  temperatures  ranging  between  0°  and  20°,  is 

79-789 -2-6077/ +  0-029349/'; 

at  temperatures  between  21°  and  40°, 

75182-2-1716/  +  001903/\ 

The  saturated  acid  contains  at  0^68*861  volumes  of  gaseous  SO3, 
and  has  a  specific  gravity  of  1*06091 ;  at  10°  it  contains  51*383 
volumes  gaseous  SO2,  and  has  the  spec.  grav.  1*05472 ;  at  20°, 
36*206  volumes  SO2,  spec.  grav.  1*02386.  The  absorbed  gas  does 
not  escape  on  fieezing — and  on  boiling,  only  completely  after  a 
long  time.  Alcohol  absorbs  a  much  larger  volume  of  sulphur 
dioxide  (at  0°  and  0*76  metre  pressure,  338*62  volumes  SO2) . 

A  table,  not  very  much  deviating  from  the  above  statements,  of 
the  solubility  of  sulphur  dioxide  in  water  at  0*76  metre  mercurial 
pressure  at  difierent  temperatures,  is  given  in  Kopp  and  Will's 
*  Jahresberichte'  for  1861,  p.  54. 

Giles  and  Shearer  (J.  Soc.  Chem.  Ind.  1885,  p.  305)  give  the 
following  table  of  the  precentage  of  SO2  in  solutions  of  various 
specific  gravities :  — 


SOLUTIONS  OP  SDLFHCKOU8  ACID. 


153 


Temp. 


15°-50. 


t» 
I* 


Spec.  grav. 


Per  cent, 
SO., 


'a* 


10051 
10102 
10148 
10204 
10252 
10297 
1-0353 


099 
205 

2-87 
404 
4-99 
5-89 
701 


Temp. 

1 
Spec.  grav. 

Per  cent. 
SO,. 

1  15°-5C. 

10399 

808 

1 

ft 

1-0438 

8-68 

1 

1-0492 

9-80 

ft 

1^541 

10-75 

1205 

10597 

ii-a5 

11°0 

106(»8 

13-09 

1 

Another  table^  for  the  temperature  15°C.,  is  given  by  Scott 
(Pharm.  Soc.  J.  &  Trans,  xi.  p.  217)  : — 


Per  cent.  SOj. 

Specific  gravity. 

Per  cent  SOj. 

Specific  gniyity 

0-5 

1C028 

5-5 

10302 

1-0 

10056 

60 

1-0328 

1-5 

1-0085 

6-5 

1-0353 

2-0 

10113 

7-0 

10377 

2-5 

10141 

7-5 

10401 

3-0 

1-0168 

80 

1-0426 

3-5 

1-0194 

:         8-5 

10450 

4-0 

10221 

90 

10474 

4*5 

1-0248 

9-5 

1-0497 

50 

10275 

100 

10520 

Much  higher  are  the  figures  given  by  Pellet  (Journ.  Soc.  Chem. 

Ind.  1902,  p.  171)  :— 

P.  c.  SO2  in  100  H,0        12  3  4  5  6 

Sp.  gr.  at  15°-17°C.  10025    1-015    10225    1030   10375    1045. 

An  apparatus  for  the  production  of  aqueous  solutions  of  sul- 
phurous  acid  has  been  described  by  Holzhausel  (G.  P.  no.  49194). 

Solutions  of  sulphurous  acid  in  the  presence  of  oxygen  are 
partly  converted  into  sulphuric  acid. 

According  to  Scott,  when  sulphur  dioxide  (mixed  with  COj) 
is  to  be  made  by  the  process  mostly  used,  viz.  that  of  heating 
sulphuric  acid  with  charcoal,  it  is  best  to  employ  acid  of  74  per 
cent.  808=165°  Tw.  If  stronger  acid  be  used,  a  portion  of  it  is 
reduced  to  sulphur,  which  may  give  iron  sulphide  with  the  iron  of 
the  apparatus ;  with  weaker  acid  sulphuretted  hydrogen  is  formed. 
In  order  to  obtain  the  gas  as  pure  as  possible,  the  washing- water 
should  be  mixed  with  lead  sulphate  or  coarsely  powdered  charcoal. 


154  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

Sulphurous  acid  forms  two  series  of  salts  (sulphites) — ^saturated 
or  normal  ones,  SO3M2 ;  and  acid  ones,  SO^MH,  isomorphous  with 
the  corresponding  carhonates. 

Sulphur  dioxide  is  absorbed  by  anhydrous  barium  oxide  at  200°, 
better  at  230° ;  by  strontium  oxide  at  230°,  better  at  290°;  in  both 
cases  the  normal  sulphite  is  formed.  Calcium  oxide  forms  at  400^ 
a  basic  sulphite,  CagSsOie,  which  at  500°  splits  up  into  sulphate 
and  sulphide.  Magnesia  absorbs  SO2  very  slowly  at  326°^  and 
slightly  above  this  the  sulphate  is  formed  (Birnbaura  &  Wittich, 
Ber.  d.  d.  chem.  Ges.  1880,  p.  651). 

The  reactions  taking  place  between  sulphur  dioxide  and  the 
oxides  and  acids  of  nitrogen  will  be  described  in  a  later  part  of 
this  Chapter. 

Injurious  action  of  Sulphurous  Acid  {Sulphur  Dioxide). — The 
quantity  of  SO2  which  may  be  present  in  the  air  without  being 
injurious  to  health  has  been  stated  by  Hirt  (^Gewerbekrankheiten/ 
p.  15)  =1  to  3  per  cent.  This  is  an  obvious  error.  Ogata  (Archiv 
f.  Hygiene,  1884,  p.  223)  found  that  0'04}  per  cent.  SO2  causes 
difficulty  of  breathiDg  after  a  few  hours ;  he  could  not  take  a  single 
full  breath  in  air  containing  0*05  per  cent.  SO2.  It  is  an  acute 
blood-poison. 

Lehmann  (Zsch.  f.  angew.  Ch.  1893,  p.  612)  shows  that  persons 
not  habituated  to  sulphurous  acid  are  very  little  affected  by 
0*012  per  mille,  but  perceptibly  so  by  001 5  per  mille  SO2.  The 
presence  of  0*030  per  mille  after  a  few  minutes  causes  strong 
irritation  of  the  nasal  membranes^  sneezings  and  slight  coughing, 
which  symptoms  decrease  after  10  minutes.  The  employes  and 
workmen  accustomed  to  it  are  but  little  affected  by  0*037  per  mille ; 
the  sensibility  to  SO2  seems  to  be  lessened  by  habitually  respiring 
air  containing  it. 

Sulphur  dioxide  is  also  very  injurious  to  vegetation,  and  is  one 
of  the  chief  constituents  of  the  '^  noxious  vapours ''  so  much  com- 
plained of  in  most  manufacturing  districts.  It  is  true  that  these 
vapours  contain  other  injurious  constituents,  chiefly  of  an  acid 
character,  viz.  sulphuric  anhydride,  hydrogen  chloride,  and  some- 
times even  the  acids  of  nitrogen.  Disregarding  the  latter,  and 
even  HCl,  which  will  be  treated  of  in  the  Chapter  devoted  to  that 
subject,  we  shall  now  enter  upon  a  description  of  the  effects 
produced  by  the  ordinary  '^  acid  smoke  *'  of  metallurgical  and 


NOXIOUS  VAPOURS.  155 

similar  works^  where  SO^^  and  generally  also  SO,i,  are  the  principal 
acids  concerned. 

A  detailed  investigation  of  the  influence  of  the  noxious  vapours 
at  Freiberg,  where  verr  large  and  numerous  smelting- works  are 
situated^  on  vegetation  and  on  the  health  of  domestic  animals 
has  been  made  by  Freytag  (abstracted  in  Wagner's  Jahresb.  1873, 
p.  180).  The  acid,  arsenic,  and  zinc  vapours  of  the  Freiberg 
smelting-works  under  favourable  circumstances,  even  with  the 
present  condensing  arrangements,  may  injure  the  vegetation  of 
the  neighbourhood  in  the  following  way :  at  a  sufficient  concen- 
tration they  are  taken  up  by  the  leaves  when  covered  with  dew ; 
on  the  evaporation  of  the  water  the  organs  affected  are  corroded 
and  reduced  to  the  same  state  as  that  which  they  assume  when 
vegetation  ceases.  This  injury  can  always  be  proved  both  by  the 
eye  and  by  chemical  analysis.  A  "  poisoning ''  of  the  soil  or  of 
the  whole  plant  is  out  of  the  question.  The  assumption  of  an 
invisible  injury  done  to  the  vegetation  by  the  smelting-works' 
vapours  and  the  awarding  of  damages  founded  thereon  are  un- 
warranted ;  they  contradict  the  fundamental  principles  of  all  exact 
investigation  and  foster  the  desire  of  the  unreasoning  multitude 
to  incessantly  raise  fresh  claims  for  damage  alleged  to  have  been 
done  by  the  works.  A  decrease  of  the  nutritive  value  of  food- 
plants,  in  cases  of  visible  injury  done  to  the  leaves,  can  only  occur 
in  consequence  of  the  loss  of  these  leaves  and  the  lessened  ability 
of  the  plants  to  decompose  carbonic  acid  and  produce  organic  matter 
therefrom.  Any  metallic  oxides  or  salts  adhering  to  the  leaves  of 
food-plants  may  become  dangerous  to  the  animal  organization  by 
causing  inflammation  of  the  mucous  membranes,  and,  under  very 
unfavourable  circumstances,  may  produce  death ;  but  this  fact  can 
always  be  established  with  certainty  by  post-mortem  examination 
and  by  chemical  analysis.  The  supposition  that  the  '^acid  disease'' 
and  tuberculosis  occurring  in  a  particular  neighbourhood  among 
the  cattle  are  produced  by  the  noxious  vapours  from  smelting- 
works  is  utterly  unfounded  and  must  be  most  emphatically  con- 
tradicted. Freytag  considers  that  air  containing  more  than  0*003 
volume  per  cent,  of  SO2  will  do  injury  to  vegetation. 

Schroeder  (Wagner's  Jahresber.  1874,  p.  277)  made  extensive 
experiments  on  the  influence  especially  of  sulphurous  acid  on  vege- 
tation, with  the  following  principal  results: — From  air  containing 


156  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

as  little  as  tjj/od  of  its  volume  of  SO2  this  gas  is  absorbed  by  the 
leaves  of  "leafy  ^'  (deciduous)  trees  and  conifers;  these  retain  it 
mostly,  a  smaller  portion  penetrating  into  the  wood^  the  bark,  and 
the  leaf-stalks,  either  as  such  or  after  oxidation  to  sulphuric  acid. 
Conifer-leaves  absorb  less  sulphurous  acid  from  the  air  for  an  equal 
surface  of  leaves  than  deciduous  trees ;  the  absorption  takes  place 
equally  over  the  whole  surface  of  the  leaf,  not  by  the  stomata^ 
and  therefore  has  no  relation  to  the  number  of  the  latter.  A 
principal  efiect  of  the  injurious  action  of  sulphurous  acid  is  its 
causing  a  check  to  the  normal  evaporation  of  water,  the  disturbance 
being  in  a  direct  ratio  to  the  quantity  of  SO2 ;  the  evaporation  is 
mostly  affected  by  absorption  of  SO3  in  sunlight,  at  a  high  tempe- 
rature and  in  dry  air.  The  transpiration  of  conifers  is  not  visibly 
lowered  by  the  same  quantity  of  sulphurous  acid  as  that  which  affects 
other  trees  (deciduous  ones).  The  injury  done  by  sulphurous  acid 
is  greater  if  the  absorption  takes  place  at  the  lower  than  if  at  the 
upper  side  of  the  leaf. 

Other  communications  on  this  subject,  partly  contradicting  those 
of  Schroeder,  have  been  made  by  Stockhart  (Wagner's  Jahresb. 
1874,  p.  2528).  According  to  his  observations  at  Zwickau,  a  distance 
of  630  metres  (=690  yards)  protects  even  the  most  sensitive  vege- 
tation against  the  effect  of  large  volumes  of  vapours,  if  they  escape 
through  chimneys  not  less  than  82  feet  high.  Conifers  are  much 
more  sensitive  than  deciduous  trees ;  the  decreasing  series  of  sen- 
sibility is — pine,  pitch-pine,  Scotch  fir,  larch,  hawthorn,  white 
beech,  birch,  fruit-trees,  hazel-nut,  horse-chestnut,  oak,  red  beech, 
ash,  linden,  maple,  poplar,  alder,  mountain-ash.  In  the  parts  of 
plants  corroded  by  sulphurous  acid,  not  this  acid,  but  sulphuric 
acid  can  be  found,  and  that  to  a  larger  extent  than  in  the  same 
parts  of  plants  collected  at  the  same  time  in  districts  free  from 
smoke. 

Schroeder  and  Schertel  (Wagner's  Jahresb.  1879,  p.  234)  found 
in  healthy  fir-leaves  0*162  to  0*237  per  cent.  SOg;  damage  was 
only  done  when  the  percentage  rose  above  0*250;  the  highest 
found  was  0*592  near  Freiberg,  1-33  in  the  Oberharz. 

Other  figures  given  by  Fricke  (Chem.  Ind.  1887,  p.  492)  state  the 
difference  in  the  amount  of  SO2  found  in  healthy  and  damaged 
plants  as  follows : — 


NOXIOUS  VAPOURS.  157 

Healthy.  Damaged. 

Beans    6119  6*551 

Buckwheat  5-110  5*880 

Grass    7-105  8-336 

Rye  3-684  5-610 

Wheat  2-179  4412 

Cabbage    27290  30-843 

Oats      2-926  6788 

Potatoes   13-000  17500 

In  most  cases  the  differences  are  too  slight  to  base  any  trust- 
worthy conclusions  on  them.  Oats,  wheats  and  potatoes  stand  the 
acid  gases  better  than  young  meadow -plants. 

Just  and  Heine  (Chem.  Industrie^  1889^  p.  252)  also  found  very 
varying  percentages  of  sulphuric  acid  in  plants  alleged  to  be 
damaged  by  SO2,  so  that  this  means  of  tracing  such  injury  is  very 
unreliable. 

F.  Fischer,  in  the  230th  volume  of  Dingler^s  Journali  has  given 
a  short  synopsis  of  the  researches  made  in  this  direction  up  to  1878. 
A  special  treatise  (in  German)  has  been  published  on  acid  smoke 
by  Bering  (Cotta,  1888). 

Morren  (Chem.  Trade  Journ.  ii.  p.  18S)  shows  that  leaves  are 
more  sensitive  than  flowers  to  sulphurous  acid.  When  present  in 
a  proportion  of  1-80^000  in  the  air,  the  leaves  of  fruit-trees  are 
visibly  affected  in  three  to  five  hours,  and  this  effect  seems  to 
spread  after  direct  action  of  the  gas  ceases.  Adult  leaves  are 
usually  more  sensitive  than  young  leaves.  The  nerves  are  least 
affected  and  usually'remain  green.  Sulphurous  acid  dissolved  in 
water  is  almost  without  effect  on  the  upper  surface,  whilst  on  the 
lower  surface  each  little  drop  causes  the  formation  of  a  spot 
visible  on  both  surfaces.  This  solution  is  not  quickly  changed 
into  sulphuric  acid  ;  the  effect  of  the  latter  is  quite  different  from 
that  of  sulphurous  acid. 

Koenig  (Dingler's  Journal,  ccxxix.  p.  299)  describes  the  appear- 
ance of  trees  destroyed  by  the  vapours  from  roasting  blende. 

Hasenclever  (Chem.  Ind.  1879,  p.  22  •)  gives  coloured  and 
photolithographic  illustrations  of  the  ravages  caused  by  acid 
vapours  and  metallic  sulphates  upon  the  leaves  of  plants  aud 
plantations  of  trees,  side  by  side  with  those  caused  by  frost,, 
autumnal  decay,  fungi,  drought,  overgrowth  of  other  trees,  &C.,. 


158  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

which  closely  resemble  the  phenomena  produced  by  tlie  acid 
vapours  from  chemical  works,  and  hence  are  frequently  wrongly 
attributed  to  the  latter  cause.  Neither  is  the  estimation  of  sul- 
phates and  chlorides  in  the  damaged  leaves  &c.  at  all  a  safe  guide 
to  the  detection  of  the  real  cause^  looking  at  the  enormous 
quantity  of  acids  sent  into  the  air  wherever  coal  is  consumed  on  a 
large  scale.  At  Stolberg,  near  Aachen,  on  a  superficial  area  of 
1600  acres,  220  chimneys  daily  emit  34.}  tons  of  sulphur  dioxide 
firom  coal^  and  nearly  51  tons  of  SO2  &om  zinc- works,  glass-works, 
&c.,  the  alkali- works  adding  only  ^  ton  (more  correctly  480  kilog.) 
of  SOs^  and  |  ton  of  HCl.  Hence  alkali-makers  ought  not  to  be 
saddled  with  the  whole,  or  even  the  chief  part,  of  the  damage 
observed  in  the  neighbourhood. 

An  important  paper  on  the  subject  in  question  has  been  pub- 
lished by  Hamburger  (Journ.  Soc.  Chem.  Ind.  1884,  p.  202).  His 
conclusions,  founded  upon  a  large  number  of  analyses  of  damaged 
leaves,  are  practically  the  same  as  Hasenclever^s,  namely,  that 
undoubtedly  injury  is  done  to  vegetation  by  the  acids  in  the 
smoke ;  but  much  difficulty  exists  as  to  proving  this  with  certainty 
in  special  cases^  and  at  all  events  the  SO2  contained  in  ordinary  coal- 
smoke  contributes  very  largely  to  the  injurious  action  popularly 
attributed  to  the  emanations  from  chemical  works. 

A  professional  forester,  Reuss,  partly  by  himself  and  partly 
together  with  Schroeder,  has  embodied  the  results  of  laborious 
work  on  this  subject  in  several  German  publications.  Their  con- 
clusions have  been  attacked  by  another  forester,  Borggreve,  but 
Hasenclever  (Chem.  Ind.  1895,  p.  496)  has  shown  many  mistakes  in 
that  criticism.  They  all  agree  in  the  conclusion  that  the  growth 
of  trees  is  only  impeded  by  acid  vapours  if  visible  damage  is 
done  to  the  leaves.  When  the  leaves  or  needles  remain  green, 
chemical  analysis  may  prove  an  action  of  acid  gases,  but  no  real 
damage. 

Winkler  (Zsch.  angew.  Ch.  1896,  p.  371)  ascribes  the  effect  of 
noxious  vapours  from  brick-kilns  &c.  principally  to  their  contain- 
ing aqueous  vapour,  which,  on  cooling,  causes  the  condensation 
of  sulphurous  and  hydrochloric  acid. 

Further  papers  on  noxious  vapours,  with  details  as  to  their 
action,  are  those  by  Hagen  (Chem.  Zeit.  1896,  p.  238),  Ost  (ibid. 
1896,  p.  165),  Nissenson  and  Neumann  (Berg-  u.  Hiittenm.  Zeit. 
1896,  p.  145),  Schroder  &  SchmitE-Durbont  (Dingler's  Joum.  ccc. 


DETECTION  OV  SULPHUROUS  ACID.  159 

p.  65),  Ost  and  Wehraer  (Chem.  Ind.  1899,  p.  233),  Seydler 
(Fischer's  Jahresb.  1899,  p.  358),  Ramann  and  Sorauer  (ibid.  1900, 
p.  832),  Wislicenus  (Zsch.  ang.  Ch.  1901,  p.  689). 

Detection  and  Estimation  of  Sulphurous  Acid  and  Sulphur  Dioxide^ 

Qualitative  reactions  of  Sulphurous  Acid. — The  sense  of  smell  is 
a  very  good  means  for  detecting  the  presence  of  SO3,  when  other 
odorous  acids  are  absent.  Gaseous  mixtures  containing  SO2  together 
with  such  acids  are  best  passed  through  an  absorbent,  e.  ff,  sodium 
carbonate,  with  which  afterwards  the  ordinary  reactions  for  SO2  are 
made.  When  passing  such  gaseous  mixtures  through  a  solution 
of  potassium  permanganate,  or  of  iodine  in  potassium  iodide,  these 
liquids  are  decolorized,  the  iodine  being  reduced  to  HI.  This  last 
reaction  may  also  be  utilized  on  test-paper.  On  the  other  hand, 
a  test-paper,  soaked  in  a  solution  prepared  by  boiling  2  grams 
wheat-starch  with  100  c.c.  of  water,  and  adding  0'2  gram  of 
potassium  iodate  dissolved  in  5  c.c.  water,  is  turned  blue  by  SO^, 
by  the  formation  of  free  iodine.  These  reactions  may  also  be 
utilized  for  recognizing  the  presence  of  SO2  when  set  free  from  its 
salts  by  the  action  of  sulphuric  acid.  One  of  the  best  reactions, 
and  one  specially  adapted  for  discovering  SO2  in  sulphuric  acid 
itself,  is  its  conversion  into  H2S  by  means  of  pure  zinc,  or, 
preferably,  aluminium  in  an  acid  solution.  The  H2S  is  then 
"recognized  by  its  reaction  on  lead  paper,  or  by  the  purple  colour 
produced  in  an  ammoniacal  solution  of  sodium  nitroprusside. 

A  solution  of  a  sulphite,  either  neutral  or  with  addition  of  some 
sodium  bicarbonate  (just  acidulated  with  acetic  acid),  when  poured 
into  a  solution  of  zinc  sulphate  containing  a  little  sodium  nitro- 
prusside, produces  a  red  colour  or  precipitate,  either  at  once  or,  if 
very  little  SO2  is  present,  after  adding  some  potassium  ferricyanide. 
This  reaction  is  not  given  by  thiosulphates,  which  are,  moreover, 
distinguished  from  sulphites  by  their  giving  (generally  only  after 
a  little  time)  a  precipitate  of  sulphur  on  being  treated  with  a 
stronger  acid.  According  to  Reinscli,  SO2  can  be  detected  by 
boiling  the  acid  solutfon  with  a  strip  of  clean  copper,  which  is 
thereby  blackened.  This  is  caused  by  the  formation  of  cupric 
sulphide,  and  the  colour  is  not  changed  by  heating  the  strip  in  a 
glass  tube ;  but  when  the  colour  is  produced  by  arsenic,  there  is  a 
sublimate  of  white  arsenious  acid  formed  in  the  tube. 

According  to  Schiitzenberger,  sulphurous  acid  contained  in  a 


160        PROPERTIES  OF  OXIDES  AND  ACIDS  OP  SULPHUR. 

solution  can  be  recognized  by  adding  a  very  little  indigo  solution 
and  agitating  with  a  zinc  rod ;  owing  to  the  formation  of  hypo- 
sulphurous  acid  (Schiitzenberger's  ^^  hydrosnlphuric  *'  acid);  HSOj, 
the  blue  colour  will  be  destroyed^  but  will  quickly  reappear  in 
contact  with  the  air. 

The  quantitative  estimation  of  sulphurous  acid  in  the  free  state  can 
take  place  either  as  will  be  described  in  the  case  of  sulphites^  or  by 
titration  with  standard  alkali.  In  the  latter  case^  however,  it  must 
be  noted  that  the  point  of  neutrality  is  reached  with  phenolphthalein 
when  the  normal  salt,  NasSOg,  has  been  formed,  so  that  each  c.c. 
of  normal  alkali  (containing  0031  NaOH)  indicates  0*032  SO,. 
Of  course,  as  is  always  the  case  with  phenolphthalein^  the  standard 
alkali  must  be  soda  or  potash,  ammouia  being  useless  for  this  pur- 
pose. But  when  employing  methyl-orauge  as  indicator,  the  point 
of  neutrality  is  reached  exactly  at  the  formation  of  NaHSOa,  so 
that  each  c.c.  of  normal  alkali  indicates  0*064  SO3.  Litmus 
gives  somewhat  uncertain  results,  and  is  therefore  useless  as  an 
indicator.  It  is  thus  possible  to  estimate  free  SOs  in  the  presence 
of  stronger  free  acids  in  this  way :  one  portion  of  the  liquid  is 
titrated  with  methyl-orange,  and  another  with  phenolphthalein  as 
indicator ;  in  the  latter  case  more  alkali  will  be  used,  and  the 
difference  of  c.c.  of  normal  alkali,  multiplied  by  0*064,  shows  the 
quantity  of  free  SO2  present  (LuDge,  J.  Soc.  Chem.  Ind.  1883, 
p.  513 ;  Thomson,  Chem.  News,  xlvii.  p.  136 ;  Blarez,  in  Compt. 
Bend.  ciii.  p.  69,  adduces  nothing  new). 

The  acid  sulphites  are  neutral  to  methyl-orange,  which  con. 
sequently  allows  us  to  estimate  any  SO3  present  over  and  above 
NaHSOg.  The  SOj  present  in  the  NaHSO«  itself  can  be  titrated 
with  normal  soda  and  phenolphthalein,  each  c.c.  of  normal  alkali 
indicating  0*064  SO3.  Normal  sulphites,  as  NajSO^,  can  be  titrated 
by  means  of  methyl-orange  and  standard  hydrochloric  or  sulphuric 
acid,  the  red  colour  appearing  when  NaHSOg  has  been  formed,  so 
that  each  c.c.  of  standard  acid  indicates  0064  SO^. 

Other  methods  of  estimating  SOj  either  in  the  free  state  or  in 
its  salts  are  based  on  its  reducing  properties.  The  reagents 
serving  for  this  purpose  are  either  a  standard  solution  of  iodine  or 
one  of  potassium  permanganate,  both  of  which  are  well  known  and 
require  no  description  here.  A  dccinormal  solution  of  either 
indicates  per  cubic  centimetre  00032  gram  SO^.  The  method 
to  be  recommended  for  testing  gaseous  SO^  in  burner-gas  will  be 


APPLICATION  OF  SULPHUROUS  ACID.  161 

described  whea  treating  of  that  gas.  Special  attention  must  be 
drawn  to  the  necessity  of  employing  water  free  from  air  in  esti- 
mating SO2.  This  is  not  necessary  if  the  solution  of  the  sulphite 
or  sulphurous  acid  is  run  into  the  solution  of  iodine  (Giles  and 
Shearer,  J.  Soc.  Chem.  Ind.  188*,  p.  197,  and  1885,  p.  303). 

In  many  cases  the  quantitative  estimation  of  sulphurous  acid 
can  take  place  by  converting  it  into  sulphuric  acid  by  means  of 
oxidizinj^ agents:  chlorine,  bromine,  iodine,  hydrogen  peroxide,  &c. 
The  sulphuric  acid  is  then  estimated  in  the  usual  way. 

Sulphur  dioxide  in  the  presence  of  hydrogen  sulphide,  which 
gases  may  exist  together  in  a  state  of  great  dilution  by  inert  gases 
(as  in  the  exit-gases  from  '^Claus  kihis'"*),  can  be  estimated  by 
passing  the  gases  through  a  solution  of  1  in  KI,  followed  by  one 
of  caustic  soda  or,  preferably,  sodium  thiosulphatc.  The  iodine 
oxidizes  H.,S  into  H.,0  +  S,  and  S0-»  into  H.,SO. :  hence  the 
acidity  of  the  solution  is  not  affected  by  II3S,  merely  by  SO2. 
On  the  other  hand,  each  c.c.  of  dccinormal  iodine  indicates 
0'003.2  gram  of  sulphur  in  either  case,  so  that  the  difference 
between  the  iodometrical  and  the  alkalimetrical  test  gives  the 
H^S  present.  The  addition  of  a  tube  with  sodium  thiosulphatc 
solution  is  necessary,  because  the  gaseous  current  carries  away 
some  iodine  which  is  retained  in  that  solution  ;  the  latter,  before 
titrating  the  iodine  solution  back,  is  added  to  it  (details  in  my 
paper,  J.  Soc.  Chem.  Ind.,  Nov.  1890). 

Applications  of  Sulphurous  Acid  {Sulphur  dioxide). 

The  greatest  quantity  of  SOo  is  produced  for  the  manufacture  of 
sulphuric  acid.  Next  to  this  in  importance  comes  its  use  for  the 
manufacture  of  wood-pulp,  mostly  in  the  state  of  calcium  bisul- 
phite (or  a  solution  of  CaSOa  in  an  excess  of  sulphurous  acid). 
One  of  the  oldest  uses  of  sulphur  dioxide,  in  the  shape  of  burning 
sulphur,  is  as  a  disinfecting  and  antiseptic  agent.  For  the  former 
purpose  it  is  not  so  much  valued  now  as  formerly,  since  it  has  been 
shown  that  many  of  the  disease-germs  resist  the  action  of  SOo  for 
a  long  time.  The  antiseptic  function  of  SO2  comes  into  play  in 
the  fumigation  of  wine-casks,  in  the  arresting  of  the  fermentation 
of  wort,  in  the  manufacture  of  glue  (where  it  acts  also  as  a 
bleaching  agent),  and  in  many  other  cases. 

In  the  textile  industries  sulphurous  acid  is  largely  used  as  a 

VOL.  I.  M 


162  PROPERTIES  OP  OXIDES  AND  ACIDS  OF  SULPHUR. 

bleaching  agent,  especially  for  wool,  silk,  straw,  &c.  It  is  not 
quite  certain  in  which  way  it  acts  in  this  case,  possibly  by  forming 
a  compound  with  the  colouring-matters  contained  in  the  fibres. 
Formerly  it  was  generally  assumed  that  the  SO2  in  bleaching 
acted  as  a  reducing  agent,  which  indeed  must  be  true  in  some 
cases,  although  probably  noc  in  all.  The  reducing  functions  of 
SO3  are  utilized  in  chemical  and  metallurgical  operations  in  too 
many  cases  to  be  enumerated  here. 


Sulphuric  Anhydride,  S0;{ 
(Sulphur  Trioxide), 

consists  of  40  per  cent,  by  weight  of  sulphur,  and  60  per  cent,  of 
oxygen.  According  to  Marignac  (Arch.  Sci.  Phys.  Nat.  xxii. 
p.  225,  1853;  Hi.  p.  236,  1875;  Iviii.  p.  228,  1877)  and  Schultz- 
Sellack(Berl.Ber.iii.p.215),it  exists  in  two  different  modifications, 
a  liquid  and  a  solid.  The  liquid,  a-anhydride,  melts  at  + 16°  C, 
and  begins  to  boil  at  +35°  (according  to  Schultz-Sellack,  at  46°). 
Spec.  grav.  at  13°= 1-9516,  at  +20°  (melted)  =1-97.  In  the 
melted  state  it  is  less  oily  than  oil  of  vitriol,  and ,  if  pure,  colourless, 
but  usually  coloured  brown  by  dust.  When  kept  for  some  time 
at  the  ordinary  temperature  (below  25°)  it  is  changed  into  the 
solid,  y9-anhydride,  whose  melting-point  is  stated  very  differently, 
from  50^  to  100°  C.  Probably  it  begins  to  melt' at  50°,  and 
gradually  passes  over  into  the  ot-modification ;  it  slowly  evaporates, 
even  at  the  ordinary  temperature.  It  forms  fine,  feathery, 
asbestos-like,  white  needles.  The  /3-anhydride  is  probably  a 
polymer  of  the  a-modification.  Buff  (Ann.  Chem.  Pharm.,  Suppl. 
iv.  p.  151)  confirms  this.  According  to  R.  Weber,  however  (Pog- 
gendorff's  Ann.  clix.  p.  313  ;  Berl.  Ber.  xix.  p.  3187),  the  sulphur 
trioxide,  obtained  absolutely  pure  and  free  from  water  by  his 
method,  is  at  the  summer  temperature  a  very  mobile,  colourless 
liquid,  which,  on  gradually  cooling,  solidifies  to  long,  transparent, 
prismatic  crystals  -similar  to  nitrate  of  potash,  quite  different  from 
the  white,  opaque  crystals  of  the  ordinary  anhydride  containing  a 
little  water.  These  crystals  melt  at  14°'8  C,  and  boil  at  46°*2. 
Under  certain  conditions  the  anhydride  can,  like  many  other 
bodies,  be  cooled  much  below  its  proper  melting-point  without 
solidifying,  but  then  solidifies  suddenly.     After  a  twelvemonth  it 


SULPHURIC  ANHYDAIDE.  163 

Still  shows  the  same  composition  and  the  same  melting-point  as 
it  had  when  freshly  prepared.  Weber  accordingly  rejected  the 
assumption  of  two  different  modifications^  and  ascribes  the 
phenomena  of  this  kind  observed  by  others,  especially  the  for- 
mation of  the  modification  resembling  asbestos,  to  a  minute 
residue  of  water.  So  much  seems  to  be  correct  in  Weber's  con- 
clusions that  the  transition  of  the  first  to  the  second  modification 
is  promoted  by  a  minute  quantity  of  water. 

Oddo,  in  1901  (Rend.  Ace.  Lincei,  [5]  x.  p.  207;  Chem. 
Centralbl.  1901,  i.  p.  969),  definitely  proved  the  existence  of  two 
modifications  by  cryoscopic  estimation  of  the  molecular  weights. 
The  compound  melting  at  13°*8  is  the  real  sulphur  trioxide,  SO3 ; 
the  fibrous  compound,  which  does  not  melt  unchanged,  but  at  50° 
slowly,  and  at  100°  quickly  changes  into  SO3,  is  disulphuric 
anhydride,  SgOc.  SOy  instantly  burns  organic  tissues  and  causes 
deep  wounds ;  S2O6  is  much  less  active  and  can  be  touched 
with    the    hand.      SO3   dissolves  at   once  in  H2S0i  ;    S2O0  but 

slowly.      Oddo  gives  the  structural  formula  of  SO3 :   p.ZL^'^^f 
ot  S^Oqi  p. S S ^. 

Schenck  (Lieb.  Ann.  cccxvi.  p.  1)  regards  the  liquid  modification 
as  a  solution  of  the  asbestos-like  polymer  in  real  SO3  in  a  state 
of  unstable  equilibrium. 

The  heat  of  formation  of  one  molecule  of  SO-  (=80  parts  by 
weight)  from  S  and  O-,  is  =  103,230  cals.  (Thomsen);  from  SO3  +  O 
=  34',400  cals.  in  the  solid  state,  or  =22,600  cals.  in  the  gaseous 
state  (Berthelot).  The  heat  of  vaporizing  1  mol.  SO3  is  =11,800 
cals.  ;  that  produced  by  dissolving  1  mol.  SO3  in  a  large  quantity 
of  water  =39,170  cals.  (Thomsen). 

In  moist  air  sulphuric  anhydride  at  once  forms  dense  white 
fumes;  with  water  it  hisses  like  red-hot  iron.  Many  organic 
substances  are  at  once  charred  by  it.  In  the  complete  absence 
of  water  it  does  not  redden  litmus.  It  gives  several  compounds 
with  sulphur,  whose  colour,  with  the  quantity  of  sulphur  decreas- 
ing, changes  from  brown  to  green  and  blue.  In  the  blue  modi- 
fication Weber  has  proved  the  presence  of  the  sesquioxide,  SgO^. 
With  sulphur  dioxide  there  seems  to  exist  a  distinct  compound, 
SO2  +  2  SOa.     With  water  SOy  at  once  combines  to  form  sulphuric 

m2 


164       PROF£KTI£S  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

acid  (SO4H2)  and  its  different  hydrates.  It  is,  however,  not  easy 
to  completely  condense  the  sulphuric  anhydride  often  produced  in 
considerable  quantity  in  technical  processes,  even  with  a  large 
quantity  of  water  and  manifold  contact,  and  special  precautions 
have  to  be  taken  for  this  purpose. 

The  anhydride  SO3,  when  conducted  through  a  red-hot  tube, 
splits  up  into  SO2  and  O,  but  is  reformed  from  these  gases  at 
a  somewhat  lower  temperature,  especially  in  the  presence  of 
platinum  and  several  metallic  oxides.  The  technical  application 
of  this  reaction  is  described  in  Chapter  XI. 

For  scientific  purposes  sulphuric  anhydride  is  made  by  gently 
heating  fuming  oil  of  vitriol,  or  by  ignitinjr  sodium  pyrosulphatc 
(Na2S207) .  Its  production  in  a  perfectly  pure  state  is  described 
by  Weber  (/.  c).  Formerly  it  was  not  used  for  technical  purposes, 
owing  partly  to  the  costliness  of  its  production,  partly  to  the 
supposed  difficulty  of  handling  and  keeping  it.  Recently,  however, 
its  production  has  been  made  so  much  cheaper  that  certain 
branches  of  manufacture  already  employ  it  advantageously.  Its 
a])plication  has  turned  out  to  be  a  very  simple  affair,  as  it  can  be 
sent  out  in  drums  made  of  tinned  iron.  Its  handling  is  certainly 
unpleasant,  since  the  contact  of  the  skin  with  liquid  anhydride, 
or  even  just  liquefying  by  absorbing  moisture,  causes  very  malig- 
nant and  slow-curing  burns.  Its  production  on  a  manufacturing 
scale  will  be  described  in  Chapter  XI. 


Pyrosulphuric  Acid,  SgOjHj 
(Structural  formula,  SO.— OH 

SO2— OH), 
contains  the  elements  of  89*89  parts  of  sulphuric  anhydride  and 
10- 11  of  water,  or  equal  molecules  of  hydrate  and  anhydride. 
A  transparent  crystalline  mass,  melting  at  35°  C,  it  decom- 
poses at  moderate  heat  into  anhydride  (SO3)  and  oil  of  vitriol 
(SO.Ho). 

Pyrosulphuric  acid  is  contained  in  the  Nordhausen  fuming  acid 
of  trade,  which  often  consists  altogether  of  it,  and  then  bears  the 
trade  name  "  solid  oleum/'  Pyrosulphuric  acid  can  also  be  easily 
obtained  from  the  ordinary  liquid  fuming  Nordhausen  acid   by 


FUMING  OIL  OF  VITRIOL.  1()5 

cooling  below  0°.  Lastly^  it  can  be  made  by  carefully  mixing 
anhydride  with  a  small  quantity  of  oil  of  vitriol.  Weber  (/.  c.) 
obtained  an  intermediate  hydrate,  H2SO4,  3  SOg,  corresponding  to 
94-69  per  cent,  of  SOg. 

Pyrosulphuric  acid  forms  salts,  of  which  those  of  the  alkaline 
metals  are  the  best  known  and  most  important.  This  sodinm 
pyrosalphate  (S^O/Nas)  is  formed  by  fusing  acid  sodium  sulphate 
(SO^NaH)  at  incipient  red-heat.  At  a  full  red-heat  it  splits  up 
further  into  neutral  sulphate  (SO^Naj)  and  sulphuric  anhydride 
(SOg) ;  this  reaction  is  sometimes  utilized  for  producing  the 
latter  compound.  In  contact  with  water,  the  pyrosulphates  are 
gradually  retransformed  mto  acid  sulphates. 

A  compound  with  14*41  per  cent.  H2O  can  also  be  obtained, 
which  crystallizes  in  thin  transparent  prisms^  fumes  in  the  air,  and 
melts  at  26°  C.     Formula— 

SO2-OH 
3  HA  4  SOg,   or        >0     +  2  SO^/^ ^ 

SO2— OH  ^^" 

The  Nordhausen  or  fuming  oil  of  vitriol,  the  manufacture  of 
which  will  be  described  in  the  11th  Chapter,  is  a  viscous  oil, 
representing  a  mixture  of  pyrosulphuric  acid  or  sulphur  trioxide 
with  sulphuric  hydrate  in  varying  proportions,  and  therefore 
solidifying  at  very  different  temperatures.  It  fumes  in  the  air, 
and  gives  out  vapours  of  anhydride,  whilst  monohydrate  remains 
behind.  Water  transforms  it  at  once  into  ordinary  sulphuric 
acid,  with  strong  evolution  of  heat.  It  is  often  coloured  brown 
by  organic  snbstances,  and,  according  to  its  mode  of  preparation, 
contains  many  other  impurities,  such  as  iron,  sodium,  calcium, 
aluminium,  &c.  (as  sulphates),  sulphurous  acid,  selenium,  organic 
matters,  &c.  When  the  receivers  used  in  its  preparation  are 
charged  with  ordinary  strong  acid,  the  impurities  of  the  latter  will 
likewise  pass  into  the  fuming  acid. 

The  subjoined  tables  refer  to  the  mixtures  of  SO3  and  H^SOg, 
comprised  under  the  designation  of  fuming  oil  of  vitriol  (abridged 
O.V.),  even  when  they  consist  mostly  of  SOg  and  are  solid  at  the 
ordinary  temperatures. 


166 


PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 


Melting-points  of  fuming  0,V, 

Knietsch  (Ber.  1901,  p.  4100)  gives  the  following  table  of 
the  fusing.points  of  fuming  sulphuric  acid  (comp.  also  under 
"  Sulphuric  Acid ''  below)  : — 


Per  cent. 

Melting-point 

Per  cent. 

MpI  ting-point 

SO3. 

SO3. 

°C. 

0 

+  100 

55 

+  18-4 

5 

+  3-5 

(K) 

+  0-7           ; 

10 

-  4-8 

65 

+  0-8                      ' 

15 

-11-2 

70 

+  90 

20 

-110 

75 

+  17-2 

25 

-  0-6 

'               80 

+220 

30 

+  15-2 

85 

+33-0  (270)» 

35 

■4-20  0 

90 

'           +34-0  (27-7) 

40 

+338 

95 

:           +360  (260)           ! 

46 

+34  8 

100 

+40-0  (17-7) 

1              50 

1 

+28-5 

The  boiling-points   of  fuming   O.V.    are   stated   by    Knietsch 
(/.  c.  p.  4110)  as  follows  : — 


1 

SO3  total 

SOafree 

Boiling-point 

Barometric 

per  cent. 

per  cent. 

°0. 

pressure,  mm. 

823 

3&1 

212 

759 

83-4 

9-63 

170 

759 

8(>-45 

20-23 

125 

759 

89-5 

42-84 

92 

759 

93-24 

6:5-20 

60 

759 

99-5 

97-2 

43 

759 

The  vapour-pressures  of  various  descriptions  of  fuming  O.V.  are 
given  in  the  same  place;  comp.  also  the  curves,  infra,  p.  174. 

Specific  gravities  of  fuming  O.  V, 

CI.  Winkler  gives  the  following  table  of  the  specific  gravities  of 
fuming  sulphuric  acid  at  20°  C;  but  it  should  be  remarked  that  he 
worked  only  with  ''  commercial  acid/^  made  by  the  old  process, 
and  that  consequently  all  the  densities  found  are  sensibly  higher 
than  those  belonging  to  pure  acids ;  nor  is  it  a  matter  of  surprise 
that  the  values    found   by  Messel  with   another  description   of 


♦  The  numbers  in  brackets  denote  the  fusing.points  of  fresh,  not  yet  polymerized 
acids. 


SPECIFIC  GRAVITIES  OF  I'UMING  O.V, 


167 


'* commercial    acid''     (see    below)    do   not   entirely   agree   with 
Winkler's  table. 


Specific 
graritj 
at20°C. 


!    1 

i    1 
i    1 

1 
1 
1 
1 
1 
1 
1 


8(J0 

8<>:) 

870 
875 
880 

8a'i 

890 
895 
900 

9a> 


1-910 


915 
920 
925 
930 
935 
9-10 
945 
950 


9J)0 
965 
970 


Percentage  of 
I    H,0. 


SO3. 


81-84 
8212 
82-41 
82-63 
82-81 
82-97 
8313 
83-43 
83-48 
83-57 
83-73 
^08 
84  56 
85-06 
a")-57 
8<>23 
86-78 
8713 
87-41 
87  65 
88-22 
88-9:3 
89-83 


18-16 
17-88 
1759 

17-37 
1719 
1703 
1687 
16-66 
1652 
16-43 
16-27 
15  92 
1544 
1494 
14-43 

13  77 

13-22 

12-87 
12-59 
12-35 
11-78 
11-08 
1017 


Percentage  of 

Q^       i  acid  of 
"'^3-     I   66°  B. 


26-45 
27-57 
28-76 
29-95 
30-38 
3103 
31-67 
3252 
33-09 
33-46 
34-10 
;i3-52 
37  27 
39-49 
4156 
44-23 
^6-46 
47-88 
49-01 
49-98 
5229 
55-13 
58-81 


73-5;') 
72-43 
71-24 
70a5 
69-62 
68-97 
(«-23 
67M8 
66-91 
66-54 
65-91 
64-48 
6273 
60-51 
58-44 
55-77 
53-54 
52-12 
50  99 
5002 
47-71 
44-87 
41-19 


Percentage  of 
free  SO,,.'  H.,SOj. 


1-54 

266 

4-28 

514 

6-42 

7-29 

816 

9-34 

10  07 

10r)6 

11-43 

1333 

15-95 

J  8-67 

21-34 

25-65 

2803 

29-94 

31-46 

32-77 

39-68 
44  64 


98  46 
97-34 
9576 
94-:i6 
93-58 

9271 
91-84 
90  66 
89-93 
89-44 
88-57 
8667 
84-a5 

8i-;« 

78-66 
74-a5 
71-97 
70-06 
68-54 
67-t^3 
64-13 
60-32 
55-.'36 


Messel  (J.  Soc.  Chem.  Ind.  1885,  p.  573)  gives  the  following 
specific  gravities  of  commercial  Nordhausen  acids,  both  at  2G°*6  C, 
as  determined  by  himself,  and  calculated  for  15°*5  C. : — 


Specimens. 


'  Percentage 

of  SO3. 


Liquid   

»»         • 

Cr^'stalline  wnss,  resembling  nitre.. 

f»  H  1» 

It  »•  II 

>»  •  »l  »» 

Liquid  

f »         

t»         

Crystallized  

II  

II  


8-3 
3^)0 
400 
44-5 
46-2 
59-4 
60-8 
650 
69-4 
72-8 
80-0 
82-0 


Specific  gravities 

at  80°  F. 
(-=26°-6C.) 

calculated 
for  60°  F. 

(=15°-5C.) 

1-842 

1-852 

1-930 

1-940 

1956 

1-970 

1-961 

1  -975 

1-963 

1-977 

1-980 

1-994 

1-992 

2006 

1-992 

2-006 

2  002 

2016 

1-984 

1-988 

1959 

1-973 

1-953 

1%7 

168 


FROFEIITIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 


Knietsch  (Ber.  1901,  p.  4101)  gives  the  following  tables  for  com- 
mercial fuming  O.V.,  made  by  the  contact  process.  The  weighings 
were  made  at  15°,  referred  to  water  of  15°,  with  brass  weights 
without  reduction  to  a  vacuum.*  The  temperatures  to  which  they 
refer  are  35°  and  45°  for  fuming  O.V.^  and  15°  for  this  and  the 
strongest  ordinary  acids. 

The  curves  (p.  174)  show  a  maximum  for  ordinary  acid  slightly 
below  the  percentage  of  monohydrate  (HgSOJ  ;  for  fuming  acids 
the  maximum  is  at  60  per  cent,  free  SOg  at  15°  C,  at  56  per 
cent.  SOj  at  35°  C,  at  50  per  cent.  SOg  at  45°  C. 

Specific  gravities  at  15°  and  45°  C. 


H,SO, 

Total  SO3 

FreaSO,   1 

Spec.  grar. 

Spec.  grav. 

per  cent. 

per  cent. 

per  cent. 

1 

at  15°  C. 

nt  45°  C. 

95-98 

1      78-35      , 

1-8418 

96-68 

7892 

1-8429 



96-99 

1      79-18      I 

1-8431 

1 

•  •  •  •    ■ 

97  66 

79-72 

18434  Max. 

••••••         1 

98-6.5 

80-53 

1-8403 



99-40 

8114 

1  a388  Min. 

1 
«•  ^ . . .  ■         1 

99-76 

81-44 

1-8418 

1 
1 

1     10000 

81-63 

o-b 

1-8.500 

1  -822             1 

1       

83-46 

100 

1-888 

:  1-858             ' 

85-30 

200 

1-920 

1-887             i 

8714 

300 

1-957 

1-920 

88-97 

400 

1-979 

;  1-945 

•  •  •    •  • 

90-81 

50O 

2-009 

1-964  Max. 

92-65 

60-0 

1,  2020    Max. 

1-959 

94  48 

700 

'  2-018 

1942 

96-32 

800 

1  2-008 

1890 

9816 

900 

1-990 

1-8(H 

30000 

1000 

1 

'  1-984 

1-814 

1 

*  The  values  for  acids  of  100  per  cent.  H^SO^  and  below  do  not  quite  agree 
with  those  found  by  Lunge  and  Naef  (comp.  later  on),  which  could  not  be  other- 
wise, as  the  latter  worked  with  pure  acids  and  referred  their  figures  to  water  of 
4°  C.  and  to  the  vacuum.  The  only  essential  de^nation  is  that  Knietsch  does  not, 
like  the  authors  mentioned,  as  well  as  Kohlrausch  and  Schertel,  find  the  minimum 
spec,  gravity  at  100  per  cent.  IlaSO^,  but  at  99-40  per  cent# 


FUMING  SULPHURIC  ACID. 


169 


Specific  gravities  of  fuming  O.V.  at  35°  C. 


Total  SO, 

1 
Free  SO-   1 

a 

i  Total  SO, 

Free  SO., 

d 

per  cent. 

per  cent. 

1 

Spec.  gray. 
1-8J86 

1   per  cent. 

1 

per  cfcnl. 

Spec.  grav. 

81-63 

0 

9118 

52 

1  -9749 

81  •«9 

:         2 

1-8270 

91-55 

54 

1-9760 

8236 

4 

1-8360 

91-91 

56 

1-9772 

8273 

6 

1-84-25 

92-28 

58 

1-9754 

8309 

8 

1-8498 

92tW) 

60 

1-9738 

83-46 

1         10 

1-8565 

93-02 

62 

1-9709 

83-82 

12 

1-8627 

93-38    I 

64 

1-9672 

84-20 

14 

1-8692 

9375 

66 

l-9<)36 

84-66 

16 

1-8756 

9411     ' 

68 

l-9<-»00 

84-92 

1«        1 

1-88:30 

94-48 

70 

19564 

8530 

20 

1-8919 

94-85 

72 

l-950i 

85-66 

22 

1-9020 

95-21 

74 

19442 

8603 

24 

1-9092 

95-58 

76 

19379 

86-40 

26 

1-9158 

95-95 

78 

1-9315 

86-76 

28 

1-9220 

1        9632 

80 

1-9-251 

8714 

30 

1-9280 

96'69 

82 

19183 

87-60 

32 

1-9338 

'        97-05 

84 

1-9115 

87-87 

34 

1-9405 

97-45 

86 

1-9046 

88-24 

36 

19174 

97-78 

88 

1-8980 

88-60 

38 

1-95:34 

9816 

90 

1-8888 

88-97 

40 

1-9584 

9853 

92 

1-8800 

89-33 

42 

19612 

98  90 

94 

1-8712 

89-70 

44 

1-9643 

99-26 

i        ^ 

1-8605 

9007 

46 

1-9672 

99  63 

98 

1-8488 

90-44 

48 

19702 

10000 

100 

1-8370 

90-81 

60 

1-9733 

1 

t 

1 

1 
1 
1 

The  specific  heats  were   found  by  Knietsch  as  follows  (those 
marked  *  were  directly  observed)  : — 


Spec.  beat. 


Total  SO3 
per  ceDt. 

Free  SO3 
per  cent. 

Spec.  Iieat. 

76-8 

0  3691  * 

78-4 

0-3574  * 

80 

0-850 

800 

0-3574  * 

81-5 

0  3478  * 

82 

2-0 

0-34o 

83-46 

100 

03417* 

84 

12-89 

0-340 

a5-48 

20-95 

0-3391  • 

86 

23-78 

0-340 

8713 

29-74 

0-3:392  * 

88 

34-67 

0-350 

88-75 

38-75 

0-3498* 

90 

45-56 

0-360 

90-1 

4(Vl 

0-3599  * 

90-73 

49-4 

1 

0-3660* 

Total  SO., 

FreeSOg 

per  cent. 

per  cent. 

1 

91 

510 

92 

5645 

93 

61-89 

93-3 

635 

94 

67-34 

94-64 

70-6 

95 

72-78 

90 

78-23 

9652 

811) 

97 

83  67 

97-92 

88-6 

99 

89-12 

99 

94-56 

lK)-8 

98-9 

100 

1000 

0-370 

0-400 

0-425 

0-43-25  * 

0-455 

0-4730  * 

0-495 

0-535 

0-5598  * 

0-5W) 

06526* 

0-650 

0710 

0-7413  * 

0-770 


170 


PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 


The  heats  of  solution  were  observed  by  Knietsch  both  by  means 
of  a  calorimeter  and  on  a  large  scale.  Those  referring  to 
fuming  O.V.  are  given  here,  those  of  ordinary  sulphuric  acid  under 
that  heading. 


SO3  total 

SOgfree 

Onlories. 

Heat  of  solu- 
tion of  solid 

per  cent. 

1 

per  cent 

1 

O.V. 

82 

20 

199 

83 

7-5 

210 

84 

12-9 

223-5 

80 

18-3 

237-5 

1 
1 

86 

23-5 

250 

1 

87 

202 

265 

88 

34-7 

278 

89 

40-1 

292 

90 

45-6 

308 

"286 

91 

ra-o 

325 

304 

92 

56-4 

344 

322 

93 

(Jl-9 

363 

340 

M 

073 

i«l 

360 

95 

72-8 

1      401 

:«0 

i          96 

78-3 

421 

402        ! 

97 

83-7 

442 

423        1 

98 

891 

465 

442 

99 

94-6 

490 

463 

UK) 

1000 

515 

486 

Knietsch  (Joe,  cit.)  gives  also  tables  of  the  electrical  resistance, 
the  velocitf/  of  outflow  (viscosity),  and  the  capillary  rising  of  sul- 
phuric acids  and  O.V.  from  0  per  cent,  to  100  per  cent.  SOg ;  the 
results  are  exhibited  in  the  curves,  infra,  p.  174. 

The  action  of  fuming  O.V.  on  iron  (cast  iron,  wrought  iron,  and 
steel)  will  be  mentioned  later  on,  together  with  that  of  ordinary  acids. 

The  analysis  of  fuming  sulphuric  acid  is  described  after  that  of 
ordinary  acid. 

Sulphuric  Acid,  HgSOi. 
Natural  Occurrence, 

Free  sulphuric  acid  is  found  very  exceptionally  in  nature,  whilst 
some  sulphates,  especially  that  of  calcium,  occur  in  enormous 
quantities. 

In  the  free  state  sulphuric  acid  has  been  found  especially  in  a 
few  springs  of  volcanic  origin,  and  in  the  rivers  fed  by  those 
springs.  One  of  the  best  known  cases  of  this  kind  is  the  Rio 
Vinagrein  Mexico,  which  contains  0111  per  cent,  free  sulphuric 
acid  (calculated  as  SO3),  and  0"091  per  cent,  free  HCl  ;  it  daily 


MONOHYDRATED  SULPHURIC  ACID.  171 

carries  into  the  sea  38  tons,  according  to  others  even  69  tons  of 
both  acids.  Many  other  similar  instances  have  been  discovered  in 
various  parts  of  the  T,vorld  (comp.  the  first  edition  of  this  work, 
i.  p.  17).  Other  cases  again  occur  from  the  oxidation  of  sulphur 
ores,  the  acid  being  expelled  by  heat  from  the  sulphates  generated 
atfirst. 

Miners  are  only  too  familiar  with  the  occurrence  of  free  acid  in 
pit-watera  from  similar  causes,  by  the  corrosion  of  metal  pumps 
and  steam-boilers  ;  even  the  leather  of  the  valves  thereby  becomes 
brittle  and  the  wooden  parts  are  charred.  In  the  case  of  vol- 
canoes, sulphuric  acid  is  formed  by  the  oxidation  of  the  sul- 
phuretted hydrogen  and  the  sulphur  dioxide  from  the  fumarolcs 
and  solfataras. 

Even  in  the  animal  kingdom  free  sulphuric  acid  has  been  found, 
viz.  in  the  salivary  glands  of  several  mollusks,  especially  of  Dolium 
^alea,  which  contain  2'47  per  cent,  free  sulphuric  acid  and  0*4 
per  cent,  free  hydrochloric  acid  (Boedeker  and  Troschel ; 
De  Luca  and  Panceri). 

Monohydrated  Sulphuric  Acid,  H2SO4. 

The  proper  sulphuric  hydrate,  commonly  known  as  mono- 
hydrated sulphuric  acid,  has  the  rational  formula  : — 

SO  -OH 

and  may  be  considered  as  containing  81*63  per  cent.  SO3  and  18'37 
per  cent,  water.  It  is  a  limpid,  colourless,  oily  liquid.  Its 
specific  gravity  at  (f  is  1*853  ;  at  15°  (compared  with  water  of  4°)  : 
1-8384  (Lunge  and  Naet),  1*8378  (Schertel),  1*8372  (Marignac, 
F.  Kohirausch,  MendelejefF)  *.  The  specific  gravity  changes  to 
the  extent  of  +0001  for  each  degree  Centigrade.  Both  the 
addition  of  very  little  SOj,  and  that  of  very  little  water  raises  the 
specific  gravity  (see  below) .  The  pure  monohydrate  solidifies  at 
about  QP  and  forms  large,  plate-shaped  crystals  which  melt  at 
-f  10*^*5  ;  they  remain  liquid  a  good  deal  below  that  temperature, 
but  solidify  on  agitation,  or  even  better  when  a  fragment  of  the 
solid  hydrate  is  introduced.  The  acid  begins  to  boil  at  290°,  but 
the  boiling-point  rises  up  to  338°  (Marignac).  This  shows  that 
it  does  not  distil  unchanged  :  in  fact  a  mixture  of  hydrated  acid, 

*  Comp.  Berl.  Ber.  1884,  pp.  1718,  2536,  2711. 


172  PROPERTIES  OP  OXIDES  AND  ACIDS  OF  SULPHUR. 

anhydride,  and  water  passes  over  (see  below).  This  dissociation 
begins  much  earlier;  the  pure  monohydrate  fumes^  that  is  gives 
oft'  S0|^  very  slightly  even  at  the  ordinary  summer  temperature^ 
distinctly  at  30°  or  40°.  Accordingly  it  cannot  be  obtained  by 
boiling  down  or  distilling  dilute  acid^  but  by  adding  an  exactly 
sufiicient  quantity  of  anhydride  to  the  strongest  acid  obtainable 
by  concentration,  or  by  cooling  such  acid  below  QP  and  several 
times  recrystallizing  the  monohydrate  in  the  same  way.  The 
latter  process  has  been  made  commercially  available  by  the  Author 
for  the  manufacture  of  monohydratic  sulphuric  acid,  which  conse- 
quently is  no  longer  a  laboratory  product,  but  has  become  an 
important  article  of  commerce  (comp.  Chap.  IX.). 

The  vapour  of  sulphuric  acid  consists  for  the  most  part,  or  even 
entirely    (according   to  the   temperature),   not   of  molecules   of 
SO4H2,  but  of  isolated  molecules  of  SO3  and  H2O  ;  theory  would 
give  to  SO4H2  (2  vols.)  a  vapour-density  of  3'862^  for  separated 
molecules  of  SO3  and  HgO  (4  vols.)  a  vapour-density  of  1*6931^ 
whilst  Deville  and  Troost  at  440°  found  it  actually  =1-74.     The 
dissociation  is  therefore  as  good  as  complete  in  the  state  of  vapour ; 
and  this  assumption  agrees  very  well  witli   our  present  notions 
concerning  the  state  of  vapour  (Dittmar,  Chem.  News,  xx.  p.  258). 
Formation  of  Sulphuric  Acid, — It  has  been  asserted  that  sul- 
phuric acid  is  formed  in  damp  flowers  of  sulphur,  even  at  the 
ordinary  temperature  ;  this  is  certainly  the  case  on  heating  sulphur 
with  water  at  200°  C,  or  by  applying  the  electric  current.    Sulphur 
is  easily  oxidized  to  sulphuric  acid  by  chlorine,  hypochlorous  acid, 
nitric  acid,  aqua  regia,  &c.     It  is  produced,  along  with  sulphurous 
acid  and  sulphur,  from  tri-,  tetra-,  and  pentathionic  acids — from 
the  former  by  merely  heating,  from  all  three  by  the  action  of 
chlorine  or  bromine,  or  even  on  the  prolonged  action  of  stronger 
acids,  which  set  the  thionic  acids  free  ;  also  the  thiosulphates  yield 
sulphuric  acid  under  the  action  of  chlorine.     All  these  decomposi- 
tions have  to  be  kept  in  view  in  alkali-making. 

Mostly  sulphuric  acid  is  formed  from  sulphur  dioxide.  The 
aqueous  solution  of  the  latter  is  gradually  transformed  into  sul- 
phuric acid  by  the  action  of  the  air  alone,  and  it  is  so  transformed 
at  once  by  chlorine,  bromine,  iodine,  hypochlorous  acid,  nitric 
acid,  and  several  metallic  salts,  such  as  manganic  sulphate, 
mercurous  nitrate,  &c.  Sulphur  dioxide  and  oxygen  conducted 
through  a  red-hot  tube  containing  platinum,  platinized  asbestos^ 


SULPHURIC  ACID  CONTAINING  WATER.  173 

ferric  oxide^  and  a  number  of  other  substances^  yield  sulphuric 
anhydride,  or  in  the  presence  of  water  sulphuric  acid.  This 
reaction,  which  was  formerly  only  of  scientific  interest,  has 
become  of  the  greatest  technical  importance  and  is,  according  to 
some  opinions,  destined  to  supersede  the  formerly  universal,  and, 
up  to  this,  most  general  process  of  making  sulphuric  acid  from 
sulphur  dioxide,  air,  and  water  by  means  of  nitrogen  oxides  as 
oxygen  carriers.  All  this  will  be  explained  in  detail  later  on. 
The  heat  of  formation  of  98  parts  SO4H3  is  : — 

Liquid.  In  diluted  solutions. 

From  SO2, 0,  HgO 54,400  72,000  calories. 

„      S,08,H20    124,000  141,000      „ 

„      S,04,H2 193,000  210,000      „ 

The  heat  of  neutralization  of  1  mol.  (98  parts)  HjSO^  by  2  mols. 
(80  parts)  NaOH  in  the  presence  of  400  mols.  of  water  is  given  by 
Thomsen  =31,380  cals.  Pickering  (Journ.  Chem.  Soc.  1889, 
p.  323)  states  it  only  =28,197  cals. 

Sulphuric  add  containing  water, — The  strongest  oil  of  vitriol 
obtainable  by  boiling-down  ordinary  pure  sulphuric  acid  contains 
a  quantity  of  water  which  is  not  stated  alike  by  different  observers 
(Marignac,  Pfaundler,  Roscoe,  Dittmar,  Lunge  and  Naef,  &c.). 
The  statements  differ  from  97*86  to  98'99  per  cent,  of  SO4H2;  it 
is  at  all  events  very  nearly  98*3  per  cent.  This  distilled  sulphuric 
acid  solidifies  a  little  below  0° ;  but  it  also  shows  the  phenomenon 
of  superfusion  in  a  very  high  degree.  It  boils  at  338°  (Marignac), 
or  315°  to  317°  C.  (Pfaundler  and  Polt).  Usually  Marignac's 
statement  is  considered  the  most  reliable ;  the  acid  of  Pfaundler 
and  Polt  probably  contained  a  little  more  water.  The  boiling 
takes  place  quietly  under  a  stronger  pressure  than  the  ordinary 
one,  but  at  a  lower  pressure  with  violent  bumping,  which  can  be 
avoided  by  putting  in  platinum  wire  or  scraps,  according  to 
Dittmar  even  better  by  conducting  a  slow  current  of  air  through 
it  during  the  boiling  (see  Chapter  VIII.,  purification  of  sulphuric 
acid). 

This  acid  of  983  per  cent.  H3SO4,  distilling  unchanged,  possesses 
a  number  of  other  peculiarities,  marking  it  out  as  representing  a 
certain  equilibrium,  or  so-called  *^  critical  concentration."  This 
comes  out  very  well  in  a  series  of  curves,  given  by  Knietsch  (Ber. 
1901,  p.  4089),  fig.  39,  p.  174.     The  boiling-points  at  that  point 


174 


PJIOPERTIGS  OF.  OXIDES  AND  ACIDS  OF  SULPHUR. 


bo 


FROPEHTiES  OF  SULFHURIC  ACID.  175 

(330°)  show  a  sharp  apex ;  below  this,  water  or  dilute  sulphuric 
acid,  above  this,  sulphuric  anhydride  is  volatilized  until  in  either 
case  the  constantly  boiling  acid  of  98*3  per  cent,  is  reached.  The 
vapour-tension  at  that  critical  concentration  is  =  zero,  measured 
at  100°  in  a  vacuum ;  the  specific  gravity  of  hydrated  acid  here 
reaches  its  maximum,  from  which  it  descends  in  both  directions ; 
the  electrical  resistance  at  this  point  begins  to  increase  suddenly 
towards  a  maximum  reached  at  nearly  100  per  cent.  H2SO1 ;  in  con- 
nection with  this  the  action  upon  iron  decreases,  which  is  of  great 
importance  for  the  durability  of  apparatus  (comp.  below). 

In  fig.  39,  curve  1,  marked  ,  shows  the  melting-points ; 

curve  2, the  specific  gravities  at  15°, .  at 

35°;    curve  3, ,  the  specific  heats;    curve  1, ,  the 

heat  of  solution;   curve    5,  o  —  o  —  o,  the  electric  resistance  at 

25°;  curve  6,  + 1 ,  the  boiling-points ;  curve  7,  •  -|- 1 , 

the   vapour-tensions    at    100°  ;    curve   8, o o  .  — ,   the 

viscosities  (times  of  outflow)  ;  curve  9,  -•-•-•-•^  the  capillarity ; 
curve  10,  -1-1-1-1-1-1-1-1-,  the  action  upon  iron. 

The  following  fact  concerning  a  property  of  sulphuric  acid  con- 
taining about  98  per  cent.  H2SO4  is  of  great  importance  in  the 
manufacture  of  sulphuric  acid  from  SOa  by  the  contact  process. 
Knietsch  found  that  the  task  of  converting  the  SO3  into  hydrated 
acid  cannot  be  accomplished  by  absorbing  it  in  a  series  of  vessels 
filled  with  water  or  dilute  acid,  although  the  heat  of  dissolution 
in  this  case  is  at  a  maximum;  but  acid  of  97  or  98  per  cent. 
HjSO^  at  once  and  completely  absorbs  the  SO3,  so  that  only  one 
vessel  is  required,  in  which  the  proper  concentration  is  maintained 
by  continuously  running  in  water  or  dilute  acids  and  running 
off  concentrated  acid.  Sackur  (Zscli.  f.  Elektroch.  1902,  p.  81) 
explains  this  by  saying  that  at  ordinary  temperatures  the  100 
per  cent,  monohydrate,  H2SO4,  is  slightly  dissociated  into 
H2SO4,  H2O  +  SO:,  (comp.  p.  172),  but  in  the  presence  of  very 
little  water  (equal  to  98  per  cent.  H2SO4)  the  partial  pressure  of 
SO3  is  at  a  minimum,  and  hence  this  acid  has  the  maximum 
absorbing  power  for  SO3.  Up  to  this  point  no  free  H2O  is 
present,  but  with  greater  dilution  it  is  found.  That  these 
dilute  acids  are  inferior  solvents  of  SOs  is  explained  by  the  fact 
observed  by  Oddo  (comp.  p.  1G3)  that  the  true  SO3,  melting  at 
14°,  is  easily  dissolved  in  H2SO1,  but  the  polymer,  SoOg,  but 
slowly.     Now  the  latter  is  formed  from  SO3  by  the  influence  of 


176  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

minute  quantities  of  water,  and  therefore  also  when  SO3  is  passed 
into  acids  below  98  per  cent.  H2SO4. 

The  ordinary  ^^  rectified  oil  of  vitriol"  always  contains  more 
water  than  that  obtainable  by  the  highest  degree  of  concentration 
or  distillation.  Exceptionally  98  per  cent,  acid  is  made  for  com- 
mercial purposes;  the  usual  rectified  O.V.,  formerly  called  170° 
Twaddel),  now  more  accurately  168°  Twaddell,  varies  in  strength 
from  96  down  to  93  or  even  92  per  cent,  of  real  monohydrate. 
This  variation  is  partly  caused  by  the  fact  that  at  the  higher  degree 
of  concentration  a  slight  difference  in  specific  gravity  corresponds 
to  a  great  difference  in  percentage  ;  partly  by  the  fact  that  the 
specific  gravity  of  commercial  acids,  owing  to  the  presence  of 
impurities,  is  always  higher  than  that  of  the  pure  acid;  but,  apart 
from  this,  the  correctness  of  ordinary  hydrometers  is  rarely  of  a 
very  high  order.  Still,  it  must  be  conceded  that  in  England  at 
least  there  is  a  possibility  of  making  the  hydrometers  all  alike, 
the  basis  of  TwaddelPs  system  being  a  plain  and  unmistakable 
one,  as  every  degree  is  equal  to  a  difference  of  0005.  But 
matters  are  far  worse  on  the  Continent  and  in  America,  where 
Baume^s  hydrometer  is  almost  universally  used;  unfortunately 
the  degrees  of  this  instrument,  as  stated  by  various  authorities, 
answer  to  very  different  specific  gravities,  and  those  of  the 
instruments  found  in  trade  often  show  even  far  greater  devi- 
ations. The  only  rational  hydrometer  on  Baume's  system  which 
rests  on  a  mathematical  basis,  and  which  should  therefore  l>e 
always  obtainable  with  a  uniform  scale,  is  that  graduated  according 
to  the  formula 

141-3--W' 

where  d  signifies  any  special  density  (specific  gravity),  and  n  the 
degree  of  the  scale  corresponding  to  it.  (The  mathematical  de- 
duction of  this  formula  is  j^iven  in  the  first  edition  of  this  work, 
pp.  20  and  21.)  This  scale  is  also  generally  accepted  in  Germany 
and  France  now.  It  is  the  only  one  in  which  the  degree  66, 
which  is  that  everywhere  accepted  for  rectified  O.V.,  comes  near 
the  real  specific  gravity  of  pure  sulphuric  acid  of  90  per  cent.,  or 
commercial  acid  of  94  to  95  per  cent.,  namely  1*840.  Unfortu- 
nately, apart  from  various  other  scales,  Gerlach's  scale  is  also 
sometimes  used,  although  this  is  far  lower  than  the  '^rational'' 
scale,   and,  to    make  the   confusion  still  greater,  the  American 


SPECIFIC  GRAVITIES. 


177 


Comparison  of  Baumi's  Hydrometers  with  the  Specific  Gravities. 


" 

' 

1 

• 

a 

Rutiontvl 
Hydrometer, 
144*3 

Baum^'ci 

Hydrometer 

(Qerlach). 

American 
Hydro- 

a- 

Rational 
Hydrometer, 
144-3 

Baum^'s 
Hydrometer 

1 

American 
Hydro- 

Q 

J                XXX  %J 

144-3 -»• 

meter. 

36 

-                       X  J^  M.    \J 

'^""144-3-»- 

(Gtorlach). 

meter. 

1 

1 

1-007 

1-0068 

1-006 

1-332 

1-3250 

1-334 

2 

1014 

10138 

1-011 

37 

1-345 

1-3370 

1-342 

3 

1022 

10208 

1-023 

38 

1-357 

1-3494 

1-359 

:    4 

1-029 

1-0280 

1-029 

39 

1-370 

1-3619 

1-368 

6 

1037 

1-0353 

1036 

40 

1 

1-383 

1-3746 

1-386 

6 

1-045 

1-0426 

1-043 

41 

1-397 

1-3876 

1-395 

7 

1052 

1-0501 

1050 

42 

1-410 

1-4009 

1-413 

8 

1060 

1-0576 

1-057 

43 

1-424 

1-4143 

1-422 

9 

1-067 

1-0653 

1-064 

44 

1-438 

1-4281 

1-441 

10 

1-075 

1-0731 

1-071 

,46 

1-463 

1-4421 

1-461 

11 

1083 

1-0810 

1-086 

46 

1-468 

1-4564 

1-470 

12 

1091 

1-0890 

1093 

47 

1-483 

1-4710 

1-480 

13 

1-100 

1-0972 

1-100 

48 

1-498 

1-4860 

1-600 

14 

1108 

1-1054 

1107 

49 

1-514 

1-5012 

1-510 

15 

1-116 

11138 

1-114 

50 

1-530 

1-5167 

1-531 

16 

1125 

1-1224 

1122 

:51 

1-540 

1-6325 

1-541 

17 

1134 

1-1310 

1136 

,  52 

1-563 

1-5487 

1-661      ' 

18 

1142 

1-1398 

1143 

53 

1-680 

1-6662 

1-573     ; 

19 

1-152 

1-1487 

1-150 

54 

1-697 

1-6820 

1-694     , 

20 

1162 

1-1578 

1158 

55 

1-615 

1-5993 

1-616 

21 

1171 

1-1670 

1172 

56 

1-634 

1-6169 

1-627 

22 

1180 

1-1763 

1-179 

1  67 

1-652 

1-6349 

1-660 

'  23 

1190 

1-1858 

1-186 

58 

1-671 

1-6533 

1-6(U 

1  24 

1-200 

1-1955 

1-201 

59 

1-691 

1-6721 

1-683 

25 

1 

1-210 

1-2053 

1-208 

60 

1-711 

1-6914 

1-705 

26 

1-220 

1-2163 

1-216 

61 

1-732 

1-7111 

1-727 

27 

1-231 

1-2254 

1-231 

62 

1-753 

1-7313 

1-747 

28 

1-241 

1-2357 

1-238 

63 

1-774 

1-7620 

1-767 

29 

1-252 

1-2462 

1-254 

64 

1-796 

1-7731 

1-793 

30 

1-263 

1-2569 

1-262 

65 

1-819 

1-7948 

1-814 

31 

1-274 

1-2677 

1-269 

66 

1-842 

1-8171 

1-836 

32 

1-285 

1-2788 

1-285 

33 

1-297 

1-2901 

1-293 

34 

1-308 

1-3015 

1-309 

35 

1-320 

1-3131 

1-317 

VOL.  I. 


N 


178 


PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 


Comparison  between  the  Degrees  of  TwaddelVs  Hydrometer  and 

Specific  Gravities, 


Degrees, 
Tw. 


1 
2 
3 
4 
5 

k\ 
7 

8 

9 

10 

11 
12 
13 
14 
15 

16 
17 
18 
19 
20 

21 
22 
23 
24 
25 

26 
27 
28 
29 
30 

31 
32 
33 
34 
35 

36 
37 

38 
39 
40 

41 
42 
43 


Specific 
Gravity. 


005 
010 
015 
020 
025 

030 
035 
040 
045 
050 

055 
060 
005 
070 
075 

080 
085 
090 
096 
100 

105 
110 
115 
120 
125 

130 
135 
140 
145 
150 

155 
160 
165 
170 
175 

180 
185 
190 
195 
200 

205 
210 
215 


Degrees, 
Tw. 


Specific      Degrees, 
Gravity.     ,     Tw. 


44 
45 
46 
47 

48 

49 
50 
51 
52 
53 

54 
55 
56 
57 
58 

59 
60 
61 
62 
63 

64 
65 
66 
67 
68 

69 
70 
71 
72 
73 

74 
75 
76 

77 
78 

79 
80 
81 
82 
83 

84 
85 
86 


1-220 
1-225 
1-230 
1-235 
1-240 

1-245 
1-250 
1-255 
1-260 
1-265 

1-270 
1-275 
1-280 
1-285 
1-290 

1-295 
1-300 
1-305 
1-310 
1-315 

1-320 
1-32.5 
1-330 
1-335 
1-340 

1-345 
1-350 
1-355 
1-360 
1-365 

1-370 
1-375 
1-380 
1-385 
1-390 

1-395 
1-400 
1-405 
1-410 
1-415 

1-420 
1-425 
1-430 


87 
88 
89 
90 
91 

92 

93 
94 
95 
96 

97 

98 

99 

100 

101 

102 
103 
104 
105 
106 

107 
108 
109 
110 
111 

112 
113 
114 
115 
116 

117 
118 
119 
120 
121 

122 
123 
124 
125 
126 

127 

128 
129 


Specific     I  Degrees, 
Gravity.  Tw. 


1 
1 
1 
1 
1 

1 
1 
1 
1 

1 

1 
1 
1 
1 
1 

1 
1 
1 
1 

1 


435 
440 
445 
450 


460 
465 
470 
475 
480 

485 
490 
495 
500 
505 

510 
515 
520 
525 
530 

535 
540 
545 
550 
555 

560 
565 
570 
575 
580 

585 
590 


600 
605 

610 
615 
620 
625 
630 

635 
640 
645 


Specific 
Gravity. 


130 
131 
132 
133 
134 

135 
136 
137 
138 
139 

140 
141 
142 
143 
144 

145 
146 
147 
148 
149 

150 
151 
152 
153 
154 

155 

ir)6 

157 
158 
159 

160 
161 
162 
163 
164 

165 
166 
167 
168 
169 

170 


1-650 
1-656 
1-660 
1-665 
1670 

1-675 
1-680 
1-685 
1-690 
1-695 

1-700 
1-705 
1710 
1-715 
1-720 

1-725 
1-730 
1-735 
1-740 
1-745 

1-750 
1-755 
1-760 
1-765 
1-770 

1-775 
1-780 
1-785 
1-790 
1-795 

1-800 
1-805 
1-810 
1-815 
1-820 

1-826 
1-830 
1-835 
1-840 
1-845 

1-850 


SPECIFIC  GKAVITIES. 


179 


manufacturers  have  adopted  again  another  scale^  based  on   the 


formala 


«=145  — 


145 


In  order  to  clear  the  way  as  far  as  possible,  we  give  herewith  tables 
(pp.  177, 178)  showing  the  value  of  a  degree  Ban  me  according  to  the 
rational  scale,  to  Gerlach's^  and  to  the  American  scale  (the  last  is 
copied  from  A.  H.  Elliott,  'Chem.  Trade  Journal,'  vol.  ii.  p.  183). 
The  percentage  of  mixtures  of  sulphuric  acid  and  water  is  in  the 
great  majority  of  cases  tested  by  the  hydrometer  only,  and  many 
tables  have  been  constructed  for  this  purpose.  It  would  be  very 
desirable,  as  Hasenclever  points  out  ( Hofmann's  Report,  i.  p.  181),  if 
all  sulphuric-acid  makers  used  the  same  reduction-tables  for  their 
calculations  ;  for  in  the  statements  on  the  yield  of  acid,  and  in 
many  other  cases^  frequently  different  tables  are  used  ;  so  that  the 
working  results  of  different  factories  are  not  always  comparable 
with  each  other.  This  very  clearly  appears  from  the  following 
comparative  Table :  — 


Degrees 


10 
1>0 
30 
M) 
oO 
60 


Spec. 
Gray. 

(Kolb). 


Percentnge  of  SO^Hj  in  the  Vitriol  according  to 


Vaiique-  D'^^eet. !    Tables  of  different  works. 

liii.  I 


1075 
11G2 
1-263 
1-^383 
1-530 
1-711 
1-812 


11-73 
24-01 
3i5-5-i 
50-41 
66-54 

l(X)-00 


6<V45 

82-34 

100  00 


11-5 
2.'V3 
36-0 
51 -C 
l>6-9 
83-3 


11-40 
23-46 
3<»-(30 
51-49 

mn 

82-80 


(>3-8 
70-4 


10-98 
21-97 
35-93 
49-94 
63  92 
79-90 


Bineau. 


110 
22-4 
34-9 
38-4 
62-7 
780 


100-0    100  00     910     97-87      1000 


Kolb. 


10-8 
222 
34-7 
48-3 
62-5 
78-1 
lOO-O 


The  totally  incorrect  tables  of  Vauquelin  and  D'Arcct  are  used, 
up  to  the  present  time,  exclusively  in  the  south  of  France. 

We  shall  here  not  take  any  notice  of  those  old  tables,  nor 
of  those  of  Ure,  Dalton,  &c.,  and  we  refer  to  our  first  edition 
«s  to  the  more  modern  and  reliable  tables  of  Bineau  and  Kolb. 
In  this  place  we  give  only  the  most  modern  and  accurate  results, 
viz.,  those  of  Lunge  and  Isler  (Zsch.  f.  angew.  Ch.  1890,  p.  129) 
for  the  strengths  up  to  142°  Tw.,  and  also  of  Lunge  and  Naef 
(Chem.  Ind.  1883,  p.  37)  *. 

*  A  very  extended  study  of  the  speciiic  gravities  of  sulphuric-acid  solutions 
has  been  published  by  Pickering  (Journ.  of  the  Chem.  Soc.  vol.  Ivii.  pp.  04  H 
seqq.).  The  reasons  why  I  do  not  see  any  occa.<«ion  for  accepting  Pickering's 
figures  in  lieu  of  my  own  are  stated  in  the  *  Journal  of  the  Society  of  Chemical 
Industry/  1890,  p.  1017. 

n2 


180 


PROPERTIES  OP  OXIDES  AND  ACIDS  OF  SULPHUR. 


•ft. 


/^ 


c 

•  mm 

s 

c 
o 
o 

'd 

•s 

£  •  • 
S! 

aS 

.a 

«*- 
o 


1 


u. 


a. 


8 


OH 

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c« 


1 

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"ir  T^  T^  T^  T^  'sr  "y*  w*  <—''"•'"•'"'  ""^  '"•  ^^  •"•  w"^  w>i  w>t  .^  w>i  «M  ■«'<  VI  wj  WW  «  . 

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acid  of 
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SPECIFIC  ORATITIE8. 


181 


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O666c>66e©66^6666666o6±)6666o66666c6oo 


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oooooocoooooc 


■    "       I  ca  o  O  ^  -M 


0  300000000  00000000000  00 


»-^^SS55c'l5'l?5?Ic^l¥lC'lS^SlS8Swo3o300COo8«S«r5S««r3C03^ 


C5  CaO 


^•QQPO'-«cqcQ^ii5tP|;»gD©Q«-*gcO'^iO«traQ^<5'^<NoO'^i-'^^b-oQq5P 


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UV    ^^^    l^.     Wl    *>W    ^Sl' 

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■       •        • 


182 


PROPERTIES  OF  OXIDES   AND  ACIDS  OF  SULPHUR. 


^  ^ 

n 

°H 

e 

'«o 

§8 

a 

r— • 

8 

I 

3 

.      1 

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5    O 

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b 

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of  Sulph 

1  J. 

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Is 

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1 

^  G. 

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• 

.Si 

-S)-! 

•« 

••"A 

•  pSi   ei 

QQ 

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g 

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•^1— C5«COOl-»'f^t>''^»7iOOiC^QO»-'^<MaO»i:t5'IX^O«SC<C-»^ 
'f:co«'?f»h<;b6i^aocic666.^(NCi«"^-^»b6«i*-qC^ 


Oiioo®cit«c^a)cp*'^cb'^o»po»p^^^:c^»7^ic:p»i:w 
6  '^  c^i  (i^i »?  cJi  rh  rH  ic  ib  cp  «i  b»  (» cC'  cs  6  6  6 »—  "^  (f^ 


—«  00  iC  p  1--  —  Tt*  or  (?i  ic  Ci  fM  »o  X  ^1  >r.  op  —  «  cc  r- 1'-  cp  CO  »*':  "^  C5  ci 
w«'iH3^ij-^^cbt^r-i^xxd>6i660'^'^'fi6i'fic?«T^ 


<^^c5<:oco?oi-t-i'-t«i.'-b-.i>i>i>-i-.o5xxxxxaDXxx^ 


^OO'^X'MOO^XC^lCOO'^'X'-iir.  X'MCCOCCl^^rt<X'-<'<^X 

<m  •  W'»  y»  V,  c,  •"*  <•  V  vj  .^.   v»   rj  v5  ^»  •  .   ^^  Ty  Ty  ■»7"  ■^T"  ^rp  ^p  "j<  Ty  »p  ^  tJ"  ^y  T 


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»ftc»^j;oL':oiCpi^p»<;o^Q»fiO^^P»^ooo^Qi^O'^0 


SPECIFIC  ORAVITIES. 


183 


M  t>. 


m 


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■        •        •        • 


^  "t   l^  -H   O  »   N 

O  ^  I'"  Ci  O  — ^  00 
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CO  to  s«  00 
^  "^  ^  -f  o 


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g5P  «0  50  CO  CO  t—  l-  r»  t>-  5P  «  lO  »it  '5  '^  Tf  "^  4?:  »C  ^  t^  00  X  Ci  Q  o  O  Q 

X0S0i05CiCi0iCsS5Ci06OOOOOOOOOO»-<'^^^-^'~''^'~*'~t 


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oooooooooooooooooooo 


Oat^lOCO--3£^»r500^5STQO"*t<CO-^C:i^lJ5CO-^CS 

» cc  CD  « CO  t^  t>- 1- 1-*  t-  r>  i-«- 1-*  I*  t'- 1"  i>-  X  ®  Qo  00 

0000003000000000000000 


0000000000000000 


^*5P3!05C0»OXiJ5'MCS'rCi'*Qi3QOJCO<Ml>"00X"^XC0i-<"«^X'MkO«(M^XCS^X 
OCkJtriOl>-Oyi2it»u'^O^lOt*»^^OQO"T-^00'*<'-Ht»"^pt*"^»-IXCeWOXiO--Xii5rH 


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r- «^Ht-H^H^H^Hi-Hi— ti-H^^i-Hi-Hi-H^-^^^— i-Hi-Hp-^^^i-h»-^i— l»-«i-H-H.—  »H^H 


184 


PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 


o 

us 


s 

8 

t   I 

^n      m  m 

^^ 

S   O 

•g 

o 

£ 


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SPECIFIC  GRAVITIES. 


185 


1— I  W  T 


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OOQQQC»OiQpQQOp»OQOQOQ<NO»3C9QpQpQ'OQOOOC 

^l>ooo5p«o©o5^paDp7>l25^-o5-H55lO^*OTh«'?^25^ 
iOib'i?bt*«6sppppp'-H.lH»l^i^flie35idio»M««-^ 


*<*  w  ^  c» 
^^p6 


t*®05p^'MeQ'-r 

tOiQiOdcOOCOCO 


•  lA      •      •      •      •  CO      •      •      • 

•  Ia        •        •        •        •  3t        •        •       • 

•  ^0        •        ■        •        •  ^0        •        ■       • 


& 


iS 


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opiApiop»cpi-<©icO'fir5cot*gQgap'-tSi^3^»2S?tr!52S2!2!:2:i2SSs 
t«i>t«aDxxxxxooxxxxxxxxa5aoxxooxxxxxxxxxx 


186  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

The  specific  gravities  were  in  each  case  estimated  at  exactly 
15^  C.  and  compared  with  water  of  4P,  the  weighings  being  reduced 
to  the  vacuum.  Special  notice  should  be  taken  that  all  older 
tables  (including  those  of  Bineau,  Otto^  and  Kolb)  are  entirely 
wrong  in  the  case  of  the  acids  of  highest  strength^  as  the  maximum 
of  specific  gravity  does  not  (as  it  is  made  to  do  in  those  tables) 
coincide  with  the  greatest  strength^  that  is,  pure  monohydrated 
sulphuric  acid,  H2SO4.  The  maximum  it  at  about  98*5  per  cent., 
and  from  this  point  the  specific  gravities  decline  to  100  per  cent. 
H2SO4;  above  this  point,  that  is  when  SO3  is  present,  they 
instantly  rise  again.  (Comp.  Kohlrausch,  Pogg.  Annal.  Erganz- 
ungsband  viii.  p.  675 ;  Schertel,  Journ.  f.  prakt.  Chemie,  [2]  xxvi. 
p.  246;  Lunge  and  Naef,  Chem.  Ind.  1883,  p.  37;  and  others.) 

Special  attention  should  be  drawn  to  the  point  that  all  tables 
indicate  the  specific  gravities  only  for  chemically  pure  acids ;  those 
for  commercial  impure  acids  are  always  higher ;  we  shall  return 
to  tliis  subject  further  on.  The  accuracy  of  the  above-given 
tables  may  be  taken  as  +005,  so  that  the  first  decimal  is  right, 
but  the  second  serves  only  for  determining  the  first. 

A  paper  by  MendelejeflF  (Zeitsch.  f.  physik.  Cb.  i.  p.  273)  on 
the  specific  gravities  of  mixtures  of  sulphuric  acid  and  water  has 
only  theoretical  interest. 

A  correction  for  any  deviation  of  the  temperature  from  15°  must 
be  made,  whenever  the  acid  tested  by  the  hydrometer  is  above  or 
below  that  temperature.  Bineau  has  given  a  small  table  for  this 
purpose,  which,  however,  is  wrong  for  the  more  dilute  acids. 
From  a  very  large  number  of  observations  made  in  the  Author's 
laboratory,  a  table  has  been  constructed  showing  the  alterations 
to  be  made  in  the  specific  gravities  observed  for  all  strengths  of 
acid,  aud  for  all  temperatures  from  0^  to  100°,  in  order  to  reduce 
them  to  15°  C.  This  table  is  found  in  Lunge  and  Hurter's 
*  Alkali- Maker's  Pocketbook  '  ;  in  this  place  we  give  only  the 
average  figures.  For  each  degree  above  or  below  15°  you  should 
add  to  or  deduct  from  the  specific  gravity  observed  : — 

00006  with  acids  up  to  l"  170 
0-0007  with  acids  from   1170  to  1-450 
00008         ,.         „  1-450  ,.  1-580 

0-0009         „         .,  1-580  „  1-750 

0-0010         „         ,,  1-750  „   1-840 


HYDRATES  OP  SULPHURIC  ACID,  187 

All  observers  agree  that  the  solutions  of  sulphuric  acid  contain 
different  hydrates.  The  literature  of  this  subject  is  very  large, 
and  we  shall  here  quote  only  the  most  important  facts  (comp.  also 
Mendelejeffy  supra,  p.  186,  and  Pickering,  p.  179).  A  sesqui- 
hydrate  of  sulphuric  acid  cannot  be  established  as  a  certain 
chemical  compound^  but  the  double  hydrate,  SO4H2  f  HgO,  is 
known  with  certainty.  It  crystallizes  from  rather  more  dilute 
acid — for  instance,  acid  of  144°  Tw.  in  the  cold.  It  contains 
84-48  monohydrate  +15-52  water  (or  68-97  anhydride  -f-3103 
water),  melts  at  +8°  C,  but,  owing  to  superfusion,  generally  only 
solidifies  below  this  temperature  (for  instance,  in  the  deptii  of 
winter) ;  at  205°  to  210°  C.  it  already  loses  1  mol.  H^O  and 
leaves  ordinary  oil  of  vitriol  behind.  The  crystals  form  large, 
clear,  hexagonal  columns  with  six-pointed  end-faces.  Spec.  grav. 
1*78  to  1*79.  By  the  crystallization  of  this  hydrate  carboys  are 
often  cracked  in  winter ;  acid  of  144""  Tw.  and  the  like  ought 
therefore  only  to  be  warehoused  in  places  where  the  temperature 
will  not  sink  too  low,  for  instance  below  the  acid-chambers. 
Stronger  or  weaker  aoid  can  1)e  exposed  to  the  cold  of  winter 
without  any  danger. 

A  third  hydrate,  SO4H2+2H2O,  is  assumed,  because,  on 
diluting  strong  vitriol  with  water  down  to  this  point  (that  is, 
corresponding  to  73*13  per  cent,  monohydrate,  or  59  70  per  cent, 
anhydride),  the  largest  contraction,  viz.  from  100  volumes  to 
92-14  volumes,  takes  place.  Bourgoin  (Bull.  Soc.  Chem.  [2]  xii. 
p.  433)  infers  the  same  from  observations  on  electrolyzing  dilute 
vitriol.  The  density  of  this  mixture  is  variously  stated  by 
different  observers  : — by  Graham  at  1*6321  ;  by  Bineau,  1*665  ; 
by  Kolb,  1-652  ;  by  Jacquelain,  1-6746.  According  to  Liebig  it 
boils  at  163°  to  170°  ;  between  193°  and  199°  it  loses  one  molecule 
of  water,  and  is  changed  into  SO2H2  +  H2O  (Graham). 

Pickering  (Chem.  News,  Ix.  p.  68)  has  obtained  a  hydrate  of 
the  formula  HjSO^,  4H2O,  containing  57*66  per  cent,  real 
sulphuric  acid.  It  fuses  at  —25°.  By  adding  a  little  water  or 
sulphuric  acid  the  fusing-point  is  at  once  lowered  to  —70°. 

The  specific  gravities  given  in  all  the  tables  refer  only  to  pure 
acid,  and  cannot  be  accepted  as  quite  correct  for  the  ordinary  acid 
of  trade,  which  always  contains  impurities.  Kolb  has  examined 
into  this  matter,  and  has  determined  the  influence  of  the  common 
impurities  upon  the  density  of  sulphuric  acid,  viz.  that  of  lead 


188  PROPERTIES  OP  OXIDES  AND  ACIDS  OP  SULPHUR. 

sulphate/ of  the  oxygen  compounds^  of  nitrogen,  and  of  sulphurous 
acid.  Arsenic,  and  perhaps  iron,  usually  occur  in  too  small  a 
quantity  in  sulphuric  acid  to  influence  its  density  ;  but  certainly 
there  may  be  cases,  not  mentioned  by  Kolb,  in  which  sulphuric  acid 
is  strongly  contaminated  with  salts  of  iron,  aluminium,  sodium,  &c. 
The  iron,  for  instance,  may  come  from  pyrites-dust ;  aluminium 
from  the  packing  of  the  Glover  tower,  or  from  the  fire-clay 
frequently  employed  for  stopping  leaks  ;  sodium  from  solutions  of 
nitrate  or  sulphate  of  soda,  which  sometimes  inadvertently  get  into 
the  chambers. 

For  saturated  solutions  of  sulphurous  acid  in  sulphuric  acid  of 
varying  density,  Kolb  (Bull.  Soc.  Ind.  de  Mulhouse,  1872,  p.  224)* 
gave  a  table  which  has  been  proved  to  be  incorrect  by  J.  T.  Dunn 
(Chem.  News,  xliii.  p.  121,  and  xlv.  p.  270).  The  latter  has  also 
shown  that  KolVs  figures  are  too  low.  By  passing  a  current  of 
pure  dry  SO2  through  sulphuric  acid  of  spec.  grav.  1*841  he  found 
that  this  acid  dissolves  : — 


Tenii:eratiire. 

At  11°-1  C. 

Volume  at  700 
pressure. 

33-78  vols. 

luillim. 

SO, 

Spec  gray,  of 

solution  at  temp. 

of  experiment. 

1-823 

„   16  1 

28-86 

«l 

,.  17-1 

28-14 

a 

„  26  -9 

19-27 

>> 

1-822 

„   42-0 

12-82 

if 

1-821 

„  50  -9 

9-47 

it 

1-818 

,.  62  -3 

7-21 

99 

1-816 

.,  84-2 

4-54 

J  » 

1-809 

Dilute  acids  dissolve  the  following  quantities,  at  temperatures 
varying  from  15°  to  16°,  reduced  to  760  millim.  pressure  : — 

Spec.  grav.  of  Absorbs  vols, 

sulphuric  acid.  SO^. 

1-753  2083 

1-626  2517 

1-456  5^987 

1-257  30-52 

1-151  31-82 

1-067  3408 

•  Given  in  our  2nd  edition,  p.  127. 


SPECIFIC  GRATITIES  OF  IMPURE  SULPHURIC  ACID. 


189 


In  sach  quantities  (up  to  saturation)  sulphurous  acid  certainly 
never  occurs  in  commercial  vitriol  ;  and  it  is  very  rarely  that  more 
than  traces  of  it  are  found  therein^  since  it  does  not  agree  with 
the  nitrogen  oxides  which  are  most  frequently  found  in  com- 
mercial vitriol.  Nitric  acid  is^  if  at  all^  only  present  in  extremely 
small  quantities  in  the  sulphuric  acid  of  trade^  and  therefore  does 
not  modify  its  density  to  a  sensible  extent ;  especially  it  will  not 
be  found  in  sulphuric  acid  of  more  than  144^  Tw.^  except  perhaps 
in  the  nitrous  vitriol  from  the  Gay-Lussac  towers  ;  but  even  this^ 
according  to  my  analyses  (see  below)  ^  under  normal  conditions 
contains  mere  traces  of  NO^H.  Nitric  oxide  can  also  be  neglected; 
neither  concentrated  nor  diluted  sulphuric  acid  dissolves  more  than 
mere  traces  of  it.  Nitrom  acid  certainly  has  a  very  marked 
effect  on  the  apparent  percentage  of  a  sulphuric  acid^  according 
to  the  hydrometrical  test,  although  only  in  "  nitrous  vitriol ''  such 
large  propo  rtions  of  nitrous  acid  occur  as  to  influence  the  specific 
gi*avity  of  the  sulphuric  acid. 

Kolb  {he.  cit.  and  our  2nd  edition,  p.  129)  has  given  a  table  for 
the  specific  gravities  of  solutions  of  N^Oa  (or  rather  of  SO5NH, 
comp.  below)  in  sulphuric  acid  which  is  useless,  as  it  is  founded 
upon  erroneous  assumptions. 

R.  Kisling  (Chem.  Ind.  1886,  p.  137)  has  examined  the  effect 
of  a  percentage  of  arsenic  on  the  specific  gravity  of  sulphuric  acid. 
The  specific  gravities  of  two  commercial  acids,  A  and  B,  were 
observed  at  15°  C.  and  calculated  for  water  of  4**  C.  and  the 
vacuum,  in  order  to  be  comparable  with  Lunge  and  Naef's  figures 
for  pure  acid  (supra,  p.  119). 


A. 


B. 


Spec.  gray.    SO^H.^   ,    Aafi^      Spec.  gray.     SOJIj 
at  15®.       per  cent,  pet  cent.   |    at  15°.       percent. 


1-8377 
I'8ii87 

ivsa^.w 

18401) 
1-8412 
1-8413 
1-8414 
1-8^15 


92-87 
93-28 
94-25 
93-60 
93-93 
93-77 


0137 
0-137 
0-192 
0-258 
0  219 
0-254 
0-231 
0-231 


1-8367 
1-8372 
18373 

1-8384 
1-8386 
1-8388 


93  82 
93-67 
9312 
93-72 
93-96 
9404 


ASA 

per  cent. 


0024 
0-035 
0028 
0037 
0037 
0039 


190  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

When  comparing  these  results  with  those  of  Lunge  and  Naef^ 
the  considerable  influence  of  the  arsenious  acid  on  the  specific 
gravity  of  sulphuric  acid  is  very  apparent. 

With  respect  to  lead  sulphate,  Kolb  found  that,  at  the  ordinary 
temperature,  there  were  dissolved  in 

100  parts  vitriol  of  1*841  spec.  grav.  0039  part. 
100         „         „       1-793  „  0011     ,, 

100         „         „        1-540  ,,  0-003     ;, 

In  more  dilute  acids  the  lead  can  hardly  be  estimated.  Nitric 
acid,  which  anyhow  occurs  in  very  small  quantities,  does  not 
strongly  influence  the  solubility  of  lead  sulphate  in  sulphuric  acid, 
nitrous  acid  not  at  all.  The  effect  of  lead  sulphate  on  the 
density  of  vitriol  can  accordingly  be  neglected  for  the  ordinary 
temperature;  at  most  it  w^ould  influence  the  fourth  place  of 
decimals. 

Although,  as  we  see,  the  impurities  of  ordinary  sulphuric  acid, 
leaving  aside  "  nitrous  vitriol,^'  have  very  little  effect  on  its 
density,  still  the  latter,  at  the  highest  degrees  of  concentration,  is 
no  trustworthy  means  of  estimating  the  percentage  of  real  SO4H2 
in  the  acid,  even  when  the  correction  for  temperature  mentioned 
on  p.  186  is  applied,  because  at  this  concentration  a  small  difference 
in  density  corresponds  to  a  very  large  difference  in  percentage. 
Many  factories  have  special  hydrometers,  in  which  the  last  few 
degrees  are  spread  over  a  large  area  and  are  further  subdivided  ; 
but  in  fact  the  density  ought  to  be  estimated  by  more  accurate 
methods,  for  the  hydrometers  are  frequently  not  reliable,  and 
certainly  not  so  unless  the  normal  temperature  for  which  they 
have  been  made  be  exactly  observed.  But  any  determination  of 
density  for  estimating  the  percentage  of  the  very  strongest  acids 
must  be  rejected,  after  what  we  have  sieen  on  p.  186.  The  acids 
from  96  per  cent,  upwards  ought  therefore  always  to  be  estimated 
alkalimetrically. 

The  following  table  of  Anthonys  will  be  of  practical  value.  It 
shows  in  column  a  how  many  parts  of  oil  of  vitriol  of  168^  Tw. 
must  be  mixed  with  100  parts  water  at  15^  or  20°  in  order  to 
obtain  an  acid  of  the  specific  gravity  b. 


HELTINQ-POINTS  OF  SULPHURIC  ACIJ). 


191 


a.    ; 

1 

h. 

a. 

h. 

a. 

h. 

1  : 

1-009 

130 

1-456 

370 

1-723       1 

2    1 

1015 

140 

1-473 

380 

1-727 

5 

1035 

150 

1-490 

390 

1-730 

10    i 

1-060 

160 

1-510 

400 

1-733 

15     ' 

1-090 

170 

1-530 

410 

1737 

20    i 

1-113 

180 

1-543 

420 

1-740 

25     1 

1140 

190 

1-556 

1      430 

1-743 

:      so  ; 

1165 

200 

1-568 

440 

1-746 

35    ; 

1-187 

210 

1-580 

450 

1-750 

40    ■ 

1-210 

220 

1-593 

460 

1-764 

45    ! 

1-229 

230 

1-606 

1      470 

1-757 

50    1 

1-248 

240 

1-620 

480 

1-760 

55 

1-265 

'       250 

1-630 

490 

1-763 

60    ; 

1-280 

260 

I        1-640 

1      500 

1-766 

65     : 

1-297 

270 

1        1-648 

510 

1-768 

70     1 

1-312 

280 

1        1-654 

520 

1-770 

75 

1-326 

290 

1-667 

630 

1-772 

80  ; 

1-340 

300 

1-678 

540 

1-774 

a5   ' 

1-357 

310 

1-689 

1     550 

1776 

90    ; 

1-372 

320 

,        1-700 

1     560 

1-777 

1)5    ' 

1-386 

330 

1-705 

580 

1-778 

100    ; 

1-398 

340 

1-710 

590 

1-780 

1      no    ; 

1-420 

350 

1-714 

600 

1-782 

120    i 

1-438 

360 

1-719 

1 

The  melting-points  of  sulphuric  acids  of  diflferent  degrees  of 
concentration  are  given  by  Payen  in  a  table  quoted  in  our  2iid 
edition,  p.  133. 

A  new  determination  by  myself  (Berl.  Ber.  1881,  p.  2649)  gave 
the  following  results  : — 


Melting-point. 

liquid, 
do. 
do. 

-8-5 
+  4'5 
+  6-5 
'+80 


Spec.  grav.  of 
acid  at  15°  0. 

Freezing-point. 

1-671     .     . 

.     liquid  at  -20°  C 

1-691     .     . 

do. 

1-712     .     .     . 

do. 

1 727     .     . 

-  7-5° 

1-782     .     . 

-8-5 

1-749     .     .     . 

-0-2 

1-767     .  .  .     . 

-I-1-6 

1.-790     .     . 

+  4-5 

1-807    .     .     . 

-90 

1-822     .     . 

.     liquid  at  -20°  C 

1-840     .     . 

do. 

-6-8 

liquid. 

do. 


192 


PROPERTIES  OF  OXIDES  ikND  ACIDS  OF  SULPHUR. 


Pickering  (J.  Chem.  Soc.  1890^  Ivii.  pp.  331  et  seq.)  has  pub- 
lished an  extensive  memoir  on  the  freezing-points  of  sulphuric 
add  and  its  solutions.  Thilo  (Journ.  Soc.  Chem.  Ind.  1893, 
p.  827)  gives  very  extended  tables  as  to  the  results  obtained  by 
him  in  B.  Pictet's  laboratory.  Pictet,  himself,  subsequently 
(Compt.  Rend.  cxix.  p.  642)  supplies  the  following  table  : — 


Pormuln. 

SOjH., 

Spec. 

1 
Freezing- 

Formula. 

SO,H, 

Spec. 

Freesing- 

per  cent. 
10000 

griiv. 

point. 
+10° 

per  cent. 

grav. 
1196 

point. 

H»SO, 

1-842 

H,JS04+  I5U3O 

26-63 

-340 

T    +H,0 
2HaO 

84-48 

1-777 

+  3 

16    „ 

25-39 

1-187 

-  26-5 

73-08 

1-650 

-70     j 

18    ., 

23-22 

1-170 

.  -  19 

4  „ 

57-65 

1-476 

-40 

20    .. 

21-40 

1-157 

-17 

6   .. 

47-57 

1-376 

-50     1 

25    , 

17-88 

1129 

-    8-5 

8   ,. 

40-50 

1-311 

-65  ; 

50    .. 

9-82 

1-067 

-    3-5 

.,       10    . 

36-25 

1-268 

-88 

75     . 

6-77 

1045 

0 

..        11    ., 

3311 

1-249 

-75 

100    .. 

516 

1-032 

+    2-5 

,.       12   ,. 

31-21 

1-233 

-55 

300    ,. 

1-78 

1-007 

+   4-5 

..       13   ., 

29-52 

1-219 

-45 

„       1000    ., 

0-54 

1-001 

+   0-5 

»       14   „ 

28-00 

1 

1-207 

-40     i 

j 

1 

Knietsch  (Ber.  1901,  p.  4100)  gives  the  following  table  of  tlie 
melting-points  of  sulphuric  acid,  ordinary  and  fuming,  from  1  per 
cent,  to  100  per  cent.  SO3,  which  I  have  supplemented  by  adding 
the  corresponding  percentages  of  HjSO^.  By  ''  melting-point  *' 
he  understands  the  temperature  at  which  the  cooled  acids  in  which 
crystals  had  commenced  to  form  remained  constant  when  the 
vessel  was  taken  out  of  the  cooling  medium  during  the  process  of 
solidification.  In  a  set  of  curves  appended  to  the  original  (com p. 
fig.  39,  p.  174)  he  also  shows  the  temperatures  at  which  the 
first  crystals  form  and  those  at  which,  on  cautiously  heating, 
the  last  crystals  were  liquefied.  The  curves  show  a  decided 
maximum  near  the  point  H2S04,H20,  a  minimum  at  the  point 
2H2S04,H80,  a  maximum  (nearly  coinciding  with  the  first) 
at  the  point  H3SO4,  a  minimum  at  4HjS04,S03,  a  strong 
maximum  at  HsS04jS03  (=pyrosulphuric  acid),  a  minimum  at 
H2S04,2S03,  and  the  highest  maximum  for  SOs  in  the  polymerized 
state. 


BOILING-POINTS  OF  SULPHURIC  ACID. 


193 


S03 

H2SO, 

Melting- 

SO3 

1 

1   H.^S04        Melting- 

SO3 

Melting- 

p.  cent.  p.  cent.. 

1 

point  °C. 

-  0-6 

-  10 

p.  cent. 

j  p.  cent.       point  °0. 

p.  cent. 

point  °0. 

1 
2 

]-22 ' 
2-45; 

•  •  • 

••■     1    below  -40° 
••  • 

82 
83 

-f  8-2 
-  0-8 

3    '     3(57j 

-  1-7 

61 

74-72             -40 

84 

-  9-2 

4    1     4-90 

-  20 

62 

75-95             -20 

85 

-110 

0 

612 

—  2*7 

63 

7717             -11-5 

86 

-  2-2 

6 

7-35 

-  3-6 

64 

78-40             -  4-8 

87 

+  13-5 

7 

8-57 

-  4-4 

65 

79  02             -  42 

88 

+260 

8 

9-80, 

-  53 

66 

80-85    ,         +1-2 

89 

+  34-2 

9 

1102 

-  6-0 

67 

82-07             +  8-0 

90 

+34-2 

10 

1225 

-  67 

68 

83-39    1         +  80 

91 

+  25-8 

11 

13-47 

-  7-2 

69 

84-52    i        H-  70 

92 

+14-2 

12 

1470 

-  7-9 

70 

85-75 

+  40 

93 

+  0-8 

13 

15-92 

-  8-2 

71 

86-97 

-  10 

94 

+  4-5 

14 

1715 

~  90 

72 

88-20 

-  7  2 

95 

+  14.8 

15 

18-37; 

-  9-3     , 

73 

89-42 

- 16-2 

96 

+20-3 

Ifi 

19-60 

-  9-8     , 

74 

90  65 

-250 

97 

+29-2 

17 

20-82 

-11-4 

:    75 

91-87 

-34  0 

98 

+338 

18 

2205 

-13-2 

1     76 

93101  ^     -320 

99 

+36-0 

19 

23-27 

-15-2 

1     77 

94-83  1 

7      -^32 

100 

+400 

20 

24-50 

-171 

'     78 

9505 

S      -16-5 

21 

25  72  1 

-2-2-5 

1     79 

96-77    i         -  5-2 

22       26-95 1 

-310 

!     80 

98-00 

+  30 

23    ;  2S17  ! 

-401 

81 

99-25 

H-  7-0 

1 

1 

81-63 

100-00 

+100 

On  hoiling  dilute  sulphuric  acid^  at  first  nothing  but  aqueous 
vapour  escapes  ;  according  to  Graham^  acid  vapour  is  mixed 
with  the  steam  ouly  when  no  more  than  2  molecules  of  water 
are  present  to  1  of  SO3 — that  is,  with  a  percentage  of  84s'48 
SO4H2  or  a  specific  gravity  of  1*78.  After  several  discussions 
about  the  loss  of  sulphuric  acid  in  concentrating  it,  by  myself. 
Bode,  Walter,  &c.,  it  may  be  assumed  that  in  manufacturing 
practice  no  sensible  loss  of  acid  takes  place  by  real  volatilizalion  up 
to  a  strength  of  144!°  or  even  of  152°  Tw. ;  but  from  violently 
boiling  acid  there  is  always  a  little  acid  carried  away  mechanically 
in  the  shape  of  small  drops,  especially  in  pans  fired  from  the  top 
and  also  in  the  Glover  tower,  or  in  a  ''  vesicular  state."  When 
the  evaporation  up  to  that  point  takes  place  quietly  at  a  moderate 
heat,  there  is  probably  no  loss  of  acid  at  all. 

The  boiling-point  of  sulphuric  monohydrateis  stated  by  Marignac 
=338^  by  Pfaundler  =317°.  The  boiling-points  of  sulphuric  acid 
containing  water  were  examined  by  Dalton  in  the  beginning  of 
this  century.  His  table,  which  was  obviously  wroiig,  has  been 
replaced  by  another,  founded  upon  the  author's  investigations 
(Berl.  Ber.  xi.  p.  370). 

VOL.  I.  O 


194 


PROPERTIES  OF  OXIDES  AND  ACID8  OF  SULPHUR. 


Table  T. 


Specific 

Teojpe- 

.   Spec.  grav. 

Percent- 

BoilJDg- 

Barometer 

rature. 

reduced  to 

j     »ge  of 

'       point. 

reduced  to  (»-: 

gravity. 

°C. 

15°  C. 

i  s6,H,. 

'       ^C. 

raillims. 

1-8380 

17 

1-844K) 

95-3 

297 

718-8 

1-8325 

16-5 

1-8334 

92-8 

280 

72;3-9 

1-8240 

15-5 

1-8242 

90-4 

264 

720-6 

1-8130 

16 

1-8140 

88-7 

257 

7260 

1-7985 

15-5 

1-7990 

86-6 

241-5 

7201 

1-7800 

15 

1-7800 

843 

228 

720-5 

1-7545 

16 

1-7554 

81-8 

218 

726-0 

1-7400 

15 

1-7400 

80-6 

209 

720-6 

1-7185 

17 

1-7203 

78-9 

203-5 

725-9 

1-7010 

18 

1-7037 

77-5 

m 

725-2 

1-6760 

19 

1-6786 

75-3 

183-5 

725-2 

1-6690 

16 

1-6599 

73-9 

180 

725-2 

1-6310 

17 

1-6328 

71-5 

173 

7252 

1-6055 

17 

1-6072 

69-5 

169 

7301 

1-5825 

15 

1-5825 

67-2 

160 

728-8 

1-5600 

17 

1-5617 

654 

158-5 

730-1 

1-5420 

17 

1-5437 

64-3 

151-5 

7301 

1-4935 

18 

l-49(iO 

59-4 

143 

7301 

1-4620 

17 

1-4635 

56-4 

133 

730-1 

1-4000 

17 

1-4015 

50-3 

124 

730-1 

1-3540 

17 

1-3554 

45-3      , 

118-5 

730-1 

1-3180 

17 

1-3194 

41-5      I 

115 

730-1 

1-2620 

17 

1-2633 

34-7 

110 

7329 

1-2030 

17 

1-2042 

27-6 

107 

732-9 

1-1120 

17 

1-1128 

15-8      , 

103-5 

732-9 

10575 

17 

1-Oo80 

8-5       1 

101-5 

735() 

Table  II. 
(Calculated  by  graphical  interpolation.) 


Percent. 

Boiling- 

1 

Percent. 

Boiling- 

Percent. 

Boiling- 

.  Percent. 

Boiling- 

SO^H,. 
6 

point. 

SO,H,. 

point. 

o 
1    118-5 

70 

point. 

1         o 
170 

;  so,H,. 

point. 

o 
101 

45 

1, 

''      86 

238-5 

10 

102 

50 

1     124 

72 

1745 

,       88 

251-5 

!      15 

1035 

53 

1285 

74 

180-6 

'i      90 

262-5 

20 

105 

5(; 

133 

76 

189 

91 

268 

25 

106-6 

60 

141-5 

78 

199 

92 

274-5 

30 

108 

62-5 

147 

80 

2()7 

93 

281-5 

35 

110 

.    65 

153-5 

82 

218-5 

14 

288-5 

40 

114 

67-5 

r 

161 

84 

<»7 

95 

21»5 

AQUEOUS-VAPOUR  TENSION  OF  SULPHURIC  ACID. 


195 


The  tension  of  aqueoiM  vapour  in  sulphuric-acid  solutions  of 
various  strengths  was  determined  by  Regnault  in  1845  (Ann. 
de  Chim.  [3]  xv.  p.  179)  for  temperatures  from  5°  to  35°  C.  We 
here  give  his  table  (for  every  other  degree),  adding  to  the  hydrates 
quoted  by  him  the  percentage  composition  and  specific  gravities. 
We  also  subjoin  SorePs  table  (p.  196),  computed  for  a  wider 
interval  of  temperatures,  better  suited  for  the  wants  of  sulphuric- 
acid  manufacture.  The  tensions  are  stated  in  millimetres  of 
mercurial  pressure. 

Reguault^s  Table  of  the  Aqueous- Vapour  Tensions  of  Dilute 

Sulphuric  Acid. 


H,80, 

+5h,o 

H,SO, 

1 

1   H,SO, 

«c. 

4-3H.,0 

'  +4H,6 

84-5o/o. 

731%. 

64-5o/„. 

57-6"  o. 

5 

1-780. 

1-654. 

1-554. 

1-477. 

0105 

0-388 

0-861 

1-2W 

7 

0108 

0-480 

0-985 

1-510 

9 

0112 

0-476 

1125 

1-753 

11 

0118 

0-527 

1-280 

2025 

13 

0-124 

0-586 

1-454 

2-331 

15 

0131 

0-651 

1-648 

2674 

17 

0139 

0-725 

1-865 

3059 

19 

0149 

0-808 

2108 

3-492 

21 

0159 

0-901 

2-380 

3-977 

23 

0171 

1-006 

2-684 

4-523 

25 

0184 

1125 

3024 

5-135 

27 

0199 

1-258 

3-405 

5-822 

29 

0216 

1-408 

3-83() 

6-594 

31 

0-235 

1-557 

4-305 

7-459 

a3 

0-256 

1-767 

4-838 

8-432 

35 

1 
1 

0-280 

1-981 

5-432 

9524 

H.,s04    n.,sOi    H2SO4 

-|-5H,0    +7H,0    +mfi 


521  %.    43-7   -0 
1-420       1-340. 


'0» 


2137 

2-464 

2-829 

3240 

3-699 

4-215 

4-793 

5-440 

6-366 

6-979 

7-892 

8-914 

10-060 

11-345 

12-785 

14-400 


3168 

3643 

4176 

4-773 

5443 

^•194 

7036 

7-980 

9039 

10-226 

11-557 

13-050 

14-723 

16-600 

18-704 

21-0(>3 


37-7 
1-287. 

4-120 

4-728 

6-408 

6-166 

7013 

7-958 

9014 

10191 

11-506 

12-974 

14-613 

16-443 

18-485 

20-765 

23-311 

26-152 


H3SO,  '  H,SO, 
-l-llH.,0  +I7H2O 
33- 1  %.    24-3  °/o. 

1-247.       1176. 


4-428 

5164 

5-980 

6-883 

7-885 

8-995 

10-222 

11-583 

13090 

14-760 

16-610 

18-659 

20-920 

23-443 

26-228 

29-314 


5-478 

6-300 

7-216 

8237 

9-374 

10-641 

l2-a>4 

13-628 

15-383 

17-338 

19-516 

21-944 

24-650 

27-66(i 

31025 

34-770 


Knietsch  (/.  c.  p.  4111)  has  also  determined  the  vapour-tensions 
of  sulphuric  acid,  both  ordinary  and  fuming,  at  various  tempera- 
tures up  to  100°  C.  As  may  be  imagined,  the  aqueous-vapour 
pressures  decline  rapidly  with  the  concentration  of  the  ordinary 
acid,  and  for  acids  from  90  to  98*6  per  cent,  they  are=0  even  at 
100°.  From  this  point  the  vapour-tension,  now  of  course  pro- 
duced by  SOs,  rises  very  rapidly,  as  is  shown  by  the  following 
table  (p.  197),  where  the  pressure  of  |  vol.  fuming  acid  +  i  vol. 
air  is  expressed  in  atmospheres. 


o  2 


• 

o 

o 

3 

1 

1 

•       • 

fee*. 

o 

•        • 

c    : 

a     ; 

9» 

183-5    2220 
1600    1950 
138-5    169-5 
118-7  '  146-0 

100-7    125-0 
83-7    1060 
700      880 

9 

s 

44-4  ,   570 
33-7  ,   43-4 

• 

I-H 

CO 

lo 

9 
fi 

00 

lb 

T-l 

9 

CO 

r-H 

• 

f-H 

CO 

00 

cb 

1 

o 

8 

o 

a  : 

• 
• 
• 
• 
• 
• 

-  : 

• 

f-H 

9 
in 

•         • 

S    i 
E    : 

• 
• 
• 
• 
• 
• 

s 

us    00    (?l    o    p 

s  ?  s  s  as 

IN 

00     iO 
CO     (N 

CO    ifi 

lO 
CI 

9   Cl 

I-H 

o 
»b 

in 
1-4 

• 

i> 

• 

• 

o 
o 

•      • 

S    : 
S    : 

o 

CO 

l-H 

CO 

C&    Cq    CO 

S  S  g 

1— 1 

9   9 
5?  § 

CO 

u-S     P 

3  s 

f-H 

00 

r-l 

• 
• 

do 

Cl 

■ 

CO 

o:> 
CO 

1 

o 

•       • 

s  i 

■    • 

g   ! 

E    : 

1-H 

Si 

.-1   »o 
3  S 

CO 
00 

■ 

CO    Th    i> 

S     CO     S 

O    •««<    ^ 
g   g   S 

So 

"^    CO 

Tjl 

CI 

oa    »o 

-H      i-H 

^H 

Cl 

f-H 

9 
lb 

9 

c^ 

<b 

md  Water  ( 

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SPECIFIC  HEAT  OF  SUIiPHt'RIC  ACID. 


197 


Temp. 

°0. 

SO3 
30  p.  c. 

SO3 
40  p.  c. 

SO3 
50  p.  c. 

SO3 

60  p.  c. 

SO3 
70  p.  c. 

SO3 

80  p.  0. 

1 

1      SO3 
100  p.  c. 

atm. 

atm. 

atm. 

atm. 

atm. 

atm. 

atm. ' 

35 

•  ■  • 

•  •  • 

•  »• 

1 

•  •  • 

•  •  • 

0-160 

1    0-400 

40 

•  •  • 

0-075 

•  •  • 

0-225^ 

0-375 

0-500 

"   0650 

45 

0050 

0125 

•  •  • 

0-360  ; 

0-576 

0-650 

0-875 

50 

0100 

0175 

0-350 

0-525 

0-775 

0-875 

1-200 

55 

0140 

0-225 

0-450 

0-675 

1025 

1-2C0 

1-600 

60 

0-200 

0-275 

ObLO 

0-825    ' 

1-400 

1-500 

1-850 

65 

0-225 

0-350 

0-700 

1025 

1-650 

1-900 

2-250 

70 

0-275 

0*400 

0-825 

1-275 

2050 

2-300 

'    2-725 

75 

oaio 

0-475 

1000 

1-570 

2-525 

2-800 

3-300 

80 

0-400 

0-575 

1150 

1-850 

3-100 

3-500 

4000 

85 

0-450 

0-675 

1-400 

2-150 

3-700 

•   4175 

4-900 

90 

0530 

0-825 

1-700 

,   2-575 

4-400 

i    5-050 

6-900 

95 

0-625 

0950 

2-050 

i    3150 

5-200 

•    6-000 

•  t* 

100 

0-730 

1-OOU 

2-400 

1 

1   3-700 

6000 

•  ■  ■ 

1      •  •  • 

The  specific  heat  of  monohydrated  sulphuric  acid  at  16^-20°  C. 
is  0*3315  (waters:  1).  Marig^ac  states  the  specific  heat  of  acid 
diluted  with  water  as  follows : — 


HjSO^ 

+     5  aq. 

=0-5764 

10  „ 

0-7212 

15  „ 

0-7919 

25  „ 

0-8537 

50  „ 

0-9155 

100  „ 

0-9545 

200,, 

0-9747 

400  „ 

0-9878 

The  following  table,  by  Bode,  is  more  convenient  for  practical 
use  (Zeitschr.  f.  angew.  Chem.  1889,  p.  244)  :  — 


Spec,  gi-av. 
1-842 
1774 
1-711 
1-615 
1-530 
1-442 
1-383 


Spec.  heat. 
0-3315 
0-38 
0-41 
0-45 
0-49 
0-55 
0-60 


Spec.  grav. 
1-020 
1-263 
1-210 
1-162 
1-116 
1-075 
1037 


Spec.  heat. 
0-67 
0-73 
0-78 
0-82 
0-87 
0-90 
0-95 


Comp.  also  Pickering  (J.  Chem.  Soc.  Ivii.  p.  90). 


198 


PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 


Kuietsch  (Berl.  Ber.  1901^  p.  4102)  gives  the  speeific  heats  of 
acids  of  higher  concentratiou  and  fuming  acids^  up  to  100  per  cent, 
anhydride.  The  curve  (fig.  39,  p.  174)-  falls  continuously  with 
the  concentration,  till  20  per  cent.  SO3  is  reached ;  it  then  rises 
again,  and  at  100  per  cent.  SO3  reaches  the  considerable  amount 
of  0*77.     The  principal  points  are  : — 


Total  SO,. 

Free  SO3. 

Sijec.  lieat. 

1 
Total  SO3. 

Free  SO,. 

S[)ec.  heat. 

80 

••• 

0-3574 

1        92 

.>t)-45 

0-400 

82 

20 

0345 

1        94 

07-34    . 

0-465 

84 

12-89 

0-340 

i        90 

78-23 

0-535 

m 

23-78 

0-340 

98 

8912 

0-050 

S8 

34-r)7 

0-350 

la) 

100 

0-770 

90 

45-56 

0-300 

■ 

Chemical  behaviour  of  Sulphuric  Acid. 

On  mixing  oil  of  vitriol  with  water  a  considerable  rise  of  tempe- 
rature takes  place,  water  being  chemically  fixed  by  the  formation 
of  certain  hydrates,  as  described  above.  Besides,  on  mixing 
concentrated  acid  with  water,  as  already  mentioned,  a  not  in- 
considerable contraction  takes  place,  which  must  equally  lead  to  an 
evolution  of  heat.  But  on  mixing  strong  sulphuric  acid  with  snow 
excessive  cold  is  produced  by  the  heat  becoming  latent  on  the 
liquefaction  of  snow,  which  considerably  exceeds  that  becoming 
free  in  consequence  of  the  chemical  combination.  This  cold, 
however,  is  only  produced  when  the  proportion  between  acid  and 
ice  does  not  exceed  certain  limits :  for  1  part  of  sulphuric  acid 
there  must  be  1^  part  of  snow  present ;  with  less  snow  there  is  a 
rise  of  temperature. 

Even  when  more  strongly  diluted  much  heat  is  liberated.  Many 
observers  have  worked  upon  this  subject ;  but  we  quote  here  only 
a  few.  Thomsen  (Deutsch.  chem.  Ges.  Ber.  iii.  p.  496)  states 
that  one  gram-molecule  (that  is  98  grams)  H2SO4  gives  the 
following  amounts  of  heat  when  combining  with  x  molecules  of 
water : — 


HEAT  OF  SOLUTION  OF  SULPHURIC  ACID, 


199 


X, 


1    . 

6272  metrical  heat-units. 

9364 

}> 

w 

3     . 

.     11108 

:j 

a 

5     .     . 

,     13082 

sy 

3} 

9    .     . 

,     14940 

jf 

yi 

19     .     . 

,     16248 

}i 

n 

49     .     . 

.     16676 

•} 

;» 

99     . 

.     16850 

j» 

;» 

199     .     . 

.     17056 

>* 

j» 

499     .     . 

.     17304 

a 

j» 

799     . 

.     17632 

i) 

;> 

1599    .     . 

,     17848 

3i 

3> 

Somewhat  higher  results  were  obtained  by  Pickering  (J.  Chem. 
Soc.  Ivii.  p.  94). 

Knietsch  (Berl.  Ber.  1901,  p.  4103)  gives  the  following  figures 
of  the  heat  of  dissolution,  found  both  in  the  laboratory  and  by 
large  scale  experiments  with  400  kgs,  water  (for  the  values  of 
fuming  acid,  see  p.  170) : — 


SO, 

H2S0, 

per  cent. 

per  cent. 

50 

61-25 

51 

62-48 

52 

63-70 

53 

64-93 

54 

66-15 

r^ 

67-38 

5<? 

r>8-t50 

57 

69-83 

58 

7105 

59 

72-28 

m 

73-.7O 

61 

74-73 

02 

75-95 

63 

77-18 

(*>4 

78-40 

♦>5 

79-63 

m 

80-85 

Calories. 


SO3 

per  cent. 


ir,so, 

per  cent. 


Caloriee. 


39 

{        67 

82-08 

93 

41 

'        6S 

83-30 

98 

44 

m 

84-53 

103 

46-5 

70 

85-75 

108 

49 

71 

86-98 

113 

51-5 

'        72 

88-20 

119 

54 

73 

8943 

126 

57 

74 

90-65 

133 

59-5 

75 

91-83 

139 

62 

76 

9310 

146 

6^3 

77 

94-33 

152 

m 

78 

95-55 

160 

72 

79 

96-78 

168 

75 

80 

9800 

178 

79 

81 

99-23 

188 

Qiyry 

8H53    , 

100-00 

193 

ss 

1 

The  curve  both  for  ordinary  and  fuming  acid  runs  on  quite 
steadily,  without  any  breaks,  so  that  the  formation  of  the  different 
hydrates  evidently  does  not  cause  any  special  heat-action. 

On  account  of  this  considerable  evolution  of  heat,  concentrated 


200  PROPERTIES  or  OXIDES  AND  ACIDS  OF  SULPHUR. 

sulphuric  acid  and  water  must  always  be  mixed  with  care :  the 
water  ought  never  to  be  poured  into  the  acid,  but  the  acid  run  in 
a  thin  jet  into  the  water  with  constant  stirring.  On  a  sudden 
mixture,  so  much  heat  is  liberated  at  once  that  the  acid  may  be 
raised  to  the  boiling-point  and  splash  about ;  and  glass  vessels  are 
easily  cracked  thereby. 

The  affinity  of  sulphuric  acid  for  water  is  also  proved  by  its 
great  hygroscopicity.  Concentrated  sulphuric  acid  is  one  of  the 
best  means  for  drying  gases ;  and  it  is  not  only  used  in  this  way 
for  innumerable  scientific,  but  also  for  some  technical  purposes — 
for  instance,  in  the  manufacture  of  chlorine  by  Deacon^s  process, 
where  the  gaseous  mixture,  having  been  deprived  of  its  hydro- 
chloric acid  by  water,  is  passed  through  a  coke-tower  fed  with 
sulphuric  acid,  in  order  to  be  deprived  of  its  moisture.  In  the 
same  way,  chlorine  gas  is  dried  for  the  process  of  utilizing  tinned 
scrap-iron  by  treatment  with  chlorine,  which  in  the  dry  state  does 
not  act  upon  iron,  but  gives  with  tin  anhydrous  tin  tetrachloride. 

Concentrated  sulphuric  acid  acts  also  upon  liquid  and  solid 
bodies  by  depriving  them  of  water  or  even  splitting  off  the  elements 
of  the  same  if  the  substance  only  contains  the  latter,  but  no  readily 
formed  water.  Upon  this  action,  too,  a  host  of  scientific  and 
technical  applications  of  sulphuric  acid  are  founded.  In  this  case 
frequently  the  Bo-called  sulphonic  acids  are  formed,  generally  com- 
pounds easily  lending  themselves  to  further  reactions.  Instances 
of  this  are: — the  formation  of  ether  by  the  splitting-up  of  sulphu- 
ric acid,  with  the  intermediate  formation  of  sulphovinic  acid ;  that 
of  ethylene  on  the  further  splitting-off  of  water;  the  preparation 
of  nitrobenzene,  picric  acid,  nitronaphthalene ;  the  manufacture  of 
resorcine  and  alizarine  by  the  alkaline  fusion  of  the  sulphuric  acids 
of  benzene  and  anthraquinone  ;  and  many  other  cases. 

The  charring  of  many  organic  substances,  such  as  wood,  sugar, 
&c.,  by  contact  with  strong  sulphuric  acid,  proceeds  from  the 
same  source.  Necessarily  this  acid,  in  its  concentrated  form,  must 
have  an  extremely  prejudicial  effect  on  the  animal  body.  The 
remedy  usually  applied,  viz.  burnt  magnesia,  cannot  do  much  good 
when  the  epithelium  of  the  oesophagus  and  the  stomach  are  once 
destroyed. 

The  affinity  of  concentrated  sulphuric  acid  for  water  is  also 
shown  by  the  fact  that  it  easily  runs  over,  when  kept  in  open 
vessels,  by  attracting  moisture  from  the  air  —  a  fact  to  be 
remembered  in  the  case  of  balances  &c. 


DECOMPOSITION  OP  SULPHURIC  ACID.  201 

Decompositions  of  Sulphuric  Add. — Some  of  these  have  been 
roentioned  already — for  instance,  that  into  anhydride  and  water  by 
evaporation.  The  mixed  vapour,  on  account  of  the  unequal  velocity 
of  diffusion  of  the  two  vapours,  can  be  separated  to  a  great  extent 
into  its  two  constituents,  so  that  at  520°  C,  in  an  hour,  a  residue  of 
60  per  cent,  monohydrate  and  40  per  cent,  anhydride,  at  445°  C. 
75  percent,  monohydrate  and  25  per  cent,  anhydride  was  obtained 
(Wanklyn  and  Robinson,  Proc.  Roy.  Soc.  xii.  p.  507).  Perhaps  a 
process  for  preparing  fuming  acid  can  be  founded  upon  this  fact. 
Even  far  below  the  boiling-point  the  dissociation  begins  in  the 
liquid  acid.  It  has  been  pointed  out  that  already  at  30°  to  40°  C. 
the  hydrate  begins  to  give  off  vapours  of  anhydride  (Marignac) , 
which  fact  has  been  confirmed  by  the  exact  researches  of  Dittmar 
(Chem.  Soc.  Joum.  [2]  vii.  p.  446)  and  Pfaundler  &  Polt  (Zeitschr. 
f.  Chemie,  xiii.  p.  ^6). 

A  more  thorough  decomposition  into  sulphur  dioxide,  oxygen,  and 
water  takes  place  on  conducting  the  vapour  of  sulphuric  acid 
through  porcelain  or  platinum  tubes  filled  with  bits  of  porcelain 
and  heated  to  a  bright  red  heat.  This  mode  of  decomposition  has 
been  recommended  by  Deville  and  Debray  as  a  *'  cheap  '^  plan  for 
making  oxygen ;  but  it  does  not  seem  to  have  answered,  owing  to 
the  insufficient  sale  of  sulphurous  acid  or  its  salts ;  it  was  expected 
to  play  a  great  part  in  the  manufacture  of  anhydride  by  Winkler's 
process,  but  even  for  this  purpose  it  has  not  been  found  economical. 

On  heating  with  charcoal  to  100°  or  up  to  150°  C,  sulphuric  acid 
yields  carbon  dioxide  and  sulphur  dioxide;  on  boiling  with  phos- 
phorus, sulphur  ;  on  boiling  with  sulphur,  sulphur  dioxide ;  by  the 
action  of  the  electric  current,  hydrogen,  oxygen,  sulphur,  &c.  (in 
dilute  sulphuric  acid  the  electric  current  merely  causes  the  decom- 
position of  water). 

Sulphuric  acid  at  temperatures  below  its  boiling-point  behaves 
as  the  strongest  of  all  acids,  and  expels  all  other  acids  from  their 
salts  when  the  solubilities  &c.  allow  this;  but,  inversely,  sodium 
sulphate  is  also  decomposed  by  hydrochloric  acid.  In  fact,  the 
*'  avidity  "  of  hydrochloric  and  nitric  acid  at  ordinary  temperatures 
much  exceeds  that  of  sulphuric  acid.  Boussingault  (Ann.  Chim. 
Phys.  [5]  ii.  p.  120)  has  shown  that  dry  hydrochloric-acid  gas  at  a 
red  heat  decomposes  the  sulphates  of  sodium,  potassium,  barium, 
strontium,  and  calcium  (see  further  on).  More  refractory  acids 
expel  sulphuric  acid  at  higher  temperatures — for  instance,  boric 
acid,  silica,  and  phosphoric  acid. 


202  FROPERTIKS  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

With  the  bases  sulphuric  acid  forms  two  principal  series  of 
salts,  viz.  acid  ones,  of  the  formula  S02QvYr>  and  neutral  ones,  of 

the  formula  SOa<^z:^J.     Very  frequently  it  also  occurs  in  basic 

salts,  rarely  in  hyperacid  salts. 

The  technical  applications  of  sulphuric  acid  to  a  great  extent 
rest  on  its  great  affinity  to  all  bases.  Of  its  salts  the  acid  and 
neutral  ones  are  soluble  in  water,  excepting  the  neutral  salts  of 
barium,  strontium,  lead,  silver,  and  mercury  (in  the  state  of 
protoxide),  which  are  little  or  not  at  all  soluble  in  water  and  dilute 
acids.  Calcium  sulphate  is  sparingly  soluble  in  water.  Most 
sulphates  are  insoluble  in  alcohol.  The  basic  sulphates  are  mostly 
insoluble  in  water,  but  soluble  in  acids.  The  sulphates  incline 
very  much  towards  the  formation  of  double  salts,  of  which  those 
are  called  alums  which  contain  a  combination  of  univalent  and 
trivalent  (corresponding  to  a  double  atom  of  quadrivalent)  metals. 

The  neutral  salts  of  the  alkali-metals,  of  calcium^  magnesium, 
silver,  manganese,  and  ferrosum,  the  latter  only  if  entirely  free 
from  acid  and  peroxide  (a  condition  very  rarely  realized),  do  not 
redden  blue  litmus-paper,  whilst  all  other  soluble  sulphates  do 
this. 

On  heating  to  a  red  heat,  only  the  neutral  sulphates  of  the 
alkalies,  of  the  alkaline  earths,  and  of  lead  remain  unchanged.  At 
a  still  higher  temperature  (that  of  melting  iron)  the  two  latter 
classes  are  also  decomposed,  but  the  alkaline  sulphates  are  vola- 
tilized without  a  change.  Even  zinc  sulphate  and  manganous 
sulphate  are  not  easily  decom])osed.  This  explains  the  difficulty 
of  completely  converting  blende  into  oxide  of  zinc. 

On  roasting,  the  decomposable  sulphates  yield  metallic  oxides, 
sulphur  dioxide,  and  oxygen.  They  are  much  more  easily  split 
up  on  heating  by  certain  additions,  such^as  coal,  iron,  &c. 

On  the  metals  sulphuric  acid  acts  in  a  very  different  way.  The 
water-decomposing  metals  in  the  cold  yield  nothing  but  hydrogen 
with  it ;  at  high  temperatures  even  zinc  and  iron  already  yield 
sulphurous  acid ;  and  zinc,  if  certain  conditions  are  obsen'ed,  can 
even  yield  sulphuretted  hydrogen  (Fordos  and  Gelis) . 

Most  of  the  heavy  metals  do  not  act  upon  sulphuric  acid  in  the 
cold  and  in  a  dilute  state  (they  yield  sulphur  dioxide  only  on 
being  heated  with  concentrated  acid),  such  as  arsenic,  antimony. 


BEHAVIOUR  OP  CAST-IRON  TOWARDS  SULPHURIC  ACID.  203 

I)i8muth^  tin,  lead,  copper,  mercury,  silver  (sulphates  being  formed 
at  the  same  time)  ;  gold,  platinum,  iridium,  abd  rhodium  do  not 
act  on  sulphuric  acid  at  any  temperature. 

While  pure  sulphuric  acid  has  hardly  any  action  whatever  on 
platinumy  even  at  its  boiling-point,  some  action  is  exercised  by  the 
impurities  never  absent  from  commercial  acid.  Impure  platinum 
may  also  be  acted  upon  to  some  extent,  but  the  action  on  gold  is  niL 
We  shall  go  into  this  subject  when  treating  of  the  concentration 
of  sulphuric  acid  in  platinum  vessels. 

The  behaviour  of  cast-iron  towards  sulphuric  acid  is  of  great 
technical  importance.  It  has  been  known  for  many  years  past 
that  concentrated  oil  of  vitriol  acts  very  little  indeed  upon  cast- 
iron,  whether  hot  or  cold,  provided  the  access  of  air  is  excluded, 
the  moisture  from  which  would  dilute  the  acid  and  cause  it  to  act 
more  strongly.  It  was,  however,  at  first  considered  an  extremely 
bold  step  when  Lancashire  alkali-makers  began  to  decompose 
common  salt  with  sulphuric  acid  in  cast-iron  pots,  as  is  explained 
in  the  Chapter  treating  of  the  manufacture  ofsaltcake. 

Since  that  period  manufacturers  have  become  much  bolder,  and 
for  many  years  past  cast-iron  vessels  have  been  employed  for 
*'  parting  ^'  alloys  of  silver  and  gold  by  boiling  sulphuric  acid,  for 
making  nitrobenzene  and  analogous  products  by  a  mixture  of 
strong  sulphuric  and  nitric  acid,  and  innumerable  other  purposes 
where  strong  acids  Ifove  to  be  manipulated  either  hot  or  cold, 
even  for  the  lasit  concentration  of  sulphuric  acid  itself.  Dilute 
sulphuric  acid,  if  the  dilution  be  not  too  strong,  acts  very  little 
on  cast-iron  in  ^he  cold  or  at  a  gentle  heat,  if  air  be  excluded ;  it 
can  hence  be  employed  for  ''acid  eggs,''  in  which  chamber-acid  is 
forced  up,  in  lieu  of  pumps,  and  similar  purposes. 

It  is  usually  assumed  that  some  descriptions  of  cast-iron  resist 
the  attar*.k  of  acids  more  than  others.  This  point,  together  with 
some  others  of  importance,  has  been  the  subject  of  experiments 
made  in  my  laboratory  (Chem.  Industrie,  1886,  p.  74)  *. 

These  experiments  lead  to  the  following  conclusions  : — 

(1)  At  the  ordinary  temperature  all  acids  down  to  106^  Tw. 
act  very  little  on  all  descriptions  of  cast-iron. 

(2)  At  100°  C.  the  action  is  much  stronger.     It  is  least  in  the 

*  A  full  report  is  also  given  in  the  second  edition  of  tliis  book,  p.  141  to 
p.  143. 


204, 


PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 


case  of  acid  of  168°  Tw.,  IJ  times  stronger  with  acid  142°  Tw., 
and  3  times  stronger  with  acid  106°  Tw. 

(3)  At  the  boiling-point  the  differences  are  far  more  pronounced. 
Acid  of  168°  Tw.  acts  very  little  even  then,  both  in  the  pure  state, 
or  as  commercial  acid  (containing  a  little  ^2^*)>  ^^  when 
containing  a  little  SO2.  But  acid  of  142°  Tw.  acts  14  times 
stronger  at  200°  than  the  same  acid  at  100°  C,  and  20  times 
stronger  than  acid  of  168°  Tw.  At  285°  C.  commercial  acid  of 
142°  Tw.  does  not  act  very  diflFerently  from  pure  acid  of  the  same 
strength.  Acid  of  106°  Tw.  at  its  boiling-point  (  =  147°C.)  acts 
less  than  acid  of  142°  Tw.  at  200°  C,  but  still  four  times  as  much 
as  acid  of  168°  Tw.  at  295°  C.  There  is  no  diflference  between 
pure  and  commercial  acid  in  this  case. 

(4)  The  differences  between  various  mixtures  of  cast-iron  are 
of  no  importance  against  acid  of  168°  Tw.  in  all  cases,  and  against 
the  weaker  acids  at  20°  and  100°  C.  But  the  latter  acids  at  their 
boiling-point  act  decidedly  less  on  charcoal-pig  and  on  chilled 
cast-iron  than  on  all  other  kinds.  A  difference  between  hot  and 
cold  casting  could  not  be  found.  The  strongest  attack  was  made 
on  Scotch  pig  and  on  mixtures  containing  such. 

In  another  series  of  tests  we  examined  the  action  of  mono^ 
hydrated  sulphuric  acid  on  various  metals,  both  on  standing  6  days 
at  20°  and  on  heating  2  hours  to  100°  C,  always  with  exclusion 
of  air.     The  loss  of  weight  was  : — 


Loss  per  cent. 

6  days  at  2  hours  at 

20^  0.  100°  C. 

Cast-iron 0041  0071 

Wrought-iron...     0*175  0313 

Copper     2*630  excessive 

Lead    3*480  3650 


Lo&s  in  fptiins  per  square 

centimetre  of  surface. 

6  days  at 

2  hours  at 

20=0. 

100°  C. 

0062 

0*015 

0-056 

0095 

1*115 

excessive 

1-790 

1*847 

Wrought-iron  is  much  more  acted  upon  than  cast-iron  by  weaker 
acids,  but  at  the  ordinary  temperature  it  resists  the  action  of  strong 
sulphuric  acid  down  to  140^  Tw.,  and  probably  even  a  little  below 
that  strength.  Where,  however,  through  the  action  of  moist 
atmospheric  air,  the  acid  gets  more  diluted,  a  very  strong  action 
sets  in.     Hence  the  wrought-iron  vessels  in  which  sulphuric  acid 


ACTION  OF  IRON  ON  SULPHURIC  ACID. 


205 


is  now  very  generally  carried  must  be  protected  inside  against 
any  access  of  air  when  empty;  and  at  the  manholes  &c.,  where 
temporary  access  of  air  is  unavoidable,  they  are  best  protected  by 
a  sheet  of  lead. 

Knietsch  (Ber.  1901,  p.  4109)  gives  the  following  table  respect- 
ing the  action  of  sulphuric  acid  (ordinary  and  fuming)  of  various 
strengths  on  cast-iron,  mild  steel  ('^Flusseisen^'),  and  puddled  iron. 
The  cast-iron  contained  2*787  percent,  graphite  and  3*55  per  cent, 
total  carbon,  the  mild  steel  0*115  per  cent,  carbon  and  the  puddled 
iron  0'076  per  cent.  The  figures  denote  the  loss  of  the  metal  per 
superficial  metre  an  hour  in  grams,  after  treating  with  acid  for 
72  hours  at  18°-20°  C,  with  exclusion  of  air. 


H.,80,       1 

SO3 

Cast-iron. 

Mild  steel. 

Puddled 

• 

percent 

1 

per  cent. 

1 
( 

iron. 

48-8 

39-9 

0-2177 

•  ••                     I 

I 

■  •  « 

61-2         , 

50-0 

0-1510      ' 

1 

03032 

67-7         ' 

55-3 

0-0847 

00789 

73-4 

59-9 

00662 

•  t  ■ 

0  0623 

79-7 

650 

0-1560 

•  ■  ■ 

0-1159 

83-7 

<^-4 

01388 

•  ■  • 

01052      1 

851 

09-5 

0-1306 

•  ■  • 

0-1034      ' 

88-2 

720 

01636 

•  •  • 

0-1417 

iK)-6 

73-9 

01760 

•  •  ■ 

0-1339 

920 

752 

00933 

•  •  • 

0-1040      ' 

930 

76-9 

00736 

00987 

00855      i 

943 

770 

00723 

00987 

00708 

95-4 

77-9      ; 

01274 

00933 

0-1209      ! 

96-8 

79-0         , 

01013 

00815 

00988      1 

98-4 

;        80-3 

00681 

00533 

0-0655    ; 

98-7 

'        80-6 

00589 

00509 

00570      i 

99-2 

1        81-0 

00568 

00418 

00504 

9930 

;        81-07 

0057 

0042 

0050 

1        99-50 

!        81-25 

0060 

0-033 

0049 

99-77 

81-45 

0-066 

0042 

0049        j 

100-00 

!        81-63 

0-087 

1       0088 

0-076        1 

total  SO, 

free  SO, 

81-8 

0-91 

0-201 

0393 

0-323 

8202 

200 

0-190 

0-285 

0-514 

8-2-28 

364 

0132 

0-441 

0-687 

82-54 

;      4-73 

0154 

0-956 

1-075 

1        82-80 

1      745 

0-151 

0-566 

1-321         i 

1        83-60 

i     1017 

0079 

0-758 

1-540 

84-20 

12-89 

0-270 

1024 

0-892        ; 

1        84-62 

16-16 

0-271 

1-400 

0-758 

8505 

18-34 

0076 

1-988 

1-530     ; 

86-00 

,        23-78 

0070 

0-245 

0-471 

88-24 

'        34-67 

0-043 

0033 

0-053        : 

9007 

4556 

1 

i       0040 

0018 

0-019 

206       PROP£KTI£S  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

Knietsch  (/.  c.  p.  4090)  makes  the  following  further  remarks  on 
this  subject.  Whereas  cast-iron  vessels  are  very  suitable  for  the 
manufacture  of  hydrated  sulphuric  acid^  this  is  not  the  case  for 
fuming  acids/  for  these,  although  they  corrode  the  metal  but 
slightly^  cause  it  to  cracky  sometimes  quite  suddenly,  with  a 
loud  report.  Evidently  the  fuming  acid  penetrates  into  the  pores 
of  the  metal,  where  it  is  reduced  to  SO2  and  HjS,  with  formation 
of  COo  from  the  carbon  of  the  cast-iron — all  of  them  gases  with 
somewhat  low  critical  temperatures  which  produce  high  tensions  in 
the  interior  of  the  metal. 

WroughUiron  (and  zinc)  is  somewhat  strongly  acted  upon  by 
fuming  acids  up  to  27  per  cent.  SO^ ;  this  is  explained  by  the 
increase  of  electric  conductivity,  apparent  from  the  curve  No.  5, 
fig.  39,  p.  174.  We  notice  that  the  minimum  lies  at  100  per  cent. 
H2SO4 :  then  the  conductivity  rises  sharply,  the  maximum  being 
at  10  to  15  per  cent,  free  SOg,  whereupon  ii  sinks  just  as  rapidly 
to  a  minimum.  At  27  per  cent,  free  SO3,  wrought-iron  is  again 
entirely  passive,  and  apparatus  made  of  it  may  serve  for  many  years 
for  the  manufacture  of  high-strength  fuming  acids. 

The  action  of  sulphuric  add  on  lead  has  been  the  subject  of 
many  experiments.  Calvert  and  Johnson  (Compt.  Rend.  Ivi. 
p.  140)  came  to  the  conclusion  that  lead  is  all  the  more  acted  upon 
the  purer  it  is,  and  that  an  energetic  action  only  takes  place  above 
the  specific  gravity  of  140°  Tw.  Similar  results  were  obtained 
by  Mallard  (Bull.  Soc.  Chem.  1874,  ii.  p.  114)  and  Hasenclever. 

Bauer  (Berl.  Ber.  1875,  p.  210)  found  that  50  grams  of 
strongest  oil  of  vitriol  (168°  Tw.)  with  0*2  gram  of  pure  lead 
produced  a  sensible  evolution  of  gas  at  175°,  stronger  at  196® ;  at 
230°-240°  suddenly  all  the  lead  is  changed  into  sulphate,  with 
formation  of  SOg,  H,  and  S.  Lead  containing  varying  quantities 
of  bismuth  (0*71  or  4  or  10  per  cent.)  was  even  more  strongly 
acted  upon,  whilst  small  quantities  of  antimony  and  copper  make 
the  lead  more  resisting  j  platinum  acts  in  a  similar  way.  Lead 
containing  10  per  cent,  tin  behaves  like  pure  lead. 

According  to  experiments  made  by  J.  Glover  (Chem.  News,  xlv. 
p.  105),  pure  lead  is  less  acted  upon  when  suspended  in  a  vitriol 
chamber  than  such  containing  0*1  to  0*75  per  cent,  copper,  or  0*1 
to  0*5  per  cent,  antimony.  N.  Cookson  (ibid.  p.  106)  found  that 
strong  acids  at  a  high  temperature  act  more  upon  lead  containing 
antimony  than  upon  pure  lead,  whilst  weaker  acid  at  a  lower 


ACTION  or  LEAD  ON  SULPHURIC  ACID.  207 

temperature  acts  the  other  way.      Comp.  also  Mactear  (Chem. 
News,  xli.  p.  236). 

In  the  North  of  England  those  rolling-mills  which  roll  the  sheet- 
lead  from  the  vitriol-works  supply  a  special  kind  of '^chemical  lead  *' 
which  is  made  from  the  melted-up  old  chamher-lead,  pipes,  &c.; 
in  this  case  many  impurities,  especially  antimony,  from  '^  regulus  '^^ 
valves,  &c.,  get  into  the  lead,  which  are  supposed  to  improve  its 
quality  for  acid-chambers. 

Napier  and  Tatlock  (Chem.  News,  xlii.  p.  314)  found  that  the 
action  of  sulphuric  acid  on  lead  at  the  ordinary  temperature  is 
accompanied  by  an  evolution  of  hydrogen,  which  may  cause  bulging 
out  of  the  closed  lead  vessels  in  which  the  acid  is  sometimes  sent 
out  for  sale. 

The  experiments  of  Veley  (J.  Soc.  Chem.  Ind.  1891,  p.  211), 
according  to  which  mixtures  of  nitrous  and  nitric  acid  have  a 
stronger  action  on  lead  than  either  acid  by  itself,  have  no  practical 
bearing  on  the  behaviour  of  the  acid  in  vitriol  chambers,  since  if 
nitric  acid  occurs  there  it  is  always  accompanied  by  nitrous  acid, 
and,  what  is  far  more  important,  the  immense  excess  of  sulphuric 
acid  greatly  modifies  all  conditions  of  the  case. 

An  extensive  investigation  made  by  myself  together  with  E. 
Schmid  has  been  published  in  Zsch.  f.  angew.  Chem.  1892,  p.  642> 
also  partly  in  Journ.  Soc.  Chem,  Ind.  1891,  p.  146.  I  here  give 
a  very  brief  summary  of  our  results,  some  of  which  are  of  great 
practical  importance. 

1.  At  higher  temperatures  the  purest  lead  iu  all  cases  resists 
both  pure  and  nitrous  sulphuric  acid,  with  or  without  access  of 
air,  much  better  than  ''  regulus  metal  '^  (82  Pb,  18  Sb)  or  ''  hard 
lead'^  (1*8  per  cent.  Sb),  or  even  soft  lead  with  only  0*2  per  cent. 
Sb.  In  the  cold,  lead  with  0*2  per  cent.  Sb  is  very  slightly  superior 
to  the  purest  lead  ;  regulus  metal  behaves  much  worse,  and  hard 
lead  worst  of  all. 

2.  Concentrated  nitrous  vitriol  is  always  more  active  than  pure 
acid.  In  the  case  of  somewhat  dilute  acid  (spec.  grav.  1*72  to 
1' 76),  nitrous  vitriol  acts  less  than  pure  acid  on  soft  lead  and  hard 
lead,  owing  to  a  protective  coating  of  lead  sulphate  being  formed. 
If  more  dilute,  the  action  is  again  stronger  (comp.  below).  In  all 
cases  nitrous  vitriol  acts  more  in  the  presence  than  in  the  absence 
of  air. 

3.  Comparing  two  samples  of  soft  lead,  the  purer  sample  was 


208  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR, 

• 

found  decidedly  better ;  even  a  very  slight  proportion  of  bismuth 
(0044  per  cent.)  acts  injuriously. 

4.  It  is  altogether  inadmissible  to  judge  of  the  resistance  of  lead 
to  sulphuric  acid  from  the  quantity  of  the  ^a*  (hydrogen)  evolved. 
Soft  lead  gives  off  at  the  ordinary  temperature^  after  a  week's 
contact^  much  gas ;  hard  lead^  although  losing  much  more  weighty 
very  little  gas  (.^^  of  the  theoretical  quantity),  probably  owing  to 
galvanic  action.  But^  on  this  account,  if  sulphuric  acid  is  to  be 
sent  out  in  tightly-closed  or  soldered-up  leaden  boxes,  they  should 
not  be  made  of  soft,  but  of  hard  lead,  since  otherwise  the  hydrogen 
may  bulge  up  or  burst  the  vessels. 

5  (a).  Lead  containing  up  to  0*2  per  cent,  copper  (alloys  con- 
tainiug  more  copper  cannot  be  homogeneously  rolled)  is  in  the  cold 
acted  upon  by  strong  sulphuric  acid  more  than  pure  lead ;  with 
nitrous  acid  there  is  not  much  difference.  At  100*^  C.  all  kinds  of 
acid  act  in  the  same  way  on  pure  lead  and  on  lead  containing  copper ; 
oonoentrated  pure  acid  rather  less  than  concentrated  nitrous  vitrol^ 
but  more  than  nitrous  vitriol  of  spec.  grav.  1-72  (comp.  No.  2). 
At  200^  C,  concentrated  acid  acts  alike  on  pure  lead  and  on  lead 
containing  0'02  per  cent.  Cu ;  lead  containing  more  copper  is 
slightly  less  acted  upon  by  pure  acid,  but  rather  more  by  nitrous 
vitriol. 

(*)  Above  200°  (225^  to  25&°)  lead  alloyed  with  1  per  cent, 
antimony  is  far  more  strongly  acted  upon  than  pure  lead  (in  the 
proportion  of  265  to  1  at  225°)  j  but  lead  containing  0*2  per  cent, 
copper  resists  the  acid  at  235°  much  better  than  pure  lead  in  the 
proportion  of  1  :  17,  and  at  255°  in  the  proportion  of  1  :  26*5. 

6  (a) .  Pure  soft  lead  gives  no  visible  evolution  of  gas  with  pure 
concentrated  sulphuric  acid  up  to  220°.  From  this  point  more  gas- 
bubbles  are  continually  given  off,  and  at  260°  the  lead  is  momentarily 
•dissolved  with  strong  frothing,  smell  of  SO2,  and  precipitation  of 
sulphur,  the  temperature  rising  to  275°. 

(b)  The  same  lead,  alloyed  with  0*2  per  cent,  of  copper,  shows  a 
-visible  evolution  of  gas  only  at  260°,  regularly  increasing  up  to  the 
boiling-point  (310°),  at  which  the  lead  is  very  gradually  dissolved. 

(c)  Soft  lead,  alloyed  with  1  per  cent.  Sb,  gives  with  sulphuric 
acid  the  first  visible  gas  at  175°,  more  strongly  at  225°,  and 
between  275°  and  280°  there  is  the  same  turbulent,  sudden 
solution  as  in  the  case  of  pure,  soft  lead.  [Bauer,  Berl.  Ber. 
1875,  p.  210,  found  similar  results;    according  to  him  0*73  per 


ACTION  OF  SULPHURIC  ACID  ON  LEAD.  209 

cent,  bismvth  lowers  the  temperature  of   sudden    decomposition 
from  240°  to  160°.] 

Hence  the  purest  lead  is  subject  to  instantaneous  solution  by 
sulphuric  acid  at  260°.  An  addition  of  1  per  cent.  Sb. raises  this 
temperature  only  about  20%  but  02  per  cent.  Cu  completely 
destroys  this  liability  to  sudden  decomposition. 

7.  The  percentage  of  oxygen  in  lead  is  very  slight  even  in 
extreme  cases,  and  does  not  seem  to  have  any  connection  with 
its  liability  to  be  acted  upon  by  acid.  But  the  latter,  as  may  be 
imagined,  is  less  when  the  density  of  the  surface  is  mechanically 
increased. 

8.  The  final  considerations  in  selecting  the  kind  of  lead  best 
suited  for  constructing  apparatus  for  the  manufacture  of  sulphuric 
acid  are  as  follows  : — 

For  vitriol-chambers^  towers^  tanks,  pipes,  and  all  other  instances 
where  the  temperature  can  rise  but  moderately,  and  certainly  never 
up  to  200°C.,  the  purest  soft  lead  is  preferable  to  every  other  rfc- 
scription  of  lead,  being  least  acted  upon  by  hot  acid,  whether  dilute 
or  concentrated,  pure  or  nitrous. 

Any  sensible  proportion  of  antimony  is  in  nearly  all  cases 
injurious;  copper  causes  at  least  no  improvement.  This,  of  course, 
does  not  apply  to  those  cases  where  the  lead  requires  an  addition 
to  its  tensile  strength,  nor  to  that  mentioned  sub  No.  4  of 
packages  for  acid  to  be  closed  air-tight.  Hence  an  addition  of 
about  0*2  per  cent,  antimony  may  be  useful  in  the  case  of  apparatus 
which  is  only  in  contact  with  cold  acid ;  but  with  warm  acid  even 
this  percentage  is  to  be  avoided. 

For  very  high  temperatures,  e.  g,,  the  hottest  boiling-down  pans, 
which  ought  not  to  be  heated  above  200°  C,  but  may  sometimes 
be  raised  to  that  point,  an  addition  of  01  to  0*2  per  cent,  copper  is 
advantageous,  while  antimony  should  be  avoided  here  under  all 
circumstances  (comp.  no.  6  b).  That  percentage  of  copper  has  no 
action  at  200°,  but  only  above  220°;  and  in  the  presence  of 
bismuth  it  protects  the  lead  from  the  sudden  destruction  sometimes 
observed. 

9.  Technical  "sulphuric  monohydrate^'  at  50°  C.  acts  far  more 
strongly  on  lead  than  concentrated  sulphuric  acid,  [The  "  mono- 
hydrate''  employed  in  our  experiments  had  attracted  a  little  water 
and  tested  only  98'85  per  cent.  H2SO4  :  its  action  upon  lead  was 
13^  times  that  of  ordinary  concentrated  acid  of  96*5  per  cent 

VOL.  I.  P 


210  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

H2SO4.     Fresh  monohydrate  of  99*5  or  99*75  per  cent,  would,  no 
doubt,  have  shown  even  more  action.] 

10.  Nordhausen  fuming  oil  of  vitriol  acts  upon  lead  much  more 
strongly  than  ordinary  concentrated  acid.  Wlien  it  contains 
20  per  cent,  free  SO3  it  has  32  times  the  effect  of  ordinary  acid  ; 
stronger  Nordhausen  acid  has  rather  less  effect  than  the  20  per  cent, 
acid,  because  a  protective  coat  of  lead  sulphate  is  formed.  At  all 
events  lead  must  not  be  brought  into  contact  with  Nordhausen  acid. 

11.  Nitric  acid  of  spec.  grav.  1*37  to  142  may  be  brought  into 
contact  with  lead  at  the  ordinary  temperature,  but  no  acid  of  less 
strength.  Stronger  acid  than  the  above  acts  more  powerfully  upon 
lead^  but  no  more  than  concentrated  sulphuric  acid.  Mixtures  of 
concentrated  sulphuric  acid  and  strong  nitric  acid  act  very  little 
indeed  upon  lead,  much  less  than  either  strong  sulphuric  acid  or 
strong  nitric  acid  by  themselves  :  such'  mixtures  can  be  treated  in 
lead  vessels  without  any  hesitation.  (Later  observations  have 
shown  that  this  applies  only  to  ordinary  temperatures  and  when 
no  moisture  can  be  attracted  from  the  air.  Hot  mixed  acids  act 
strongly  on  lead.) 

12.  Mixtures  of  sulphuric  acid  and  nitroso-sulphuric  acid, 
partly  also  containing  nitric  acid,  all  of  them  originally  containing 
0*1  per  cent.  N,  but  by  heating  to  65°  C.  brought  to  the  state  in 
which  they  can  really  exist  in  vitriol-chambers,  give  the  fol- 
lowing results  : — If  a  little  nitric  acid  is  added  to  dilute  sulphuric 
acid,  and  the  mixture  is  heated,  a  little  HNO3  is  volatilized,  but 
no  nitrosyl-sulphuric  acid  is  formed  until  the  concentration  has 
reached  spec  grav.  1*5.  From  this  point  oxygen  escapes,  and  at 
spec  grav.  1*768  the  whole  of  the  HNOj  has  vanished,  SOgNH 
appearing  in  its  stead.  Inversely,  nitric  acid  is  formed  from 
nitrous  sulphuric  acid  on  diluting  it;  in  the  case  of  prolonged 
heating,  this  evidently  takes  place  not  by  splitting  up  into  HNOs 
and  NO,  but  by  absorption  of  oxygen  from  the  air. 

The  action  of  the  acid  on  lead  is  least  just  about  the  lowest 
point  where  the  nitrosyl-sulphuric  acid  is  stiU  capable  of  existing. 
It  increases  with  its  dilution,  and  in  proportion  to  this,  evidently 
through  the  formation  of  nitric  acid,  equally  with  its  concen- 
tration,  and  later  on  rapidly  so,  the  action  of  stronger  sulphuric 
acid  combining  with  that  of  nitrosyl-sulphuric  acid  and  nitric  acid. 
The  minimum  action  is  between  spec.  grav.  1-6  and  1*6 — that  is,  just 
at  that  concentration  above  or  below  which  the  acid  ought  not  to  be 


ACTION  OF  SULPHUKIC  ACID  ON  LEAD  AND  ZINC.  211 

kqi)t  in  vitriol-chambers.     This  proves  that  it  is  not  rational  to 
keep  the  acid  in  the  first  chamber  too  strong  (comp.  Chap.  VII.). 

Bis  muih  is  generally  (as  shoAvn  above)  considered  very  injurious 
to  the  resis ting-quality  of  lead  for  sulphuric  acid.  H.  O.  Hofmann 
(Min.  Ind.  v.  p.  398)  certainly  states  that  bismuth  up  to  2  per  cent., 
or  up  to  the  amount  usually  found  in  commercial  lead^  does 
not  affect  its  resistance  in  vitriol-chambers^  and  that  it  is  far  more 
important  that  the  surface  should  be  clean  and  smooth^  to  prevent 
droplets  of  condensed  acid  adhering  to  the  lead.  While  the 
second  part  must  be  accepted  without  contradiction^  the  first 
(concerning  the  bismuth)  is  contrary  to  every  other  experience. 
In  a  special  case  which  has  come  under  my  notice,  two  Glover  towers 
behaved  quite  differently,  one  of  them  going  without  lead  repairs 
for  13  years,  the  other  one  being  damaged  before  two  years  were 
over.  Analysis  proved  the  lead  to  be  of  almost  identical  compo- 
sition in  both  cases ;  but  the  first  contained  O'OOl,  the  second 
0'012  per  cent,  bismuth. 

According  to  Junge  (Sachs.  Jahrb.  f.  Berg-  u.  Hiittenwesen, 
1895)  some  acid-makers  prefer  lead  desilverized  by  the  Pattinson 
process  to  that  treated  by  the  Parkes  process,  because  the  latter 
is  supposed  to  contain  more  zinc ;  but  Hofmann  proves  this  to  be 
contrary  to  facts ;  Parkes  lead  contains  less  zinc,  but  more 
bismuth,  than  Pattinson  lead.  It  is  not  denied  that  in  concen- 
trating-pans  Pattinson  lead  stands  better  than  Parkes  lead.  This 
would  be  explained  by  the  fact  that  Pattinson  lead  contains  more 
copper  and  less  bismuth  than  Parkes  lead  (comp.  supra,  p.  209). 

Fluorine  sometimes  occurs  in  blende,  and  the  fluorides  may 
cause  trouble,  as  they  are  converted  into  HF  in  the  Glover  tower, 
and  this  acid  contaminates  the  sulphuric  acid.  Trost  (Chem.  Zeit. 
1902,  p.  12)  asserts  that  even  a  very  slight  quantity  of  HP  in 
sulphuric  acid  causes  great  wear  and  tear  of  the  lead  of  Glover 
towers  and  chambers,  not  only  directly,  but  by  facilitating  the 
corrosion  by  sulphuric  acid  and  the  nitrogen  acids.  Most  descrip- 
tions of  blende  contain  only  traces  of  fluorine,  but  once  he  found 
7  per  cent.  (The  experiments  quoted  in  the  original  do  not  show 
any  essential  difi^erence  between  pure  acids  and  those  containing  up 
to  2  per  cent.  HP  in  their  action  on  lead.  Gaseous  HF  seems  to 
act  much  more  than  that  contained  in  sulphuric  acid.) 

About  the  behaviour  of  zinc  towards  sulphuric  acid,  I  will  only 
quote  the  fact  that  concentrated  acid  yields  hydrogen,  together 

p2 


212  JPROPERTIBS  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

M'ith  hydrogen  sulpliide,  down  to  acid  of  the  formula  SO4H3, 

5  H2O.     Acid  of  the  formula  SO4H2,  6  HgO  yields  pure  hydrogen 
(Muir  and  Robb^  Chem.  News,  xlv.  p.  70). 

nn  is  not  acted  upon  by  acid  of  the  formula  SO4HS,  3  H^O. 

Behaviour  of  Sulphurous  and  Sulphuric-  Acid  towards  the  Oxides 
of  Nitrogen. — The  reactions  between  the  oxides  and  acids  of  sul- 
phur and  nitrogen  are  of  extreme  importance  for  the  theory  of 
the  sulphuric  acid  process  in  general,  and  for  the  recovery  of 
the  nitrogen  compounds  in  particular. 

The  older  researches  in  this  field,  of  Clement-Desormes,  Dalton, 
Davy,  Berzelius,  Gay-Lussac,  W.  Henry,  Gaultier  de  Claubry,  De 
la  Provostaye,  A.  Rose,  Koene,  Weltzien,  Rebling,  and  Miiller, 
have  now  merely  an  historical  interest.  The  modern  literature  of 
this  subject  begins  with  the  labours  of  B.  Weber,  during  the  years 
1862  to  1867,  published  in  the  Journ.  f.  prakt.  Chem.  Ixxxv. 
p.  423  and  c.  p.  37;  Poggendorflfs  Annalen,  cxxiii.  p.  34-1,  cxxvii. 
p.  543,  cxxx.  p.  277  ;  and  partly  in  Dingler's  Polyt.  Journal,  clxvii. 
p.  453.  Other  very  important  papers  have  been  published  by  CI. 
A.  Winkler  ('  Researches  on  the  Chemical  Processes  going  on  in 
the  Gay-Lussac  Towers,'  Freiberg,  1867),  by  Rammelsberg  (Ber. 
d.  deutsch.  chem.  Gesellsch.  1872,  p.  310),  by  Michaelis  and 
Schumann  (ib.  1874,  p.  1075). 

My  own  researches  referring  to  this  subject  are  found  in  the 
following  publications : — 1877  :  Berl.  Ber.  x.  pp.  1073  &  1432. 
1878  :  Berl.  Ber.  xi.  pp.  434  &  1229  \  Dingler's  Journal,  ccxxviii. 
pp.  70,  548,  &  553.  1879 :  Dingler's  Journal,  ccxxxiii.  p.  63 ; 
Berl.  Ber.  xii.  pp.  357  &  1058.     1881 :  Berl.  Ber.  xiv.  pp.  2188 

6  2196.  1882  :  Berl.  Ber.  xv.  pp.  488  &  495.  1884 :  Chem. 
Ind.  1884,  p.  5.  1885  :  J.  Soc.  Chem.  Ind.  pp.  31  &  447 ;  Berl. 
Ber.  xviii.  pp.  1376,  1384,  1391 ;  J.  Chem.  Soc.  xlvii.  pp.  457  & 
405.  1888  :  Berl.  Ber.  xxi.  pp.  67  &  3223.  1889  :  Zeitsch.  f. 
angew.  Chemie,  pp.  265  &  385.  1890  :  ibid.  p.  195.  1899  :  ibid, 
p.  393. 

Of  the  different  oxides  of  nitrogen,  nitrous  oxide,  N2O,  need 
not  detain  us  here.  It  is  very  slightly  soluble  in  sulphuric  acid, 
much  less  so  than  in  pure  water,  as,  once  formed,  it  is  not  oxidized 
again  into  NO  or  higher  nitrogen  oxides ;  it  is  altogether  lost  for 
the  manufacture  of  sulphuric  acid,  nor  does  it  form  any  chemical 
compound  with  that  acid. 

Nitric  oxide,  NO,  was  said  by  Henry  and  Plisson  to  be  absorbed 


BEHAVIOUR  OF  NITRIC  OXIDE  TO  SULPHURIC  ACID.  213 

by  oil  of  vitriol^  if  left  a  loDg  time  in  contact  with  it,  with  forma- 
tion of  nitrous  p}'rosu]phuric  anhydride  (see  below) ;  but  Berzelius^ 
Gay-Lussac,  and  many  others  have  long  ago  refuted  this  state- 
ment^ more  especially  Winkler  (/.  c.  p.  58).  In  fact  the  sulphuric 
acid  of  the  absorbing-apparatus  cannot  retain  that  portion  of  the 
nitrogen  oxides  which  have  been  reduced  to  the  state  of  nitric 
oxide ;  and  from  this  follows  the  necessity  of  an  excess  of  oxygen 
in  the  gas  issuing  from  the  chambers^  since  only  this  prevents  the 
existence  of  nitric  oxide  in  the  same.  Small  quantities  of  nitric 
oxide  may,  however,  escape  oxidation  even  in  the  presence  of 
oxygen,  and  are  hence  found  in  the  chamber  exit-gases. 

The  solubility  of  NO  in  sulphuric  acid,  although  not  nil,  is 
extremely  slight.  CI.  Winkler  already  in  1867  showed  that  it  is  not 
absorbed  by  strong  vitriol.  Kolb  also  made  experiments  with  acids 
of  varying  concentration  (Bull.  Soc.  Indust.  Muhl.  1872,  p.  225), 
and  has  found  that  acid  of  1*841  does  not  absorb  even  traces  of 
NO;  acid  of  1*749  to  1*621  merely  traces  (2  to  6  milligrams  to 
100  grms.  acid) ;  acid  of  r4?26  absorbs  0*017  grm.  NO  ;  acid  of 
1*327,  0*020  grm.  NO  to  100  grms.  My  own  experiments  (Journ. 
Soc.  Chem.  Ind.  1885,  p.  447,  and  1886,  p.  82  ;  also  Berl.  Ber. 
1885,  p.  1391,  and  1886,  p.  Ill)  show  that  concentrated  O.V. 
absorbs  per  c.  c.  only  00000593  grm.  =  0035  c.  c.  NO,  and  acid 
of  sp.  grav.  1*500  only  half  that  quantity. 

In  the  presence  of  oxygen  nitric  oxide  is  absorbed  by  sulphuric 
acid  (Bussy,  Winkler) ;  but  then  it  is  really  nitrous  acid  which  is 
absorbed ;  and  Winkler  was  the  first  to  prove  that  it  is  precisely  the 
presence  of  sulphuric  acid  which  causes  the  oxidation  not  to  pro- 
ceed beyond  the  formation  of  nitrous  acid,  the  latter  combining 
afterwards  with  the  sulphuric  acid  to  form  nitroso-sulphuric  acid 
and  water : — 

2  S03(OH)2  +  N303=2  S02(OH)(ONO)  +  HjO. 

In  several  of  the  above-quoted  papers  I  have  given  clear  proofs 
of  the  same  fact,  viz.,  that  on  passing  nitric  oxide,  together  with 
a  very  large  excess  of  free  oxygen,  through  strong  sulphuric  acid, 
nothingbut  nitroso-sulphuric  acid  is  formed,  which  means  that  2N0 
lake  up  only  1  0;  but  once  out  of  the  range  of  the  acid,  imme- 
diately above  it,  the  reaction  2N0-f  02=N204  sets  in,  and  this 
compound,  when  afterwards  meeting  sulphuric  acid,  yields  equal 
molecules  of  nitric  acid  and  of  nitroso-sulphuric  acid  (vide  infra). 


214  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

Nitrous  acid, — Real  nitrous  acid,  HNOj,  is  not  known  in  the 
pure  state,  only  in  that  of  dilute  solutions.  When  dissolving 
nitrous  anhydride^  NjOg,  in  water,  some  nitrous  acid  is  formed 
and  remains  dissolved  in  the  excess  of  water,  but  much  splits  up 
according  to  the  formula : 

3N02H  =  2NO  +  N03H  +  H20. 

The  anhydride,  N2O3,  also  called  nitrogen  tetroxide,  is  known 
as  a  dark  blue  liquid  which  boils  below  0°C.  The  vapours  imme> 
diately  dissociate  for  the  most  part  into  NO  and  NO2  (with  more 
or  less  N3O4,  according  to  temperature),  but  a  small  quantity  of 
N2O3  evidently  exists  even  in  the  state  of  vapour.  We  shall  not 
here  enter  upon  the  much  debated  question  concerning  the  exist- 
ence of  N203in  the  gaseous  state,  but  merely  quote  the  literature: 
Luck  (Berl.  Ber.  1878,  pp.  1232  &  16i3),Vitt  (ibid.  p.  2188), 
Ramsay  &  Cundall  (Journ.  Chem.  Soc.  xlvii.  pp.  187,  672),  Lunge 
(ibid.  p.  457 ;  Zsch.  anorg.  Chem.  vii.  p.  209),  and  Dixon  & 
Peterkin  (Proc.  Chem.  Soc,  May  1899,  p.  115). 

Although  there  is  no  doubt  about  the  fact  that  most  of  the 
"  nitrous  vapours,"  formerly  considered  as  N2O3  in  the  state  of  gas 
or  vapour,  is  in  reality  principally  a  mixture  of  nitrogen  oxide  (NO) 
and  peroxide  (which,  for  the  sake  of  simplicity,  we  shall  in  this  case 
consider  as  NO2),  with  very  little  N2O8,  we  must  bear  in  mind  the 
equally  undoubted  fact  that  a  mixture  of  equal  molecules  of  NO 
and  NO2  behaves  in  all  its  reactions  towards  other  chemical  com- 
pounds exactly  as  if  it  were  N20g.  When  passed  into  an  alkaline 
solution,  it  quantitatively  yields  a  nitrite  : 

2NaOH  +  NO  +  N02=2NaN02  +  H20. 

When  brought  into  contact  with  concentrated  sulphuric  acid  it  is 
quantitatively  converted  into  nitroso-sulphuric  acid  : 

2H2SO4  +  NO  +  NO2  =  2SO5NH  +  H20. 

We  have,  therefore,  the  right  to  assume  that  such  a  mixture  of 
equal  molecules  of  NO  and  NO2  chemically  comes  to  the  same  thing 
as  gaseous  N2O3;  and  we  shall  throughout  this  book  simplify  many 
of  our  explanations  and  discussions  by  speaking  of  the  above 
mixture  as  N20g,  although  physically  it  is  only  a  mixture  of  NO 
and  NO2.  We  are  all  the  more  entitled  to  do  this,  since  there  is 
no  doubt  that  some  N2O3  exists  in  the  gaseous  state  as  such,  and 


BEHAVIOUR  OP  NITROUS  ANHYDRIDE  TO  SULPHURIC  ACID.       215 

since^  according  to  the  law  of  mass  action^  this  N2O3  must  be 
constantly  reformed  when  taken  away  by  some  chemical  reaction. 

I  have  all  the  more  right  to  take  this  line,  since  everybody 
speaks  of  distilling  sulphuric  acid  or  subliming  ammonium 
chloride,  although  we  know  that  on  distillation  nearly  all  sulphuric 
acid  is  split  up  into  SOg  and  H2O,  which  recombine  on  conden- 
sation (comp.  p.  172),  and  ammonium  chloride  in  the  state  of 
vapour  is  mostly=NH3  +  HCl. 

Nitrous  anhydride  {nitrogen  trioxide),  N2O3,  dissolves  in  sul- 
phuric acid,  all  the  more  easily  when  the  latter  is  concentrated, 
but  also,  as  we  shall  see,  when  it  contains  a  certain  amount  of 
water.     The  reaction  taking  place  is  this  : 

2  H2SO4  +  N203=2  SO5NH  -f  H2O. 

Rammelsberg  {/.  c.)  asserts  that  when  nitrous  anhydride  is  em- 
ployed in  excess,  nitric  acid  and  nitric  oxide  are  also  formed  : 

H2SO4  +  2  N2O3 = SO5N  H  +  HNO3  -I-  2  NO  ; 

but  this  reaction  only  takes  place  in  presence  of  water,  and  the 
formation  of  nitric  acid  and  nitric  oxide  must  be  regarded  as 
a  secondary  reaction,  owing  to  the  well-known  action  of  free 
nitrous  acid  on  an  excess  of  water.  Where  there  is  enough  sul- 
phuric acid  and  no  excess  of  water,  Rammelsberg's  reaction  does 
not  come  into  play. 

The  compound  formed  by  the  action  of  nitrous  acid  on  sulphuric 
acid  of  the  empirical  formula  SO5NH  has  long  been  known, 
both  in  the  solid  state,  as  ''  chamber-crystals,''  and  dissolved  in 
an  excess  of  sulphuric  acid,  as  '*  nitrous  vitriol " ;  but  its  true 
composition  and  nature  have  only  comparatively  recently  been 
elucidated. 

The  easiest  way  of  preparing  the  chamber -crystals  in  a  state  of 
purity  is  by  conducting  sulphur  dioxide  into  well-cooled  fuming 
nitric  acid  until  the  whole  mass  has  been  converted  into  a  magma, 
but  not  until  the  nitric  acid  has  been  entirely  decomposed,  and 
drying  the  crystallized  mass  on  a  porous  slab  under  a  bell-jar  over 
some  oil  of  vitriol.  Obtained  in  this  way,  or  collected  in  the  con- 
necting-pipes of  vitriol-chambers  or  other  places  where  there  is  a 
deficiency  of  steam,  they  consist  of  four-sided  prisms  or  ortho- 
rhombic  crystals;  but  generally,  when  prepared  on  the  small  scale, 
they  appear  as  a  scaly,  feather-like,  or  granular  mass,  colourless 


216       PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

and  transparent*  Their  fusing-point  is  stated  by  Weltzien=73°, 
by  Gaultier  de  Claubry=12(r  to  130°;  but  they  are  partly 
decomposed  before  fusing^  with  evolution  of  red  fumes. 

The  composition  of  chamber-crystals  was  formerly  uncertain ; 
the  question  was,  in  the  language  of  the  older  chemists^  whether 
they  were  a  compound  of  sulphuric  acid  with  nitrogen  peroxide  or 
with  nitrous  a^id  (nitrogen  trioxide).  Miiller  (Ann.  Chem.  Pharm. 
cxxii.  p.  1)  still  pronounced  for  the  former;  but  R.  Weber  proved 
in  1862^  and  more  rigorously  in  the  following  yeaf,  by  estimating 
all  their  constituents  according  to  unexceptionable  methods^  that 
their  formula  must  be  constructed  on  the  second  supposition. 
His  results  were  as  follows : — 

Molecular  weight.  Calculated.  Found. 

2SO3 160  62-39  6400 

N3O3 76  29-92  27-96 

H2O  18  7-69  10-50 

SOg,  N3O3,  H2O 254  100-00         102-46 

This  formula  has  also  been  confirmed  by  Michaelis  and  Schumann 
(Ber.  1874,  p.  1075),  who  at  the  same  time  maintained,  from  the 
products  of  decomposition  by  phosphorus  perchloride,  that  the  com- 
pound whose  molecular  weight  has  to  be  halved  must  be  regarded  as 

OH 

nitromlphonic  acid,  S02<(>tq  — that  is,  as  sulphuric  acid,  one  of 

whose  hydroxyls  is  replaced  by  the  nitro  group,  or  as  nitric  acid, 
for  whose  hydroxyl  is  substituted  the  sulpho  group.  This  mode 
of  explaining  the  constitution  of  that  substance  cannot,  however, 
be  strictly  maintained.  Both  from  its  formation  and  the  decom- 
position, it  is  certain  that  it  does  not  contain  the  nitro  group 
NO2,  but  the  nitroso  group  NO.  Its  formula  must  therefore  be 
written : 

and  it  must  be  called  nitrosyl  sulphate,  or,  more  correctly,  nitroso- 
sulphuric  acid,  which  means  sulphuric  acid,  one  of  whose  hydrogen 
atoms  is  replaced  by  the  nitroso  group,  that  is  the  radical  of 
nitrous  acid,  NO  (OH).     It  is  a  mixed  anhydride  of  sulphuric  and 


NITROSO-SULPHURIC  ACID.  217 

nitrous  acid^  as  is  proved  both  by  its  formation  and  its  decom- 
position by  water. 

There  exists  also  a  complete  anhydride  of  nitroso-sulphuric 
acid^  of  the  empirical  formula^  NjOs^  2  SOg,  which  is  rationally 
written : 

NO\Q 

bat  this  is  only  formed  by  mixing  liquid  sulphur  dioxide  and  nitro- 
gen tetroxide  in  the  cold  under  pressure  (Provostaye),  or  sulphuric 
anhydride  with  dry  nitric  axide  (H.  Rose)^or  by  heating  sulphuric 
anhydride  with  nitrogen  tetroxide  (Weber),  none  of  which  reac- 
tions are  possible  in  the  manufacture  of  sulphuric  acid. 

Neither  is  this  the  case  with  the  compound  produced  by  R. 
Weber  (Poggend.  Annalen^  clxii.  p.  602)  by  conducting  sulphuric 
anhydride  into  the  most  highly  concentrated  nitric  acid,  which 
has  the  empirical  formula  N20fi,  4  SO3,  3  HgO. 

Nitroso-sulphuric  acid  is  formed  not  merely  as  above  indicated, 
but  in  many  other  ways.  We  have  already  mentioned  its 
formation  from  sulphur  dioxide  and  nitric  acid : 

S02  4-  NOsHrr  S02(0H)  (ONO). 

It  is  also'  formed  when  a  mixture  of  strong  sulphuric  and  nitric 
acids  is  heated,  oxygen  being  evolved  (A.  Rose) : 

H2SO4  +  HNO3 = SOa  (OH)  (ONO)  -I-  HjO  +  O. 

On  the  other  hand,  sulphur  dioxide  can  form  that  compound  even 
with  the  lower  oxides  of  nitrogen,  if  there  is  water  and  (except 
with  Nj04,  where  this  is  unnecessary)  oxygen  present.  In  the 
perfectly  dry  state  sulphur  dioxide  does  not  act  on  the  dry  nitro- 
gen oxides  ;  but  in  presence  of  the  smallest  quantity  of  water 
'^ chamber-crystals"  are  formed,  if  SOj  meets  with  N2O4,  or  with 
NO  or  N2O3  and  oxygen.  Winkler  has  shown  that,  in  an  atmo- 
sphere of  moist  carbon  dioxide^  nitrogen  trioxide  does  not  form 
chamber- crystals  with  sulphur  dioxide,  but  nitrogen  peroxide  does 
so,  and  he  distinguishes  N2O3  and  N2O4  in  this  manner.  The 
fumes  of  N2O3,  with  an  excess  of  SO2  and  H2O,  but  in  the  absence 
of  oxygen,  give  no  chamber-crystals  at  all;  they  are  decolorized, 
nitric  oxide  and  sulphuric  acid  being  formed.     If  oxygen  or  air 


218  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

is  admitted^  chamber-crystals  instantly  appear^  and  this  is  also 
the  case  when  nitrogen  peroxide  meets  sulphurous  acid  in  the 
presence  of  water.  These  observations  of  Winkler's  have  been 
repeatedly  confirmed;  but  we  must  now  add  that  what  he 
called  "  fumes  of  N2O3 "  is  in  reality  mostly  a  mixture  of  equal 
molecules  of  NO  and  N02^  behaving  chemically  like  N2O3. 

As  some  points  had  not  been  entirely  cleared  up  by  pre- 
vious investigators^  and  there  were  partial  contradictions  among: 
their  results^  I  undertook  a  new  investigation  on  the  interaction  of 
sulphur  dioxide  and  nitric  oxide,  with  or  without  the  presence 
of  water  (Berl.  Ber.  xiv.  p.  2196),  which  led  to  the  following 
results : — 

1 .  DiT  NO  and  SO2  have  no  action  upon  one  another,  be  it  at  the 
ordinary  temperature,  or  at  50°  or  at  100°,  provided  that  air  and 
moisture  are  rigorously  excluded. 

2.  NO,  SO2,  and  water  act  in  such  a  way  that  as  much  N2O  is 
formed  as  corresponds  to  the  quantity  of  SO2  originally  present. 
A  reduction  down  to  N  could  not  be  established. 

3.  If  NO  and  SO2  meet  in  the  presence  of  dilute  sulphuric  acid, 
of  spec.  grav.  1*455,  no  reduction  of  NO  to  N2O  takes  place,  even 
when  there  is  a  very  large  excess  of  SO2  present,  whether  the 
digestion  be  carried  on  for  many  hours  at  ordinary  temperature  or 
at  60°.  Even  with  acid  of  spec.  grav.  1*32  no  reduction  of  NO  by 
SO2  could  be  established. 

4.  If  NO,  SO2,  and  oxygen  meet  in  the  presence  of  water,  a 
slight  but  distinct  reduction  down  to  N2O  takes  place.  If,  how- 
ever, in  lieu  of  water,  dilute  acid  of  spec.  grav.  1*32  is  employed, 
no  such  reduction  can  be  observed. 

The  bearing  of  these  results  on  the  theory  of  the  chamber- 
process  will  be  discussed  later  on  (Chapter  VII.) . 

A  further  investigation  by  myself  (Berl.  Ber.  xviii.  p.  1384; 
Journ.  Chem.  Soc.  xlvii.  p.  465)  confirmed  the  above  results.  It 
was  shown  that  in  the  dry  state  nitric  oxide  combines  with 
an  excess  of  oxygen  to  form  N2O4  exclusively,  or  nearly  so ; 
dry  nitric  oxide  in  excess  with  oxygen  yields  N2O8  along  with 
N2O4;  in  the  presence  of  water,  NO  with  an  excess  of  oxygen  is 
altogether  converted  into  nitric  acid.  If,  however,  NO  meets  O 
in  immediate  contact  with  concentrated  sulphuric  acid,  there  is 
neither  N2O4  nor  HNO3  formed,  even  with  the  greatest  excess  of 
oxygen;    oxidation  proceeds  only  to  the  stage  of  N2O3,  which. 


ACTION  OF  WATER  ON  CHAMBER-CRYSTALS.  219 

however,  is  not  formed  in  the  free  state^  but  passes  into  nitroso- 
salphuric  acid  : 

2  S04H2+2NO-f  0=2S02(OH)(ONO)  +  H2O. 

Outside  the  immediate  contact  with  the  acid  the  reaction  is 
again  as  before  with  dry  gases,  viz.  2N04-02  =  N204;  that  is, 
here  NO  is  oxidized  to  a  higher  state  than  within  the  sulphuric 
acid. 

A  very  elaborate  investigation  of  the  interaction  between 
nitrous  and  sulphurous  acid  was  published  by  Raschig  (Lieb. 
Ann.  ccxli.  pp.  161  et  seq.).  He  found  a  number  of  new  com- 
pounds^ and  rectified  some  of  the  statements  of  Fremy  and  Claus 
concerning  compounds  formerly  described  by  them.  He  also 
discovered  a  very  convenient  method  of  preparing  hydroxylamine. 
But  as  nearly  all  Raschig's  experiments  were  made  with  alkaline 
solutions^  and  those  which  were  performed  with  acid  solutions  were 
made  under  conditions  utterly  different  from  those  of  a  lead 
chamber,  namely  at  the  freezing-point,  we  cannot  stop  to  give  any 
details  of  his  results.  Under  the  just-mentioned  circumstances, 
apart  from  NjO  and  NO,  amidosulphonic  acid,  hydroxylamine, 
and  ammonia  are  observed,  but  only  in  small  quantities;  and 
above  the>low  temperatures  employed  by  Raschig  the  occurrence 
of  those  substances  is  altogether  too  uncertain  and  minimal  to  be 
taken  into  consideration  for  our  purposes. 

Action  of  water  on  chamber^cry stats. — ^These  crystals  are  very 
deliquescent;  they  absorb  water  rapidly  from  ordinary  air.  In  con- 
tact with  a  little  more  water,  they  dissolve  quickly  with  evolution 
of  heat,  much  nitric  oxide  being  given  off.  When  introduced 
into  a  large  quantity  of  water,  they  dissolve  without  visible  evolu- 
tion of  gas  ;  but  in  point  of  fact  nitric  oxide  is  formed  as  well, 
also  nitric  acid,  together  with  nitrous  acid.  This  has  led  to  many 
attempts  at  explanations,  and  Rammelsberg  and  Philipp  have 
asserted  that  exactly  \  of  the  nitrogen  appears  as  NO,  §  as  nitrous 
acid,  and  ^  as  nitric  acid  : 

16  SO,(OH)(ONO)  +9H80=16  SO4HS  +  4NO 
-f2N02(OH)+5N20a. 

But  this  complicated  and  very  unlikely  reaction  need  not  be 
assumed  at  all.     Every  fact  observed  in  this  c<»nnection  can  be 


220  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

quite  Simply  explained  by  the  following  reaction : 

S02(0H)  (ONO)  +  Hfi = SO4HJ  +  NO(OH) ; 

that  is,  nitroso-sulpuric  acid  takes  up  the  elements  of  water,  to 
form  sulphuric  acid  and  nitrous  acid ;  the  latter^  as  is  well  known, 
is  unstable  in  .the  presence  of  an  excess  of  water,  and  hence 
partly  splits  up  into  nitric  oxide  and  nitric  acid : 

In  the  presence  of  less  water,  nitrous  anhydride  can  be  formed 
from  chamber-crystals,  and  escapes  in  the  shape  of  brown  fumes 
(of  course  mostly  dissociated  into  nitric  oxide  and  peroxide) : 

2S02(OH)(ONO)  4-H20=2S04H2  +  N208- 
For  nearly  every  purpose  nitroso-sulphuric  acid  or  its  solution 
in  sulphuric  acid  may  be  regarded  as  a  solution  of  nitrous  acid  in 
sulphuric  acid. 

The  behaviovr  of  nitroso-sulphuric  add  towards  sulphuric  acid  of 
various  concentrations  is  of  great  interest  for  our  purposes.  In 
concentrated  oil  of  vitriol  the  crystals  dissolve  easily  and  without 
decomposition.  This  solution  is  stable  enough  to  be  distilled 
without  losing  any  nitrous  acid,  whilst  the  isolated  crystals  are 
decomposed  on  being  gently  heated.  I  have  shown  (Zeitsch.  f. 
angew.  Chemie,  1888,  p.  661,  and  1890,  p.  447)  that  on  distilling 
such  a  solution  for  four  hours,  when  40  per  cent,  of  the  sulphuric 
acid  had  passed  over,  the  distillate  contained  only  5  per  cent.,  the 
residue  95  per  cent,  of  the  nitrous  acid,  none  of  it  having  been 
destroyed.  It  is  possible  to  obtain  solutions  of  1*9  sp.  gr.  ;  they 
evolve  with  water  nitric  oxide,  inflame  phosphorus  at  62°  C,  oxidize 
sulphur  and  many  metals  on  distillation  with  evolution  of  NO  ; 
heated  with  ammonium  sulphate  to  160°  they  evolve  nitrogen  gas. 
Sulphur  dioxide  evolves  nitric  oxide;  but  a  solution  of  nitroso- 
sulphuric  acid  in  strong  oil  of  vitriol  (of  170°  Tw.),  even  ou  long- 
continued  treatment  with  dry  sulphur  dioxide,  is  only  incompletely 
decomposed,  and  on  addition  of  water  still  shows  the  presence  of 
nitious  acid  by  the  evolution  of  brown  vapours.  This  explains 
the  fact  (well  known  to  manufacturers)  that  concentrated  sulphuric 
acid  contaminated  by  nitrous  acid  is  only  with  difficulty  purified 
by  sulphur  dioxide.  At  a  higher  temperature  sulphur  dioxide 
decomposes  chamber-crystals  with  evolution  of  nitrous  oxide 
(Fremy).    Further  statements  respecting  the  behaviour  of  sulphur 


ACTION  OF  NITROGEN  PEROXIDE  ON  SULPHURIC  ACID.  221 

dioxide  towards  the  solution  of  chamber-crystals  in  sulphuric  acid^ 
the  so-called  '^  nitrous  vitriol/^  will  be  made  when  examining  the 
process  going  on  within  the  Glover  tower.  It  is  remarkable^  and  o£ 
great  importance  for  the  practice  of  sulphuric-acid  making,  that 
even  dilute  acids  of  170  down  to  1*55  sp.  gr.  dissolve  the  crystals 
in  the  cold  without  decomposition;  the  decomposition  only 
commences  when  the  specific  gravity  of  the  dilute  acid  has  fallen 
below  1*55 — that  is,  below  the  density  of  ordinary  chamber-acid. 

Nitrogen  peroxide^,  whether  in  the  state  of  a  liquid  or  a  gas, 
strongly  acts  on  sulphuric  acid.  If,  according  to  Weber,  nitrogen 
peroxide,  made  by  gently  heating  fuming  nitric  acid  [and  there- 
fore not  quite  free  from  nitric  acid] ,  be  added  to  sulphuric  acid  of 
different  degrees  of  concentration,  the  following  is  observed: — 
The  strongest  oil  of  vitriol,  down  to  1*7  sp.  gr.,  absorbs  the 
nitrogen  peroxide  without  coloration.  Acid  of  1*55  turns  yellow; 
here  the  nitrogen  peroxide  is  probably  absorbed  to  a  large  extent 
similarly  as  by  nitric  acid,  and  no  decomposition,  as  represented 
by  the  equation  on  page  223,  has  taken  place,  whilst  this  has  to 
be  assumed  in  the  case  of  the  stronger  acids.  Acid  of  1*49  turns 
greenish  yellow;  of  1*41  intensely  green;  acid  of  1*31  turns  blue 
and  evolves  nitric  oxide,  which  on  applying  a  gentle  heat  escapes 
with  violent  eflfervescence.  Weak  acids  are  only  coloured  for  a 
short  time.  Prom  this  Weber  inferred  : — that  acids  of  1*8  to  1*7 
combine  with  nitrogen  peroxide  with  formation  of  nitroso-sulphuric 
acid ;  weaker  acids  simply  absorb  it ;  and  the  more  dilute  acids 
decompose  it  with  formation  of  nitric  oxide,  nitrous  acid,  and  nitric 
acid.  The  action  of  sulphurous  acid  on  these  mixtures  is  different 
according  to  their  concentration.  As  mentioned  above,  the  solu- 
tion of  chamber-crystals  in  concentrated  sulphuric  acid  is  but 
incompletely  decomposed  even  by  a  prolonged  action  of  sulphurous^ 

*  We  shall  generally  give  this  name  to  the  compound  formerly  called 
"  hyponitric  acid  "  and  now  sometimes  "  nitrogen  tetroxide  "  or  "  nitrogen 
dioxide. '^  It  is  well  known  that  in  the  gaseous  state  it  consists  of  a  mixture  of 
molecules  of  NO,  and  N^O^,  of  varying  proportions,  according  to  the  tempera- 
tui-e.  At  a  low  temperature,  especially  in  the  liquid  state,  it  is  SN2O4;  above 
140^'= NO^.     The  following  are  the  intermediate  proportions  : — 

At  2(3-7  '^  C 80  per  cent.  N^O^    20  per  cent.  NO,. 

„    39*8    „      71        „        „  20        „  „ 

„    60-2    „      47        „        „  63        „ 

„    80-6   „      23        „        „  77        „ 


V 


222       PROPERTIES  OP  OXIDES  AND  ACIDS  OP  SULPHUR. 

acid ;  but  the  yellow  mixture  of  1*55  sp.  gr.  and  the  coloured,  more 
dilute,  acids  are  decomposed  with  strong  effervescence  of  nitric 
oxide.  It  will  be  shown  afterwards  what  part  all  these  reactions 
play  in  the  recovery  of  the  nitrous  gas  in  the  manufacture,  where 
the  object  is  first  to  absorb  the  gas  in  sulphuric  acid  of  1*7,  and 
then  again  to  liberate  it  from  that  solution. 

Winkler  gave  a  different  account  of  the  behaviour  of  liquid 
nitrogen  peroxide  from  that  of  Weber.  He  stated  that  it  may 
be  mixed  with  sulphuric  acids  down  to  142°  Tw.,  but  that  it 
yields  a  solution  totally  different  from  that  of  chamber-crystals  in 
sulphuric  acid,  viz.,  one  of  a  yellow  colour  and  constantly  evolving 
red  fumes.  On  heating,  it  effervesces  and  gives  off  streams  of 
gaseous  nitrogen  peroxide ;  if  the  mixture  is  made  with  sulphuric 
acid  of  142°  Tw.,  the  NO2  completely  volatilizes  far  below  the 
boiling-point  of  sulphuric  acid,  so  that  the  residue  on  dilution 
with  water  does  not  decolorize  potassium  permanganate.  If,  how- 
ever, acid  of  170°  Tw.  has  been  employed,  the  liquid  on  heating 
certainly  yields  up  the  larger  portion  of  its  NOj ;  but  the  residue 
behaves  like  a  solution  of  chamber-crystals  in  sulphuric  acid,  and 
on  being  mixed  with  water  it  evolves  red  fumes  which  can  be 
proved  to  be  NjOs,  not  NO2,  by  their  not  forming  any  chamber- 
erystals  with  moist  SO2. 

There  are  some  essential  differences  between  the  statements  of 
Weber  and  those  of  Wiiikler,  more  especially  so  far  as  the  beha- 
viour of  nitrogen  peroxide  is  concerned,  which  were  cleared  up  by 
my  own  researches  (see  below) . 

If  concentrated  sulphuric  acid  is  mixed  with  a  little  concentrated 
nitric  acid,  and  sulphur  dioxide  is  passed  into  the  mixture,  the 
nitric  acid  in  the  cold  is  only  reduced  to  nitrous  acid,  which 
remains  combined  with  the  sulphuric  acid  :  this  compound  resists 
the  further  action  of  the  sulphur  dioxide,  similar  to  the  solution 
prepared  from  concentrated  oil  of  vitriol  and  chamber-crystals. 
On  the  other  hand,  more  dilute  mixtures  of  sulphuric  and  nitric 
acid,  below  1*7  spec,  grav.,  are  more  or  less  easily  decomposed  by 
SO2,  in  the  ratio  of  their  dilution. 

Since  the  labours  of  Weber  and  Winkler  did  not  in  all  points 
agree  with  one  another,  and  the  subject  seemed  to  call  for 
another  investigation,  I  undertook  a  long  research  (Dingler's 
Journal,  ccxxxiii.  p.  63),  the  conclusions  of  which  (also  published 
in  the  Berl.  Her.  xii.  p.  1058)  are  as  follows  : — 


BEHAVIOUR  OF  NITROGEN  OXIDES  TO  SULPHURIC  ACID.  223 

1.  Nitrogen  peroxide,  under  ordinary  circumstances,  cannot 
exist  in  contact  with  sulphuric  acid,  but  at  once  splits  up  into 
nitrous  acid,  which,  with  a  portion  of  the  sulphuric  acid,  yields 
nitroso-sulphuric  acid  and  nitric  acid  (dissolving  as  such),  thus  : — 

NA  +  S0,(0H),  =  S02(0H)(0N0)  +N08H. 

2.  Nitroso-sulphuric  acid,  on  dissolving  in  an  excess  of  sulphuric 
acid,  forms  a  colourless  liquid,  but  only  up  to  a  certain  limit  of 
saturation,  which  is  all  the  higher  the  more  concentrated 
the  sulphuric  acid.  This  limit  for  acid  of  sp.  gr.  1*84  is  not  yet 
reached  at  55-34  milligrams  N208=185  millig.  S02(0H)(0N0) 
in  1  cubic  centim.  of  acid. 

3.  Beyond  that  limit  at  first  a  yellowish  tint  appears,  of  course 
with  stronger  acids  only  when  more  nitroso-sulphuric  acid  is  pre- 
sent than  with  weaker  acids.  This  took  place  with  a  mixture  of 
sp.  gr.  1*887  (made  from  pure  sulphuric  acid  of  sp.  gr.  1'84), 
containing  in  1  cub.  centim.  147  milligrams  Nj03=372  milligr. 
S02(0H)(0N0),  and  also  with  acid  of  sp.  gr.  1*706,  containing  in 
1  cub.  centim.  only  56*7  milligr.  N2O3=190  milligr.  SOsCOH) 
(ONO).  Since  these  acids  also  are  rendered  colourless  by  pro- 
longed boiling,  the  excess  of  nitroso-sulphuric  acid  seems  to  be 
rather  loosely  held;  but  the  temperature  of  the  water-bath  is  not 
sufScient  to  affect  it. 

4.  The  phenomenon  observed  by  Winkler,  a  mixture  of  strong 
vitriol  and  nitrogen  peroxide  showing  an  orange-colour  even  when 
cold,  emitting  red  vapours,  and  exhibiting  a  tempestuous  evolution 
of  nitrogen  peroxide  on  being  gently  heated  (which  proves  the 
existence  of  unchanged  nitrogen  peroxide),  can  evidently  take 
place  only  when  the  mixture  contains  far  more  N^O^  than  the 
strongest  mentioned  above,  or  the  strongest  ever  occurring  in 
vitriol-works  under  any  circumstances.  Many  experiments  of 
heating  in  the  water-bath  for  a  prolonged  period  demonstrate  the 
absence  of  free  Ns04  in  all  cases  observed.  Still  less  can  the 
presence  of  nitrogen  peroxide  be  assumed  in  more  dilute  acids ;  it 
is  therefore  inadmissible  to  cite  it  as  such  in  analyses. 

5.  All  nitrous  vitriols,  t.  e,  solutions  of  nitroso-sulphuric  acid 
in  sulphuric  acid,  whether  they  contain  nitric  acid  at  the  same 
time  or  not,  on  being  heated  far  below  their  boiling-point  assume 
a  golden-yellow  or  even  darker  yellow  colour,  but  entirely  lose  it 
again  on  cooling.     This  change  of  colours  may  be  repeated  any 


224  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

number  of  times.  It  hardly  indicates  a  loosening  of  the  com- 
bination^ since  this  proves  to  be  very  stable  even  at  much  higher 
temperatures ;  but  it  may  rather  be  compared  to  the  deeper  colour 
which  ferric-chloride  solutions  assume  on  being  heated. 

6.  The  stability  of  nitroso-sulphuric  acid  in  its  solution  in  sul- 
phuric acid  is  very  great^  even  at  the  boiling-point^  providing 
the  specific  gravity  is  not  below  1'70.  It  is  true  that  on  boiling 
it  some  nitrogen  is  always  lost^  and  all  the  more  the  less  con- 
centrated the  acid  is ;  but  if  the  boiling  takes  place  so  that  the 
vapour  cannot  condense  and  flow  back^  there  is  some  nitroso- 
sidphuric  acid  found  in  the  residue,  even  from  acid  of  sp.  gr.  1'65 
(comp.  p.  221) .  But  if  the  vapour  is  condensed  and  the  condensing 
liquid  (which,  in  the  case  of  vitriol  of  sp.  gr.  1*80  or  below,  consists 
of  very  dilute  acid  or  almost  pure  water)  is  allowed  to  flow  back, 
a  considerable  loss  is  caused  by  denitration. 

7.  Down  to  a  concentration  of  sp.  gr.  1*65  the  affinity  of  sul- 
phuric acid  for  nitrous  acid,  t.  e.  the  tendency  to  the  formation  of 
nitroso-sulphuric  acid,  is  so  great  that  any  nitric  acid  present  at 
the  same  time,  whether  added  as  such  or  formed  by  the  decompo- 
sition of  nitrogen  peroxide,  is  reduced  with  loss  of  oxygen,  and 
employed  to  form  nitroso-sulphuric  acid.  In  the  case  of  acid  of 
sp.  gr.  1*71  and  upwards,  this  transformation  takes  place  almost 
completely  after  a  brief  boiling,  but  at  sp.  gr.  1*65  only  incom- 
pletely. This  is  a  further  argument  against  the  existence  of  N2O4 
in  the  solution. 

8.  Below  sp.  gr.  1*65  the  nitroso-sulphuric  acid  possesses  so 
little  stability  that,  for  instance,  from  acid  of  sp.  gr.  1*60  some 
nitrogen  oxides  (but  only  a  very  small  percentage)  are  expelled  in 
the  water-bath,  and  nearly  all  of  them  by  boiling  for  a  short  time. 
In  the  case  of  acid  of  sp.  gr.  1*5,  it  is  evident  that,  even  without 
heating,  the  nitrous  acid  added  is  partly  decomposed  into  nitric  acid 
and  nitric  oxide ;  but  after  heating  for  an  hour  in  the  water-bath 
a  considerable  quantity  of  nitroso-sulphuric  acid  remains  undecom- 
posed,  whilst  another  portion  has  been  converted  into  sulphuric 
acid.  In  the  case  of  still  weaker  acids,  of  course  these  phenomena 
occur  even  to  a  greater  extent ;  but  it  is  Yery  probable  that  even 
very  dilute  sulphuric  acid  may  contain,  while  cold,  a  little  nitroso- 
sulphuric  acid  if  reducing-agents  are  absent. 

9.  Most  of  the  nitric  acid  present  along  with  nitroso-sulphuric 
acid  in  dilute  acids  (of  sp.  gr.  1*5  and  under)   remains  behind  in 


BEHAVIOUR  OF  NITROGEN  PEROXIDE  TO  SULPHURIC  ACID.       225 

the  liquid  even  after  prolonged  boiling.  If,  therefore^  the  nitrous 
yitriol  of  acid-works,  in  consequence  of  a  faulty  process,  contains 
nitric  along  with  nitrous  acid,  it  cannot  possibly  be  completely 
denitrated  by  hot  water  or  steam,  in  which  case  a  less  strength 
than  sp.  gr.  1*5  is  never  reached ;  the  denitration  can  be  only 
effected  by  reducing-agents,  such  as  sulphur  dioxide  in  the  Glover 
tower  or  mercury  in  the  nitrometer.  In  the  latter  it  can  be  very 
clearly  seen  with  how  much  more  difficulty  and  slowness  the  deni- 
tration goes  on  in  the  presence  of  nitric  acid. 

10.  The  tendency  to  form  nitroso-sulphuric  acid  is  so  strong 
that  even  if  a  large  quantity  of  air  (oxygen)  is  passed  through 
sulphuric  acid  along  with  nitrons  acid  no  oxidation  to  N3O4  or 
N3O0  takes  place,  just  as  in  the  case  of  oxygen  and  NO. 

11.  Nitrous  acid  cannot  be  absorbed  by  caustic-soda  solution 
without  loss,  because  a  portion  of  it  is  decomposed  into  nitric  acid 
and  nitric  oxide. 

12.  The  purple  colour  which  is  developed  in  nitrous  vitriol  by 
the  action  of  redacing-agents  is  caused  by  a  solution  of  nitric 
oxide  in  such  acids,  and  is  possibly  produced  by  a  very  unstable 
compound  of  nitrogen  and  oxygen,  midway  between  NO  and 
N,0«. 

Although  my  experiments  had  decidedly  proved  (comp.  No.  1 
and  4  of  the  just-quoted  conclusions)  that  nitrogen  peroxide  does 
not  dissolve  as  such  in  sulphuric  acid,  with  formation  of  an 
unstable  solution  from  which  the  N2O4  can  be  drawn  off  by  heat- 
ing, the  former  erroneous  assertion  of  Winkler  (since  that  time 
recognized  as  such  by  himself)  did  not  vanish  from  chemical 
literature,  and,  for  instance,  gave  rise  to  a  decidedly  erroneous 
explanation  of  the  process  of  Lasne  and  Benker  for  treating  the 
absorption  in  the  Gay-Lussac  tower.  This  caused  me  to  investi- 
gate the  subject  once  more  (Berl.  Ber.  xv.  p.  488).  I  pointed  out 
that  mixtures  of  pure  nitrogen  peroxide  with  even  somewhat  dilute 
sulphuric  acid,  down  to  spec.  grav.  1*65,  behave  quantitatively  as 
mixed  solutions  of  equal  molecules  of  nitroso-sulphuric  acid  and 
nitric  acids ;  that  on  prolonged  heating  in  a  watei'-bath  such  solu- 
tions in  acid  of  spec.  grav.  1*75  do  not  lose  any,  and  in  acid  of 
spec.  grav.  1*65  only  very  little,  of  their  nitrogen  compounds.  On 
prolonged  boiling  part  of  the  latter  escapes,  but  a  large  quantity 
of  nitroso-sulphuhc  acid  remains  behind,  more  than  that  originally 
present,  part  of  the  nitric  acid  having  passed  into  it  with  loss  of 

VOL.  I.  Q 


226  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

oxygen.  The  idea  of  a  "  loose  '^  union  between  NgO^  and 
sulphuric  acid  must  therefore  be  entirely  abandoned ;  and  from 
this  follows  the  fallacy  of  the  idea  held  by  some  manufacturers 
that  N2O4  is  less  easily  absorbed  by  sulphuric  acid  than  N2O3, 
and  that  therefore  much  N2O4  is  lost  in  the  Gay-Lussac  tower. 
I  directly  disproved  this  idea  by  showing  that  vapours  of  nitrogen 
peroxide  are  most  easily,  quickly,  and  completely  absorbed  by 
sulphuric  acid  of  spec.  grav.  1-71,  such  as  is  used  in  the  Gay- 
Lussac  tower,  and  that  this  (colourless)  solution  is  not  changed 
either  by  long  heating  to  100°  or  by  passing  a  current  of  air  for  a 
long  time  through  it. 

A  concluding  investigation  on  the  behaviour  of  nitrogen  per- 
oxide towards  sulphuric  acid  has  been  made  by  myself  together 
with  Weintraub  (Zsch.  angew.  Ch.  1899,  p.  393),  of  which  I  here 
give  merely  a  summary  of  the  results. 

1.  The  reaction  between  sulphuric  acid  and  nitrogen  peroxide 
is  reversible,  since  the  nitric  acid  formed  has  some  action  on 
nitroso-sulphuric  acid,  forming  sulphuric  acid  and  nitrogen 
peroxide : 

H2SO4  +  NA  Z  SO5NH  +  HNO3. 

In  mixtures  of  sulphuric  acid  and  nitrogen  peroxide  an  equili- 
brium is  formed,  all  four  substances — sulphuric  acid,  nitrogen 
peroxide,  nitroso-sulphuric  acid,  and  nitric  acid — being  present  at 
the  same  time.     2.  In  contact  with  concentrated  sulphuric  acid 
(95  per  cent.  H2SO4)  nearly  all  the  nitrogen  peroxide  is  converted 
into  nitroso-sulphuric  and  nitric  acid.     The  inverse  reaction  sets 
in  to  a  sensible  extent  only  when  very  little  sulphuric  acid  is  present 
in  comparison  with  nitric  acid,     3.  The  affinity  of  sulphuric  acid 
for  nitrogen  peroxide  quickly  decreases  with  the  increase  of  water, 
so  that  in  the  case  of  sulphuric  acid  of  spec.  grav.  1*65  the  action 
of  nitric  acid  on  nitroso-sulphuric  acid  begins  to  prevail ;  there- 
fore very  much  of  the  nitrogen  peroxide  added  remains  in  the  free 
state,  although  the  quantity  of  HNO3,  which  is  only  formed  by 
the  reaction  itself,  is  but  small.     4.  In  the  practice  of  sulphuric- 
acid  manufacture,  the   quantity  of  sulphuric  acid  in  the  con- 
centrated state  so  largely  prevails  over  that  of  the  nitric  acid,  that 
all  nitrogen  peroxide  may  be  practically  regarded   as  quantita- 
tively changed  into  SO3NH  and  HNO3.     This,  of  course,  also 
holds  good  when  absorbing  nitrous  gases  in  concentrated  sulphuric 
acid  for  analytical  purposes.     Therefore  the  conclusions  No.   1 


REDUCTION  OP  NITROSULPHURIC  ACID.  227 

and  No.  4  (p.  223),  although  not  mathematically  exact,  are  to  all 
intents  and  purposes  valid. 

77i€  tension  of  nitrous  acid  in  presence  of  dilute  sulphuric  acid 
at  different  temperatures  is  a  matter  of  great  importance  for  the 
theory  of  the  formation  of  sulphuric  acid  in  the  lead-chambers. 
The  first  observations  on  this  point  were  published  by  Sorel 
(Zsch.  angew.  Ch.  1889,  p.  272) ;  but  these  have  become  obsolete 
by  the  far  more  extended  observations  published  by  myself  in  the 
Zeitsch.  f.  angew.  Chemie,  1891,  pp.  37  et  seq.  The  tables  con- 
structed from  these  indicate  the  loss  of  N2O3  suflfered  by  acids 
of  four  different  concentrations,  containing  quantities  of  N2O3 
varying  from  1  gram  per  litre  upwards,  in  a  current  of  air"  at 
temperatures  from  50°  to  90°  C.  (pp.  228-231) . 

The  behaviour  of  nitroso-sulphuric  acid  towards  reducing 
reagents  is  of  the  greatest  importance,  both  for  the  chamber- 
process  in  general  and  for  the  recovery  of  nitrogen  compounds. 
The  most  important  of  the  reagents  in  question  is  sulphur  dioxide, 
which  acts  as  follows  : — 

2SO2(0H)(ONO)+SO2+2H2O  =  3SOJl3  +  2NO; 

that  is,  it  forms  with  nitroso-sulphuric  acid  both  sulphuric  acid 
and  nitric  oxide.  This  is  the  leading  reaction  of  the  Glover  tower, 
as  we  shall  see  hereafter;  and  it  must  also  occur  within  the 
chambers,  more  especially  in  the  first  part  of  the  set. 

Sorel  (Zeitsch.  f.  angew.  Ch.  1888,  p.  273)  has  shown  that  if  a 
mixture  of  SO2  and  O  is  made  to  react  upon  nitrous  sulphuric  acid 
and  NO,  there  may  be  either  a  reduction  of  nitrous  acid  to  NO 
or  an  oxidation  of  NO  to  N0O3  (i^  the  shape  of  SO5NH),  accord- 
ing to  variations  in  the  following  conditions :  temperature,  dilution 
of  the  acid,  proportion  between  SOj  and  O,  percentage  of  NO. 
The  extreme  cases  were  well  known  before :  a  reduction  takes 
place  at  high  temperatures,  with  scarcity  of  oxygen  and  excess  of 
water ;  an  oxidation  with  excess  of  oxygen,  concentrated  acid,  and 
low  temperatures.  For  the  intermediate  cases  Sorel  made  some 
special  experiments,  from  which  it  followed  that  in  identical 
mixtures  an  increase  of  the  temperature  from  70°  C.  to  80°  C. 
was  suflScient  to  change  the  oxidation  into  reduction.  At  equal 
temperatures  a  reduction  took  place  when  the  gaseous  mixture 
contained  31  per  cent.  SO2,  10  per  cent.  O,  59  per  cent.  N,  but 
an  oxidation  with  a  mixture  of  21  SO,,  12*1  O,  66*9  N,  &c.     The 

q2 


228 


PROPERTIES  OF  OXIDES  AND  ACIDS  OP  SULPHUR. 


1.  Nitrous  vitriol  of  spec,  grav.  1*720  (say,  78  per  cent.  H2SO4). 


1 

N^O  3  originally ' 

Loss  of  N2O3  in  grams  per  litre  at 

present. 
Grams  in  1  litre. 

1 

50°. 

60°. 

70°. 

80°. 

W.      1 

1 

■  ■  ■ 

•  ■  • 

... 

0006 

2 

•  •  • 

■  •  ■ 

•  •  • 

0018 

3 

■  •  • 

•  •  • 

•  •  • 

0025     ' 

4 

•  ■  • 

■  •  • 

•  •  ■ 

0031 

r> 

•  *  • 

■  ■  • 

•  •  • 

0087 

6 

•  ■  • 

»  • » 

• «  ■ 

0-0i3     ; 

7 

■  •  • 

•  •• 

0006 

0-056 

8 

•  •  • 

•  ■  • 

0010 

0-068 

9 

•  •  • 

•  •  m 

0012 

0081 

10 

•  ■  ■ 

•  •  ■ 

0018 

0-093 

11 

•  ■  • 

•  •  • 

0-025 

0112 

12 

•  ■  • 

»  •  • 

0030 

0125     1 

13 

... 

•  ■  • 

0-031 

0-143 

14 

•  •  • 

•  ■  • 

0043 

0168     ' 

15 

•  •  • 

0006 

0056 

0193 

16 

•  «  • 

0-010 

0068 

0-218 

17 

•  ■  ■ 

0-006 

0087 

0250 

18 

•  •  • 

0012 

0106 

0-281      i 

19 

•  •  • 

0-025 

0125 

0-318     1 

'JO 

«  •  ■ 

0-031 

0150 

0-356     . 

21 

•  •  • 

0043 

0175 

0-400     1 

n 

•  ■  • 

0-064 

0-200 

0-450 

23 

•  •  • 

o-6o6 

0081 

0-237 

0-500      1 

24 

0006 

0018 

0-100 

0-275 

0-550     1 

25 

0012 

0-031 

0125 

0-312 

0-600     , 

26 

0018 

0-043 

0150 

0-3.56 

0-662      . 

27 

0031 

0-062 

0-181 

0-400 

0-725     I 

28 

0-043 

0081 

0-212 

0-450 

0-800 

29 

0062 

0-100 

0-25(3 

0-500 

0-850 

30 

0081 

0-125 

0-293 

0-550 

0-956 

31 

0093 

0162 

0-337 

0-612 

1-043 

32 

0112     ' 

0200 

0-387 

0-641 

1-125 

33 

0125 

0-237 

0-391 

0-743 

1-206     i 

34 

0-143 

0-275 

0-476 

0-806 

1-287     1 

35 

0156 

0-312 

0-525 

0-868 

1-375     1 

36 

0175 

0-350 

0-575 

0-931 

1-456     1 

37 

0193 

0381 

0-618 

1-000 

1543     ' 

38 

0-206 

0-418 

0-662 

1062 

1-625      • 

39 

0-237 

0-456 

0-718 

1-125 

1-712     , 

40 

0'2(i8 

0-500 

0-775 

M93 

1-800     ' 

41 

0-293 

0-543 

0-831 

1*256 

1-890 

42 

0-325 

0-587 

0-887 

1-331 

1-975      . 

43 

0-350 

0-631 

0-937 

1-400 

2062 

44 

0-376 

0-675 

0-993 

1-468 

2-150 

45 

0-406 

0-712 

1-050 

1-537 

2-237     ' 

46 

0437 

0-756 

1106 

l-60(i 

2-3-25 

47 

0-462 

0-800 

1-162 

1-675 

2-392 

48 

0-493 

0-837 

1-218 

1-743 

2-500 

49 

0518 

0-881 

1-268 

1806 

2-587 

50 

0-550 

0-931 

1-325 

1 

1-875 

2-675 

1 

TENSION  OF  NITHOUS  ACID  IN  SULPHURIC  ACID. 


229 


2.  Acid  of  spec.  grav.  1-686  (say,  76  per  cent.  H2SO4). 


N2O3  originallj 

Lots  of  NjOs  in  grams 

per  litre  at 

1       present. 

G^faiiiB  in  1  litre. 

50^ 

60 

mm   ^m  ^w  — 

'       70". 

'      80°. 

90**. 

8 

•  •  m 

1 

•  a 

■   ■  • 

«  ■  • 

0025 

9 

m  m 

•  ■ 

■  a  ■ 

•  •  ■ 

0036 

10 

»  • 

•  ■ 

•  •  • 

0-012 

0050 

11 

^  - 

•  • 

•  •  • 

0018 

0062 

12 

■  • 

•  • 

•  •  • 

0-025 

0086 

13 

•  ■ 

*  ■ 

0-010 

0050 

0125 

14 

•  ■ 

1 
1 

0012 

0-075 

0-162 

15 

•  1 

•  •  « 

0025 

0100 

0-225 

16 

•  • 

•  ■  i 

0050 

0-150 

0-286 

17 

•  •  4 

0010 

0062 

0-200 

0-350 

18 

•  m  M 

0-012 

0-100 

0-262 

0-436 

19 

■  •  • 

0025 

0-150 

0-350 

0-525 

20 

•  •  ■ 

0-060 

0186 

0425 

0-625 

21 

•  •  ■ 

0075 

0-250 

0-525 

0-750 

22 

■  ■  • 

0112 

0-300 

0-650 

0-975 

23 

•  *  • 

0136 

0-350 

0-775 

1-200 

24 

•  •  ■ 

0175 

0-400 

0-900 

1-436 

20 

O-OIO 

0-200 

0-462 

1-025 

1-662 

26 

0-012 

0-236 

0-512 

1175 

1-900 

27 

0025 

0-262 

C-562 

1-300 

2-125 

28 

0036 

0-800 

0-612 

1-436 

2-350 

29 

0-050 

0-336 

0-675 

1-575 

2-600 

30 

0-062 

0-362 

0-750 

1-700 

2-812 

31      ; 

0-100 

0-412 

0-850 

1-812 

3086 

:f2 

0136 

0-462 

0-950 

1-975 

3-350 

33 

0-186 

0-512 

1050 

2100 

3-625 

34 

0-225 

0575 

1150 

2-236 

3-900 

;i6 

0-275 

0-625 

1-250 

2-362 

4175 

36 

0-312 

0-675 

1-336 

2-500 

4-450 

37 

0-350 

0-725 

1-436 

2-625 

4-736 

;« 

0-400 

0525 

1-536 

2762 

5000 

39 

0-436 

0-836 

1-636 

!      2-900 

5-275 

40 

0-486 

0-886 

1-736 

3025 

5-550 

41 

0-550 

0-950 

1-850 

3-160 

5-850 

42 

0-612 

1050* 

1-986 

3-275     , 

6125 

43 

0-686 

1125 

2112 

3-412 

6-400 

44 

0-750 

1-212 

2-250 

3-525 

0-700 

45 

0-825 

1-300 

2-325 

3-736 

6975 

46 

0-886 

1-386 

2-500 

3-825 

7-250 

47 

0-962 

1-475 

2-636 

3-962 

7-536 

48 

1025 

1-512 

2-762 

4-100 

7-825 

49 

1100 

1-650 

I 

2-886 

4-236 

8-100 

230 


PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 


3.  Acid  of  spec.  grav.  1*633  (say,  71*5  per  cent.  H2SO4). 


NjOj  originally 

present. 
Grams  in  1  litre. 


1 

2 

3 

4 

f) 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

Ifi 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

80 

31 

32 


50°. 


0012 
0-050 
0-100 
01H2 
0-212 
0-300 
0-400 
0-500 
0-600 
0-700 
0-800 
0-871 
0-986 
1-086 
1-186 
1-275 
1-375 
1-475 
1-562 
1-662 
1-812 
1-975 
2-18(5 
2-436 
2-700 
3-000 
3-312 
3-6(>2 
4-025 
4-412 
4-800 
5-23C> 


Lobs  of  N.^Og  in  grams  per  litre  at 


60°. 


0-025 
0-075 
0150 
0-212 
0-300 
0-425 
0-562 
0-712 
0-835 
0-936 
1125 
1-262 
1-400 
1-536 
1-675 
1-800 
1-936 
2-036 
2-250 
2-412 
2-612 
2-812 
3062 
3-336 
3-(i36 
3-950 
4-300 
4-636 
5-012 
5-412 
6-836 
6-325 


70°. 


0036 
0-08(» 
0186 
0-300 
0-436 
0-636 
0-836 

i-a% 

123(> 
1-436 
1-636 
1-825 
2-03(i 
2-225 
2-412 
2-612 
2-786 
2-975 
3-18(i 
3-400 
3-650 
3-912 
4-250 
4-612 
5-000 
5-412 
5-850 
6-325 
6-812 
7-350 
7-950 
8-575 


80°. 


0100 
0-225 
0-350 
0-536 
0-736 
1000 
1-275 
1-550 
1-812 
2-086 
2-350 
2-636 
2-900 
3175 
3-450 
3725 
4-000 
4-262 
4-550 
4-85(» 
5-162 
6-512 
6912 
6-350 
6-800 
7-300 
7-812 
8-400 
8-025 
9-675 
10-386 
11175 


90°. 


0150 
0-300 
0-436 
0-612 
0-825 
1-112 
1-425 
1-750 
2-062 
2-375 
2-712 
3075 
3436 
3-800 
4-162 
4-512 
4-886 
5-236 
6-600 
6-986 
6-400 
6-862 
7-425 
803(1 
8-662 
9-362 
10-150 
11-000 
11-986 
13126 
14-500 
16-362 


reaction  of  SO2  on  nitrous  sulphuric  acid  is  nothing  like  so  simple 
as  previously  assumed.  If  the  acid  exceeds  the  strength  of  1  '630, 
the  SO2  does  not  reduce  the  NjOs  to  NO,  but  forms  with  it  and 
sulphuric  acid  nitroso-sulphuric  acid,  so  long  as  there  is  oxygen 
in  excess  and  the  atmosphere  contains  more  N2O3  than  corresponds 
to  the  tension  of  the  acid  in  question  at  that  special  temperature 
(comp.  above).  Otherwise  reduction  to  NO  takes  place.  Acids 
below  spec.  grav.  1'600  are  able  to  fix  N2O3  under  the  same  con- 
ditions, but  only  at  comparatively  low  temperatures;  at  higher 
temperatures  there  is  reduction  even  in  the  presence  of  an  excess 
of  O  and  N2O3. 


REDUCTION  OF  NITROSO-SULPHURIC  ACID. 


231 


4.  Acid  of  spec.  grav.  1*60  (say,  69  per  cent.  H2SO4). 


N.jOa  originally 

Loss  of  NgOg 

in  grams  per  litre  at 

present. 

Grams  in  1  litre. 

50°. 

'       60°.       ' 

70°. 

80°. 

90°. 

1 

0050 

0086 

0175 

0336 

0-412 

0 

0100 

0-236 

0-436 

0-725 

0-912 

a 

0-325 

0-525 

0-775 

1-150 

1-500 

4 

()o62 

0-836 

1-250 

1-910 

2-100 

T) 

0-812 

1-I.tO 

1-500 

2120 

2-700 

6 

1050 

1-450 

1-900 

2-500 

3-350 

7 

l-28(i 

1-800 

2-350 

3100 

4-112 

s 

1-512 

2-150 

2-800 

3-725 

4-900 

{) 

1-750 

2-425 

3-250 

4-336 

5-686 

10 

1-975 

2-812 

3-712 

4-900 

6-475 

11 

2-250 

3-162 

4-436 

5-265 

7-300 

ll> 

2-512 

3-536 

4-675 

6-325 

8-125 

la 

2-786 

3-936 

5150 

7012 

8-962 

14 

3065 

4-2.M) 

5-650 

7-700 

9-750 

1.3 

3-3^) 

4-612 

6-125 

8-400 

10-625 

16 

3-600 

4-975 

6-612 

9125 

11-462 

17 

3-862 

5-350 

7-100 

9-525 

12-250 

18 

4150 

5-712 

7600 

10-462 

13136 

19 

4-425 

6-075 

8086 

11-350 

13-975 

2() 

4-700 

6-425 

8-5()2 

11-850 

14-800 

Another  reducing  agent  whose  action  had  formerly  been  over- 
looked is  carbon,  in  the  shape  of  the  coke  employed  for  packing 
the  Gay-Lussac  tower.  I  have  shown  (J.  Soc.  Chem.  Ind.  1885, 
p.  31)  that  coke  has  a  very  strong  reducing-action.on  nitric  acid 
dissolved  in  sulphuric  acid,  which  goes  far  towards  explaining 
the  fact  that  the  "  nitrous  vitriol  "  from  the  Gay-Lussac  towers 
never,  except  under  altogether  exceptional  circumstances,  contains 
any  nitric  acid,  even  when  considerable  quantities  of  N2O4  had 
been  present  in  the  exit  gases.  But  the  reduction  goes  further; 
some  N2O3  itself,  in  the  shape  of  nitroso-sulphuric  acid,  is  by  the 
coke  reduced  to  lower  nitrogen  oxides  and  is  thus  lost.  This  has 
been  proved  by  myself  in  my  laboratory  (Zeitsch.  f.  angew.  Chem. 
1890,  p.  195)  ;  and  as  it  is  a  matter  of  importance,  we  give  the 
results  obtained  in  the  following  table  (p.  232). 

It  will  be  seen  that  at  40°  C.  two  hours'  contact  reduced  the 
percentage  of  NgOg  by  2"4  to  4'5  per  cent. ;  at  7QP  the  reduction 
sometimes  went  as  far  as  28  per  cent.  The  latter  temperature 
ought  never  to  occur  in  a  Gay-Lussac  tower,  but  it  does  occur 
regularly  in  Glover  towers  up  to  the  top.     The  conclusion  is  that 


232 


PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SVI-PHUR. 


1 
1 

Percentage  decrease 

Material  used. 

Tempe- 
!  rature. 
«>C. 

1 

;    Time 
(hours). 

1 

Original 
percentage 

grams.     1 

in 
grms. 

HA- 

■ 

of  the  N„0 
originallj 
present. 

1. 

2Jitrous  Vitriol  of  spec.  grar.  r8375 

GsB  Coke  in  lumps    .. 

....       16 

24      ' 

18-93 

0-330 

1-71 

>t            ft            ** 

....       14 

2 

18-92 

0-539 

2-86 

II            II            •• 

....       70 

2 

19-30 

0742 

3-84 

Oven  Coke  in  lumps  .. 

....       15 

24 

19-30 

0-285 

'         1-48 

ft           ft            '• 

....       40 

2 

18-92     , 

0-362 

1-91 

II            If            •  • 

....       70 

2 

19-30 

0-452 

2-34 

Ghis  Coke  in  powder  .. 

....       15 

24 

19-30 

0-790 

4-09 

tf            tf            " 

....       40 

2 

18-92 

0-858 

4-54 

>f            t*            • • 

....       70 

2 

lH-22     > 

0-903 

5-57 

tt            tt            •' 

....     100 

2 

16-22 

4-611 

i       28-43 

Oven  Coke  in  powder 

15 

24 

19-30     ; 

0-379 

1         1-96 

'1               tf 

...       40 

2 

1892 

0-451 

2-38 

1*                1* 

...       70 

2 

16-22 

0-527 

1         3-25 

...     100 

2 

16-22 

1 

2-770 

1708 

1 

2.  Nitrous  Vitriol  of  spec.  grav.  1-725. 

Gas  Coke  in  powder  . . 

.....      15 

'      24 

19o0     1 

0-333 

1        1-98 

»•            i» 

...J      40 

;     2 

19-50     1 

0-574 

;       2-^ 

M                           tt 

70 

2 

19-50 

0-891 

4-57 

ft                           ■»                            •  ■ 

....;     100 

2 

1               1 

19-50      . 

1 

3-410 

17-49 

coke  packing  should  be  entirely  avoided  in  Glover  towers,  and 
that  it  is  not  advisable  even  for  Gay-Lussac  towers  (comp. 
Chap.  VI.). 


Analysis  of  Sulphuric  Acid. 

Qualitatively  sulphuric  acid  is  always  recognized  best  by  the 
white  precipitate  of  barium  sulphide  which  it  gives  with  barium 
chloride,  both  in  the  free  state  and  in  the  solutions  of  its  salts, 
even  when  very  much  diluted.  This  precipitate  mostly  settles  down 
as  a  heavy  powder,  but  in  extremely  dilute  liquids  occasionally 
appears  only  after  some  little  time  as  a  white  cloud.  Barium 
sulphate  is  as  good  as  insoluble  in  water,  solutions  of  salts,  and 
free  dilute  acids ;  in  concentrated  acids  it  is  a  little  soluble, 
especially  on  heating,  also  in  concentrated  sulphuric  acid  itself 
and  in  solutions  of  ferric  chloride.  On  the  other  hand,  in  a  very 
concentrated  liquid  free  from  sulphuric  acid,  but  containing 
much   hydrochloric  or,  especially,    nitric  acid,   the   addition    of 


£STIMATION  OF  SULPHURIC  ACID.  233 

barium  chloride  may  cause  a  precipitate  of  barium  chloride  itself 
or  of  barium  nitrate^  which,  however,  is  distinguished  from 
barium  sulphate  by  its  crystalline  appearance,  and  even  more  by 
vanishing  on  dilution  of  the  liquid ;  barium  seleniate  is  distin- 
guished from  barium  sulphate  by  its  solubility  bn  boiling  with 
concentrated  hydrochloric  acid,  and  by  its  behaviour  with  the  blow- 
pipe. The  reaction  proves  the  presence  of  sulphuric  acid  either 
in  its  free  state  or  in  its  salts.  In  order  to  find  sulphuric  acid  in 
the  free  state  in  the  presence  of  sulphates  of  acid  reaction,  either 
the  alcoholic  solution  of  the  substances  can  be  tried  with  barium 
chloride  (free  acid  being  soluble,  but  all  sulphates  insoluble  in 
absolute  alcohol) ,  or  the  charring  properties  of  concentrated  oil 
of  vitriol  are  made  use  of  by  evaporating  the  solution  mixed  with 
a  little  cane-sugar  in  a  small  porcelain  capsule  on  the  water-bath, 
and  observing  whether  a  blackening  of  the  sugar  takes  place. 
This  reaction,  however,  also  takes  place  with  the  sulphates  of 
very  weak  bases,  such  as  alumina  or  ferric  oxide ;  nor  can  sul- 
phuric acid  be  distinguished  with  certainty  in  this  way  from 
hydrochloric  or  nitric  acid ;  but  in  phosphoric,  acetic,  tartaric  acid, 
&c.  a  very  small  proportion  of  sulphuric  acid  can  be  proved  by  this 
reaction.  Another  reaction  for  free  sulphuric  acid,  as  well  as  for 
any  strong  free  acid,  is  that  with  methyl-orange :  the  latter  does 
not  change  colour  by  adding  metallic  salts,  but  is  changed  by  the 
smallest  quantity  of  free  sulphuric  acid. 

In  insoluble  sulphates  the  acid  is  recognized  by  fusing  them  with 
alkaline  carbonates,  or  by  boiling  with  concentrated  solutions  of 
the  same  and  filtering  the  solution  of  the  alkaline  sulphate  formed 
thereby  from  the  insoluble  carbonates,  or  with  the  blowpipe,  on 
charcoal,  by  the  formation  of  sodium  sulphate,  according  to  well- 
known  methods. 

The  quantitative  estimation  of  free  sulphuric  acid  for  technical 
purposes  is  almost  exclusively  effected  by  volumetric  methods  or 
by  the  hydrometer.  In  both  cases,  of  course,  impurities  will  have 
a  disturbing  action ;  but  for  technical  purposes  they  may  nearly 
always  be  neglected  (compare  p.  187  et  seq,).  The  hydrometric 
estimation  of  sulphuric  acid  has  been  already  described  in  detail; 
and  we  shall  here  only  point  out  again  that  the  temperature  must 
not  be  neglected  in  this  case. 

The  volumeirical  estimation  of  free  acid  generally  takes  place 
by  means  of  a  standard  solution  of  potash,  soda,  or  ammonia. 


234  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

According  to  the  accuracy  required,  either  a  normal  solution  is 
used  (that  is,  one  containing  per  litre  an  equivalent  expressed  in 
grams),  or  a  semi-  or  decinormal  solution,  &c. 

Formerly  tincture  of  litmus  was  most  frequently  used  as  indi- 
cator. Litmus  is  not  well  fidapted  for  working  in  artificial  light : 
the  red  appears  almost  as  clear  as  water,  the  blue  like  a  dark 
violet;  but  the  transition  from  bright  red  into  purple,  &c.,  cannot 
be  seen  with  certainty.  This  can  be  remedied  by  monochromatic 
light,  if  the  artificial  light  be  coloured  yellow  by  common  salt : 
the  red  appears  clear  as  water,  the  blue  like  deep  black  ;  and  the 
transition  is  even  sharper  than  in  daylight. 

Litmus  has,  moreover,  the  disadvantage  that  it  is  sensitive  to 
all  weak  acids  as  well,  and  that  it  is  destroyed  by  sulphuretted 
hydrogen.  If,  therefore,  carbonates  are  to  be  tested  with  it,  thia 
must  be  done  at  a  boiling  heat,  and  the  boiling  must  be  prolonged 
for  some  time.  If  any  sulphides  are  present,  an  excess  of  acid 
must  be  added,  and  all  the  H2S  expelled  by  prolonged  boiling ; 
only  then  should  the  litmus  be  added,  and  the  analysis  finished 
by  re-titrating.  This  makes  application  of  litmus  very  troublesome 
in  alkalimetry  ;  in  fact  a  real  error  is  introduced  by  the  necessity 
of  long  boiling,  if  this  is  done  in  glass  vessels  which  yield  up  some 
alkali  thereby.  In  acidimetry  this  drawback  is  less  felt,  but  only 
when  the  standard  alkali  is  kept  entirely  free  from  carbonates, 
which  is  very  difficult  in  the  daily  practice  of  alkali-works. 

Fhenolphthalein  has  in  many  cases  taken  the  place  of  litmus.  It 
is  one  of  the  most  sensitive  indicators  known,  and  the  change  from 
no  colour  in  acid  solutions  to  a  decided  pink  with  the  faintest  trace 
of  free  alkali  is  easily  noticed  even  in  artificial  light.  But  this 
indicator  has  two  drawbacks  :  it  is  too  sensitive  even  towards  the 
weakest  acids  [e,g,  CO2),  and  it  fails  in  the  presence  of  ammonia. 
The  former  circumstance  entails  exactly  the  same  difficulties  as  in 
the  case  of  litmus.  Hence,  while  phenolphthalein  is  the  best  of  all 
indicators  for  titrating  weak  acids,  it  is  decidedly  inferior  to  methyl- 
orange  for  the  titration  of  alkalies  containing  carbonates  or 
sulphides,  and  in  the  acidimetry  of  strong  acids. 

The  indicator  which  in  alkali  and  acid  works  is  now  universally 
employed  is  methyUorange  *.     This  is  sulphobenzene-azodimethyl- 

*  I  have  proposed  this  name  for  the  indicator  introduced  by  me,  in  lieu  of 
the  commercial  names  of  Poimer's  Orang^  No.  III.  or  helianthin  (Chem.  News, 
xliv.  p.  288) ;  and  it  has  been  generally  adopted. 


METHYL-ORANGE  AS  INDICATOR.  235 

aniline^  or  the  sodium  salt  of  this  compound  : 

(SOgNa)  CeH4-N2-CeH4N(CH3)„ 

%vhich  is  employed  in  an  aqueous  solution  of  1  in  2000  water,  or 
even  more  dilute^  and  a  very  small  quantity  of  the  solution  is 
used  for  each  test.  It  is  best  to  keep  it  in  a  bottle  with  a 
perforated  cork^  a  glass  tube  drawn  out  to  a  point  and  inserted  in 
the  cork  serving  as  a  pipette  for  regulating  the  supply.  Methyl- 
orange  is  orange  in  neutral  solutions  or  in  the  presence  of  free 
alkali,  but  is  faintly  yellow  in  very  dilute  solutions,  and  no  more 
ought  to  be  added  to  the  liquid  to  be  tested  than  suffices  to  colour 
it  just  perceptibly  yellow.  In  this  case  a  single  drop  of  fifth- 
normal  sulphuric  or  hydrochloric  acid  will  cause  a  transition  into 
red.  But  when  too  much  of  the  indicator  has  been  added,  so 
that  the  colour  of  the  solution  is  orange,  the  transition  into  red 
(or,  rather,  in  this  case  into  pink)  is  only  gradual,  and  therefore 
useless.  Warm  solutions  behave  in  a  similar  manner.  It  is 
therefore  a  distinct  rule  to  be  observed  with  methyl-orange,  to 
employ  as  little  as  possible  of  it,  and  to  work  always  at  the 
ordinary  temperature.  This  is  made  possible  by  the  fact  that 
methyl-orange  is  not  acted  upon  by  weak  acids,  such  as  COj,  HjS, 
acetic  acid,  &c. ;  and  this  is  undoubtedly  one  of  its  most  valuable 
properties,  since  the  trouble  and  loss  of  time  in  boiling  the  liquids, 
and  the  error  introduced  in  the  case  of  glass  vessels,  are  thereby 
avoided.  Both  NajCOg  and  NaHCOg  can  be  titrated  directly  in 
the  cold  just  as  well  as  NaOH^  the  total  available  soda  being 
always  indicated.  Sulphurous  acid  behaves  in  the  manner  explained, 
sui/ra  (p.  160),  that  is,  the  compound  NajSOs  is  alkaline,  NaHSOg 
neutral,  to  methyl-orange.  Oxalic  acid,  as  well  as  other  strong 
organic  acids,  come  in  between  sulphurous  acid  and  the  strong 
mineral  acids ;  no  sharp  results  can  be  obtained  with  them, 
and  hence  oxalic  acid  cannot  serve  as  standard  acid  with  methyl - 
orange.  On  the  other  hand,  ammonia,  which  cannot  be  titrated 
with  phenolphthalein,  behaves  quite  normally  towards  methyl- 
orange,  just  like  potash  and  soda.  The  normal  sulphates  of 
peroxide  of  iron,  alumina,  &c.,  which  give  an  acid  reaction  with 
litmus,  are  neutral  towards  methyl-orange,  so  that  any  free  acid 
present  with  them  can  be  estimated  by  means  of  this  indicator. 

Methyl-orange  is  destroyed  by  nitrous  acid.      Nevertheless  it 
can  be  easily  employed  in  titrating  sulphuric  or  nitric  acid  con- 


236  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

tainiDg  nitrous  acid  in  two  ways  :  either  by  adding  the  indicator 
shortly  before  the  saturation  is  completed  and  quickly  finishing 
the  titration^  or  by  supersaturating  the  acid  with  caustic  soda  and 
retitrating  with  standard  acid. 

Nitrous  acid  acts  upon  methyl-orange  like  a  strong  mineral 
acid,  and  is  therefore  completely  saturated  before  the  pink  colour 
has  changed  to  yellow,.if  there  is  not  time  for  the  colouring-matter 
to  be  destroyed. 

The  tropseolins,  formerly  recommended  as  indicators^  are 
nothing  like  so  sensitive  as  methyl-orange,  and  are  best  not  used 
at  all  as  indicators^  especially  since  several  totally  distinct  com- 
pounds are  comprised  under  this  name,  and  the  dealers  do  not 
always  supply  that  which  is  really  wanted. 

Free  sulphuric  acid  (including  that  contained  in  commercial 
ferric  or  aluminium  sulphate,  or  any  other  sulphate)  is  estimated 
by  adding  a  drop  of  methyl-orange  solution,  which  causes  a  pink 
colour,  and  then  adding  a  standard  solution  of  alkali,  till  the  pink 
tint  has  changed  into  pure  light  yellow.  It  is  best  to  check  this 
by  reproducing  the  faint  pink  shade  by  means  of  a  drop  of  standard 
acid. 

The  normal  alkaline  solution  itself  is  best  standardized  by 
means  of  a  normal  acid,  be  it  sulphuric  or  hydrochloric  acid ; 
and  this  on  its  part  is  best  standardized  by  pure  ignited 
sodium  carbonate,  which  is  easily  obtained  or  prepared — 
for  instance,  by  washing  and  igniting  sodium  bicarbonate.  If 
sodium  carbonate,  bought  as  chemically  pure,  dissolves  in  water 
without  any  residue,  and  shows  by  the  ordinary  reagents  no 
chloride  or  sulphate,  or  only  unweighable  traces  of  these,  it  can 
be  used  at  once  for  standardizing  normal  acids  after  moderately 
igniting.  If  methyl-orange  be  used  as  indicator,  this  roundabout 
way  need  not  be  taken,  especially  at  works*  laboratories,  but  pure 
sodium  carbonate  itself  can  be  used  as  acidimetrical  liquid,  either 
in  a  normal  solution  containing  53  grams  per  litre  or  in  more 
dilute  solutions.  The  latter  are  more  to  be  recommended,  since 
the  really  normal  solution  causes  efBorescences  of  sodium  carbonate 
at  the  lower  ends  of  the  burettes,  &c.,  which  does  not  happen  with 
semi-normal  or  weaker  solutions,  at  least  not  for  some  time. 

Although  it  is  more  important  in  alkalimetry  than  in  acidimetry, 
we  will  here  treat  of  the  standard  acid  itself.  As  such  many 
factory-chemists  use  sulphuric  acid,  but  we  recommend  as  more 


STANDARD  ACID.  237 

suitable  hydrochloric  acid,  both  because  it  can  be  used  for  esti- 
mating  alkaline  earths  us  well^  and  because  it  admits  of  a  twofold 
way  of  checking  the  standard^  either  volumetrically  by  pure  sodium 
carbonate,  or  gravimetrically  by  argentic  nitrate.  The  gravimetric 
estimation  of  sulphuric  acid  by  barium  chloride  is  nothing  like  so 
accurate  as  the  estimation  of  HCI  in  the  shape  of  AgCl.  Oxalic 
acid,  most  strongly  recommended  by  Mohr,  and  formerly  used 
by  very  many  chemists,  has  great  drawbacks.  It  is  extremely 
difficult  to  prepare  in  the  perfectly  pure  and  dry  state,  without 
losing  some  of  the  water  of  crystallization ;  it  does  not  keep  in 
weak  solutions,  and  it  cannot  be  employed  with  methyl-orange. 

For  standardizing  normal  acids,  sometimes  a  solution  of  pure 
sodium  carbonate  is  made,  of  which  portions  are  taken  out  with  a 
pipette.  For  the  most  accurate  estimations  it  is,  however,  always 
preferable  to  weigh  each  portion  of  sodium  carbonate,  directly  after 
igniting  and  cooling,  into  the  beaker,  since  it  is  never  possible  to 
measure  as  accurately  as  to  weigh,  because,  among  other  reasons, 
the  volumetrical  apparatus  very  rarely  agree  quite  accurately  one 
with  another.  In  spite  of  the  trouble,  it  should  most  certainly  not 
be  neglected  to  compare,  in  the  first  instance,  the  pipettes  with  all 
the  measuring-flasks,  in  order  to  see  whether  the  former  fill  the 
latter  precisely  ;  secondly,*  to  calibrate  the  burettes  accurately,  in 
which  case  it  will  often  be  found  that  the  upper  parts  diflTer  by 
several  per  cent,  from  the  middle  and  lower  parts,  and  cause  a 
corresponding  error.  Of  course  the  burettes  must  again  be  com- 
pared with  the  other  measuring-apparatus. 

The  standard  acid  is  made  to  represent  equivannts,  not  molecules ; 
that  is,  if  sulphuric  or  oxalic  acid,  it  will  contain  one  half  of  the 
molecular  weight  in  grams,  viz.  49  or  63  grams,  because  these 
acids  are  bivalent ;  but  if  it  is  the  univalent  hydrochloric  or  nitric 
acid,  it  will  contain  the  total  molecular  weight,  viz.  36'46  grams 
HCI,  or  65  grams  NO3H.  First  of  all,  the  acid  is  diluted  a  little 
less  than  necessary,  and  it  is  found  out  how  many  cub.  centims. 
of  it  are  required  for  a  certain  quantity  of  sodium  carbonate. 
From  this  the  quantity  of  water  is  computed  which  is  required 
for  obtaining  an  exactly  normal  acid ;  and  after  mixing  this  with 
the  acid  the  accuracy  of  the  standard  is  ascertained  by  repeated 
titrating  with  sodium  carbonate.  Not  less  than  2  to  3  grams  of 
the  latter  should  be  taken  for  each  test.  If  litmus  is  to  be  the 
indicator,  to  the  alkaline  solution  drops  of  tincture  of  litmus  are 


238  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

added  till  it  becomes  very  markedly  blue,  then  acid  till  strong 
effervescence  sets  in ;  and  the  liquid  is  now  made  to  boil ;  then  to 
the  hot  liquid  gradually  more  and  more  acid  is  added,  till  the  blue 
colour  has  passed  through  the  purple  and  reddish  purple  of  the 
CO2  reaction  to  the  bright  red  of  the  SO4H2  reaction.  The  liquid 
cooled  by  the  addition  of  acid  must  be  constantly  heated  again. 
Often,  after  several  minutes^  boiling,  the  apparently  red  liquid 
again  turns  purple  and  then  blue.  When  working  with  boiling 
liquids  there  is  never  any  doubt,  to  a  single  drop,  respecting  the 
point  where  the  pure  red  sets  in.  The  test  must  be  made  in  a 
porcelain  capsule,  not  in  a  glass  beaker.  Precisely  the  same 
troublesome  method  must  be  employed  with  phenolphthalein.  All 
this  trouble  is  saved  by  using  methyl-orange  as  indicator  and 
working  in  the  cold. 

When  a  perfectly  accurate  normal  acid  has  been  obtained,  the 
normal  alkali,  whether  ammonia,  soda,  or  potash,  is  most  easily 
made  from  it ;  and  this  is  now  used  for  the  acidimetric  test  of 
sulphuric  acid.  Concentrated  sulphuric  acid  must,  of  course,  first 
be  diluted  in  the  usual  manner. 

Analysis  of  Fuming  Oil  of  VitnoL 

Several  communications  have  been  made  on  this  subject,  as  by 
Ftirstenau  (Chemiker-Zeitung,  1880,  p.  18),  Moller  (ibid.  p.  569), 
Becker  (ibid.  p.  600),  W^inkler  (Chem.  Ind.  1880,  p.  194),  Clar  and 
Gaier  (ibid.  1881,  n.  251).  We  shall,  in  the  first  instance,  prin- 
cipally  describe  tW  methods  contained  in  Lunge  and  Hurter's 
Alkali-Maker's  Hand-book,'  as  derived  from  practical  information, 
with  a  few  improvements. 

In  the  present  case  even  the  taking  of  t/w  sample  is  not  quite  a 
simple  task.  Measuring  it  in  a  pipette  is  out  of  the  question,  it 
must  be  weighed.  But  even  for  this  purpose  the  article,  if  solid, 
must  be  first  liquefied.  This  is  comparatively  easy  with  partly 
crystallized  acid  or  with  solid  pyrosulphuric  acid;  these  can  be 
liquefied  without  any  danger  in  a  closed  vessel  by  gently  heating 
to  30°  in  a  sand-bath.  Soldered-up  tins  are  generally  placed  in  a 
suitably  heated  stove.  There  is  no  sensible  loss  of  strength  if  the 
aperture  for  this  purpose  is  previously  opened  and  at  once  covered 
with  a  watch-glass.  This  prevents  any  pressure  within  the  vessel 
during  the  heating,  which  must  otherwise  be  guarded  against  in 


ANALYSIS  OP  PUMINQ  OIL  OP  VITRIOL.  239 

Opening  it.  The  case  is  different  with  products  containing  a  larger 
percentage  o£  anhydride.  These  do  not  liquefy  completely,  a  por- 
tion always  remaining  in  the  state  of  a  gelatinous  residue.  This 
residue  is,  however,  composed  exactly  like  the  liquid  portion,  so 
that  the  sample  may  be  taken  out  of  the  latter  without  any  danger 
of  making  a  mistake. 

The  sample  is  weighed  either  in  glass  bulbs  or  in  a  glass  tap- 
tnbe.     The  former  are  very  thin  bulbs  of 
about  J  inch  diameter,  ending  each  way  in  Fig.  40. 

a  capillary  tube  (fig.  40).  The  liquefied 
acid  (2  or  3  grams)  is  sucked  into  the  bulb, 
without  danger  to  the  operator,  by  means  of 
a  bottle  closed  with  an  india-rubber  cork, 
through  which  passes  a  tightly- fitting  glass 
tap,  connected  at  its  free  end  with  an  elastic 
tube.  Suction  is  applied  to  the  latter,  the 
tap  is  closed,  the  elastic  tube  is  drawn  over 
one  of  the  capillary  ends  of  the  weighing- 
bulb,  and  by  opening  the  tap  a  sufficient 
quantity  of  acid  is  admitted  into  the  bulb. 

The  capillary  tube  ia  cleaned  and  one  of 
the  two  ends  is  sealed  at  the  lamp.  The 
other  end  can  be  left  open  without  fear  of 
any  loss  of  SO3  or  attraction  of  moistiu-e  during  wcigliin<r.  The 
weighing  is  best  done  on  a  small  platinum  crucible  with  two  nicks, 
on  which  the  ends  of  the  bulb  can  rest.  If  the  latter  should  be 
accidentally  broken,  the  acid  runs  into  the  crucible,  not  on  the 
balance.  Then  the  bulb,  open  end  downwards,  is  put  into  a  small 
Erlenmeyer  flask,  into  the  neck  of  which  it  should  fit  exactly 
(fig.  40),  find  which  contains  so  much  water  that  the  capillary 
tube  dips  pretty  far  into  it  to  prevent  any  loss  of  SO^  on  mixing 
the  acid  with  water.  Now  break  off  the  other  point,  allow  the 
acid  to  run  out,  squirt  a  few  drops  of  water  into  the  upper  capillary, 
and  ultimately  rinse  the  whole  bulb-tube  by  repeated  aspiration  of 
water.  Dilute  the  liquid  to  500  c.c.  and  take  50  e.c.  for  each  test. 
The  testing  is  done  with  fifth-normal  solution  of  soda  (1  c.c.= 
0008  grm.  SO3)  and  litmus  or  methyl-orange  aa  indicator.  The 
acidity  found  is  diminished  by  that  proceeding  from  SO.,  found 
by  titrating  another  sample  with  iodine. 

In  lieu  of  the  bulb-tube  (first  proposed  by  Clar  and  Gaier)  we 


240 


PROPEKTIES  OF  OXIDES  AND  ACIDS  OP  SULPHUR. 


prefer  the  glass  tap-tnbe,  as  shown  in  fig.  41.  The  tap  should  be 
tight  without  greasing,  and  the  tube  below  it  should  taper  gradu- 
allr.  It  is  charged  by  suction,  in  the  same  way  as  described  above, 
with  about  0*5  grm.  of  Nordhausen  acid,  no  more,  in  order  to  be 
able  to  titrate  it  directly,  without  taking  an  aliquot  portion.  After 
the  proper  quantity  of  acid  has  been  introduced,  the  tap  is  closed. 


Fig.  41. 


Fig.  42. 


the  tube  is  cleaned  outside  with  filtering-paper,  aud  it  may  be 
weighed  at  once,  without  any  fear  of  a  change  of  weight  during  the 
operation.  It  is,  however,  preferable  to  employ  a  tube  (as  shown 
in  fig.  42)  ground  into  an  outer  glass  case,  which  is,  of  course, 
tared  together  with  the  empty  tube. 

After  weighing,  place  the  tube  point  downwards  in  water,  or,  in 
the  case  of  nearly  pure  anhydride  or  the  strongest  Nordbausen 


ANALYSIS  OF  FUMING  SULPHURIC  ACID.  241 

acids,  in  a  layer  of  crystallized,  coarsely  powdered  Glauber's  salt, 
and  slowly  run  out  the  contents.  Then  squirt  a  drop  of  water  from 
above  into  the  tube,  allow  it  to  stand  for  a  moment,  and  rinse 
thoroughly  with  water.  Anhydride  once  melted  for  the  purpose 
of  filling  the  tube  remains  liquid  enough  to  complete  the  weighing 
and  running  out  without  requiring  to  be  heated  again. 

The  most  convenient  apparatus  for  weighing  oflF  fuming  sul- 
phuric acid  (as  well  as  other  fuming  acids  or  substances  evolving 
vapours)  is  the  ''bulb-tap  pipette,'^  proposed  by  Lunge  &  Rey 
(Zeitsch.  f.  angew.  Chem.  1891,  p.  165),  and  shown  in  fig.  42, 
in  which  both  the  filling  as  well  as  the  weighing  and  discharging 
are  performed  without  any  loss  of  vapours  and  without  requiring 
any  special  aspirating-apparatus.  Above  tap  a  there  is  a  bulb  b, 
rather  less  than  an  inch  in  diameter,  and  above  this  a  second  tap  c. 
The  lower  portion  of  the  pipette  is  ground  into  a  glass  tube  (/,  closed 
at  the  bottom.  In  the  conical  part  of  the  pipette  there  is  a  groove  &, 
reaching  halfway  down,  the  corresponding  half  of  the  groove  / 
being  in  the  outer  tube.  By  turning  the  pipette  in  the  latter,  the 
tube  d  can  be  made  to  communicate  with  the  outer  air,  or  the 
reverse.  When  the  pipette  is  to  be  used,  close  tap  a,  suck  at  the 
top  with  the  mouth,  and  before  leaving  off  shut  tap  c,  so  that  the 
bulb  b  contains  a  partial  vacuum.  Dip  the  point  of  the  pipette 
into  the  acid  and  open  a ;  the  acid  will  rise  up,  but  a  is  shut 
before  it  gets  so  far,  or  even  sooner,  when  enough  has  got  in. 
Clean  the  pipette  outside,  put  it  into  dy  and  weigh.  In  most  ordi- 
nary cases  (with  other  acids,  ammonia,  &c.)  the  grooves  e  and /are 
made  to  communicate ;  water  is  squirted  through  c  into  b  and  then 
run  through  a,  with  the  contents  of  the  pipette,  into  d,  the  air 
escaping  through  e  and/.  The  dilute  acid  is  run  into  a  beaker  and 
titrated.  In  the  case  of  Nordhausen  acid  it  is  preferable  to  take 
the  pipette  out  of  d,  rinse  the  latter  into  a  beaker,  run  the  contents 
of  the  pipette,  by  opening  a,  into  water  or  Glauber's  salt  contained 
in  the  same  beaker,  then  squirt  water  through  c  (during  which 
time  a  may  be  closed),  and  rinse  the  pipette  into  the  same  beaker. 
The  sucking  at  c  is  quite  sufficient  to  produce  the  necessary 
rarefaction  of  air  in  6,  and  no  vapours  are  lost,  as  is  inevitable 
with  any  other  kind  of  aspiration. 

Very  strong  oleum  (70  per  cent.  SO3  and  upwards)  is  best 
-weighed  in  glass  bulbs  (p.  239)  sealed  at  both  ends ;  these  are 
put  into  a  bottle  containing  sufficient  water,  which  is  closed  by  a 

VOL.  I.  u 


242  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

ground-in  stopper ;  the  bulb  is  smashed  by  shaking  the  bottle,  and 
the  titration  is  made. 

The  sampling  of  solid  sulphuric  anhydride  is  not  an  easy  matter^ 
This  substance,  which  is  now  a  regular  article  of  trade  and  is  sent 
out  in  iron  bottles,  is  much  too  compact  and  tough  to  enable  a 
sample  to  be  taken  out  by  means  of  an  auger.  Before  using  it,  it 
is  always  heated  in  a  stove  till  it  has  completely  liquefied ;  but  in 
this  state  the  bottle  on  opening  emits  such  a  dense  cloud  of  fumes 
that  any  sampling  is  out  of  the  question.  The  way  out  of  the 
diflBculty  is  this : — In  a  stoppered  bottle  some  lumps  of  the  solid 
anhydride  are  weighed  off  on  a  large  balance  and  are  theYi  mixed 
with  a  sufficient  quantity  of  accurately  analyzed  monohydrated 
sulphuric  acid,  to  form  an  acid  of  70  per  cent.  SOg,  which  is 
liquid  at  ordinary  temperatures.  The  solution  is  promoted  by 
gently  heating  the  bottles,  say  to  30°  or  40°  C,  with  the  stopper 
loosely  put  on.  At  last  a  sample  is  taken  out  by  means  of  the 
pipette  described  above  (p.  240)  and  the  analysis  performed  in  the 
usual  \rayj  taking  account  of  the  slight  proportion  of  water  present 
in  the  *'monohydrate^'  employed. 

Rosenlecher  (Zeitsch.  anal.  Ch.  xxxvii.  p.  209)  describes  the 
method  employed  at  Freiberg.  A  number  of  bulbs  are  made  from  a 
glass  tube,  6  or  8  mm.  wide,  of  the  form  shown  in  fig.  43,  and  keeping 

Fig.  43. 


them  exactly  to  the  dimensions  indicated.  The  capillary  ends  are 
contracted  before  a  spirit-lamp  to  ^  mm.  bore,  in  the  case  of  very 
strong  anhydride  to  ^  mm.  The  bulbs  are  filled  by  aspiration  by 
means  of  a  capillary  rubber  tube  drawn  over  the  shorter  end,  in 
case  of  need  interposing  a  test-tube  filled  with  soda  crystals.  The 
suction  is  continued  until  the  acid  arrives  in  the  bulbs  before  the 
heavy  fumes  enter  the  shorter  capillary.  All  the  bulbs  are  turned 
with  the  points  of  the  capillaries  upwards,  cleaned  outside,  and 
placed  in  a  paste-board  box  provided  with  nicks.  The  weighing  is 
performed  in  a  platinum  crucible  (p.  239)  or  on  a  specially  made 
wire  stand.     No  attraction  of  moisture  need  be  feared  during  the 


ANALYSIS  OP  FUMING  SULPHURIC  ACID. 


243 


weighing,  but  the  bulbs  must  not  be  heated  by  touching  them 
with  the  fingers.  They  are  then  placed  in  bottles,  charged  with 
20  or  30  c.c.  water  of  ordinary  temperature  and  the  indicator^  in 
such  manner  that  the  acid  does  not  flow  out.  The  wetted  stopper 
is  put  tightly  in^  the  bottles  are  placed  sideways  (up  to  this 
time  the  colour  of  the  indicator  should  not  have  changed)^  the 
bulbs  broken  by  shakings  and  then,  after  the  white  fumes  have 
vanished,  the  titration  is  performed  in  the  bottle  itself. 

The  results  of  titration  are  first  calculated  for  the  total  (com- 
bined and  uncombined  with  water)  SOs,  each  c.  c.  of  normal  soda 
solution  indicating  0*040  grm.  SOg,  and  the  proportion  of  free 
SO3  and  HgSO^  present  is  then  read  off  by  means  of  the  following 
formula  :  S03=S— 4*444  (100— S),  in  which  SO3  denotes  the  free 
sulphur  trioxide,  and  S  the  total  SOg  as  found  by  titration. 

This  calculation  is  saved  by  the  following  table,  computed  by 
Knietsch  (Ber.  1901,  p.  4114)  :— 


S03 

SO3 

SO3 

SO3 

SO3 

SO3 

SO3 

Total.  Free. 
81-63     00 

Total. 

Jrr€e. 

Total.  Free. 

1 

Total. 

Free. 

Total 
92-2 

Free. 

Total. 

Free. 
71-7 

Total.  Free. 

84-3    14-6 

87  0    29-2 

89-6 

43-4 

57-5 

94-8 

97-4 

85-8 

81-7   ' 

0-4 

84-4 

151 

87-1 

29-8 

89-7 

43-9 

92-3 

581 

94-9 

72-2 

97-5    86-4 

81-8 

0-9 

84-6 

15-6 

87-2 

303 

89-8 

44-5 

92-4 

58-6 

95-0 

72-8 

97-6  ;  86-9 

81-9 

1-5 

84-6 

16-2 

873    30-9 

89-9 

450 

92-5 

59-2 

951 

73-3 

07-7 

87-5 

820 

20 

84-7 

16-7 

87-4    31-4 

900 

45-6 

92-6 

59-7 

95-2 

73-9 

97-8 

88-0 

82-1 

26 

84-8 

17-2 

87-5 

31-9 

901 

461 

92-7 

60-3 

95-3 

74-4 

97-9 

88-6 

82-2 

31 

84-9    17-8 

87-6 

32-5 

902 

46-6 

92-8 

60-8 

95-4 

750 

980  :  89-1 

82-3 

3-6 

85-0 

18-3 

87-7 

330 

90-3  ;  47-2 

92-9 

61-3 

95-5 

75-5 

98-1    89-7 

82-4 

4-2 

851 

18-9 

87-8    33-6 

90-4  1  47*7 

930 

61-9 

95-6 

761 

98-2  1  90-2 

82-5 

4-7 

85-2 

19-4 

87-9    341 

90-5  '  48-3 

931 

62-4 

95-7 

76-6 

98-3 

90-7 

82-6 

5-3 

85-3 

200 

88  0    34-7 

90  6    48-8 

93-2 

630 

95-8 

771 

98-4 

91-3 

82-7 

5-8 

85-4 

20-5 

88-1    35-2 

90  7  i49-4 

93-3 

63-5 

95-9 

77-7 

98-5 

91-8 

'82-8 

6-4 

85-5 

210 

882    35-8 

90-8  J49-9 

93-4 

641 

960 

78  3 

98-6  i  92-4 

82-9 

69 

85-6 

21-6 

88-3    36-3 

90-9 

50-5 

93-5 

64-6 

961 

78-8 

98-7    92-9 

830 

7*5 

85-7 

22-2 

88-4    36-8 

91-0 

510 

93-6 

65-2 

96-2 

793 

98-8 

93-5 

83-1 

8-0 

8o-8 

22-7 

88-5    37-4 

911 

51-6 

93-7 

65-7 

96-3 

79-9 

98-9 

940 

83-2 

8-5 

85-9 

23-2 

886    37-9 

91-2  '  521 

93-8 

66-2 

96-4 

80-4 

990 

94-6 

83-3 

91 

860 

23-8 

88-7    38-5 

91-3  ,  52-6 

93-9 

66-8 

96-5 

81-0 

991    951 

83-4 

96 

861 

24-3 

88-8    39-0 

91-4  '  53-2 

940 

67-3 

96-6 

81-5 

99-2    95-6 

83-5 

10-2 

8<5-2 

249 

88-9    39-6 

91-5 

537 

94-1    67-9  1 

96-7 

820 

99-3    96-2 

83-6 

10-7 

863 

2o-4 

890    401 

91-6 

54-3 

942 

68-4 

9('v8 

82-6 

994    96-7 

83-7 

11-3 

86-4 

260 

89-1     40-6 

91-7 

54-8 

94-3 

690 

969 

831 

99-5  ;  97-3 

83-8 

11-8 

860 

26-5 

89-2  :41-2 

91-8    55-4  1 

94-4 

69-5 

970 

83-7 

99-6  1  97-8 

839 

12-3 

86-6 

27  0 

89-3    41-7 

91-9 

55-9 

94-5 

701 

97-1 

84-2 

99-7    98-4 

84  0 

12-9 

86-7  ,27-6 

89-4    42-3 

920 

56-4 

94-6 

70-6 

97-2 

848 

99  8    98-9  ' 

841 

13-4 

86-8    28-1 

89-5  i  42-8 

921 

570 

94-7 

71-2 

97-3 

85-3 

99-9    99-5 

84-2 

140 

860 

28-7 

..-) 

k:^ 


242  PROPERTIES  OP  OXIDES  AND  ACIDS  OP  SULPHUR. 

ground-in  stopper;  the  bulb  is  smashed  by  shaking  the  bottle,  and 
the  titration  is  made. 

The  sampling  of  solid  sulphuric  anhydride  is  not  an  easy  matter^ 
This  substance^  which  is  now  a  regular  article  of  trade  and  is  sent 
out  in  iron  bottles^  is  much  too  compact  and  tough  to  enable  a 
sample  to  be  taken  out  by  means  of  an  auger.  Before  using  it^  it 
is  always  heated  in  a  stove  till  it  has  completely  liquefied;  but  in 
this  state  the  bottle  on  opening  emits  such  a  dense  cloud  of  fumea 
that  any  sampling  is  out  of  the  question.  The  way  out  of  the 
diflSculty  is  this : — In  a  stoppered  bottle  some  lumps  of  the  solid 
anhydride  are  weighed  off  on  a  large  balance  and  are  theti  mixed 
with  a  sufficient  quantity  of  accurately  analyzed  monohydrated 
sulphuric  acid,  to  form  an  acid  of  70  per  cent.  SOg,  which  ia 
liquid  at  ordinary  temperatures.  The  solution  is  promoted  by 
gently  heating  the  bottles,  say  to  30°  or  40°  C,  with  the  stopper 
loosely  put  on.  At  last  a  sample  is  taken  out  by  means  of  the 
pipette  described  above  (p.  240)  and  the  analysis  performed  in  the 
usual  way,  taking  account  of  the  slight  proportion  of  water  present 
in  the  ''monohydrate^'  employed. 

Rosenlecher  (Zeitsch.  anal.  Ch.  xxxvii.  p.  209)  describes  the 
method  employed  at  Freiberg.  A  number  of  bulbs  are  made  from  a 
glass  tube,  6  or  8  mm.  wide,  of  the  form  shown  in  fig.  43,  and  keeping 

Fig.  43. 


them  exactly  to  the  dimensions  indicated.  The  capillary  ends  are 
contracted  before  a  spirit-lamp  to  ^  mm.  bore,  in  the  case  of  very 
strong  anhydride  to  i  mm.  The  bulbs  are  filled  by  aspiration  by 
means  of  a  capillary  rubber  tube  drawn  over  the  shorter  end,  in 
case  of  need  interposing  a  test-tube  filled  with  soda  crystals.  The 
suction  is  continued  until  the  acid  arrives  in  the  bulbs  before  the 
heavy  fumes  enter  the  shorter  capillary.  All  the  bulbs  are  turned 
with  the  points  of  the  capillaries  upwards,  cleaned  outside,  and 
placed  in  a  paste-board  box  provided  with  nicks.  The  weighing  i& 
performed  in  a  platinum  crucible  (p.  239)  or  on  a  specially  made 
wire  stand.     No  attraction  of  moisture  need  be  feared  during  the 


ANALYSIS  OF  FUMING  STTLPHURIC  ACID. 


243 


weighing,  but  the  bulbs  must  not  be  heated  by  touching  them 
with  the  fingers.  They  are  then  placed  in  bottles,  charged  with 
20  or  30  c.c.  water  of  ordinary  temperature  and  the  indicator^  in 
such  manner  that  the  acid  does  not  flow  out.  The  wetted  stopper 
is  put  tightly  in,  the  bottles  are  placed  sideways  (up  to  this 
time  the  colour  of  the  indicator  should  not  have  changed)^  the 
bulbs  broken  by  shaking,  and  then,  after  the  white  fumes  have 
vanished,  the  titration  is  performed  in  the  bottle  itself. 

The  results  of  titration  are  first  calculated  for  the  total  (com- 
bined and  uncombined  with  water)  SOs,  each  c.  c.  of  normal  soda 
solution  indicating  0*040  grm.  SOa,  and  the  proportion  of  free 
SO3  and  H3SO4  present  is  then  read  ofE  by  means  of  the  following 
formula  :  S03=S— 4-444  (100— S),  in  which  SOa  denotes  the  free 
sulphur  trioxide,  and  S  the  total  SO^  as  found  by  titration. 

This  calculation  is  saved  by  the  following  table,  computed  by 
Knietsch  (Ber.  1901,  p.  4114)  :— 


S03 

SO3 

SO3 

SO3 

SO3 

SO3 

SO3 

Total. 
81-63 

Free. 
00 

ToUl.  Free. 

Total. 

Free. 

Total. 

Free. 
43-4 

Total 
92-2 

Free. 

Total. 

Free. 
71-7 

Total.  Free- 

84-3    14-6 

87  0 

29-2 

89-6 

57-6 

94-8 

97-4 

85-8 

81-7 

0-4 

84-4 

151 

87-1 

29-8 

89-7 

43-9 

92-3 

581 

94-9 

72-2 

97-5    86-4 

81-8 

0-9 

84-5 

15-6 

87-2 

303 

89-8 

44-5 

92-4 

58-6 

95-0 

72-8 

97-6  1  86-9 

81-9 

1-5 

84-6 

16-2 

87-3 

30-9 

89-9 

450 

92-5 

59-2 

951 

733 

07-7  1  87-5 

82-0 

20 

84-7 

16-7 

87-4 

31-4 

900 

45-6 

92-6 

59-7 

95-2 

73-9 

97-8  1  88-0 

821 

2-6 

84-8 

17-2 

87-5 

31-9 

901 

461 

92-7 

60-3 

95-3 

74-4 

97-9  !  88-6 

82-2 

31 

84-9    17-8 

87-6 

32-5 

90-2 

46-6 

92-8 

60-8 

95-4 

750 

980  '  89-1 

82-3 

36 

850 

18-3 

87-7 

330 

90-3 

47-2 

92-9 

61-3 

95-5 

75-5 

98-1    89-7 

82-4 

4-2 

851 

18-9 

87-8 

33-6 

90-4 

47-7 

930 

61-9 

95-6 

761 

98-2 

90-2 

82-5 

4-7 

85-2 

19-4 

87-9 

341 

90-5 

483 

931 

62-4 

95-7 

76-6 

98-3 

90-7 

82*6 

5-3 

85-3 

200 

880 

34-7 

906 

48-8 

93-2 

630 

96-8 

771 

98-4 

91-3 

82-7 

5-8 

85-4 

20-5 

88-1 

35-2 

907 

49-4 

93-3 

63-5 

95-9 

77-7 

98-5    91-8 

82-8 

6-4 

85-5 

210 

88-2 

35-8 

90-8 

49-9 

93-4 

641 

960 

78  3 

98-6    92-4 

82-9 

69 

850 

21-6 

88-3 

36-3 

90-9 

50-5 

93-5 

64-6 

961 

78-8 

98-7    92-9 

830 

7-5 

85-7 

22-2 

88-4 

36-8 

91-0 

510 

93-6 

65-2 

96-2 

793 

98-8 

93-5 

83-1 

8-0 

85-8 

22-7 

88-5 

37-4 

911 

51-6 

93-7 

65-7 

96-3 

79-9 

98-9 

940 

83-2 

8-5 

85-9 

23-2 

88-6 

37-9 

91-2 

521 

93-8 

66-2 

96-4 

80-4 

99  0  :  94-6 

83-3 

91 

86-0 

23-8 

88-7 

38-5 

91-3 

52-6 

93-9 

66-8 

96-5 

810 

991    951 

83-4 

96 

861 

24-3 

88-8 

39-0 

91-4 

53-2 

940 

67-3 

96-6 

81-5 

99-2    95-6 

83-5 

10-2 

86-2 

24-9 

88-9 

39-6 

91-5 

53  7 

94-1 

67-9 

96-7 

820 

99-3    96-2 

83-6 

10-7 

86-3 

25-4 

890 

401 

91-6 

54-3 

94-2 

68-4 

9^-8 

82-6 

994    96-7 

83-7 

11-3 

86-4 

260 

89-1 

40-6 

91-7 

54-8 

94-3 

690 

96-9 

831 

99-5    97-3 

83-8 

11-8 

86-5 

26-5 

89-2 

41-2 

91-8 

a.)*4 

944 

69-5 

970 

83-7 

99-6    97-8 

839 

12-3 

86-6 

27-0 

89-3 

41-7 

91-9 

55-9 

94-5 

701 

97-1 

84-2 

99-7    98-4 

840 

12-9 

86-7 

27-6 

89-4 

42-3 

92-0 

56-4 

94-6 

70-6 

97-2 

848 

998    98-9  ' 

841 

13-4 

86-8 

281 

89-5 

42-8 

921 

570 

94-7 

71-2 

97-3 

85-3 

99-9  1  99-5 

84-2 

140 

1 

860 

28-7 

k2 


242  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

ground-in  stopper ;  the  bulb  is  smashed  by  shaking  the  bottle,  and 
the  titration  is  made. 

The  sampling  of  solid  sulphuric  anhydride  is  not  an  easy  matter^ 
This  substance^  which  is  now  a  regular  article  of  trade  and  is  sent 
out  in  iron  bottles^  is  much  too  compact  and  tough  to  enable  a 
sample  to  be  taken  out  by  means  of  an  auger.  Before  using  it^  it 
is  always  heated  in  a  stove  till  it  has  completely  liquefied;  but  in 
this  state  the  bottle  on  opening  emits  such  a  dense  cloud  of  fumes 
that  any  sampling  is  out  of  the  question.  The  way  out  of  the 
diflSculty  is  this  : — In  a  stoppered  bottle  some  lumps  of  the  solid 
anhydride  are  weighed  off  on  a  large  balance  and  are  theti  mixed 
with  a  sufficient  quantity  of  accurately  analyzed  monohydrated 
sulphuric  acid,  to  form  an  acid  of  70  per  cent.  SOg,  which  is 
liquid  at  ordinary  temperatures.  The  solution  is  promoted  by 
gently  heating  the  bottles,  say  to  30°  or  40°  C,  with  the  stopper 
loosely  put  on.  At  last  a  sample  is  taken  out  by  means  of  tho 
pipette  described  above  (p.  240)  and  the  analysis  performed  in  the 
usual  way,  taking  account  of  the  slight  proportion  of  water  present 
in  the  "monohydrate^'  employed. 

Rosenlecher  (Zeitsch.  anal.  Ch.  xxxvii.  p.  209)  describes  the 
method  employed  at  Freiberg.  A  number  of  bulbs  are  made  from  a 
glass  tube,  6  or  8  mm.  wide,  of  the  form  shown  in  fig.  43,  and  keeping: 

Fig.  43. 


them  exactly  to  the  dimensions  indicated.  The  capillary  ends  are- 
contracted  before  a  spirit-lamp  to  ^  mm.  bore,  in  the  case  of  very 
strong  anhydride  to  J  mm.  The  bulbs  are  filled  by  aspiration  by 
means  of  a  capillary  rubber  tube  drawn  over  the  shorter  end,  in 
case  of  need  interposing  a  test-tube  filled  with  soda  crystals.  The 
suction  is  continued  until  the  acid  arrives  in  the  bulbs  before  the 
heavy  fumes  enter  the  shorter  capillary.  All  the  bulbs  are  turned 
with  the  points  of  the  capillaries  upwards,  cleaned  outside,  and 
placed  in  a  paste-board  box  provided  with  nicks.  The  weighing  i& 
perfoimed  in  a  platinum  crucible  (p.  239)  or  on  a  specially  made 
wire  stand.     No  attraction  of  moisture  need  be  feared  during  the 


ANALYSIS  OF  FUMING  SULPHURIC  ACID. 


243 


weighing,  but  the  bulbs  must  not  be  heated  by  touching  them 
with  the  fingers.  They  are  then  placed  in  bottles,  charged  with 
20  or  30  c.c.  water  of  ordinary  temperature  and  the  indicator^  in 
such  manner  that  the  acid  does  not  flow  out.  The  wetted  stopper 
is  put  tightly  in,  the  bottles  are  placed  sideways  (up  to  this 
time  the  colour  of  the  indicator  should  not  have  changed),  the 
bulbs  broken  by  shaking,  and  then,  after  the  white  fumes  have 
vanished,  the  titration  is  performed  in  the  bottle  itself. 

The  results  of  titration  are  first  calculated  for  the  total  (com- 
bined and  uncombined  with  water)  SOg,  each  c.  c.  of  normal  soda 
solution  indicating  0*040  grm.  SOb,  and  the  proportion  of  free 
SO3  and  H2SO4  present  is  then  read  ofE  by  means  of  the  following 
formula  :  S03=S— 4*444  (100— S),  in  which  SOa  denotes  the  free 
sulphur  trioxide,  and  S  the  total  SOg  as  found  by  titration. 

This  calculation  is  saved  by  the  following  table,  computed  by 
Knietsch  (Ber.  1901,  p.  4114)  :— 


S03 

SO3 

SO3 

SO3 

SO3 

SO3 

SO3 

Total. 
81-63 

Free. 
0-0 

ToUl.  Free. 

1 
Total.  Free. 

1 

Total. 

Free. 
43-4 

TotaL 
92-2 

Free. 

Total. 

Free. 

Total.' Free. 

1 
1 

1 
97-4  i  85-8 

84-3 

14-5 

87  0 

29-2 

89-6 

57-5 

94-8 

71-7 

81-7 

0-4 

84-4 

151 

87-1  :29-8 

89-7 

43-9 

92-3 

58-1 

94-9 

72-2 

97-5    86-4 

81-8 

0-9 

84-5 

15-6 

87-2    30  3 

89-8 

44-5 

92-4 

58-6 

95-0 

72-8 

97-6    86-9 

81-9 

1-5 

84-6 

16-2 

873    30-9 

89-9 

450 

92-5 

59-2 

951  ,73-3 

07-7    87-5 

82-0 

20 

84-7 

16-7 

87-4  ,  31-4 

900 

45-6 

92-6 

59-7 

95-2    73-9 

97-8  ;  88-0 

82-1 

2-6 

84-8 

17-2 

87-5 

31-9 

901 

461 

92-7 

60-3 

95-3 

74-4 

97-9 

88-6 

82-2 

31 

84-9 

17-8 

87-6 

32-5 

902    46-6 

92-8 

60-8 

95-4 

750 

98-0 

89-1 

82-3 

36 

850 

18-3 

87-7 

330 

90-3  !  47-2 

92-9 

61-3 

95-5    75-5  1 

981 

89-7 

1 
82-4 

82-5 

4-2 

851 

18-9 

87-8    33-6 

90-4 

47-7 

930 

61-9 

95-6 

761 

98-2 

90-2 

4-7 

85-2 

19-4 

87-9  '  341 

90-5 

48-3 

931 

62-4 

95-7 

766 

98-3    90-7 

82-6 

5-3 

85-3 

200 

88  0  '  34-7 

90-6 

48-8 

93-2 

630 

95-8 

771 

98-4    91-3 

82-7 

5-8 

85-4 

20-6 

88-1    35-2 

907 

49-4 

93-3 

63-5 

95-9 

77-7 

98-5    91-8 

82-8 

6-4 

85-5 

210 

88-2    35-8 

90-8 

49-9 

93-4 

641 

960 

783 

98-6  |92-4 

82-9 

69 

85-6 

21-6 

88-3    36-3 

90-9    50-5 

93-5 

64-6 

961 

78-8 

98-7    92-9 

830 

7-5 

85-7 

22-2 

88-4    36-8 

910    510 

93-6 

65-2 

96-2 

79-3 

98-8    93-5 

831 

8-0 

85-8 

22-7 

88-5    37-4 

911    51-6 

93-7 

65-7 

96-3 

79-9 

98-9    940 

83-2 

8-5 

85-9 

23-2 

88-6    37-9 

91-2    521 

93-8 

66-2 

96-4 

80-4 

99  0    94-6 

83-3 

91 

800 

23-8 

88-7    38-5 

91-3    52-6 

93-9 

66-8 

96-5    810 

991    951 

83-4 

96 

861 

24-3 

88-8    39-0 

91-4    53-2 

940 

67-3 

96-6  !81-5 

99-2    95-6 

83-5 

10-2 

86-2 

24-9 

88-9    39-6 

91-5 

537 

94-1 

67-9 

96-7    820 

99-3    9tJ-2 

83-6 

10-7 

86-3 

25-4 

890    401 

91-6 

54-3 

94-2 

68-4 

96-8    82-6 

994    96-7 

83-7 

11-3 

86-4 

260 

89-1   I40-6 

91-7 

54-8 

94-3 

690 

969    831 

99-5    97-3 

83-8 

1 11-8 

86-6 

26-5 

89-2  '41-2 

91-8 

55-4 

94-4 

69-5 

970    83-7 

99-6    97-8 

839 

12-3 

86-6 

27-0 

89-3    41-7 

91-9 

55-9 

94-5 

701 

97-1  184-2 

99-7    98-4 

84  0 

12-9 

86-7 

27-6 

89-4    42-3 

92*0 

56-4 

94-6 

70-6 

97-2 

848 

998    98-9 

841 

13-4 

86-8 

28-1 

89-5  ;42-8 

921 

57-0 

94-7 

71-2 

97*3  !  85-3 

99-9  i  99-5 

84-2 

140 

1 

86-9 

28-7 

1 

1 

K^ 


244  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

This  table  serves  also  for  the  frequently  performed  operation  of 
mixing  Nordhausen  acid  of  a  certain  percentage  of  SO3  with 
concentrated  sulphuric  acid  in  order  to  produce  an  acid  with  a 
smaller  percentage  of  SOg,  This  can  be  done  by  means  of  a 
formula  given  by  Gerster  (Chem.  Zeit.  1887,  p.  3), 


a?=100 


a 


where  x  represents  the  quantity  of  sulphuric  acid  which  must  be 
added  to  100  parts  of  the  Nordhausen  acid ;  a  the  total  sulphur 
trioxide  in  100  parts  of  the  acid  desired ;  b  the  total  SO3  in  100 
parts  of  the  Nordhausen  acid  to  be  diluted  ;  c  the  total  SO3  in  100 
parts  of  the  ordinary  acid  to  be  used  for  diluting.  The  values  of 
a  and  b  are  taken  from  the  preceding  table ;  c  is  easily  calculated 

80 
by  multiplying  the  percentage  of  HgSO^  with  —  or  0'816.     An 

example  will  make  this  clearer.  Supposing  there  is  a  Nordhausen 
acid  of  25'5  per  cent.  SOs  in  stock,  as  well  as  sulphuric  acid  of 
98*2  per  cent.  H2SO4,  and  an  acid  of  19  per  cent.  SO3  is  required, 
we  have  then  : 

a=85-l  ;  6=86-3;  c=98x  0-816=80-1, 

a?=100  . =100  --- — — —  =  -,^-=24. 

a—c  851  —  80-1       o 

That  is  :  by  mixing  100  parts  of  acid  of  25-5  per  cent.  SOs  with 
24  parts  of  sulphuric  acid  of  98*2  per  cent.  H2SO4,  Nordhausen 
acid  is  obtained  containing  19  per  cent.  SOg.  [In  reality  the 
strength  of  the  mixed  product  will  be  slightly  below  that  calculated, 
as  a  certain  loss  of  SO3  is  hardly  avoidable  in  the  manipulation.] 

In  Zsch.  f.  angew.  Chem.  1895,  p.  221,  I  have  drawn  attention 
to  the  fact  that  in  allowing  for  the  SO3  sometimes  a  serious  mis- 
take is  committed.  The  SO2  is  always  tested  for  by  iodine  solution, 
and  is  then  subtracted  from  the  total  acidity.  Here  we  must 
consider  that  the  neutrality-point  in  the  case  of  phenolphthalein 
is  reached  when  1  SOj  has  been  combined  with  2  NaOH,  but  in 
the  case  of  methyl-orange  only  1  NaOH  is  consumed  for  1  SOj. 
Litmus  cannot  be  used  at  all,  as  it  gives  uncertain  results  between 


ANALYSIS  OF  FUMING  SULPHURIC  ACID.  245 

these  two  limits.  With  methyl-orange  1  c.c.  normal  soda 
solution  indicates  0-040  gram  SOs,  but  0064  gram  SOj.  Hence 
for  each  c.c.  of  decinormal  iodine  solution  only  0*05  c.c.  of 
normal  or  0*1  c.c.  of  semi-normal  solution  of  NaOH  must  be 
deducted.  If  this  is  overlooked,  a  very  serious  mistake  is  com- 
mitted ;  for  since  everything  which  is  not  present  as  SO3  or  SO2 
is  assumed  to  be  water,  the  incorrect  allowance  for  SOj  will  cause 
not  merely  a  deficiency  of  SOg,  but  a  surplus  of  HjO ;  and  as  this 
must  be  represented  as  combined  with  4*444  its  weight  of  water, 
far  too  little  free  SO3  is  found. 

A  practical  instance  will  illustrate  this.  3*5662  grams  fuming 
acid  were  diluted  to  500  c.c,  and  100  c.c.  (=0*71124  gram) 
employed  for  each  test.  This  consumed  5*40  c.c.  iodine  solu« 
tion,  =5*40x0-0032=001728  gram  SO2  or  2*43  per  cent.  SOg. 
On  titrating  with  seminormal  soda  solution  and  methyl-orange, 
34*40  c.c.  was  used.  By  erroneously  deducting  0*2  X5'40=  1*08 
c.c,  there  remained  3332  cc.=s0*6664  gram  SOg  or  93*70  per 
cent.  The  fuming  acid  therefore  would  have  contained  93*70  per 
cent.  SOg,  2*43  SO2,  3*87  HgO.  The  387  H^O  is  =  17*20  SOg, 
and  the  free  SOg  would  be  =93-70— 17*20  =76*50  per  cent. 

In  reality  the  5*40  c.c.  decinormal  iodine  corresponds  to  only 
0*54  c.c  seminormal  soda,  leaving  32*86  c.c. =0*6772  gram 
808  =  95*21  per  cent.  Composition  of  the  acid  :  95*21  per  cent. 
SOg,  2*43  SO3, 2*36  H2O.  The  236  HgO  is  =10*49  SOg,  leaving 
95*21  -  10*49= 84*72  per  cent,  free  SOg.  Hence  by  that  erroneous 
calculation  the  factory  committed  an  error  of  8*25  per  cent,  to  its 
own  disadvantage  I 

Exactly  the  same  result  ia  obtained  when  performing  the  calcu- 
lation by  means  of  the  above  table. 

We  have,  as  already  mentioned,  assumed  everything  as  HgO 
which  has  not  been  found  to  be  present  as  SOg  and  SOj.  But  it 
is  advisable  to  estimate  the  fixed  impurities  as  well,  since  otherwise 
their  weight,  multiplied  by  4i'A4A!,  is  erroneously  deducted  from 
the  free  SOg. 

Setlik  (Chemiker-Zeitung,  1889,  p.  1670)  proposes  to  substitute 
the  following  method  for  the  titration  of  Nordhausen  acid  by 
caustic-soda  solution  : — 50  or  100  grms.  are  weighed  out  in  a  long- 
necked  flask,  and  water  is  dropped  in  very  slowly  from  a  burette, 
divided  into  ^^  c.c,  till  the  fuming  has  ceased.  During  the 
operation  the  flask  must  be  well  cooled.     In  order  to  observe  the 


246       PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

finishing  pointy  the  flask  must  be  agitated  after  adding  each  drop 
of  -water  till  the  fumes  have  been  entirely  absorbed  by  the  acid. 
When  no  fumes  whatever  are  formed  at  the  surface  and  a  drop^ 
falling  into  the  middle  of  the  acid,  dissolves  quietly^  the  end  is 
reached.  Acid  of  more  than  35  per  cent.  SOg  must  be  previously 
diluted  with  monohydrated  sulphuric  acid.  It  is  claimed  that  this 
plan  is  much  more  expeditious  and  quite  as  exact  as  the  alkali- 
metrical  way  ;  but  the  analytical  proofs  adduced  by  Setlik  himself 
do  not  bear  this  out  (there  are  deviations  up  to  0*9  per  cent.  SO3) , 
and  we  can  regard  his  method  only  as  a  test  for  individual  use,  but 
not  between  buyer  and  seller. 

Rabe  (Chem.-Zeit.  1901,  p.  345)  estimates  the  strength  of  fuming 
(or  ordinary)  jsulphuric  acid  by  utilizing  the  fact  that  Nordhausen 
acid  loses  its  property  of  fuming  in  contact  with  air  as  soon  as  all 
its  SOj  has  been  converted  into  SO4H8  by  the  water  present  in 
ordinary  sulphuric  acid  containing  less  than  100  per  cent. 
SO.Hj: 

a  Hj^SO^  +  c  H3O  +  b  H2SO4  +  c  SO4 
=a  H2SO4  +  AH2SO4  +  CH8SO4. 

We  require,  to  begin  with,  to  know  the  percentage  of  a  certain 

sample  of  strong  chemically  pure  sulphuric  acid,  say  95  per  cent. 

H3SO4  +  5  per  cent.  H2O,  which  is  ascertained  in  the  usual  way 

by  titration.     This  acid  we  run  from  a  glass-tap  burette  into  a 

beaker  containing  25  c.c.  of  Nordhausen  acid,  repeatedly  agitating 

and  blowing  upon  the  acid  (cooling  is  generally  unnecessary),  until 

the  acid  in  the  beaker  does  not  form  any  more  fumes  on  shaking. 

Suppose  we  require  for  this  24*8  c  c.  of  the  acid  A^  containing 

95  per  cent.  HjO  and  5  per  cent.  HoO.     If  we  wish  to  ascertain 

the  strength  of  another  sample  (B)  of  concentrated  ordinary  acid, 

we  run  this  from  a  burette  into  25  c.c.  of  the  same  Nordhausen 

acid  as  before.      Suppose  we  now  require  30*5  c.c.  of  acid  B ; 

24*8  X  5 
this  proves  that  acid  B  contains  =4'07  per  cent.  H2O. 

If  no  impurities  were  present,  this   would  mean  a  strength  of 
95-93  per  cent.  HjSO^. 

On  the  other  hand,  the  percentage  of  SO3  in  Nordhausen  acid 
can  be  ascertained  as  follows : — Starting  with  pure  (say,  30  per 
cent.)  Nordhausen  acid  (C),  we  run  in  concentrated  ordinary  acid  Z>, 


ANALYSIS  OF  FaMINO  SULPHURIC  ACID,  247 

and  find  that  59*4  c.c.  of  acid  D  is  required  to  make  the  fuming  of 
25  c.c.  acid  C  disappear.  We  now  try  an  unknown  Nordhausen 
acid  E,  and  find  that  25  c.c.  of  it  require  49'8  c.c.  acid  D.  This  gives 
us  the  proportion  30  :  594= a? :  49*8  for  the  percentage  of  free 

SOjin  acid  E,  ^=  — ^^74-  =  25-15  per  cent.  SO3.      1  c.c.  of 

30 
acid  D  had  indicated  59^=0*505  per  cent,  free  SO3;  hence  we 

need  only  multiply  the  c.c.  of  acid  D  required  for  suppressing 
the  fumes  of  25  c.c.  of  any  unknown  Nordhausen  acid  by  the  same 
coeflScient,  viz.  0'505. 

[Rabe's  method  yields  very  quick  results,  and  is  probably  quite 
suitable  for  rough  tests  in  the  ordinary  routine  of  acid-making. 
There  is  no  weighing,  only  measuring,  and  any  colour  or  opacity 
of  the  acids  does  not  interfere  with  the  test.  But  as  the  differ, 
ence  of  specific  gravities  is  neglected,  this  forms  an  element  of 
uncertainty,  and  this  is  greatly  increased  by  the  evident  difficulty 
of  keeping  a  stock  of  exactly  analyzed  and  chemically  pure  con- 
centrated and  Nordhausen  acid  without  any  change.  As  com- 
mercial acids  always  contain  certain  impurities,  these  influence 
the  results  as  well.  The  only  real  advantages  of  this  method  over 
that  of  Set.lik  are  that  no  cooling  is  required  during  the  operation, 
and  that  the  large  amount  of  concentrated  acid  is  more  accurately 
read  off  than  the  small  amount  of  water,  but  otherwise  Setlik's 
method  is  preferable.] 

Nordhausen  acid  is  always  sold  by  the  percentage  of  uncom- 
bined  sulphuric  anhydride  it  contains  (not  taking  any  account  of 
the  pyrosulphuric  acid,  which  is  considered = SO3  4-  H2SO4) .  Thus 
'^  30  per  cent.  Nordhausen  acid  '^  means  a  mixture  of  30  parts  by 
weight  of  SOs  with  70  parts  of  H2SO4.  The  price  of  SO3  is  rela- 
tively higher  in  weak  than  in  strong  acids,  as  in  manufacturing  it 
the  5  or  more  per  cent,  of  water  contained  in  ordinary  ^'  rectified 
oil  of  vitriol ''  must  be  saturated  with  SO3,  each  part  of  water 
requiring  4'444  parts  of  SO3  to  form  H8SO4.  It  is  therefore 
decidedly  more  advantageous  to  dilute  strong  Nordhausen  acid 
with  the  strongest  obtainable  rectified  O.V.,  or  still  better  with 
monohydrated  sulphuric  acid. 

The  estimation  of  sulphuric  acid  in  sulphates  has  been  described, 
pp.  64  et  $eq. 


248  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

Estimation  of  the  Impurities  of  Sulphuric  Acid. 

The  impurities  of  sulphuric  acid  are  recognizable  qualitatively  in 
the  following  manner  : — A  residue  on  evaporating  sulphuric  acid  in 
a  platinum  crucible  may  contain  sulphates  of  sodium  (more  rarely 
of  potassium),  of  calcium,  aluminium,  iron,  lead;  copper,  zinc,  or 
other  metals  occur  rarely  in  sensible  quantity.     Ammonium  sul- 
phate is  sometimes  present  in  somewhat  large  quantities  (Gintl, 
Chem.-Zeit.  1879,  p.  653).     The  individual  substances  are  sought 
for  by  the  ordinary  analytical  methods.     Iron  is  already  betrayed 
by  the  colour  of  the  residue  after  ignition,  and  can  also  be  detected 
in  the  acid  itself,  without  evaporating  it,  by  the  ordinary  reagents, 
such   as  potassium  ferrocyanide,  potassium   sulphocyanide,   &x;. 
Lead  is  often  shown  as  a  white  precipitate  of  sulphate  on  diluting 
concentrated  vitriol  with  water — ^further,  by  adding  one  or  two 
drops  of  hydrochloric  acid,  by  which  white  clouds  are  formed, 
which  vanish  on  addition  of  more  hydrochloric  acid  or  on  heating  ; 
with  more  certainty  it  is  shown  by  diluting  (even  weaker  acid) 
with  three  or  four  times  its  volume  of  strong  alcohol.     The  pre- 
cipitate must,  of  course,  be  examined  further — for  instance,  with 
the   blowpipe,   by   reduction   on  charcoal   to   metallic   lead,   by 
moistening  with  ammonium  sulphide  (which  blackens  it),  &c. 
■   Arsenic  is  recognized  by  sulphuretted  hydrogen  in  a    dilute 
solution,    more   safely   by   Reinsch's   test — diluting   with   equal 
volumes  of  water  and  pure  hydrochloric  acid,  and  immersing  a 
bright  copper  foil,  which,  after  gentle  heating,  is  covered  with  a 
fast-adhering  slate-grey  precipitate,  which,  according  to  Lippert, 
is  a  compound  of  copper  and  arsenic,  Cu6As2   (if  the  arsenic  is 
present  as  arsenic  acid,  the  reaction  only   sets  in  after  longer 
heating) ;  further,  by  Marsh's  apparatus,  in  which,  by  means  of  pure 
zinc  and  water,  the  arsenic  is  given  off  as  arseniuretted  hydrogen, 
and  is  proved  by  reduction  in  a  red-hot  tube  (Berzelius),  or  by 
lighting  the  gas  and  holding  a  piece  of  porcelain  in  the  flame,  on 
which  any  arsenic  appears  as  spots.     Since  it  is  difficult  to  procure 
zinc  absolutely  free  from  arsenic,  it  is  well  to  substitute  aluminium 
foil  for  it.     There  may  be  arsenic  acid  as  well  as  arsenious  acid 
present ;  this  can  be  proved  by  neutralizing  with  ammonia  and 
adding   magnesia   mixture :    any   precipitate   must   contain   the 
arsenic  acid,  the  filtrate  the  arsenious  acid. 

Selmi  (Gazz.  Chimica,   x.  p.  40)   asserts  that  arsenic  can  be 
detected  in  acid  which   gives  no   reaction  by   Marsh's  test,  by 


DETECTION  OP  IMPURITIES  OF  SULPHURIC  ACID.  24:9 

adding  to  1000  grams  of  the  acid  300  grams  water  and  some  lead 
chloride^  distilling  and  testing  the  first  portions  of  the  distillate 
with  sulphuretted  hydrogen. 

Seybel  and  Wikander  (Chem.-Zeit.  1902,  p.  50)  prove  the 
presence  of  arsenic  in  sulphuric  or  hydrochloric  acid  by  the 
yellow  precipitate  of  AsJg,  produced  by  the  addition  of  a  solution 
of  potassium  iodide.  Sulphuric  acid  should  be  diluted  to  45'  B., 
hydrochloric  acid  should  be  employed  in  the  concentrated  state. 
The  reaction  is  interfered  with  by  free  chlorine,  ferric  salts,  nitrous 
acid  (which  equally  cause  a  yellow  coloration  by  the  formation  of 
free  iodine) ,  and  by  lead,  which  forms  yellow  Pb J2 .  (Unfortunately 
commercial  acids  mostly  contain  one  or  the  other  of  these 
impurities.) 

The  Committee  of  the  Society  of  Chemical  Industry,  and  of  the 
Society  of  Public  Analysts,  in  1901,  recommend  the  Marsh- 
Berzelius  test  as  the  most  reliable  and  sensitive^  being  capable  of 
recognizing  1  part  As  in  7  millions.  Their  detailed  prescriptions 
refer  more  particularly  to  the  detection  and  appropriate  valu- 
ation of  arsenic  in  beer  and  food- materials  (Journ.  Soc.  Chem. 
Ind.  1902,  pp.  94  et  seq,). 

Of  volatile  substances  sulphuric  acid  may  contain : — hydrochloric 
acid  (from  the  common  salt  present  in  the  nitrate  of  soda),  to 
be  proved  by  nitrate  of  silver,  after  having  diluted  the  acid,  silver 
sulphate  being  also  very  soluble  ;  hydrofluoric  acid,  to  be  proved 
by  heating  in  a  platinum  dish  covered  by  a  glass  plate  coated 
with  wax  and  containing  scratched-in  figures;  sulphurous  acid, 
to  be  proved  by  the  decolorization  of  a  weakly  blue  solution  of 
iodized  starch,  or  very  accurately  by  reduction  with  zinc  or 
aluminium  to  sulphuretted  hydrogen,  which  is  recognized  by  its 
turning  lead-paper  brown  or  by  colouring  purple  an  alkaline  solu- 
tion of  sodium  nitroprusside  (comp.  pp.  159  et  seq.).  The  oxygen 
compounds  of  nitrogen  are  nearly  always  present  in  the  sulphuric 
acid  of  trade.  They  are  recognized  in  the  simplest  manner,  and 
with  nearly  as  much  precision  as  by  any  other  test,  either  by  the 
decolorization  of  a  drop  of  dilute  solution  of  indigo  on  heating, 
or  by  carefully  pouring  a  solution  of  ferrous  sulphate  on  the  acid 
contained  in  a  test-tube,  so  that  the  liquids  do  not  get  mixed. 
In  the  presence  of  traces  of  nitrous  acids  or  of  higher  nitrogen 
oxides  a  brown  ring  will  be  formed  at  the  point  of  contact;  if 
more  be  present,  the  iron  solution  is  coloured  brown  or  black  ; 


250  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

but  after  some  time  it  loses  colour  again^  especially  if  it  has 
become  warm  by  the  reaction.  Selenium  also  gives  a  red  ring 
similar  to  that  given  by  traces  of  nitrogen  oxides ;  but  the  colour, 
instead  of  gradually  vanishing,  after  standing  for  a  time  turns 
into  a  red  precipitate  at  the  bottom  of  the  test-tube.  Nitrous 
and  hyponitric  acids  are  also  recognized  by  turning  blue  a  solution 
of  starch  containing  potassium  iodide. 

The  most  sensitive  reagent  for  nitrogen  acids  is  diphenylamine, 
which  is  most  conveniently  employed  in  a  solution  of  0*5  grm.  in 
100  c.c.  concentrated  sulphuric  acid,  diluted  with  about  20  c.c.  of 
water.  A  few  c.c.  of  this  solution  is  poured  into  a  test-tube  or 
conical  glass,  and  the  solution  to  be  tested  is  carefully  poured 
on  the  top,  so  that  the  liquids  mix  only  gradually.  If  traces 
of  nitrogen  acids  are  present,  a  fine  blue  colour  is  produced  at 
the  point  of  contact.  But  as  all  other  oxidizing  substances,  also 
selenious  acid,  produce  the  same  blue  colour,  errors  may  occur 
through  the  (very  frequent)  presence  of  selenium,  which  gives 
the  blue  reaction  with  diphenylamine  even  in  the  absence  of  any 
trace  of  nitrogen  acids.  It  is  therefore  necessary  to  test  first  with 
ferrous  sulphate,  as  described  above. 

As  I  have  shown  in  Zsch.  f.  angew.  Chem.  1894,  p.  345,  the 
diphenylamine  reaction  is  best  employed  in  the  following  manner  : 
0'5  gram  white  diphenylamine  is  dissolved  in  100  c.c.  pure  strong 
sulphuric  acid,  adding  20  c.c.  water  ;  the  heat  assists  in  dissolving 
the  substance,  and  the  reagent  keeps  in  well-stoppered  bottles  a 
long  time  without  turning  brown.  When  testing  for  nitrogen 
acids,  pour  a  few  c.c.  of  the  specifically  heavier  liquid  into  a  test- 
tube  and  carefully  pour  the  specifically  lighter  liquid  on  the  top, 
so  that  the  layers  only  gradually  mix.  The  presence  of  as  little 
as  ^\)  milligram  nitrogen  in  the  shape  of  nitrogen  acids  per  litre 
is  indicated  by  a  blue  ring  forming  at  the  surface  of  contact  of 
both  liquids,  most  easily  perceived  by  holding  the  glass  sideways 
against  a  white  background.  Both  nitric  and  nitrous  acid  are 
indicated  in  this  way. 

Brucine  indicates  only  nitric  acid  if  there  is  a  great  excess  of 
strong  sulphuric  acid  present ;  neither  selenium  nor  nitrous  acid 
interfere  with  this  test,  but  nitrous  acid  equally  reacts  with 
brucine  if  there  is  but  little  sulphuric  acid  and  much  water 
present,  say  1:2.  In  order  to  detect  nitric  acid  by  itself,  an 
aqueous  solution  to  be  tested  should   contain  at  least  §  of  its 


DETECTION  OF  NITROGEN  ACIDS  IN  SULPHURIC  ACID.  251 

volume  of  strong  sulphuric  acid.  The  brucine  can  be  added  either 
as  powder  or  dissolved  in  pure  strong  sulphuric  acid^  say  1  c.c.  of 
a  solution  of  0*2  gram  brucine  in  100  c.c.  strong  acid^  for  50 
c.c.  of  the  solution  to  be  tested,  of  which  |  must  consist  of  strong 
sulphuric  acid.  If  as  little  as  y^  milligram  nitric  nitrogen  be 
present^  a  pink  colour  is  produced  which  gradually^  on  heating 
very  quickly,  passes  through  orange  into  yellow.  In  Zschr.  f. 
angew.  Chem.  1894,  p.  347,  I  have  shown  how  this  test  can  be 
utilized  for  a  quantitative  colorimetric  estimation  of  small 
quantities  of  nitric  acid.  Gomp.  also  ibidem,  1902,  pp.  1,  170, 
and  241. 

Most  reagents,  like  diphenylamine,  ferrous  sulphate,  and  indigo, 
indicate  both  nitric  and  nitrous  acid.  There  are  far  more  reagents 
which  prove  the  presence  of  nitrous  acid  (or  nitrites)  alone,  not 
that  of  nitric  acid  :  for  instance,  a  mixture  of  starch  solution  with 
a  solution  of  iodide  of  zinc  (a  blue  colour  being  produced),  and  of 
various  organic  amines,  which  with  nitrous  acid  form  corresponding 
azo-colours  (Griess,  Berl.  Ber.  xi.  p.  624) .  Of  these  the  most 
frequently  used  are :  metaphenylcne  diamine,  which  produces  a 
yellow  colour  with  0*1  milligram  nitrous  acid  in  a  litre,  or  else  a 
combination  of  sulphanilic  acid  and  a-naphthylamine  (reagent  of 
Griess).  I  have  shown  (Zeitschr.  f.  angew.  Chem.  1889,  p.  666) 
that  it  is  best  to  mix  both  substances,  dissolved  in  dilute  acetic 
acid,  at  once,  and  to  keep  this  solution  ready  for  use ;  any  nitrous 
acid  getting  in  from  the  laboratory  air  is  thus  betrayed  from  the 
outset  by  the  reagent  turning  pink.  This  colour  can  be  removed 
by  shaking  up  with  zinc  dust  and  filtering.  For  actual  use,  the 
solution  to  be  tested  for  nitrous  acid  is  heated  up  to  about  80^  C, 
and  a  few  c.c.  of  the  mixed  reagent  added  to  it,  when  a  rose-colour 
will  be  developed  with  less  than  f  f)\7o  mgr.  N2O3  in  one  or  two 
minutes.  Solutions  containing  too  much  nitrous  acid  give  only 
a  yellow  colour.  In  order  to  obtain  a  reagent  which  is  not  dis- 
coloured on  keeping,  a  little  of  the  a-naphthyl amine  is  boiled  with  a 
few  c.c.  of  water,  the  hot  solution  is  poured  oflF,  and  only  this  is 
used,  mixing  it  with  dilute  acetic  acid  and  a  dilute  solution  of 
sulphanilic  acid. 

If  any  nitrous  acid  present  is  carefully  destroyed  by  treatment 
with  urea,  the  ordinary  reagents,  like  diphenylamine,  ferrous 
sulphate,  and  indigo,  will  indicate  any  nitric  acid  present,  this  not 
being  acted  upon,  by  urea. 


252       PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

Selenium  can  be  detected  by  the  red  colour  imparted  to  a  solution 
of  ferrous  sulphate,  which  after  some  little  time  turns  into  a  red 
precipitate  (not  vanishing  on  heating  like  the  brown  colour  produced 
by  nitric  oxide),  or  by  means  of  sulphur  dioxide.  According  to 
Jouve  (Chem.  Centralbl.  1901,  i.  p.  1889)  codein  or  morphine 
prove  the  presence  of  selenium,  but  only  when  0*5  per  cent,  is 
present,  SO2  when  merely  O'Ol  per  cent. ;  all  of  these  act  only 
on  selenious,  not  upon  selenic  acid.  Both  acids,  however,  are 
proved  by  the  red  colour  produced  by  the  action  of  acetylene, 
if  O'OOl  per  cent.  Se  is  present.  A  little  HCl  hastens  the  sepa- 
ration of  Se,  which  dissolves  in  the  hot  sulphuric  acid  with  green 
colour. 

Orlow  (Chem.  Centralbl.  1901,  i.  p.  480)  also  rejects  codein 
and  prefers  SO2,  especially  on  heating.  5  parts  H2SO44-IO  parts 
water  +  10  parts  SO2  solution  give  a  red  precipitate  at  once 
with  0*3  per  cent.  H2Se203,  but  also  with  0*03  per  cent,  after 
standing  a  few  days  or  heating  a  few  hours.  Even  0*003  per 
cent,  gives  a  rose-colour.  Rosenheim  (ibid.  1901,  ii.  p.  234)  dis- 
cusses at  length  the  influence  of  selenium  on  the  ordinary  tests 
for  arsenic. 

The  quantitative  estimation  of  the  impurities  contained  in  sul- 
phuric acid  is  best  carried  out  with  various  portions  of  the  sample. 
Usually  only  the  following  are  looked  for.  Lead  is  estimated  by 
diluting  the  acids,  if  concentrated,  with  its  own  volume  of  water 
and  twice  the  volume  of  absolute  alcohol,  when  all  of  it  is 
precipitated  by  PbSO^.  Iron  is  estimated  by  reducing  with  pure 
zinc  and  titrating  with  potassium  permanganate ;  not  leaving  out 
of  sight  its  action  upon  SO2,  N2O3,  &c.  A  very  convenient 
colorimetric  method  for  estimating  traces  of  iron  has  been  de- 
scribed by  me  in  Zsch.  f.  angew.  Ch.  1896,  p.  3 ;  comp,  also  my 
^Chera.  techn.  Untersuchungsmethoden,' i.  p.  325.  Arsenide 
estimated  by  reducing  any  arsenic  acid  to  arsenious  acid  by  a 
stream  of  SO2,  expelling  this  by  CO2,  and  precipitating  by  H2S. 
The  presence  of  lead,  antimony,  copper,  platinum,  &c.  makes  this 
process  very  complicated  (comp.  thereon  McCay,  Amer.  Chem. 
Journ.  vii,  no.  6).  If  the  quantity  of  As  is  somewhat  considerable, 
it  can  be  reduced  to  AS2O3  by  SO2,  followed  by  CO2 ;  the  liquid 
is  then  neutralized  by  soda,  and  the  AS2O3  titrated  by  iodine 
solution  (Kisling,  Chem.  Ind.  1886,  p.  137).  Further  particulars 
are  given  in  my  *  Untersuchuugsmethoden,^  i.  p.  327. 


ESTIMATION  OF  NITROGEN  ACIDS  IN  SULPHURIC  ACID.  253 

The  volatile  impurities  of  sulphuric  acid  are  estimated  as 
follows : — 

Sulphurous  acid,  if  at  all  present  ia  weighable  quantities^  can  be 
estimated  by  a  solution  of  iodine  according  to  Bunsen's  method. 
The  acids  of  nitrogen  (nitrous,  hyponitric,  and  nitric)  cannot  easily 
be  present  along  with  sulphurous  acid  in  sensible  quantity  ;  their 
quantity  is  very  considerable,  however,  in  certain  intermediate 
manufacturing  products  ('^nitrous  vitriol'');  and  the  methods  for 
estimating  it  are  therefore  of  great  importance.  Also  in  chamber- 
acid  and  in  more  concentrated  products  there  is  much  oftener 
nitrous  or  even  nitric  acid  present  than  sulphurous  acid ;  and  in 
this  case  the  estimation  of  even  minute  quantities  is  sometimes  of 
importance,  because  they  exert  a  very  injurious  action  during  the 
concentration  of  the  acid  in  platinum. 

Nitric  oxide,  as  shown  on  p.  212,  is  soluble  in  sulphuric  acid 
only  in  extremely  slight  quantities,  inappreciable  in  any  ordinary 
mode  of  testing.  In  practice  accordingly  no  account  need  be 
taken  of  nitric  oxide,  especially  in  the  case  of  the  stronger  acids, 
since  in  any  case  it  cannot  be  present  in  sufficient  quantity  for 
estimation ;  and  the  latter  need  only  refer  to  the  proper  acids  of 
nitrogen.  Of  these,  again,  only  nitric  and  nitrous  acid  need  be 
taken  into  account.  Nitrogen  peroxide,  NjO^  (formerly  called 
hyponitric  acid),  when  dissolved  in  sulphuric  acid  behaves  exactly 
like  a  mixture  of  equal  molecules  of  nitric  and  nitrous  acid  (p.  223). 
Nitrous  acid  itself  does  not  exist  in  any  but  rather  dilute  sulphuric 
acid ;  in  somewhat  concentrated  acid  it  exists  as  nitroso-sulphonic 
acid,  S05j(OH)(ONO)  (comp.  pp.  215  et  seg.).  The  solution  of 
this  compound  in  sulphuric  acid  behaves,  however,  towards  oxi- 
dizing agents  and  in  most  other  respects  exactly  like  a  solution  of 
nitrous  acid,  which,  in  fact,  is  formed  from  it  by  dilution  with 
water.  Ordinarily  in  doing  this,  part  of  the  NOgH  is  decomposed 
into  NO  and  NOjH  (p.  219),  but  this  decomposition,  which  would 
interfere  with  the  analysis,  can  be  prevented  by  proper  precautions, 
as  we  shall  see  later  on. 

First  of  all  we  must  describe  the  methods  for  estimatins:  the 
total  nitrogen  acid,  that  is  nitrous  and  nitric  acids  together,  in 
which  case  the  result  can  be  calculated  as  NzO^  N2O5,  NO3H,  &c. 
Frequently,  for  technical  purposes,  the  N  is  calculated  as  NOaNa. 

Of  the  many  methods  proposed  for  this  end  I  only  mention  those 
which  are  employed  for  technical  purposes. 


254  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

The  method  of  Pelouze,  raodiiied  by  Fresenius  and  others,  is 
only  adapted  for  the  estimation  of  nitric  acid ;  it  is,  however,  some- 
times used  for  estimating  a  mixture  of  this  and  of  nitrous  acid, 
after  the  latter  has  been  converted  into  nitric  acid,  for  instance,  by 
chlorine,  potassium  bichromate,  permanganate,  &c.  It  is  founded 
upon  the  fact  that  free  nitric  acid  oxidizes  ferrous  chloride  or 
sulphate,  according  to  the  equation 

6  FeClg  +  2  NO3H  +  6  HCl = 6  FeCU  +  2  NO  +  4  H^O. 
By  means  of  potassium  permanganate  the  ferrous  salt,  not  oxidized 
by  nitric  acid,  is  estimated,  and  the  quantity  of  the  latter  is  calcu- 
lated from  that  of  the  ferrous  salt  consumed. 

This  method  is  described  in  great  detail  in  our  first  edition, 
vol.  i.  pp.  54  to  58,  and  second  edition,  vol.  i.  pp.  173  to  176;  it 
is  not  repeated  here,  as  the  much  handier  nitrometer  method  has 
made  it  obsolete. 

Another  class  of  methods  based  upon  the  action  of  ferrous  salts 
on  the  nitrogen  acids  is  that  first  proposed  by  Schloesing,  and 
subsequently  modified  by  many  others.  In  this  class  of  methods, 
the  process  is  carried  on  in  such  manner  that  all  nitrous  and 
nitric  acid  present  is  converted  into  nitric  oxide,  NO,  which  is 
then  estimated  in  various  ways — mostly  by  measuring  its  volume 
as  a  gas.  This  method  is  very  much  used  by  agricultural  chemists, 
especially  in  the  modification  introduced  by  Grandeau.  A  table 
for  reducing  the  volumes  of  NO  to  weights  of  N2O5  for  various 
temperatures  and  pressures  has  been  calculated  by  Baumann 
(Zeitschr.  f.  angew.  Chem.  1888,  p.  662 ;  reprinted  in  Journ.  Soc. 
Chem.  Ind.  1889,  p.  135).  For  nitrous  vitriol  this  method  is 
seldom  used,  because  it  is  far  more  troublesome  than  the 
nitrometric  methods  to  be  subsequently  described. 

Many  methods  are  based  on  the  reduction  of  the  nitrogen  acids 
to  ammonia  by  means  of  zinc,  iron,  or  a  combination  of  both. 
All  the  older  forms  of  these  methods  have  been  superseded  by 
the  modification  introduced  by  Ulsch  (Zsch.  angew.  Ch.  1891, 
p.  241 ;  Lungers  '  Untersuchungsmethoden,'  i.  p.  275),  which  is 
extensively  used  for  the  estimation  of  nitrate  of  soda,  but  seldom 
for  the  nitrogen  acids  present  in  sulphuric  acid. 

The  process  which  is  now  mostly  used  for  the  estimation  of  the 
total  nitrogen  adds  in  sulphuric  acids  (as  well  as  for  that  of  nitrate 
of  soda,  comp.  p.  96,  of  nitro-glycerin,  and  for  many  analogous 
purposes)  is  the    nitroineter  method,  founded   upon   a   reaction 


NITROMETER  METHOD.  255 

discovered  by  Walter  Crum  (Phil.  Mag.  1840,  xxx.  p.  426).  It 
consists  in  agitating  the  substance  in  question  with  mercury  in 
presence  of  a  large  quantity  of  sulphuric  acid,  by  which  means  all 
the  nitrogen  acids  are  converted  into  nitric  oxide,  NO,  whose 
volume  is  ascertained  by  gasometric  methods.  Crumbs  process  had 
been  occasionally  employed  for  the  estimation  of  nitrates,  e.g.,  by 
Frankland  and  Armstrong;  and  had  been  specially  recommended 
for  nitrous  vitriol  by  G.  E.  Davis  (Chem.  News,  xxxvii.  p.  45). 
But  it  attracted  very  little  attention,  least  of  all  with  technical 
chemists,  because  it  was  cumbersome  and  expensive  (requiring  a 
mercury  trough)  and  withal  gave  no  very  trustworthy  results^ 
owing  to  the  diflSculty  of  manipulation.  I  drew  fresh  attention 
to  this  process  (Berl.  Ber.  xi.  p.  436),  and  made  it  generally 
accessible,  both  by  proving  its  accuracy  under  the  circumstances 
here  mentioned,  and  by  devising  for  it  a  special  instrument,  which, 
made  its  manipulation  extremely  easy  and  simple.  This  instru- 
ment, which  has  since  found  a  great  variety  of  applications  in 
gasometric  and  gas- volumetric  analyses,  some  of  which  are  men- 
tioned in  other  parts  of  this  work,  has  been  called  the  ^'Nitrometer','' 
It  is  made  in  various  shaped  for  various  purposes;  the  shape  which 
is  used  in  testing  nitrous  vitriol  is  shown  in  fig.  44.* 

Its  principal  portion  is  a  glass  tube,  a,  of  a  little  over  50  cub. 
centims.  capacity,  divided  into  tenths  of  a  cub.  centim.  At  the 
bottom  it  tapers  to  fit  an  elastic  joint ;  at  the  top  it  ends  in  a 
funnel  c  communicating  with  the  inner  part  of  the  tube  by  a  three- 
way  tap.  Its  plug  has  one  bore,  through  which  the  measuring- 
tube  communicates  with  the  funnel,  and  another  bore  through 
which  the  contents  of  the  funnel  can  be  run  off.  The  division  of 
the  measuring-tube,  a,  begins  from  the  tap  itself,  and  goes  from 
the  top  downwards.  The  tube  a  hangs  in  a  clamp  e,  which  can  be 
instantaneously  opened  by  a  spring,  so  that  the  tube  can  be  taken 
out.  Another  clamp/,  sliding  on  the  same  stand,  carries  a  plain 
cylindrical  glass  tube,  b,  tapering  below,  of  the  same  contents  and 
about  the  same  diameter  as  the  measuring-tube.  The  lower  ends 
of  the  two  tubes  are  connected  by  a  thick  elastic  tube,  b  slides 
up  and  down  in  its  clamp  with  friction.      In  order  to  use  the 

*  Since  I  first  published  my  above-quoted  paper,  Campbell,  Davis,  Dupont, 
and  others  have  made  known  apparatus  very  similar  to  mine,  for  which  they 
have  adopted  my  name,  **  Nitrometer."  Not  one  of  these,  however,  combines 
all  the  advantages  found  in  the  instrument  constructed  by  me. 


XOb  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

apparatus,  b  is  placed  so  that  its  lower  eiid  is  rather  higher  than 
the  tap  rf,  and,  the  latter  heing  opened,  mercury  is  ])oured  in 


through  b  till  it  just  comes  up  to  the  funuel  c.  Aa'it  flows 
iuto  a  from  helow,  it  will  not  allow  any  air-bubhles  to  remain  in 
the  tabe.     The  tap  d  is  now  closed ;  i  is  lowered ;  and  the  acid 


NITROMETER.  257 

to  be  tested  is  run  into  the  fannel  c  by  means  of  a  fine  pipette.  *  Of 
course  it  is  necessary  to  have  an  idea  of  the  maximum  quantity  of 
NO  which  may  be  given  off  without  expelling  the  mercury  from  the 
tube  altogether^  and  the  quantity  of  sulphuric  acid  must  be  taken 
accordingly.     By  carefully  opening  the  tap  d,  the  acid  is  run  into 
a  without  any  air  being  allowed  to  enter;  in  a  similar  way  the 
funnel  c  is  washed  out  twice  by  means  of  pure  concentrated  sul- 
phuric acid.      It  is  not  advisable  to  put  more  than  8  to  10  cub. 
centim.  of  acid  into  the  apparatus  ;  much  better  only  4  to  5  cub. 
centim.  altogether  are  used;  but  in  any  case  there  must  be  an 
excess  of  strong  sulphuric  acid  present.     Now  the  tube  a  is  taken 
out  of  the  spring  clamp  and  well  shaken  up.     The  evolution  of  gas 
in  the  case  of  nitrous  acid  commences  at  once — ^the  acid  taking  a 
purple  colour^  in  the  case  of  nitric  acid^  after  a  minute  or  so. 
The  reaction  is  ended  by  violent  shaking  for  one  or  two  minutes. 
Sometimes  it  takes  a  long  while  before  the  acid  clears  and  the 
froth  subsides,  but  generally  this  is  effected  in  a  very  short  time ; 
anyhow  it  is  necessary  to  wait  a  little,  so  that  the  apparatus  may 
assume  the  temperature  of  the  air.      Now  by  sliding  b  up   or 
down^  the  level  of  the  mercury  in  this  tube  is  so  placed  that  it  is 
as  much  higher  than  that  of  a  as  corresponds  to  the  vitriol ;  say, 
for  each  7  millim.  of  acid  1  millim.  of  mercury;  or  else  the  level 
of  the  mercury  is  made  the  same  in  both  tubes^  and  the  height  of 
mercury  corresponding  to   the  layer  of   vitriol   in   the   tube   is 
deducted  from  the  barometrical  pressure.     In  the  former  case,  it 
is  easy  to  ascertain  after  reading  off  whether  the  proper  compensa- 
tion for  the  height  of  the  acid  column  has  been  made  or  not.     It 
is  only  necessary  to  cautiously  open  the  tap  d^  over  which  a  drop 
of  acid  has  been  left  standing.     If  this  is  sucked  in,  and  the  level 
of  the  acid  falls,  there  has  been  too  little  pressure,  and  vice  versd. 
The  volume  of  the  nitric  oxide  can  be  read  off  to  .^^  cub.  centim. ; 
it  is  reduced  to  0°  and  760  millim.  mercurial  pressure,  and  the 
percentage  of  the  acid  calculated  from  it.     Each  cub.  centim.  of 
NO^   measured   at  QP  and   760  millim.,  corresponds   to   1*343 
milligr.  NO,  or  1701  railligr.  N^Os,  or  2-417  milligr.  N^Og,  or 
4*521  milligr.  NO3K,  or  3*805  milligr.  NOjNa.    By  this  process,  of 
coui*se,  nitric  and  nitrous  acids  cannot  be  distinguished,  but  are 
always  estimated  together. 

After  reading  off,  b  is  again  placed  higher,  the  tap  d  is  opened 
so  that  tube  a  communicates  with  the  small  outlet  tube,  and  thus 

VOL.  I.  8 


258  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

first  the  nitric  oxide  and  then  the  sulphuric  acid^  muddy  irith 
mercuric  sulphate,  is  driven  out.  When  the  mercury  begins  to 
run  out  as  well,  the  tap  is  closed^  and  everything  is  again  ready 
for  a  new  testing.  If  any  sensible  quantities  of  sulphurous  acid  be 
present  (as  proved  by  the  smell),  it  is  best  to  add  a  very  little 
powdered  potassium  permanganate  to  the  sulphuric  acid,  avoiding 
any  considerable  excess. 

The  nitrometer  was  first  provided  with  a  three-way  tap  on 
CI.  Winkler's  principle,  with  one  transverse  and  one  longitudinal 
bore ;  but  now  another  arrangement,  known  as  the  ^^  Greiner- 
Friedrichs ''  or  the  "  Geissler-Miescher ''  tap,  and  shown  in  the 
diagram,  is  preferred,  which  admits  of  much  easier  manipulation 
and  is  far  less  liable  to  leakage. 

It  has  been  stated  by  T.  Bayley  that  it  is  necessary  to  dilute 
the  acid  contained  in  the  nitrometer  at  the  close  of  the  experi* 
ment,  in  order  to  expel  the  nitric  oxide  dissolved  by  the  sul- 
phuric acid,  otherwise  an  error  of  about  0*5  c.c.  is  committed. 
I  have  proved  this  to  be  wrong,  no  measurable  quantity  of 
NO  being  dissolved  by  the  acid  contained  in  the  nitrometer 
(Joum.  Soc.  Chem.  Ind,  1885,  p.  447,  and  1886,  p.  82).  This 
could  not  be  contradicted  by  Mr.  Bayley,  who,  however,  con- 
tended that  the  iron  contained  in  the  acid  as  ferrous  sulphate 
acted  as  solvent  for  NO.  I  replied  to  this  (Chem.  News,  1886, 
liii.  p.  289)  that  the  quantity  of  iron  found  in  any  commercial 
acid  would  never  lead  to  any  appreciable  error  of  this  kind, 
more  particularly  as  it  would  be  present  as  ferric  sulphate. 

From  the  volume  of  NO  read  o£E,  and  reduced  to  0°  C.  and  760 
mm.,  the  nitrogen  compounds  present  are  calculated  by  the 
foUowing  table  (p.  259),  in  which  column  a  gives  milligrams,  and  b 
per  cent,  by  weight,  when  employing  in  the  nitrometer  1  c.c.  acid 
of  140°Tw. 

Ill  spite  of  the  very  great  convenience,  speed,  and  accuracy 
of  the  nitrometric  estimation  of  the  nitrogen  acids,  many  chemists 
might  have  abstained  from  using  it  because  the  unavoidable 
reduction  of  the  volume  of  NO  to  0°  C.  and  760  millim.  pressure 
appeared  too  tedious  to  them.  In  order  to  overcome  this  ob- 
jection, I  have  calculated  tables  which  admit  of  reducing  any 
volume  of  gas  from  1  to  100  from  any  given  temperature  to  0°  C, 
and  from  any  given  pressure  to  760  millim.,  by  simple  reading  ofi*. 
These  tables  were  given  in  the  Appendix  to  my  first  edition ;  they 


GAS-VOLUMETER. 


259 


N. 


NO. 


N,03. 


NO3H. 


cc. 
NO.  ! 


a. 


1. 

0-627 

2. 

1-254 

3. 

1-881 

4. 

2-508 

5. 

3135 

6. 

3-762 

7. 

4-389 

8. 

5016 

9. 

5-643 

A. 


a. 


b. 


a. 


0-0366 
i  a0732 
01098 
01464 
01830 
0-2196 
02662 
0-2928 
0-3294 


1-343 
2-686 
4-029 
5372; 
6-715; 
8-058' 
9-401, 
10-744 
12087 


0-0785 
01570 
0-2355 
0-3140 
0-3925 
0-4710 
0-5495 
0-6280 
0-7065 


1-701 

3-402 

5103 

6-804 

8-5061 

10-206 

11-907 

13-606: 

15-3091 


00995 
01990 
0-2985 
0-3980 
0-4975 
0-5970 
0-6965 
07960 
0-8955 


2-8201 
6-6401 
8-460 
11-280 
14-100 
16-920 
19-740 
22-560i 
25-380 


0-1648 
0-3296 
0-4944 
0-6592 
0-8240, 
0-9888 
11536 
1-3184 
1-4832, 


3-805 
7-610 
11-415 
15-220 
19025 
22-830 
26-635 
30-4401 
34-2451 


0-2225 
0-4450 
0-6675 
0-8900 
11125 
1  -3360 
1-5575 
l-7800; 
2-0025! 


are  also  contained  in  Lunge  and  Hurter's  ^  Alkali-Maker's  Pocket- 
book/  and  are  also  separately  published  for  use  as  wall-tables 
by  F.  Vieweg  &  Sohn,  Brunswick.  Other  tables,  requiring  very 
little  more  time  for  use^  are  found  in  Winkler-Lunge's  ^  Hand- 
book of  Gas- Analysis/  2nd  edition^  pp.  177  et  seq. 

I  abstain  here  from  giving  these  or  any  other  tables^  as  an 
instrument  invented  by  myself,  and  called  the  *^  gas-volumeter  '^ 
(Zeitschr.  f.  angew.  Chem.  1890,  p.  139;  Berliner  Berichte,  1890, 
p.  440),  has  made  unnecessary  all  calculations  and  tables  in 
connection  with  the  reduction  of  volumes  of  gases  to  QP  and  760 
millim.  This  instrument,  as  shown  in  fig.  45  (p.  260),  consists  of 
three  glass  tubes,  all  joined  by  very  strong  elastic  tubes  to  a  three- 
way  pipe  D,  and  sliding  upwards  or  downwards  in  strong  clips. 
Tube  A  is  the  measuring-tube,  B  the  reduction-tube,  C  the  level- 
tube.  A  is  divided  into  tenths  of  cub.  centim.  and  generally  holds  50 
c.c. ;  where  larger  volumes  of  gases  are  to  be  measured  it  is  shaped 
like  B,  and  holds  60  or  100  c.c.  in  the  upper,  wider  portion,  and 
another  40  c.c.  (divided  into  ^  c.c.)  in  the  lower,  narrower  portion. 
The  ^'  reduction-tube  "  B  holds  100  c.c.  in  the  upper  part,  and 
another  30  cc.  (divided  into  ^-^  c.c.)  in  the  lower  part.  This  tube  is 
set  once  for  all  in  the  following  way : — After  putting  the  apparatus 
together  and  partly  filling  it  with  mercury,  the  temperature  close 
to  B  and  the  barometric  pressure  are  taken,  and  it  is  calculated, 
by  the  well-known  formula 

(273  4-0760 
273x/5> 

(where  /  denotes  the  temperature  in  0®  C,  b  the  height  of  the  baro- 
meter in  millimetres),  what  would  be  the  volume  of  100  c.c.  dry 
air  under  the  then  atmospheric  conditions.     (This  calculation  can 

s2 


260 


PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR, 


be  abridged  by  using  any  of  the  above-mentioned  tables^  if  they  are- 
at  hand.)  Suppose  ^=20^^  6=^750  millim.  In  this  ease  100  c.c. 
of  dry  air  would  occupy  the  volume  108*8  c.c.  We  now  move  B  and 
C  so  that,  tap  /being  open,  the  level  of  the  mercury  in  B  is  at  108*8,^ 


Fig.  45. 


whilst  the  mercury  in  C  is,  of  course,  at  the  same  level.  Previously 
to  this  we  have  introduced  a  drop  of  strong  sulphuric  acid*into  B,. 
but  not  sufficient  to  reach  over  the  meniscus  of  the  quicksilver^ 
which  would  be  an  impediment  to  taking  the  readings ;  this  is  done, 
because  gases  have  afterwards  to  be  measured  in  the  dry  state. 


GA8-VOLUMETEE.  261 

(In  the  more  frequent  ease  in  which  tliis  instrument  is  employed 
for  measuring  moist  gases,  in  lieu  of  sulphuric  acid,  a  drop  oE  water 
is  introduced  into  B,  and  the  calculation  is  made  by  deducting  from 
the  barometric  pressure  the  tension  of  aqueous  vapour  correspond- 
ing to  the  existing  temperature.)  Now  tap  /  is  closed,  and  is 
secured  so  that  no  air  can  enter  or  escape  through  it.  In  lieu  of 
this  tap  a  capillary  tube  may  be  provided  which  is  sealed  by  a 
small  flame,  after  having  put  a  perforated  piece  of  asbestos  card- 
board over  the  top  of  tube  B,  to  prevent  its  temperature  rising 
during  the  sealing-operation.  The  best  way  of  closing  tube  B 
is  by  means  of  a  mercury-scaled  tap  as  described  by  me  in  Berl. 
Bar.  1892,  p.  8158. 

It  is  quite  evident  that  every  time  the  level-tube  C  is  raised  so 
that  the  mercury  in  B  rises  to  the  point  100,  the  air  within  B  is 
compressed  to  the  volume  it  would  occupy  at  0^  and  760  millim. 
independent  of  the  temperature  and  barometric  pressure  actually 
existing.  Now  suppose  we  have  evolved  or  carried  over  into  tube 
A  a  certain  volume  of  gas,  and  we  adjust  the  position  of  the  three 
tubes  so  that  the  mercury  in  B  stands  at  lOO*^,  and  that  in  A 
exactly  at  the  same  level,  it  is  evident  that  the  gas  in  A  is  under 
the  same  pressure  as  in  B ;  and,  supposing  its  temperature  to  be 
the  same  (which  will  be  the  case  if  the  two  tubes  are  close 
together),  the  gas  in  A  will  be  equally  compressed  as  that  in  B  to 
the  volume  it  would  occupy  at  0^  and  760  millim.  barometric 
pressure.  The  reading  taken  in  A  thus  yields  at  once  the  corrected 
volume  without  having  to  look  at  a  thermometer  or  barometer,  or 
use  any  calculations  or  tables. 

Tube  A  might  be  an  ordinary  nitrometer ;  but  it  is  far  prefer- 
able to  use  it  only  as  a  measuring-tube,  and  thus  to  keep  it  always 
clean  and  dry,  whilst  the  nitrometric  operation  proper  is  carried 
out  in  the  auxiliary  '^  agitating-vessel "  E.  This  is  a  non- 
graduated  vessel,  holding  100  to  150  c.c,  and  connected  by  a 
strong  elastic  tube  with  the  level-tube  F.  The  vessel  E  bears  at  the 
top  the  usual  three-way  tap  and  cup  c.  The  side-tube  a  can  be 
closed  by  a  small  ground-on  cap  b,  or  else  by  an  india-rubber  cap. 
Before  commencing  the  analytical  operation,  the  tube  F  is  raised 
so  that  the  mercury  just  issues  out  of  a ;  cap  b  is  now  put  on  and 
tap  c  is  closed.  Now  the  nitrous  vitriol  (or  solution  of  nitrate  of 
soda,  comp.  p.  96)  is  introduced  through  c,  by  carefully  lowering 
F,  so  that  only  the  liquid,  but  no  air,  enters  into  E;  strong 


262  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

sulphuric  acid  follows^  to  rinse  out  cup  c ;  the  tap  is  now  entirely 
closed^  and  E  is  violently  shaken  till  the  decomposition  is  complete 
and  no  more  NO  is  given  off.  The  cap  b  prevents  the  mercury  in 
tube  a  from  being  thrown  out  in  the  shaking.  The  instrument  is 
allowed  to  cool  down^  and  is  then  put  in  the  position  shown  in  the 
diagram^  so  that  the  small  tubes  a  and  d  are  on  the  same  level. 
Previously  a  short  piece  of  india-rubber  tube  has  been  slipped  over 
d,  and  by  raising  C  the  mercury  has  been  forced  right  to  the  end 
of  d.  Now  cap  b  is  taken  off,  and  a  is  introduced  into  the  short 
elastic  tube,  till  the  glass  tubes  a  and  d  touch.  Now  tube  C  is 
lowered  and  F  raised  (as  shown  in  the  diagram) ,  and  tap  o  is 
cautiously  opened  {e  having  been  left  open  before).  The  gas 
will  thus  be  transferred  from  E  into  A ;  at  the  moment  when  the 
sulphuric  acid  has  entered  into  the  bore  of  e^.but  before  it  has  got 
inside  of  A,  tap  e  is  closed.  Now  the  reading  is  taken  as  described 
above ;  the  apparatus  EF  may  be  detached  at  any  time  and 
cleaned  as  occasion  requires. 

The  readings  of  the  volume  of  NO  taken  in  tube  A  may  be 
converted  into  grams  of  N2O3  or  NaNO^,  &c.,  by  means  of  the 
table  given  on  p.  259.  If  nitrate  of  soda  has  to  be  analyzed^  each 
c.c.  will  indicate  3*805  milligr.  NaNOs ;  hence,  if  0*8805  gram  of 
nitrate  were  employed  for  the  test,  the  numbei*  of  c.c.  of  NO 
would  at  once  indicate  the  percentage  of  NaN03.  In  the  case  of 
nitrous  vitriol  the  quantity  will  usually  not  be  weighed,  but 
measured  by  means  of  a  pipette,  and  the  results  obtained  must 
then  be  divided  by  the  specific  gravity  of  the  acid  to  reduce  them 
to  weight  percentage.  If  the  acid  is  near  140^  Tw.,  this  is 
unnecessary;  for  in  this  case  a  1  c.c.  pipette  will  deliver  1*70 
gram  acid,  and  as  each  c.c.  of  NO  indicates  0*0017  NjO^,  this 
means  that  the  number  of  c.c.  read  off  is  exactly = tenths  of  a  per 
cent,  of  N2O3  by  weight  of  the  nitrous  vitriol. 

We  now  proceed  to  the  estimation  of  nitrous  acid,  or,  more 
properly  speaking,  of  nitrososulphuric  acid,  present  in  sulphuric 
acid,  which  is  mostly  sufiScient  for  testing  the  "  nitrous  vitriol " 
from  the  Guy-Lussac  tower. 

Among  all  the  analytical  methods  founded  upon  the  oxidation 
of  nitrous  acid,  both  the  most  convenient  and  the  most  accurate 
is  that  Yiith  potassium  permanganate,  first  proposed  by  Feldhaus. 
Even  for  scientific  purposes  there  is  not  a  more  accurate  method 
for  estimating  nitrous  acid  in  an  acid  solution  than  this,  if  other 
oxidizable  bodies  be  absent. 


PERMANOANATE  METHOD  FOR  NITROUS  ACID.  263 

Even  nitric  oxide  is  oxidized  by  this  reagent^  according  to  this 
equation : 

10NO+6MnO4K  +  9SO4H2=10NO3H  +  3SO4K2  +  6SO4Mn 

+4H2O. 

Accordingly  the  seminormal  solution  of  permanganate,  each  cub. 
centim.  of  which  corresponds  to  0*004  O,  will  show  0*005  NO  for 
each  cub.  centim.  Thus^  on  the  one  hand^  nitric  oxide  can  be 
estimated  quantitatively  by  this  reagent :  on  the  other  hand,  the 
nitric  oxide  would  make  the  estimation  of  nitrous  acid  inaccurate 
if  it  were  present  at  the  same  time,  which,  fortunately,  is  not  the 
case  in  sulphuric  acid  to  an  appreciable  extent. 

Nitrous  acid  itself  is  oxidized  by  permanganate,  according  to 
the  equation : 

5  N2O3 + 4  Mn04K + 6SO4H, = 10  NO3H  +  2  SO4K2 + 4  SOiMn 

+  H2O. 

Here  every  cub.  centim.  of  seminormal  permangauate  solution 
corresponds  to  0*0095  gram  N^Os. 

The  process  formerly  in  use,  where  the  permanganate  solution 
was  run  into  the  nitrous  vitriol,  has  been  shown  to  be  quite 
inaccurate  by  my  investigations  (owing  to  the  formation  of  NO  and 
HNO3)  ^^d  has  been  replaced  by  the  plan  proposed  by  myself, 
namely,  manipulating  in  the  following  way : — ^The  permanganate 
is  not  run  into  the  acid,  but,  on  the  contrary,  a  certain  volume 
of  permanganate  solution  is  taken,  and  the  nitrous  vitriol  is  run  in 
from  a  burette  slowly,  and  with  constant  shaking,  till  the  liquid  is 
just  decolorized.  In  the  cold  there  is  some  loss  of  time,  since  the 
very  dilute  solution  of  permanganate  is  no  longer  acted  upon  instan- 
taneously. This  loss  of  time  can  be  avoided  by  working  at  30^ 
to  40°  C,  but  no  higher.  When  working  with  concentrated  suU 
phnric  acid,  this  temperature  is  attained  without  any  special  means  ; 
otherwise  the  permanganate  solution  is  heated  up  beforehand.  If 
seminormal  solution  is  employed,  it  is  diluted  with  about  100  c.c. 
of  tepid  water.  Sometimes  a  brown  precipitate  (of  hydrated  man- 
ganese peroxide)  is  formed  in  the  operation ;  but  this  dissolves 
later  on,  and  the  final  result  is  quite  as  correct  in  these  as  in  any 
other  cases. 

In  testing  chamber  acid,  at  most  5  c.c.  of  seminormal  per- 
manganate should  be  employed ;  otherwise  the  quantity  of  sul- 
phuric acid  required  for  decolorizing  it  will  be  inconveniently 
large.     For  proper  "  nitrous  vitriol ''  from  the  Gay-Lussac  tower 


264 


PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 


up  to  50  C.C.  permanganate  may  be  taken«     If  the  number  of  c.c. 

of  permanganate  is  called  Xy  and  that  of  the  acid  required  for 

decolorizing  it  y,  the  quantity  of  N2O3  present,  in  grams   per 

9*5  X 
litre  of  acid  is — ,  calculated  as 


y 


NO.H  = 


or  as 


NaNO«= 


8 


15-75^ 

y      ' 

21-25  a? 

y 


The  following  table  saves  the  calculation  in  all  cases  in  which 
a?=50.  The  column  y  gives  the  number  of  cub.  centim.  of  nitrous 
vitriol  used^  a  the  percentage  in  grams  per  litre^  and  b  the  per- 
centage by  weight  for  acid  of  140°  Tw.  (For  other  strengths  the 
percentage  by  weight  is  calculated  by  dividing  the  figures  of  column 
a  by  10  times  the  specific  gravity.)  The  figures  in  column  a  also 
indicate  0*01  lb.  avoirdupois  per  gallon^  or^  as  nearly  as  possible^ 
ounces  per  cubic  foot. 


Table  for  testing  Nitrous  VitrioU 


Acid 

N,0,. 

NO.H. 

NOjNa. 

consumed. 

1 

y- 

a. 

b. 

a.                   h. 

a. 

/>. 

c.c. 

griu8.  per 

per  cent,    j 

grins,  per      per  cent. 

grins,  per      per  cent.  | 

litre. 

1 

litre. 

litre. 

10 

47-5 

2-80 

78-8             4-62 

106-2 

6-22 

11 

432 

2-54 

71-6             4-20 

96-5       '      5-65       1 

12 

396 

2-33 

65-7             3-85 

88-0 

518 

13 

!      36-5 

216 

60-6             3-55 

81-7 

4-78       ! 

14 

340 

200       1 

56-2             3i^ 

75-9             4-44       1 

15 

i      31-7 

1-86       ' 

52-5             307 

70-8             414 

16 

29-5 

1-74 

49-3             2-89 

66-4             391 

17 

27-9 

1-64       , 

46-3             2-71 

62-5       ;      3-6.') 

18 

26-4 

1-55 

43-7             2-56 

590             346 

19 

25-0 

1-47 

41-5             2*43 

559             327 

20 

23-7 

1-38 

39-3       1      230 

.^•1              311 

21 

22-6 

1-33 

37-5       '      219 

50-6             2-96 

22 

21-6 

1-27 

85-7             2-09 

48-3             2-82 

23 

20-6 

1-21 

34-2             200 

46-3             2-71 

24 

19-8 

117 

32-8             1-92 

44-4             2-60 

25 

190 

112 

31-5              1-84 

42-5             2-49 

26 

18-3 

108 

30-3             1-77 

40-8             2-39 

27 

17-6 

103       ' 

291             1-71 

39-4              230 

28 

170 

100 

281              1-64 

380             222 

29 

1(V4 

096 

27-1             1-58 

36-7              2  15 

30 

15-8 

0-93       ' 

26-3             1-54 

a5-5              208 

* 

ANALYSIS  OP  NITROUS  VITRIOL. 


265 


Table' for  testing  Xitroue  Vitriol  (continaed). 


Acid 

yfir 

yo,n. 

NO,Na. 

consumed. 

1 

y. 

a. 

b. 

a. 

b. 

a. 

b. 

cc. 

flrms.  per 
litrer    , 

percent 

grms.  per 
litre. 

per  cent. 

gnof.  per 
litre. 

.   per  cent. 

31 

15-3 

0-90 

25-5 

1-49 

343 

2-01 

32 

14-8 

0-87 

24-6 

1-44 

33-3 

la'i 

33 

14-4 

0-85 

2:^9 

1-40 

323 

1-89 

34 

13-9 

0-82 

232 

1-36 

313 

1-84 

;i5 

13-6 

0-80 

22-5 

1-32 

304 

1-78 

m 

132 

0-78 

21-9 

1-28 

29-5 

173 

tyi 

128 

«J-75 

21-3 

1-25 

28-7 

1-68 

38 

12-5 

0-73 

207 

1-21 

280 

1-64 

39 

12-2 

0-72 

20^ 

118 

27-3 

160 

40 

11-9 

0^70 

19-7 

115 

266 

1-56 

41 

11-6 

0-68 

19^2 

112 

25-9 

1-52 

42 

11-3 

i>66 

18-8 

110 

25-3 

1-4S 

43 

11-0 

0-65 

18-3 

1-07 

247 

14.5 

44 

108 

0-63 

17-9 

1-(X5 

24-2 

1-42 

45 

10-6 

0-62 

175 

1-02 

236 

1-38 

46 

10-4 

061 

171 

11)0 

231 

ia'» 

47 

10-1 

059 

16-8 

0-98 

226 

1-32 

48 

9-9 

0.")8 

16-4 

iym 

222 

V3{) 

49 

9-7 

0-57 

161 

0-97 

21-7 

1-27 

50 

9-5 

0-56 

15-8 

0-925 

213 

1-25 

.w 

86 

050 

14-4 

O&i") 

19-3 

113 

60 

7-9 

0-46 

131 

0-7a3 

17-7 

CK^i 

65 

7-3 

0-43 

121 

o-7a> 

16-4 

(K« 

70 

68 

044) 

11-2 

0-65.) 

15-2 

0-89 

75 

63 

0-37 

10-5 

0615 

1415 

OS27 

80 

5  9       1 

0-35 

9-85 

0-575 

133 

0-778 

So 

r}-(i 

0-33 

9-2 

0  538 

12  5 

0-730 

90 

rrS 

031 

8-7 

0-510 

11-8 

0  692 

95 

5-0 

0-29 

8-3 

0-4rt5 

11-2 

0-(>.V) 

100 

■^■^      ! 

0-28 

79 

1 

0462 

10-6 

0-020 

In  the  presence  ot  other  oxidizable  substances,  such  as  sulphurous 
acid^  ferrous  salts^  organic  substances,  &c.,  all  oxidation  methods 
•are  of  course  inexact — whether  the  bleaching-powder,  or  the 
bichromate,  or  the  permanganate  process.  Generally  those  im- 
purities are  too  insignificant  to  do  any  harm;  but,  especially 
where  large  quantities  of  nitrous  acid  are  present,  as  in  the 
nitrous  vitriol  from  the  6ay-Lussac  towers,  the  permanganate 
process  is  quite  sufficient  for  the  purpose  of  checking  the  course 
of  manufacture.  Of  the  oxidizable  substances  only  arsenious 
acid  sometimes  occurs  in  sufficient  quantities  to  affect  the  results 
sensibly,  but  to  a  small  extent  only,  in  nitrous  vitriol,  where  it  is 
mostly  changed  into  arsenic  acid. 


266  PROPERTIES  OF  OXIDES  AND  ACIDS  OF  SULPHUR. 

The  estimation  of  nitrous  acid  by  means  of  'aniline^  which  is 
converted  into  a  diazobenzol  salt,  the  end  of  the  reaction  being 
shown  by  potassium  iodide  and  starch,  has  been  practised  for  some 
time  at  several  colour- works,  long  before  it  was  published  by  Green 
and  Ridea]  (J.  Soc.  Chem.  Ind.  1886,  p.  633).  According  to 
comparative  tests  made  in  my  laboratory,  it  offers  no  advantage 
whatever  over  the  very  much  less  troublesome  permanganate 
method,  and  may  lead  to  serious  errors  (Zsch.  angew.  Ch.  1891,. 
p.  629,  1902,  p.  169). 

Minute  quantities  of  nitrogen  acids  cannot  be  quantitatively  esti- 
mated by  the  above  methods,  but  the  colorimetric  estimation  of  slight 
quantities  of  nitrous  acid,  as  I  have  shown  in  Zsch.  f.  angew.  Ch. 
1894,  p.  848,  can  be  performed  by  Griess's  reagent,  modified  as 
follows  : — 0*1  gram  white  a-naphthylamine  is  dissolved  by  boiling 
in  100  c.c.  water  for  a  quarter  of  an  hour;  then  5  c.c.  glacial 
acetic  acid  (or  its  equivalent  in  ordinary  acetic  acid)  and  a  solution 
of  1  gram  sulphanilic  acid  in  100  c.c.  water  are  added.  The 
solution  is  kept  in  a  well-stoppered  bottle ;  if  it  turns  pink  it  is 
decolorized  by  shaking  with  zinc-dust  and  filtering.  A  very  slight 
colour  does  not  interfere  with  its  use,  as  only  1  c.c.  is  employed  for 
50  c.c.  of  the  solution  to  be  tested.  1  c.c.  of  the  reagent  indicates- 
-J  J^^  milligram  nitrous  nitrogen  in  100  c.c.  water  by  turning  the 
water  pink  in  10  minutes.  Strong  mineral  acids  retard  or  stop 
the  reaction,  but  this  can  be  remedied  by  adding  a  large  excess  of 
pure  sodium  acetate. 

For  quantitative  use  a  standard  solution  is  prepared  as  follows : — 
0'0493  gram  pure  sodium  nitrite,  containing  O'OIO  gram  nitrogen,, 
is  dissolved  in  100  c.c.  water,  and  10  c.c.  of  this  solution  is  drop 
by  drop  added  to  90  c.c.  pure  sulphuric  acid;  the  resulting 
mixture  contains  y^^  milligram  of  nitrous  nitrogen  in  a  perfectly 
stable  form.  Two  colorimeter  cylinders  are  charged  as  follows  : — 
Each  of  them  receives.  1  c.c.  of  the  Griess-Lunge  reagent,  40  c.c. 
of  water,  and  about  5  grams  of  solid  sodium  acetate.  To  one  of 
these  is  added  1  c.c.  of  the  standard  solution,  to  the  other  1  c.c.  of 
the  acid  to  be  tested.  The  contents  of  each  cylinder  are  at  once 
thoroughly  mixed,  and  after  5  or  10  minutes  the  colours  are 
compared.  If  they  do  not  correspond,  the  more  strongly  coloured 
liquid  is  diluted  up  to  the  point  where  layei*s  of  equal  thickness, 
show  the  same  depth  of  colour  in  both  solutions,  and  the  percentage 
of  nitrous  nitrogen  is  calculated  from  the  amount  of  dilution. 


COLORIMETRIC  ESTIMATION  OF  NITRIC  ACID.  267 

Very  minute  quantities  of  nitric  acid  are  best  estimated  by  the 
colorimetric  brucine  process,  described  by  me,  Zsch.  angew.  Ch. 
1894,  p.  347,  the  principle  of  which  consists  of  comparing  the 
yellow  colour  obtained  by  heating  to  about  70^  with  brucine 
with  a  standard  solution  of  nitric  acid.  As  a  rule,  nitric  acid 
is  not  estimated  by  itself  in  sulphuric  acid,  but  indirectly,  by 
estimating  the  total  nitrogen  acids  by  means  of  the  nitrometer 
(p.  253)  and  deducting  the  nitrous  acid  found  by  the  permanganate 
method  (p.  262). 


268  PRODUCTION  OF  SULPHUR  DIOXIDE. 


CHAPTER  IV. 

THE  PEODUCTION  OF  SULPHUR  DIOXIDE. 

A,  Brimstone-burners. 

Already  in  the  historical  part  attention  has  been  drawn  to  the 
point  that  important  progress  was  made  in  the  manufacture  of 
sulphuric  acid  when  the  periodical  combustion  of  sulphur  within 
the  acid-chambers  was  replaced  by  continuous  work  in  special 
apparatus  attached  to  the  chambers.  This  led  to  making  the 
sulphur-burners  altogether  independent  of  the  chambers^  and  con- 
veying the  gas  generated  in  the  former  by  a  flue  into  the  latter. 

Whilst  in  the  old  periodical  style  of  working  only  the  oxygen 
actually  present  in  the  chamber  could  come  into  play,  and  there- 
fore after  every  combustion  the  chamber  had  to  be  supplied  with 
fresh  air  by  opening  the  door  and  a  special  valve,  of  course  at  the 
expense  of  much  inconvenience  and  loss  of  gas,  in  the  continuous 
method  of  work  the  necessary  air  constantly  enters  the  burner  by 
suitable  openings  at  the  same  rate  as  the  products  of  combustion 
are  aspirated  into  the  chamber  by  the  draught  prevailing  through- 
out the  apparatus.  The  continuity  of  work  must  be  further 
aided  by  employing  a  combination  of  several  burners^  so  that  there 
shall  always  be  burning  sulphur  present.  There  are  also  burners 
to  which  the  brimstone  is  continuously  supplied,  in  order  to  avoid 
the  drawback  of  irregular  supply  of  air  and  gas  occurring  even  with 
the  combination  of  several  ordinary  burners. 

The  plainest  sulphur-burners,  such  as  were  the  most  usual  in 
England,  are  represented  in  figs.  46  to  48.  The  burner  consists 
of  a  brick  chamber  covered  by  an  arch,  the  bottom  being  formed 
by  a  cast-iron  plate,  a,  separately  shown  in  fig.  48.  This  plate 
at  the  two  long  sides  and  one  of  the  ends  has  a  somewhat  slanting- 
up  flange  of  3  inches  height — in  front,  however,  only  1  inch,  so 
as  to  get  out  the  ashes  more  easily.     The  plate  does  not  go  right 


iNE-BURNBKS. 


through  the  burner,  but  leaves  the  last  third  oE  it  free ;  in  this 
part  of  the  chamber  the  sulphur  vapour,  which  is  always  formed, 
can  mix  with  the  excess  of  air  and  be  burned.  Rarely,  how- 
ever, is  this  completely  performed,  and  there  is  generally  some 

Fig.  46. 


sulphur  carried  away  ucbumed.  This  not  only  causes  a  loss,, 
but  also  easily  leads  to  the  chamber-acid  getting  muddy  and  being 
covered  with  a  thin  film  of  sublimed  sulphur,  which  prevents  the 
contact  between  the  bottom  acid  and  the  gas,  very  necessary  for 
the  chamber  process.      The  burner  is  further  provided  with  aa 


270  "  PRODUCTION  OF  ISULPHUR  DIOXIDE. 

iron  door^  b^  sliding  in  a  frsnne  and  adjustable  by  a  chain  and 
balance-weight;  also  witb  a  pipe^  c,  for  taking  away  the  gas. 
An  air-channel,  d,  below  the  plate  is  in  connection  with  a  small 
chimney,  or  sometimes  only  with  the  open  air,  in  order  to 
cool  the  metal  plate  to  some  extent  and  prevent  the  sublimation 
of  sulphur.  There  are  always  several  furnaces  of  this  kind 
combined  together ;  each  of  them,  with  plates  of  8  feet  x  4  feet, 
can  bum  5  cwt.  of  brimstone  in  24  hours,  which  is  put  in  in 
6  portions,  one  every  4  hours  ;  if  four  furnaces  are  combined,  one 
of  them  is  charged  every  hour,  ,  Sometimes,  however,  much  larger 
and  more  frequent  charges  are  made  (see  below  *) ,  In  these  burners, 
usually  at  the  same  time,  the  nitric  acid  is  liberated  by  placing  cast- 
iron  pots,  provided  with  three  feet  and  containing  a  mixture  of  nitre 
and  vitriol,  amidst  the  burning  sulphur  by  means  of  large  tongs. 

For  a  start  the  plates  are  heated  by  a  small  fire  of  wood  shavings, 
the  door  being  left  open,  not  till  the  iron  becomes  red-hot,  but 
only  till  the  first  charge  of  sulphur  ignites  of  its  own  accord  or 
can  be  easily  lighted  by  a  red-hot  iron;  the  further  charges  always 
find  the  burner  sufficiently  warm.  A  special  fire-grate  below  the 
plate,  to  be  used  only  at  the  start,  is  sometimes  provided,  but  is 
quite  unnecessary.  The  admission  of  air  is  regulated  by  opening 
the  door.  A,  more  or  less  widely;  and  its  position  is  fixed  by 
putting  a  wedge  underneath  it,  or  by  hooking  the  balance-chain 
to  a  nail  driven  into  the  brickwork  outside.  At  the  commence- 
ment, when  the  chambers  are  filled  with  air^  the  damper  in  the 
draught-tube  is  only  opened  gradually,  to  drive  away  the  air  more 
thoroughly. 

The  style  of  working  is  generally  rather  rough;  it  must  be 
mentioned  that  such  burners  are  nowadays  seldom  found  in  large 
works,  where  more  supervision  can  be  used.  Before  the  attendant 
pulls  up  the  door,  he  convinces  himself  regarding  the  state  of  the 
chambers  so  as  to  judge  how  much  nitre  he  is  to  ^'pof  along 
with  the  brimstone.  Often  the  nitre  is  merely  measured  by  guess- 
work. First  the  brimstone  is  thrown  in  ;  the  door  is  immediately 
let  down,  then  a  sufficient  quantity  of  chamber-acid  is  poured 
into  the  nitre-pots,  always  by  guesswork;  the  door  is  opened 
again^  and  the  pots  are  placed  in  the  brimstone,  now  already  on 

♦  Davis  (Chemical  Engineering,  ii.  p.  123)  states  that  up  to  21b.  of  brimstone 
cBn  be  burned  per  square  foot  per  hour.  This  is  more  than  the  maximum 
I  have  ever  found  in  practice.  It  is  best  not  to  reckon  upon  much  more  than 
1  lb.  per  square  foot  per  hour. 


OLD  BBIUSTONE-BUBNEBS.  271 

fire,  by  meaoB  of  au  iron  fork  made  for  the  purpose.  The  heat 
produced  by  the  progress  of  the  combustion  drives  off  the  nitric 
scid,  and  this  enters  the  chambers  along  with  the  sulphur  dioxide. 

When  the  time  is  up,  the  door  is  raised  agaiu,  and  the  ashes  are 
raked  out;  first,  however,  the  uitre-pots  are  Lifted  out  and  emptied 
of  their  liquid  contentH.  Then  a  new  charge  is  made  as  above, 
and  so  forth.  In  all  other  sulphur-burners,  excepting  the  con- 
tinuous ones,  the  work  is  carried  on  in  the  same  manner :  only  the 
iatrodnction  of  the  nitre  sometimes  takes  place  in  a  less  rough 
way,  or  nitric  acid  is  used  directly  in  the  chambers. 

It  is  a  sign  that  the  burner  is  working  well  if  the  brimstone 
bums  with  a  pure  blue  flame ;  as  soon  as  the  flame  takes  a  brown 
tinge,  it  indicates  that  much  sulphur  is  Bubliming,  and  care  must 
then  be  taken  to  cool  the  plate,by  the  flue  underneath. 

A  somewhat  more  perfect  apparatus  is  shown  in  fig.  49.     A  is 

Fig.  40. 


the  foundation,  B  the  chamber  for  burning  the  sulphur,  C  the  gas- 
pipe.  The  foundation  carries  a  cast-iron  plate  which  covers  the 
whole  furnace-bottom  and  is  inclined  a  little  forward.  The 
combustion-chambers  are  at  the  sides  bounded  by  brick  walls, 
but  in  front,  at  the  back,  and  at  the  top  by  cast-iron  plates ;  in 
front  also  are  the  charging-doors,  b  b,  and  small  openings,  a  a, 
provided  with  slides  for  regulating  the  access  of  air.  The  furnace- 
bottom  is  divided  by  3-  or  4-inch  iron  bars  into  three  compart- 
ments, corresponding  to  the  doors  and  draught-boles,  which  are 
served  by  turns.  Inside  the  pots  are  visible,  into  which  the  mixture 
of  nitre  and  sulphuric  acid  is  charged.    The  details  of  construction 


272  PRODCCTION  OP  SULPHUK  DIOXIDE. 

are  often  very  different  from  those  shown  in  the  diagram ;  there  are 
humers  with  more  or  fewer  working  eompartments,  with  different 
regolatiou  of  air,  with  rails  over  the  bottom  plates  for  pushing  in 
a  box  instead  of  the  nitre-pots,  &c.  The  nitre-pots  must  receive 
a  very  small  chaise :  otherwise  the  danger  of  boiling  over  is 
considerable,  and  the  sodium  sulphate  among  the  sulphur  is  very- 
troublesome.  When  nitric  acid  is  used  in  the  chambers,  the 
nitre-pots  are  not  required  at  all. 

Sometimes  the  iron  sides  of  the  sulphur  •burners  are  made  double, 
and  an  air-channel  is  left  in  the  space  between.  Thns,  of  course, the 
temperature  of  the  burner  can  be  regulated  to  a  nicety  by  opening 
up  a  draught  through  the  double  iron  wall  when  the  burner  gets 
too  hot,  and  shutting  up  the  draught  when  it  gets  too  cold. 

Fi^.  "lO.  Fig.  1)1. 


The  diagrams  figs.  50  to  53  show  a  set  of  two  burners  free  from 
most  of  the  drawbacks  mentioned.  Fig.  53  is  a  sectional  plan 
taken  at  two  different  levels ;  tig,  52  a  longitudinal  section ;  fig.  50 
half  front  elevation,  half  cross  section  ;  fig.  51  back  elevation. 

a  is  the  cast-iron  bottom  plate  for  burning  the  sulphur;  it  is 
carried  hollow  on  pillars ;  and  the  channels  b  b  formed  thereby 
underneath  the  plate  communicate  with  the  outer  air  by  the  open- 
ing c,  so  that  the  plate  can  be  cooled  from  below.  The  channels, 
d  d,  left  in  the  foundation  a  little  further  below,  communicate  with 


IMPBOVED  BKIUSTONI-BUBNEKI. 


this  system,  aod  ultimately  end  outside  </.  Owing  to  the  differ- 
ence of  level  and  temperature,  the  air  most  always  enter  at  rf'  and 
get  out  at  e;  its  quantity  can  be  easily  regulated  by  partially 
closing  c.     The  door  e  is  hung  in  the  usual  way.     The  gas  of  the 


burner  does  not  go  straight  to  the  chamber,  but  first  ascends 
through  the  opening  /  iuto  a  space  separated  from  the  burner 
proper  by  an  arch.  Just  above  the  opening  there  is  a  grating,  on 
which  the  nitre-pots  are  put,  being  introduced  by  the  door  ff. 

VOL.  I.  T 


274  PRODUCTION  OF  SULPHUR  DIOXIDE. 

There  is  here  a  small  hole  h,  lined  with  an  iron  tube^  for  admit- 
ting a  little  more  air  to  the  upper  compartment  and  burning  any 
sublimed  sulphur.  The  gas  first  returns  to  the  front,  then  back 
again  through  the  hole  t  and  the  second  half  of  the  upper  com. 
partment,  and  at  last  escapes  through  the  cast-iron  pipe  k^  common 
to  two  burners,  whose  upper  stories  are  accordingly  not  built 
alike,  but  are  symmetrical. 

This  burner  (known  to  inyself  from  actual  use)  admits  of 
very  good  regulation;  the  sublimed  sulphur  on  its  long  course 
through  the  upper  story  is  either  deposited  as  such  or  burnt,  and 
cannot  get  into  the  chambers.  The  boiling-over  of  the  nitre-pots 
can  here  be  rendered  harmless  by  simple  contrivances.  This 
burner  is  in  some  points  analogous  to  that  of  Harrison  Blair  (see 
p.  277)^  but  it  is  much  simpler  and  adapted  for  a  smaller  scale  of 
work.  As  a  rule  the  working-doors  are  closed  within  a  very  small 
fraction,  and  the  admission  of  air  to  the  upper  story  is  regulated  by 
more  or  less  closing  the  hole  b.  Four  such  furnaces  work  together ; 
every  half-hour  one  of  them  is  charged  with  ^  cwt.  of  brimstone. 

Fish  (B.  C.  p.  7757, 1891)  makes  the  burner-bed  incline  to  one 
side,  so  that  the  sulphur  can  be  gradually  moved  towards  that  side, 
where  the  ashes  are  raked  out. 

In  order  to  escape  the  drawback  common  to  all  sulphur-burners, 
viz.  the  high  temperature  causing  a  sublimation  of  sulphur  (which 
some  have  tried  to  avoid  by  wetting  the  brimstone  with  water), 
and  even  to  turn  it  to  some  use,  the  cover  of  the  burner  is 
occasionally  employed  for  drying  wet  materials ;  it  has  sometimes 
been  made  in  the  shape  of  a  pan  for  heating  water  or  for  con- 
centrating  acid,  which  is  the  most  rational  plan. 

A  large  brimstone-burner,  covered  in  with  evaporating-pans,  is 
shown  in  figs.  54  to  56.  Fig.  54  is  a  sectional  elevation  on  the 
lines  E  F  G  H  of  fig.  55  ;  fig.  55  is  a  plan  on  lines  A  B  C  D  of 
fig.  54  ;  fig.  56  a  front  view.  These  diagrams,  representing  a 
furnace  at  work  in  America,  have  been  kindly  supplied  by  Dr. 
Karl  F.  Stahl,  of  Johnstown  (Pa.).  Its  bottom,  roof,  and  sides 
are  formed  of  cast-iron  plates,  1  in.  thick,  with  6-in.  flanges  bolted 
together  and  caulked  with  rust-cement.  A  brick  wall,  9  in.  thick, 
is  carried  all  round,  leaving  a  hollow  space  of  2  in.  from  the  plates ; 
a  few  of  the  bricks  near  the  top  and  bottom  are  put  in  loosely,  which 
permits  of  air-cooling  in  very  hot  weather.  The  lead  pans  placed 
on  the  iron  roof  are  3'  6"  x  10'  \0f'  x  7",  the  weight  of  the  lead 


STAHL  S  BKIMSTONE-BUHNEK. 


276  PBUDtlCTION  OF  SUI.PRVR   DIOXIDE. 

beiug  8  to  12  lb.  per  super,  foot.  The  furnace  bottom  consists  of 
five  plates,  as  seen  in  fig.  55  ;  on  each  of  the  three  front  plates 
(3'  6"  X  12')  from  1000  to  1300  lb.  of  brimBtoue  can  be  burnt  in 
24  hour?. 

An  arrangement,  made  by  Kuhlmann,  for  combining  a  steam- 
boiler  with  a  sulphur-burner  (1st  edition  of  this  work,  pp.  139, 
140),  did  not  answer  at  alt,  and  has  been  discontinued. 

All  the  Bulphur-burnere  hitherto  described  are  built  on  the 
intermittent  plan ;  and  unless  a  number  of  them  were  working 
together,  they  would  yield  a  very  unequal  current  of  gas.  As  the 
sulphur  must,  of  course,  be  allowed  to  bum  off  as  completely 

Fig.  r,fi. 


as  possible,  the  furnace  in  the  final  stage,  and  especially  just 
before  being  recharged,  yields  very  little  sulphur  dioxide,  whilst  it 
is  not  possible  to  regulate  the  draught  so  that  exactly  so  much  less 
air  is  introduced  as  less  sulphur  is  burnt.  When  at  last  the  door 
is  opened  for  a  new  chai^,  a  very  large  quantity  of  air  rushes 
into  the  burner  and  further  on  to  the  chambers,  without  any 
sulphur  dioxide  whatsoever.  This  irregularity,  very  prejudicial  to 
the  chamber  process,  is  certainly  to  a  great  extent  neutralized 
by  the  fact  that  always  sevend  furnaces  (three,  four,  five,  or 
more)  work  together  in  such  a  way  that  they  are  charged  in 
turns ;  for  instance,  with  a  four  hours'  shift  and  four  (iirnaces 


CONTINDOUS  BRIM3ION£-BURK£a3.  277 

one  furnace  is  charged  each  hour,  and  thua  gives  out  least  gas 
when  its  ueighboun  are  fully  burning.  It  has,  however,  been 
several  times  attempted  to  construct  really  coTitinuous  burners, 
which  would  save  much  labour,  and,  moreover,  give  a  much 
better-regulated  current  of  gas  than  can  be  obtained  with  single 
burners. 

Two  such  continuous  burners  have  been  constructed  by  Petrie ; 
we  refer  for  diagrams  and  descriptions  to  our  1st  edition,  pp.  141 
and  142. 

Fig.  57. 


The  object  pursued  by  Petrie  is  attained  in  a  more  perfect  way 
by  the  furnace  of  Harrison  Blair,  in  which  the  volatilization  of 
the  sulphur,  which  otherwise  is  a  source  o£  inconvenience,  is 
utilized  to  make  the  burning  coutinuoua.  The  apparatus  consists 
of  three  parts,  one  of  which  serves  for  partly  burning  the  sulphur 
and  entirely  volatilizing  the  unburnt  portion ;  the  second  serves 


278  PRODUCTION  OF  SULPHUR  DIOXIDE. 

for  completely  burning  the  latter  portion,  the  third  for  decom- 
posing the  nitre.     Although  the  two  former  compartments  are 
at  a  full  red-heat  during  the  process,  sublimation  of  sulphur  is  as 
good  as  impossible ;  and  the  process  is  as  nearly  continuous  as 
possible,   since  the  residue  need  only  be  withdrawn  once  in  24 
hours.     Fig.  57  shows  a  plan,  fig.  58  a  sectional  elevation,  of  this 
burner.    A  is  the  space  corresponding  to  an  ordinary  burner- 
plate,  which  has  rather  high  sides  and  a  descent  towards  the  door  ; 
but  2  feet  from  the  door  it  rises  again  a  little,  so  that  the  residue 
raked  to  that  part  can  burn  out  completely  before  it  is  removed 
by  the  door  B,  which  takes  place  once  in  24  hours.     When  this 
has  been  done,  the  residue  raked  together  from  the  other  parts  of 
the  burner  is  brought  to  the  same  place  and  allowed  to  burn  for 
24  hours  again.     The  bottom  of  the  burner  is  not  made  of  iron, 
but  of  closely-set  bricks  with  well-grouted  joints.     This  space  A  is 
9  feet  long,  6  feet  wide,  and  1  foot  high.     The  door  B  is  an  iron 
plate,  loosely  sliding  in  a  frame,  but  a  little  slanting  so  that  it 
closes  almost  air-tight,  and  is  easily  removed.     It  is  perforated  by 
a  number  of  holes,  which  can  be  either  partly  or  entirely  closed 
by  a  slide.     The  brimstone  is  either  put  in  once  every  24  hours 
through  the  working-door,  or  gradually  through  a  funnel  C.     C  is 
continued  by  a  7-inch  cast-iron  pipe  to  within  6  inches  from  the 
bottom  of  the  chamber;  it  is  surrounded  by  a  wider  pipe  to 
protect  it  against  being  burnt  too  quickly.     The  funnel  and  its 
continuation  are  always  filled  with  brimstone ;  and  this  is  con- 
tinually  replaced  as  it  melts  off  at  the  bottom.    The  simpler  method 
of  charging  once  every  24  hours  through  the  door  seems  after  all 
to  have  succeeded  best.     The  admission  of  air  through  B  is  regu- 
lated so  that  only  sufficient  sulphur  is  burnt  for  keeping  up  the 
heat  of  the  furnace ;  the  largest  part  is  simply  evaporated.     At 
the  same  time  the  regulation  of  the  access  of  air  allows  of  spread- 
ing the  process   evenly  over  the  whole  day.     The  walls  of  the 
furnace  are  made  1  ^  brick  thick,  in  order  to  retain  the  heat. 
The  mixed  gas  and  vapours  enters  through  an  opening  of  9  X  9 
inches   (which   can  be  closed  by  a  fire-clay  damper  D)    into 
the  combustion-space  proper,  E  £,  8  x  6  feet,  divided  by  three 
partitions  into  four  compartments,  communicating  alternately  in 
front  and  back  by  openings  9  inches  square.     Here  at  the  same 
time  fresh  air  enters  by  the  opening  F,  which  is  provided  with  a 
damper  of  3  x  8  inches.     Now  sufficient  air  is  admitted  for  burning 


CONTINUOUS  BRIMSTONE-BURNERS.  279 

all  the  sulphur^  which  can  be  recognized  with  certainty  by  the 
fact  that  on  opening  the  plug  G  the  entering  air  does  not  produce 
a  new  flame.  The  roof  of  the  combustion-space^  E^  is  formed  of 
fire-tiles^  above  which  a  second  story,  the  nitre-oven,  is  situated. 
There  are  three  rows  of  nitre-pots,  N,  separated  by  reticulated 
brickwork^  which  also  serves  to  support  another  roof  of  fire-tiles 
for  covering  the  nitre-oven^  altogether  18  inches  high.  The 
diagram  shows  how  the  hot  gas  circulates  round  the  nitre- 
pots.  The  pots  are  renewed  every  six  hours,  so  that  every  two 
hours  another  row  of  pots  has  its  turn.  The  hot  gas,  mixed  with 
the  nitre-gas,  first  passes  underneath  the  cast-iron  dome,  H^  for  a 
partial  cooling,  then  through  an  iron  pipe^  24  feet  high,  into 
a  small  cooling-chamber  18  feet  long,  5  feet  wide,  and  1^  foot 
high  (whose  bottom  and  top  are  covered  with  water)  ^  and  then 
into  the  lead-chambers.  Sometimes  steam  is  admitted  into  the 
combustion-furnace,  which  is  said  to  hasten  the  formation  of  sul- 
phuric acid.  With  a  furnace  of  the  dimensions  stated,  26  tons 
of  brimstone  per  week  are  said  to  have  been  burnt  in  a  per- 
fectly satisfactory  way,  corresponding  to  the  work  of  15  ordinary 
burners ;  by  cutting  off  part  of  the  air  it  was  possible  to  reduce 
the  sulphur  burnt  to  5  or  6  tons  per  week.  For  an  equal  chamber- 
space  much  more  sulphur  can  be  burnt  than  with  ordinary  burners 
without  any  damage  to  the  process,  owing  to  the  even  work  and 
the  avoiding  of  any  excess  of  air.  Indeed  Blair's  burner  is  much 
commended,  and  probably  would  have  been  more  extensively  em- 
ployed, but  that  soon  after  its  invention  most  large  works  (and  only 
such  can  do  with  it)  have  passed  over  from  brimstone  to  pyrites. 

At  the  present  time,  of  course,  nobody  would  think  of  such  a 
way  of  cooling  the  gas  as  is  shown  here  in  the  cast-iron  dome  H. 
We  would  employ  its  heat  in  a  Glover  tower,  or  previously  for 
concentrating  acid.  We  would  also  replace  the  potting  arrange- 
ment shown  in  the  diagram  by  the  more  perfect  arrangements  to 
be  described  later  on  in  connection  with  pyrites-kilns ;  or  we 
would  leave  it  out  altogether,  and  supply  the  chambers  witli 
liquid  nitric  acid  through  the  Glover  tower. 

A  modification  of  the  principle  of  burning  the  subliming  sul- 
phur by  introducing  air  behind  the  burner  was  patented  by 
H.  Glover  (No.  3774,  1879).  He  arranges  behind  the  burner  a 
chamber,  loosely  packed  with  bricks,  in  which  the  vaporized 
sulphur  deposits  before  it  can  get  into  the  lead-chambers.     This 


280  PRODUCTION  OF  SULPHUR  DIOXIDE. 

brick  chamber,  when  it  is  partially  filled  with  sublimed  sulphur, 
is  burned  out  by  admitting  air  into  it.  The  heat  is  utilized  for 
concentrating  acid,  and  the  gases  are  eventually  passed  into  a 
Glover  tower,  where  they  do  all  the  necessary  denitrating  work. 
This  system  is  at  work  at  a  Philadelphia  factory,  and  gives  entire 
satisfaction,  as  observed  by  myself,  no  repairs  having  been  required 
after  the  lapse  of  five  years. 

This  arrangement  is  shown  in  fig.  59.  A  is  the  usual  burner- 
plate,  B  the  feeding-apparatus  (on  the  same  principle  as  used  in 
Blair's  burner)  ;  the  burner-gases,  with  the  subliming  sulphur, 
pass  into  the  chamber  C,  where  they  meet  air  entering  through  the 
pipes  F,  either  cold  or  previously  heated  by  waste  heat.  The 
mixture  further  passes  through  chamber  D,  containing  a  network 
of  fire-bricks  like  that  used  in  a  Siemens'  recuperator  ;  the  mix- 
ture and  combustion  here  become  perfect,  and  the  gases,  now 
entirely  deprived  of  free  sulphur,  pass  away  through  H  and  the 
flue  IK.  On  their  way  a  platinum  dish,  E,  for  concentrating  sul- 
phuric acid,  is  placed  on  the  top  of  chamber  D,  and  further  (leaden) 
pans,  J  and  G,  are  employed  for  a  first  heating  of  the  acid.  From 
here  the  acid  gas  passes  into  a  Glover  tower,  where  it  is  still  hot 
enough  to  concentrate  all  the  Gay-Lussac  acid  (equal  to  1^  times 
the  daily  make  of  the  chambers)  up  to  150°  Tw.,  and  impart  to  it 
a  temperature  of  127°  to  132°  C.  The  lead  pans  G  J  and  platinum 
dish  E  produce  daily  9000  lb.  of  acid  of  91  or  92  per  cent.  HjSO^ 
from  chamber-acid  of  about  123°  Tw. ;  that  is,  two-thirds  of  the 
acid  made  from  the  4000  lb.  of  brimstone  burnt  on  plate  A. 
Since  this  acid  is  taken  directly  from  the  chambers  (the  Glover- 
tower  acid  being  used  exclusively  in  the  Gay-Lussac  tower),  and 
since  the  concentration  is  not  driven  to  a  higher  point  than  92 
per  cent.,  the  platinum  dish  never  requires  any  cleaning  out  of 
iron  salts  &c. 

Another  sulphur-burner,  on  the  principle  of  continuously  sup- 
plying liquid  sulphur,  is  that  employed  at  the  works  of  M.  de 
Hemptinne,  at  Brussels,  and  shown  in  figs.  60  and  61  (taken 
from  the  '  Bulletin  du  Musee  de  ^Industrie  de  Belgique,'  January 
1882,  sent  to  me  by  the  Author).  It  consists  of  a  cast-iron  arch 
A,  strengthened  by  bracings,  and  resting  on  a  large  flanged 
wrought-iron  plate  with  flat  rivets  which  can  be  heated  or  cooled 
by  flues  underneath.  On  this  plate  there  are  placed,  side  by  side 
and  as  level  as  possible,  four  cast-iron  plates  with  3-inch  upright 


H.  olotbb's  beihstons>burner. 


PftODttCTION  OF  SULPaVK  DIOXIDE. 


BRIM8TONE-BUANERS  FOR  WOOD-PULP  WORKS.  283 

flanges^  intended  for  burning  the  sulphur,  which  is  supplied  by 
four  spouts  from  a  cast-iron  box  C,  divided  into  four  compartments 
and  built  into  the  front  wall^  as  shown  in  the  diagram.  Perpen- 
dicular partitions  D  serve  as  lutes  for  preventing  the  burner-gas 
from  blowing  out  in  front ;  if  the  combustion  should  spread  to 
the  fronts  a  cover  (not  shown  here)  would  at  once  put  out  the 
flame.  Thus  the  supply  of  sulphur  takes  place  regularly ;  the  four 
hinged  doors  a  a  in  front  serve  merely  for  the  entrance  of  the  air 
and  for  clearing  out  the  cinders.  The  arch  A  consists  of  ten 
pieces  bolted  together ;  it  is  covered  by  light  sheet-iron  shutters, 
E  E,  bent  to  the  same  shape  and  covered  with  a  mixture  of  loam 
and  straw,  which  can  bs  raised  or  lowered  by  a  chain,  pulleys, 
and  counterpoises.  This  admits  of  regulating  the  heat  of  the 
chamber ;  if  it  rises  too  much,  one  or  more  of  the  shutters  E  E 
are  raised.  An  alarum  thermometer,  I,  in  a  copper  tube,  indicates 
the  temperature.  The  gases  escape  through  the  metal  pipe  F, 
resting  on  a  thick-walled  cast-iron  box  G,  from  which  the  deposit 
formed  can  be  withdrawn  through  J.  Throujgh  H  an  extra  supply 
of  air  can  be  let  into  the  tube  F.  [This  arrangement  for  supple- 
mentary combustion  is  decidedly  imperfect.] 

For  producing  cold  and  dry  sulphur  dioxide,  free  from  sulphuric 
acid,  such  as  is  specially  useful  for  preparing  liquors  for  manu- 
facturing wood-pulp^  N^methy  (G.  P.  No.  48285)  recommends  the 
combination  of  a  sulphur-burner,  cooled  from  the  outside  by 
water  running  down  the  sides,  with  a  chamber,  placed  underneath, 
filled  with  iron  borings,  in  which  the  sulphuric  acid  is  retained. 
From  here  the  gas  passes  through  a  number  of  flat,  perpendicular, 
iron  boxes,  cooled  by  water  running  down  their  sides,  and  then 
into  the  apparatus,  where  it  is  to  be  absorbed  by  milk  of  lime,  &c. 

W.  Maynard  (patented  as  a  communication  to  A.  M.  Clark, 
No.  6982,  1884)  draws  the  gas  out  of  the  chamber  where  it  is 
generated  (by  burning  sulphur  in  cups)  by  means  of  a  goose-neck 
pipe  leading  from  the  top  of  the  chamber  to  a  closed  box  provided 
with  a  funnel  delivering  into  another  box  below.  Water  is 
discharged  by  a  pipe  into  this  funnel,  which  has  grooved  sides, 
so  that  the  liquor  running  round  as  well  as  downwards  forms  a 
vortex,  and  draws  away  the  vapours  generated  in  the  burning- 
chamber.  This  arrangement  is  evidently  not  intended  for  sul- 
phuric-acid making,  but  for  preparing  a  solution  of  sulphurous 
acid. 


PRODUCTION  OF  BOLTBDB  PIOXIDK. 
Fig.  6-2. 


BRIMSTONE-BURNERS  FOR  WOOD-PULP  WORKS^  ETC.  285 

The  following  arrangement^  by  Korting  Brothers^  serves  for 
preparing  comparatively  small  quantities  of  sulphur  dioxide  from 
sulphur,  for  bleaching,  in  the  manufacture  of  glue,  for  saturating 
the  liquors  in  sugar-works,  and  the  like.  It  is  also  used  in  wood* 
pulp  works.  A  (figs.  62  and  63)  is  a  cast-iron  retort  provided  with 
a  perforated  dish  a,  in  which  the  sulphur  is  placed-  B  is  a 
Korting^s  injector,  made  of  regulus  metal  (5  lead,  1  antimony), 
which,  by  means  of  a  steam-jet,  aspirates  air  through  the  holes  £6 
into  A  and  causes  the  sulphur  to  burn.  The  vapours  are  forced 
downwards  in  the  inner  tube  of  the  cast-iron  cooler  C,  whilst  cold 
water  flows  in  the  annular  space  between  the  two  tubes,  entering 
at  the  bottom  and  running  out  at  the  top.  The  box  D,  on  which 
the  cooler  is  mounted,  serves  for  retaining  any  sublimed  sulphur 
and  other  impurities.  From  here  a  tube  leads  the  purified  SO2  to 
the  place  where  it  is  to  be  utilized. 

The  N^methy  burners,  Korting  burners,  and  others,  are 
especially  used  in  Germany  and  Austria  for  the  manufacture  of 
bisulphite  of  lime,  to  be  employed  in  the  manufacture  of  paper- 
pulp  (called  ^'  cellulose  ")  from  wood.  A  number  of  other  burners 
serving  for  this  purpose  are  described  in  the  ^  Papier-Zeitung ' 
for  1894,  pp.  1478  &  1830. 

In  Germany,  in  1900,  33  paper-works  made  sulphite  cellulose 
by  means  of  brimstone,  of  which  they  consumed  15,000  tons 
against  33  works  employing  70,000  tons  pyrites.  Both  together 
made  by  this  process  350,000  tons  wood-pulp. 

The  following  analysis  of  the  residue  from  the  sulphurs-burners 
has  been  made  by  Richardson  (Richardson  and  Watts, '  Chemical 
Technology,^  vol.  i.  pt.  v.  p.  198)  : — 

Sodium  sulphate  *    13*77 

Calcium  sulphate  t  28*49 

Calcium  silicate  t 15*91 

Sodium  silicate 1*10 

Ferric  oxide  and  alumina    . . .  2*80 

Water  and  sulphuric  acid*...  13*05 

Insoluble  24-29 


99-41 


*  The  fiodium  sulphate  and  the  free  sulphuric  acid  (or  rather  the  acid  sul- 
phate) evidently  come  from  the  nitre-pots  boiling  over, 
t  The  lime  no  doubt  partly  comes  from  the  brickwork  of  the  furnace. 


286  PRODUCTION  OF  SULPHUR  DIOXIDE. 

A  special  cooling  of  the  gas  from  sulphur-burners  for  manu- 
facturing sulphuric  acid  (as  distinct  from  that  of  bisulphite  of  lime) 
is^  as  a  rule;  not  only  unnecessary^  but  even  injurious ;  so  that,  for 
instance^  in  the  furnace  shown  in  figs.  50  to  53  the  vertical  metal 
pipe  conveying  the  gas  to  the  chamber  had  to  be  protected  against 
cooling  by  a  brick  jacket.  Even  where  no  cooling  takes  place  by 
water-pans^  steam-boilers^  &c.^  the  gas  gets  into  the  draught-pipe 
sometimes  at  only  about  100°  or  120°  G.  temperature^  which  is  just 
sufficient  not  to  allow  the  nitric  acid  to  condense  before  it  gets 
into  the  chambers^  a  contingency  decidedly  to  be  avoided.  Where 
water-tanks,  acid-pans^  &c.  are  used,  the  temperature  of  the  gas 
is  said  to  come  down  as  low  as  40°  C. ;  in  this  case  only  liquid 
nitric  acid  can  be  used  for  the  chambers.  In  Blair^s  or 
Glover's  continuous  burner  the  temperature  certainly  rises  much 
higher;  and  in  this  case  a  cooling-arrangement^  such  as  that 
described,  was  formerly  thought  indispensable,  before  means  had 
been  found  of  utilizing  the  heat  of  the  gases  in  a  Glover  tower  or 
otherwise. 


B.  The  Production  op  Sulphur  Dioxide  from  Pyrites. 

1.  Breaking  the  Pyrites. 

The  pyrites,  as  it  comes  into  the  market,  is  always  sufficiently 
pure  to  make  a  separation  from  gangue  unnecessary,  except  in 
the  case  of  pyrites  picked  from  coals  (^^  coal-brasses,''  p.  41) ;  but 
this  is  only  a  locally-used  by-product. 

It  is,  however,  always  necessary  to  break  up  the  larger  lumps  in 
order  to  bum  the  pyrites  completely  ;  and  this  is  always  done  at 
the  works  themselves — except  in  a  few  cases,  where  they  buy  smalls 
direct  from  the  mines.  The  majority  of  the  factories  break  the 
ore  by  hand;  and  it  is  found  that  various  descriptions  of  ore 
behave  very  differently  in  that  respect.  The  Norwegian  ore  is  the 
hardest ;  here  the  large  lumps  have  to  be  broken  with  great  labour 
by  means  of  20-lb.  fore-hammers.  The  Westphalian  ore  is  much 
more  easily  broken — still  more  easily  the  Spanish  aftd  Portuguese 
and  some  of  the  French  ores ;  these,  however,  make  a  good  deal 
more  smalls,  10  per  cent,  and  more.  The  softest  ore  is  that  from 
Chessy,  consisting  of  loosely  aggregated  individual  crystals,  which 


BREAKING  THE  PYRITES.  287 

by  a  blow  of  the  hammer  fall  to  powder.  Some  of  the  Spanish 
ores  are  equally  roughly  crystallized ;  these  ores  are  very  trouble- 
some for  use  as  lumps. 

In  England  the  ore  is  generally  broken  so  that  all  the  pieces 
pass  through  a  sieve  with  3-inch  holes.  On  the  other  hand^  as 
few  smalls  as  possible  are  made.  The  broken  ore  must  be  sifted 
again  to  separate  the  smalls^  for  which  purpose  some  works  pass  it 
through  a  half-inch^  others  through  a  quarter-inch  riddle.  What 
remains  on  the  riddle  is  lumps ;  what  passes  through,  smalls ^  fines, 
or  dust.  Each  of  them  has  to  be  treated  separately.  It  is  very 
important  that  the  ore  be  used  neither  in  too  large  nor  in  too  small 
pieces.  In  the  former  case  it  does  not  burn  right  through  ; 
there  remain  green  cores  in  the  interior  of  the  cinders,  which 
can  be  seen  on  breaking  them  up.  These  large  lumps  also  get 
too  hot  on  burning,  and  may  cause  the  formation  of  slags  (scars) 
by  production  of  FeS,  as  will  be  subsequently  explained.  If,  on 
the  other  hand^  the  pieces  are  too  small,  they  prevent  too  much 
the  access  of  air,  and  similar  results  follow  in  this  as  in  the 
former  case. 

It  is  quite  obvious  that  the  pyrites-burners  can  be  worked  to 
full  advantage  only  if  the  ore  is  in  pieces  of  as  uniform  size  as 
possible,  and  it  would  hence  be  the  best  plan,  although  it  is  hardly 
practicable  in  reality,  to  separate  the  broken  ore  into  a  number  of 
sizes,  to  be  burnt  in  separate  kilns.  At  Oker  formerly  the  ore 
was  broken  to  walnut  size  for  the  grate-burners  as  shown  later  on. 
For  deep  kilns,  as  now  altogether  used  there,  the  ore  is  broken  into 
pieces  of  2^  inches  side.  The  fines,  sifted  through  ^-inch  sieves, 
are  burned  in  a  Rhenania  blende  furnace  (comp.  later  on). 

Owing  to  the  great  manual  labour  required  for  the  breaking  of 
pyrites,  the  same  mechanical  stone-breakers  have  been  introduced 
for  this  purpose  which  originally  were  made  for  road-metal.  One 
of  these  machines  is  that  of  Blake,  built  by  Messrs.  Marsden  of 
Leeds,  which  is  shown  in  figs.  64  and  65,  This  machine  is  made 
of  various  sizes,  and  accordingly  varies  in  the  amount  of  work 
turned  out  and  in  the  size  of  stones  it  can  attack.  A  and  B  are  the 
two  active  parts,  the  ^^jaws.^'  A  is  fast  and  perpendicular,  B 
movable,  and  makes  with  A  an  angle  of  72^,  by  oscillating  a  little 
round  the  fixed  shaft  D.  This  movement  is  communicated  to  the 
jaw  B  from  the  main  shaft,  H,  by  means  of  the  angle-lever,  EE', 
and  the  crank  motion,  6  H,  so  that  the  angle-lever  presses  the  jaw 


FRODtlCTION  OF  SULPHUR  BIOXIDE. 


MKCHANICAL  STONE-DREAKERS. 


B  against  the  atones  Rharged^  the  return  motion  of  B  being  caused 
by  a.  spring,  F,  cased  in  india-rubber.  The  angle-lever  is  adjust- 
able by  the  wedge,  N,  lying  behind  its  arm  E'.  The  rollerj  C, 
causes  the  broken  stones  to  be  regularly  ejected ;  it  receives  its 
motion  by  a  belt  from  the  main  shaft,  by  means  of  the  pulleys, 
Kj  L,  and  the  expandiug  roller,  M.  The  crank-shaft,  H,  is  also 
driven  by  a  belt  from  the  fast  and  loose  pulleys,  1 1'.  The  machine 
is  mounted  on  a  four-wheeled  bogie.  It  makes  a  great  deal  of 
noise  and  needs  frequent  repairs ;  but  the  jaws,  which  principally 
suffer,  are  so  arranged  as  to  be  easily  replaced. 

Blake's  engine  has   been  improved  by  Broadbent  &  Son,  of 

rig.  (HI. 


Staleybridge,  who  have  replaced  the  spring  bedded  in  india-rubber 
by  a  simple,  easily-adjustable  lever  arrangement,  which  saves 
labour  as  compared  with  the  original  contrivance.  Output,  accord- 
ing to  size,  from  40  to  130  tons  in  teu  hours ;  price  £140  to  £375. 

At  Oker,  a  steam-engine  of  12  horse-power  drives  two  stone- 
breakers,  mounted  one  above  the  other.  The  higher  one  breaks 
the  large  stones  roughly,  the  lower  one  down  to  the  proper  size. 
They  supply,  in  the  case  of  very  hard  ore,  of  2J  inches,  60  tons, 
with  milder  ore,  72  tons  per  shift  of  ten  hours. 

A  crushing-mill  was  invented  by  Jfotte,  at  Dampreny,  near 


290  PRODUCTION  OP  BULPBUB  DIOXIDE. 

Charleroi,  which  has  been  improved  by  the  Mftrkische  Maaehinen 
Pabrik  (G.  P.,  October  16th,  1877;  'Dingler's  Journal/  ccxxvii. 
p.  58).  The  principle  is  that  of  a  peculiar  kind  of  mortar,  vith 
hollow  bottom,  in  which  the  crushing  is  done  by  a  pestle,  as  seen 
in  fig.  66.  Whether  this  mill  is  really  preferable  to  the  older 
stone-breaking  machines  experience  will  show. 


Durand  and  Chaptal's  etone-brcaker  consists  of  a  number  of 
hammers  attached  to  a  horizontal  revolving  shaft.  It  is  said  to 
make  less  dust  than  other  atone-breakers.  The  smallest  apparatus 
breaks  from  8  to  25  tons  o£  stone  in  10  hours,  with  an  expenditure 
of  2  or  3  horse-power,  the  larger  size  from  80  to  130  tons,  with 
6  horse -power. 

Vapart's  breaking-mill  (address,  "Chinee,  Vieille  Montagne") 
works  centrifugally, 

The  Humboldt  Engineering  Company  at  Cologne  (Germ.  Pat. 
1906,  Jan.  12,  1878)  manufacture  stone-breakers  which  do  twice 


PYRITES-BURXEKS  FOR  LUMP9.  291 

« 

the  work  of  those  formerly  in  use,  with  the  expenditure  of  the 
same  force. 

Other  improvements  in  stone-breakers  have  been  invented  by 
Brown  ('  Scientific  Americau/  1879,  p.  194)  and  Welter  (Qerman 
Patent,  No.  7494,  March  5,  1879). 

A  machine  very  much  recommended  is  Breuer's  '*  Sectorator '' 
(G.  P.  30477),  supplied  by  Ernst  Maetz,  Berlin,  S.W.  As  shown 
in  fig.  67,  it  contains  a  straight  breaking-jaw,  a,  firmly  connected 
with  the  solid  frame,  whilst  the  movable  jaw,  &,  is  suspended  in 
two  steel  trunnions,  and  is  partially  revolved  against  the  jaw  a, 
thus  crushing  the  material.  Tlie  angle  between  the  two  jaws  is 
rather  acute,  so  that  large  pieces  are  easily  caught  apd  carried 
forwards  towards  the  bottom  slit.  If  both  jaws  were  arched,  the 
material,  especially  large  pieces,  would  be  able  to  escape  upwards 
for  a  long  time,  until  gradually  broken  up.  The  width  of  the 
bottom  slit  is  adjustable  by  a  wedge  even  during  work,  so  that 
any  size  can  be  obtained.  The  plate  c  behind  the  excentric  sheave, 
which  is  easily  exchanged,  is  of  cast-iron  and  of  a  smaller  section 
than  any  other  part  of  the  machine  subjected  to  a  breaking-strain, 
so  that  in  case  of  excessive  strain  by  the  passage  of  a  foreign  body 
(iron,  &c.),  that  plate  must  give  way  before  any  other  part  of  the 
machine. 

Even  at  some  large  works  they  prefer  dispensing  with  mechani- 
cal stone-breakers,  principally  for  two  reasons.  The  first  of  these 
is  that  they  make  more  dust  than  breaking  by  hand ;  but  since 
dust  is  now  even  more  profitably  burnt  than  pieces,  this  reason  is 
no  longer  valid.  The  other  reason  is,  that  at  large  works  there 
is  always  a  certain  number  of  men  who  are  incapacitated  for  other 
work,  or  who  are  temporarily  unoccupied,  and  these  are  best  set 
to  stone-breaking. 

2.  Pyrites-burners  for  Lumps. 

Among  the  apparatus  for  burning  pyrites  in  the  manufacture  of 
sulphuric  acid,  a  distinction  has  to  be  made  between  those  intended 
for  lumps  and  those  intended  for  smalls.  It  is  indispensable  to 
keep  both  kinds  apart,  and  to  employ  dificrent  apparatus,  or  at  least 
processes,  for  them ;  for  if  the  broken  ore  is  put  into  the  burner 
without  separating  the  smalls,  the  air-channels,  which  ought  to 
remain  between  the  pieces,  are  soon  partly  stopped  up  with  powder. 


292  PRODUCTION  OF  SULPHUR  DIOXIDE. 

and  the  access  of  air  becomes  irregular;  thus  scars  are  formed 
and  proper  iirork  is  then  impossible.  Apart  from  the  coarser  and 
finer  powder  obtained  on  breaking,  a  great  deal  of  smalls  comes 
into  the  trade  direct  from  the  mines^  obtained  there  by  the  use  of 
water  for  separating  the  ore  from  the  gangue. 

Where  cupreous  pyrites  is  roasted  without  any  regard  to  the 
utilization  of  the  sulphur,  the  only  object  being  the  extraction  of 
the  copper,  usually  no  regular  kilns  are  employed  at  all,  but  the 
ore  is  burnt  in  '^  heaps/^  This  is  done  on  an  enormous  scale  in 
the  south  of  Spain ;  but  the  damage  to  health  and  vegetation  has 
been  so  great  that  a  law  has  been  passed  compelling  manufac^ 
turers  to  abate  this  nuisance.  In  order  to  avoid  the  necessity 
of  building  the  very  large  number  of  closed  kilns  which  would 
be  required  for  that  purpose,  various  proposals  have  been  made. 
We  quote  that  of  Fleming  (E.  P.  10153,  1887).  Above  the 
roasting-heap,  and  extending  downward  over  the  whole  portion 
(about  one-third)  which  emits  the  fumes,  is  suspended  an  iron 
hood,  lined  with  tar  and  painted  outside  with  a  non-conducting 
material.  The  hood  is  supported  by  chains  from  two  pairs  ot 
shear-legs,  and  the  whole  is  strengthened  by  iron  stays.  At  one 
end  of  the  hood  is  a  pipe,  by  which  the  roaster  gases  are  led  to 
condensing-flues,  to  separate  arsenious  acid,  and  thence  into  vitriol- 
chambers.  If  the  gases  have  excess  of  air,  they  are  led  through 
calcining-furnaces  ;  if  insufficient,  more  can  be  supplied  by  regu- 
lating-dampers in  the  flues.  [Apart  from  all  other  objections  to 
this  process,  the  "  iron  hood  lined  with  tar "  is  sure  to  be  not 
very  durable.] 

The  burning  of  pyrites  in  lumps  (pieces)  for  the  manufacture  of 
sulphuric  acid  is  always  done  in  such  a  way  that  the  combustion 
heat  of  the  pyrites  is  utilized  for  maintaining  the  process  without 
employing  any  extraneous  fuel.  The  apparatus  used  for  this  purpose 
are  called  "kilns"  or  "burners.'^  In  the  first  edition  of  this 
work  (pp.  151-154)  there  will  be  found  a  description  of  the  old 
and  now  abandoned  kinds  of  kilns,  with  many  diagrams — as  the 
burner  originally  employed  by  Farmer,  the  first  shape  of  tall  kilns 
without  grates,  the  Oker  kilns  for  roasting  the  Bammelsberg  ores. 
These  kilns  (except  Farmer's)  are  constructed  without  grates ;  they 
are  still  used  for  roasting  poor  ores,  lead-matte,  &c.  In  the 
same  edition  there  is  a  description  of  the  Belgian  hearth-furnaces 


MODERN  FREIBERG  KILNS. 


and  of  the  Marseilles  furnaces,  both  of  them  very  faulty  and  quite 
antiquated  (pp.  157  &  158).  This  also  holds  good  of  the  yarious 
descriptions  and  illustrations  of  "  Freiberg  kilns,"  still  given  in  our 
second  edition  (pp.  214^318).      Instead  of  these,  I  am  enabled, 


through  the  kindness  of  the  respective  authorities,  to  show  the  kilns 
used  at  the  present  day  (1902)  at  Freiberg  and  at  Oker,  at  the 
Government  vrorks  carried  on  at  those  localities. 


PRODUCTION  OF  SULPHUR  DIOXIDE. 

Tig.oa. 


MODERN  VREIBERO  KILNS.  295 

For  poor  ores  and  intermediate  products  which  must  be  treated 
at  metallurgical  works  (pp.  81  et  seq.)  furnaces  are  required  of  a 
different  kind  from  the  grate-burners  now  uniTersally  employed 
for  good  pyrites  in  lumps.  The  style  of  kilns  now  used  at  the 
Muldenhiitten  near  Freiberg  is  shown  in  figs.  -68,  69^  70.  They 
serve  for  poor  iron-pyrites  containing  blende  and  arsenical  pyrites^ 
as  well  as  for  lead-  and  copper-matte. 

The  grate  formerly  employed  at  Freiberg  has  been  replaced 
by  slanting  cast-iron  plates^  ff.  The  air  do^  liot  now  enter 
through  special  channels^  but  through  the  discharging  and  working 
holes,  a  shows  the  charging  hopper^  b  the  channel  through  which 
the  charge  gets  into  the  kiln^  c  the  erit  channel  for  the  roasting 
gases^  d  openings  for  spreading  out  the  charge,  e  working-holes^ 
f  discharging-holes.  Each  kiln  roasts  about  25  cwt.  of  pyrites 
per  24  hours ;  5  kilns  are  combined  in  a  set.  The  sulphur  is 
roasted  off  to  4  or  5  per  cent,  in  the  cinders. 

For  richer  and  purer  pyrites,  at  Freiberg  grate-burners  are 
employed  consisting  of  three  kilns,  with  25  square  feet  grate  sur- 
face each,  and  a  distance  of  4  feet  from  th^  movable  grates  to  the 
crown  of  the  arch.  Each  set  roasts  about  86  cwt.  pyrites  per 
24  hours  down  to  2  or  3  per  cent.  S. 

The  kilns  now  used  (1902)  at  Oker  are  exactly  like  the  Freiberg 
kilns  just  described.  They  are  of  two  different  sizes — deeper 
kilns  (with  a  layer  of  ore  9  ft.  deep)  serve  for  the  poorer  ores, 
shallower  kilns  (the  ore  lying  6  feet  deep)  for  the  richer  ores 
(described  p.  83).  The  English  grate-burners,  formerly  employed 
at  Oker,  have  not  been  found  suitable  for  this  class  of  ores. 

Kilns  of  the  just-described  kind  have  been  found  indispensable 
for  roasting  poor  ores,  matte,  &c.,  where  the  sulphuric  acid  is  a 
by-product  and  where  the  heat  generated  in  the  process  is  less 
than  when  roasting  ordinary  pyrites,  containing  at  least  40  per 
cent,  sulphur,  usually  a  good  deal  more,  such  as  is  now  universally 
employed  for  the  manufacture  of  sulphuric  acid  as  a  principal 
product.  For  such  richer  ores  the  kilns  or  burners  ought  always 
'  to  be  constructed  with  grates  and  ash-pits.  This  causes  a  con- 
siderable improvement  in  the  working  of  the  furnaces.  Where 
the  air  has  merely  to  pass  through  a  mass  of  burnt  ore,  its 
quantity  cannot  possibly  be  regulated  at  the  inlet,  but  only  by 
dampers  at  the  other  end  of  the  furnace.  It  is  even  a  more  serious 
disadvantage  that  in  this  case  the  subdivision  of  the  air  inside  the 


396  PRODUCTION  OF  SULPHUR  DIOXIDE. 

burner  must  be  very  irregular.  According  to  the  greater  or  smaller 
■  I'esistauce  offered  fay  the  individual  portions  of  the  layer  of  pyrites, 
the  air  vill  pass  through  Tery  unequally,  and  in  less  quantity 
at  the  places  where  most  pyrites  is  lying  and  where  it  is  most 
required.  The  addition  of  a  grate  and  a  closed  ash-pit  alters 
the  state  of  the  case  at  once,  in  this  way,  that  only  a  definite 
quantity  of  air  need  be  admitted  into  the  ash-pit,  and  that,  more- 
over, this  air  must  first  spread  equally  uudenieath  the  grate  and 
rise  all  over  the  area  of  the  burner.  Thus  the  ore  is  much  more 
completely  burnt,  and  at  the  same  time  richer  gas  is  obtained, 
which  leads  to  a  better  chamber-process,  higher  yield  of  acid,  and 
smaller  consumption  of  nitre ;  the  operation  of  drawing  out  the 
burnt  ore  becomes  much  more  regular  and  oders  a  greater  guarantee 
against  raw  ore  getting  into  it  ;  lastly,  it  does  not  happen  so 
often  that  fused  masses  ("scars")  are  formed  in  the  burner, 
although  also  in  the  case  of  grates  this  easily  happens  if  the 
method  of  working  ie  faulty. 

The  introduction  of  grates  led  to  further  improvements — to 
begin  with,  a  diminutipn  of  the  height  of  the  burners,  which  made 
them  much  handier  for  working,  and  wbicb  acted  especially  well 
with  more  easily  fusible  ores,  although  in  some  places  the  other 
extreme  of  too  low  layers  o£  pyrites  has  been  resorted  to. 

Fig.  n. 


The  different  kinds  of  grate-burners  which  were  introduced  into 
England  about  1860,  and  have  been  employed  up  to  this  day  both 
there  and  in  many  factories  abroad,  are  shown  in  figs.  71—75. 


ENGLISH  ORATB-BU&NEBS. 


Figs.  71,  72,  73  show  a  somewhat  simple  eoastructioa,  which 
cao  t>e  made  with  open  sand-castiogs ;  figs.  74  and  75  a  more 
expensive  kind  of  front  plates^  requiring  planing,  turning,  &c. :  the 


latter  are  much  neater  and  cleaner,  because  no  putty  is  required 
for  the  doors.  Sometimes  these  front  plates  undoubtedly  become 
8  little  warped,  and  then  the  doors  are  not  tight  without  putty. 

Fig.  71  shows  two  burners  in  front  elevation  and  one  in  section, 
the  first  burner  without  doors.     Fig.  73  is  a  cross  section,  showing 

Fig.  73. 


two  rows  back  to  back;  fig.  73  a  sectional  plan,  half  taken  just 
over  the  grate,  half  through  the  middle  of  a  door,  a  is  the  working- 
opening,  with  the  door  b,  which^slides  in  the  grooved  ledges,  c  c. 


298  PRODUCTION  OF  STTLPnUR  DIOXIDE. 

cast  to  the  front  plate.  The  small  door  d,  only  to  be  used  excep- 
tionally, is  arranged  in  precisely  the  same  way.  The  openings  of 
the  brickwork  inside  are  protected  by  small  metal  plates ;  e  is  the 
movable  cover  of  the  ash-pit,  provided  with  air-boles ;  //  are  the 
grate>bearers ;  the  front  bearer  /,  at  the  same  time  carries  the 
bottom  plate  for  the  front  wall,  and  is  perforated  with  round  holes  ; 
while  //are  cut  out  in  semicircles.  The  arches  are  sprung  parallel 
with  the  working- doors,  and,  by  the  draught-holes  g  g,  are  in 
connection  with  the  gas-flues,  A  h.  The  latter,  like  the  burners, 
are  cased  in  metal  plates ;  they  are  covered  with  fire-tiles. 

Fig.  74. 


A  somewhat  more  costly  but  more  perfect  arrangement  is  shown 
in  figs.  74  and  75,  in  front  elevation  and  two  sectional  elevations. 
a  is  the  working-door,  with  the  small  slide  b  for  observing  the  in- 
terior of  the  burner;  it  turns  on  hinges,  and,  as  shown  in  fig.  75, 
lies  on  a  projection  of  the  front  plate,  slanting  forward  towards  the 
bottom ;  all  the  metal  parts  coming  into  contact  are  planed  and 
faced,  so  as  to  close  air-tight.  The  doors  c  c  for  the  grate  aud  d 
for  the  asb-pit  are  constructed  in  the  same  way,  whilst  the  rarely 
ased  doors  e  and/  (the  latter  for  the  gas-fiue)  are  made  in  the 
simple  manner  shown  in  fig.  71.  The  burners  are  supposed  to 
be  the  last  of  the  row ;  so  that  the  nitre-oven  g,  with  the  semi- 
cylindrical  trough  h,  the  saucer  t,  and  the  hopper  k  are  immediately 
joined  to  them.    The  diagrams  are  all  on  a  scale  of  1  to  50. 


ENGLISH  FYKITES-BI'B.MERS,  299 

Euglislt  pjiites-bumers  geaerallf  have  a  moderate  area  of 
gratca,  about  4  or  5  feet  wide,  and  4^  to  6  Eeet  from  f roDt  to  back. 
The  inner  walls  sometimes  rise  quite  perpeudicnlarly ;  more 
frequently  the  two  sides  and  the  back  slant  a  little  outwards,  up 
to  the  level  of  the  working-door,  to  the  extent  of  about  9  inches, 
sometimes  only  6  inches,  in  width,  and  half  as  inacb  in  the  back  ; 
from  that  level  the  walls  rise  again  perpendicularly  up  to  the  roof. 
The  front  wall,  which  is  only  9  inches  thick,  and  mostly  protected 
by  a  1-incb  or  l^-inch  metal  plate,  rises  perpendicularly,  and  is  per- 
forated with  several  working-holes.  The  ash-pit  has  either  vertical 
sides  or,  more  rarely,  sides  converging  towards  the  bottom,  in 
order  to  facilitate  the  removal  of  the  cinders.      Its  depth  varies 


from  16  to  24  inches.  The  level  of  the  working-doors,  which 
determines  the  depth  of  the  layer  of  pyrites,  varies  from  1  foot 
8  inches  to  2  feet  6  inches ;  but  the  former  depth  is  considered 
by  most  English  acid-makers  too  little,  at  any  rate  for  average 
ores,  and  they  prefer  a  depth  of  between  2  feet  and  2  feet 
4  inches,  but  nearer  the  higher  than  the  lower  limit.  In 
(iermany,  the  depth  of  ore  is  only  1  foot  6  inches,  even 
down  to  1  foot  4  inches  (comp.  p.  305).  The  reason  for  this  is 
the  fear  of  scarring,  which  English  experience  with  the  same  ores 
proves  to  be  unfounded.  The  height  from  the  upper  level  of  the 
ore  to  the  abutment  of  the  arch  is  usually  about  equal  to  that 
of  the  working-door,  say  9^  to  12  inches,  and  from  there  up  to 
the  crown  of  the  arch  another  8  or  9  inches.  The  arch  itself  is 
either  sprung  from  side  to  side,  as  is  the  custom  on  the  Tyne 


300  PRODUCTION  OF  SULPHUR  DIOXIDE. 

(whereby  the  walls  are  made  to  bear  the  weight  more  equally  and 
the  working  through  the  doors  is  facilitated)^  or,  as  is  usual  in 
Lancashire,  from  front  to  back  (which  is  more  advisable  in  the 
case  of  two  rows  of  burners  being  built  back  to  back,  in  which  case 
the  arch  is  sprung  over  both  burners  together,  with  a  supporting 
wall  in  the  centre).  In  any  case  it  is  advisable  to  build  the 
burners  back  to  back,  even  with  arches  sprung  from  side  to  side, 
wherever  it  is  locally  possible ;  thus  one  back  wall  is  saved,  the 
heat  is  kept  up  better^  and  a  common  gas-flue  can  be  employed. 

The  gaS'fiue  of  the  English  burners  is  always  at  the  top,  each 
burner-arch  having  a  hole  of- 4  to  5  inches  square  leading  into  it. 
These  holes  are  not  always  provided  with  dampers;  but  by  gradually 
increasing  the  size  of  the  whole  as  the  distance  from  the  main 
shaft  becomes  greater,  evenness  of  draught  is  produced.  The  flue 
itself  can  be  made  of  bricks  set  in  tar  and  sand,  and  covered  with 
fire-tiles.  Most  modern  works  prefer  forming  it  by  a  second  arch, 
about  6  or  12  inches  above  the  burner-roof,  reaching  right  across 
the  whole  burner,  and  supported  by  the  front  plate  being  made  high 
enough. 

The  principal  feature  of  the  English  pyrites-burners,  which  is 
used  in  all  continental  works  as  well,  except  in  some  burners  for 
metallurgical  purposes  (Mansfield  or  Freiberg  kilns),  is  the  employ- 
ment oi  grate-bars  of  square  or  oblong  section,  movable  in  bearings, 
and  leaving  larger  or  smaller  spaces  between  them,  according  to 

Fig.  76. 


Fig.  77. 


^    -i 


their  position.  (According  to  Hasenclever,  in  Hofmann's  'Bericht,' 
1875,  i.  p.  158,  movable  grate-bars  have  been  used  in  Prance  ever 
since  184*.)  Fig.  76  represents  such  a  grate-bar,  showing  ako 
the  parts  which  are  forged  or  cast  round,  so  that  they  can  easily 
turn  in  the  respective  hollows  of  the  bearers.  Bars  2  inches 
square  are  usually  made  of  wrought  iron ;  the  oblong  bars,  2  by 


GRATES  FOR  PYRITES-BURNERS. 


301 


3  inches^  which^  being  turned  on  edge^  leave  a  larger  space^  and 
therefore  only  suit  larger  pieces,  are  mostly  of  cast  iron.  The 
grate-bars  rest  on  cast-iron  bearers,  as  shown  in  fig.  17 ;  in  the 
shallower  kilns  (4^  to  5  feet  from  front  to  back)  there  are  two 
such,  in  the  deeper  kilns  (5  feet  3  inches  to  6  feet  from  front 
to  back  inside)  three.  According  to  this,  of  course,  two  or  three 
rounded  places  must  be  made  on  the  bars  themselves.  Lest  these 
should  be  weakened  too  much,  the  diameter  of  the  round  parts  in 
the  square  bars  is  equal  to  the  side  of  the  square,  in  the  oblong 
ones  equal  to  the  smaller  side.  In  any  case  the  front  piece  of  each 
bar,  where  it  projects  beyond  the  bearing-bar,  remains  square 
or  oblong,  so  that  it  can  be  turned  round  its  axis  by  means  oE  a 
suitable  key  (fig.  78) .  The  intervals  between  the  grate-bars  are 
mostly  mafiaged  so  that  with  2-inch  bars  they  are  about  2  inches 
when  the  bars  are  in  the  situation  shown  in  fig.  79 ;  but  if  they  are 
turned  90  degrees,  as  in  fig.  80,  the  intervals  will  only  amount  to 
1^  inch.  In  another  actual  instance  the  diameter  of  the  bars 
was  ]|  inch,  the  clear  distance  in  the  straight  position  1^  inch, 
in  the  diagonal  position  1  inch.  If,  lastly,  the  situation  is  as 
in  fig.  81,  where  half  of  the  bars  are  turned,  the  intervals  will  be 


Fig.  78. 


between  the  two  above  limits;  and  as  each  bar  can  be  turned 
separately,  many  combinations  can  be  produced.  Usually  the  bars 
stand  as  in  fig.  80 — that  is,  all  with  their  diagonals  in  a  horizontal 
plane,  or  with  the  smallest  possible  intervals,  so  that  the  pieces  of 
ore  cannot  fall  through.  As  soon  as  a  portion  of  the  ore  has  to 
be  removed,  the  attendant  takes  hold  of  the  front  end  of  the  bar 
with  his  key,  and  moves  it  a  few  times  from  side  to  side.  Thus  a 
kind  of  crushing  action  will  be  exercised  on  the  cinders  getting 
between  the  two  bars,  the  intervals  arc  momentarily  enlarged,  and 


304 


PRODUCTION  OF  SULPHUR  DIOXIDE. 


the  cinders  jammed  between  the  bars  are  forced  downwards.  Of 
coarse  great  strength  is  required  for  this  work.  At  the  same 
time,  by  the  action  of  the  key,  the  pyrites  is  loosened  up  to 
a  certain  height.  The  workman  now  goes  from  one  bar  to 
another,  generally  missing  one,  and  shakes  them,  according  to 
his   perception,  so   far  that  an   equal  quantity  of   burnt  ore  is 


^.y.    « 


Fig.  79. 
Fig.  80. 


1 


\: 

Fig.  81. 


drawn  out  all  over  the  area  of  the  grate.  That  which  has  fallen 
through  is  allowed  to  lie  in  the  ash-pit  till  the  time  comes, 
once  every  24  hours,  for  opening  the  bottom  door  and  taking 
away  the  cinders.  A  new  shape  of  bars,  which  was  said  to 
possess  great  advantages  over  the  ordinary  angular  ones,  was 
patented  by  W.  Helbig  (Dingl.  Journ.  ccxxvii.  p.  67)  and  is  shown 
on  p.  222  of  our  second  edition,  but  omitted  here,  as  it  seems  to 
have  found  no  practical  application.  It  was  a  cast-iron  bar  with 
a  worm-thread  all  round  it. 

A  burner  patented  by  Harlan  &  Grenshaw  (G.  P.  100,243) 
contains  hollow  grate-bars,  with  tapering,  narrow  chambers,  rising 
vertically  nearly  to  the  top  of  the  layer  of  pyrites,  so  that  the  air 
enters  not  merely  at  the  bottom  above  the  grate,  but  also  higher 
up,  nearly  to  the  top  of  the  pyrites. 

Dr.  Burgemeister  (private  communication)  employs  bars  made 
of  a  cruciform  section.  When  turning  these  round,  the  smaller 
pieces  easily  fall  through ;  the  larger  lumps  get  between  the  bars 
and  either  pass  through  on  turning  back  or  are  crushed.  The 
following  diagram  shows  the  different  positions  of  the  bars  : 

+   +  +   + 

X     X     X     X 

It  is  a   great  improvement  (but  rarely  met  with,  because  it 


•    DISCHARGING  THE  BURNT  ORE.  303 

necessitates  a  somewhat  complicated  plant)  if  the  ashpit  is  deep 
enough  for  introducing  an  iron  bogie  below  the  grate  whose  top 
equals  the  whole  surface  of  the  grate  in  size  ;  the  ash-pit  door^  of 
course^  must  be  correspondingly  large.  The  cinders  in  that  case  fall 
direct  into  the  bogie,  and  can  be  wheeled  out  in  a  few  moments ; 
usually  they  have  to  be  raked  out  by  hand,  during  which  time 
the  door  must  stand  open,  and  much  false  air  gets  into  the 
burner.  Where  there  are  not  two  rows  of  burners  built  back  to 
back,  it  is  possible  to  charge  on  one  side  and  discharge  on  the 
other;  but  there  is  not  much  advantage  in  this  arrangement,  which 
takes  a  great  deal  of  space. 

The  discharging  of  the  burnt  ore  {cinders)  is  sometimes  expedited 
by  iron  bogies  running  on  tramways,  which  are  introduced  into  the 
ash-pits,  and  into  which  the  cinders  fall  as  the  grates  are  shaken. 
This  very  suitable  plan  necessitates  a  system  of  tramw^ays  and 
turn-tables,  as  well  as  a  lowering  of  the  whole  floor.  The  follow- 
ing simple  and  equally  efficient  plan  seems  therefore  worthy  of 
recommendation.  It  is  a  tilting-box  (figs.  82  &  83) .  There  are 
two  independent  parts  : — first,  an  iron  box,  of  suitable  dimensions, 
with  two  outside  pivots  near  the  upper  edge ;  secondly,  a  light 
but  strong  wheeled  frame,  which  ends  in  forks  fitting  under  the 
pivots.  As  shown  in  the  diagram,  the  whole  is  used  like  an 
ordinary  iron  wheelbarrow  on  any  hard  ground.  But  by  lifting 
up  the  handle  the  box  is  first  lowered  to  the  groimd,  then  the 
forks  slip  out  and  the  frame  can  be  run  back.  Similarly  the  box 
is  taken  up  again  by  running  the  frame  in,  and  depressing  the 
handles  till  the  forks  take  hold  of  the  pivots.  The  boxes  can 
be  made  to  fit  into  the  ash-pits,  and  the  cinders  discharged  into 
them  directly  from  the  grates.  Of  course  other  applications  of 
this  barrow  will  present  themselves  in  chemical  works. 

In  order  not  to  be  obliged  to  open  the  whole  ash-pit  when 
shaking  the  bars,  all  the  best  furnaces  are  provided  with  a  slit 
in  the  front  plate,  through  which  the  ends  of  the  bars  are 
accessible.  Except  whilst  the  bars  are  being  shaken,  the  slit  is 
covered  by  a  door,  which  is  best  made  in  two  halves. 

Norrington  (£.  P.  No.  4131,  1878)  makes  the  ash-pit  doors  to 
slide  in  horizontal  frames,  and  connects  all  the  doors  of  a  set  of 
burners  by  jointed  rods,  so  that  they  can  all  be  moved  together  in 
a  horizontal  plane  by  means  of  an  endless  screw  and  gearing  at 
one  end.     All  the  ash-pit  doors  are  thus  opened  and  shut  at  the 


304  PKOOUCTION  OF  8ULPHUH  DIOXIDE, 

same  time.  This  is  always  done  whenever  any  one  of  the  working- 
doors  is  opened  bo  that  no  gas  can  blow  out,  as  the  air  cannot 
enter  in  any  otlier  way.  According  to  information  from  Messrs. 
Charles  Norrington  &  Co.,  Plymouth,  this  arrangement  effects  a 

llg.  8-2. 


considerable  saving  of  nitrate  of  soda  and  of  sulphuric  acid  ;  owing 
to  the  regularity  of  draught,  all  kilns  burn  equally  well.  This 
statement  is  confirTned  by  Dr.  Ballard  (Report  to  the  Local 
Government  Board,  1879,  p.  180) . 

According  to  a  communication  from  Mr,  K.  Walter,  a  simple 
means  of  preventing  the  blowing  out  of  gas  at  the  working-door 
during  charging  is  this  :  to  arrange  a  flue  underneath  the  burners, 
in  connection  with  the  chimney,  which  is  opened  during  the 
charging  just    suflicient    to    prevent   any   blowing   out   at    tl\e 


PREVENTING  NUISANCE  DURING  THE  DISCHARGING.  305 

working-door.  Less  gas  is  lost  and  less  nuisance  is  produced  in 
this  way  than  is  otherwise  the  case  from  the  working-doors.  With 
this  arrangement  the  ash-pits  require  only  loosely  put-on  wrought- 
iron  doors. 

In  England  it  would  probably  not  be  allowed  to  discharge  the 
gas  into  the  chimney,  even  for  a  short  time  :  this  objection  is 
overcome  by  the  following  plan  : — 

Hasenclever  (Chem.  Ind.  1895,  p.  494)  describes  the  following 
arrangement  for  preventing  any  escape  of  gas  from  the  burner- 
doors  into  the  working-shed  during  the  time  the  doors  are  open 
for  charging.  In  some  cases  the  chambers  are  placed  high  enough 
over  the  burners  (say,  at  least,  18  feet  above  the  floor)  to  secure 
sufficient  draught  at  all  times;  but  even  then  the  false  air 
entering  during  the  time  of  charging  may  be  troublesome  in  the 
lead  chanjbers.  The  device  proposed  by  Jurisch  (Ueber  die 
Gefahren  f iir  die  Arbeiter  in  chemischeu  Fabriken,  p.  37)  that  a 
by-pass  should  be  made  from  the  burners  directly  into  the 
chambers,  which  should  be  opened  by  means  of  a  damper  every 
time  a  burner  is  charged,  is  altogether  impracticable,  and  is  evi- 
dently not  practiced  anywhere.  The  difficulty,  however,  is  solved 
by  connecting,  during  the  time  the  kilns  are  being  charged,  the 
ash-pit  (by  means  of  a  special  flue)  with  a  chimney  producing  but 
little  draught,  so  that  no  burner-gas  is  drawn  downwards  into  the 
flue  and  the  chimney,  but  the  burning  of  pyrites  in  the  kiln  is 
interrupted. 

This  is  done  at  the  Rhenania  Chemical  Works  by  means  of  the 
arrangements  shown  in  flgs.  84-87,  which,  at  the  same  time, 
illustrate  the  form  of  burners  (p.  299)  frequently  employed  on 
the  Continent,  where  the  burners  have  a  common  gas-space,  the 
pyrites  lies  on  the  grate  in  rather  shallow  layers  (19^  inches), 
and  the  cinders  are  removed  by  means  of  bogies    run   under- 
ground into  the  ash-pit.     The  burner-gas  in  the  ordinary  way 
passes  from  the  dust-chamber  through  pipe  h  into  the  Glover 
tower.     Each   time  the  cinders  are  let  down   into    the  ash-pit 
by  shaking  the  grate-bars,  damper  b  c  d  e  (fig.  86)  is  shut  down, 
so  as  to  close  flue  /  against  the  outer  air,  but  not  hermetically, 
and  damper  S  is  opened,  which  leads  through  g  into  a  chimney, 
which  is  not  connected  with  any  furnace,  and  is  only  25  or  30 
feet  higli,  so  that  it  just  projects  over  the  roof   of    the   shed. 
The  small  quantity  of  air  which  enters  round  damper  b  c  d  e 

VOL.  I.  X 


DOORS  AND  BKICKWOKK  OP  PYRrrBS-BUKXERii.  307 

18  partly  drawn  into  this  chimney,  and  the  pyrites  consequently 
bums  so  slowly  that  no  gas  issues  from  the  doors  a,  ai,  a^,  a^. 
The  men  now  charge  the  burner  with  fresh  pyrites  through  these 
doors,  shut  the  doors, let  down  damper  S,  and  raise  damper  b  c  de, 
whereupon  the  evolution  of  sulphur  dioxide  recommences,  and 
goes  on  all  the  more  regularly  the  more  burners  are  united  in  the 
same  set.  Experience  has  shown  that  no  sulphur  dioxide  is  drawn 
down  into  fff  during  the  operation,  so  that  none  can  escape 
through  the  special  chimney. 

The  Stassfurter  Chemische  Fabrik,  vormals  Vorster  &  Griineberg 
(G.  P.  100,708),  arranges  a  flue  connecting  two  sets  of  burners, 
or  the  single  burners  of  a  set,  below  the  level  of  the  grates.  In 
this  case,  when  the  charging-doors  of  one  burner  are  open  and 
those  of  the  other  burner  are  shut,  the  air-openings  below  the 
grate  being  shut  in  both,  the  second  burner  will  draw  its  supply 
of  air  from  the  first,  through  its  open  doors,  so  that  no  gas  will 
blow  out  of  these. 

In  properly  constructed  pyrites-kilns,  all  doors  for  charging, 
working,  shaking  of  the  bars,  and  getting  out  the  cinders  either 
run  horizontally  in  grooves,  or,  still  better,  they  are  hung  on 
hinges ;  and  the  door-frame,  cast  upon  the  front  plate,  is  made  to 
slant  forwards  below^  sometimes  also  sideways,  so  that  the  door 
lies  fast  upon  it  by  its  own  weight.  As  both  the  door-frame  and 
the  edges  of  the  door  touching  it  are  planed,  the  doors  close  tight 
without  any  luting,  whilst  those  running  in  grooves  must  be  made 
tight  with  lime-putty. 

All  brickwork^  so  far  as  it  is  affected  by  the  heat  (that  is,  the 
walls  above  the  grates,  the  arch,  and  the  gas-flue)^  is  lined  with 
fire-bricks;  the  total  thickness  in  front  is  one  brick, behind  (or  as 
the  partition  between  two  rows  of  burners)  two  bricks.  The  side 
walls  dividing  each  two  burners  of  a  row  are  1^  or  2  bricks  thick, 
but  they  diminish  upwards  to  one  brick.  The  roof  need  only  be 
4i  inches  thick.  The  mortar  is  fire-clay,  as  usual;  in  the  colder 
parts,  such  as  vertical  gas-shafts,  flues,  &c.,  this  docs  not  stand  so 
well  as  boiled-down  tar  and  sand. 

F.  J.  Falding  (Min.  Ind.  vii.  p.  666)  constructs  the  first  layer 
behind  the  cast-iron  front  plates  of  hollow  bricks,  so  that  air- 
channels  are  formed  from  the  grates  upwards  to  the  top  of  the 
burner.  This  keeps  the  burner-room  cool  and  easier  to  work  in, 
at  the  same  time  retaining  heat  for  concentration  in  acid  pans  on 

x2 


308  PRODUCTION  OF  SULPHUR  DIOXIDE. 

the  top  of  the  burners,  or  for  increasing  the  efficiency  of  the 
Glover  tower,  or  for  supplying  the  burners  themselves  with  hot 
air,  which  is  an  advantage  in  some  cases. 

Of  course  the  burners  are  well  bound  together,  either  by  special 
uprights  and  tension-bars,  or  by  flanges  cast  to  the  front  plates, 
provided  with  holes  for  the  cross-bars  (fig.  73) . 

Opinions  as  to  what  size  the  burners  are  to  be  made  vary  a 
good  deal.  Mostly  smaller  burners  are  met  with,  about  4  feet 
6  inches  to  5  feet  from  the  outside  to  the  inside  of  the  back  wall. 
The  reason  given  for  this  is  that  longer  grates  cannot  be  served  so 
well,  and  that  in  a  larger  burner  the  newly-charged  ore  forms  too 
shallow  a  layer  (the  depth  of  the  whole  layer  of  pyrites,  including 
the  partially  burnt  ore,  is  not  in  question  here).  I  have,  how- 
ever, worked  for  a  good  many  years  with  larger  burners,  nearly 

6  feet  from  the  front  to  the  back  end  of  the  grate,  and  have  burnt 
my  ore  better  than  the  majority  of  other  works  using  the  smaller 
burners.  Certainly,  the  usual  7-cwt.  charge  had  to  be  all  put  in 
at  once,  whilst  in  the  smaller  burners  it  is  introduced  in  two  halves 
every  12  hours;  and  many  practical  men  assert  that  a  12-hours' 
is  preferable  to  a  24-hours'  charging ;  but  this  is  not  borne  out 
by  experience.  It  is,  however,  a  decided  mistake  to  try  burning 
a  much  larger  charge  on  the  larger  grate,  say  8  or  9  cwt.  This 
can  only  be  done  with  poor  ores,  such  as  are  not  in  use  at  the  present 
day,  except  locally ;  richer  ores,  especially  those  containing  copper, 
are  sure  to  be  fluxed  by  the  heat  getting  too  high,  and  cause  the 
greatest  trouble.  As  a  result  of  long  experience,  I  am  inclined  to 
consider  a  grate-surface  of  4  feet  6  inches  by  5  feet  8  inches,  and 
a  depth  of  pyrites  of  2  feet  3  inches,  very  favourable  for  burning 

7  cwt.  of  48-per-cent.  Spanish  ore,  changing  once  every  24  hours. 
The  rate  of  burning  just  mentioned  equals  30  lbs.  of  48-per-cent. 

pyrites  per  superficial  foot  of  grate  in  24  hours.  With  poorer  ore 
(40  to  42  per  cent.)  I  have  certainly  burnt  in   the  same  grate 

8  cwt.  (=35  lbs.  per  square  foot),  and  with  38-  or  40-per-cent.  ore 
even  9  cwt.  (=  nearly  40  lbs.  per  square  foot).  In  England  the 
maximum  quantity  of  pyrites  burnt  per  square  foot  of  grate  will 
very  rarely  exceed  40  lbs.  of  48-per.ccnt.  pyrites ;  reliable  figures 
from  one  of  the  largest  works  arc  35^  and  39  lbs.  But  in  Grerman 
works,  according  to  Hascnclevcr,  using  Westphalian  pyrites,  the 
proportions  are  ll'G,  445,  57'8,  CO'3,  and  G5'0  lbs.  (Wagner's 
Jahrcsb.  1871,    p.  212).       Bode    (ib.    1874,  p.  245)  quotes  for 


\ 


SIZE  OF  FYaiTlSS-BURNEHS.  309 

Westphalian  pyrites  of  41  or  42  per  cent.,  50*7  fo  640  lbs.;  for 
Norwegian  ore  of  the  same  strength,  38*3  lbs. ;  for  Valais  ore, 
with  35  per  cent,  sulphur,  up  to  92  lbs.  per  square  foot  in  24 
hours.  Favre  (Monit.  Scient.  1876,  p.  271)  states  as  the  most 
favourable  ratio  in  his  experience  55*3  lbs.  of  40-per.cent.  pyrites 
per  square  foot  in  24  hours. 

At  the  Oker  works,  in  1901,  the  roasting  area  of  the  three  deep 
kilns  (p.  295).  serving  for  a  chamber  set  of  5289  cub.  metres 
amounted  to  33*55  superficial  metres,  that  is  000634  sup.  met. 
per  cub.  met.  of  chambers.  The  quantity  of  ore  roasted  per 
square  metre  in  24  hours  was  0*45  ton  copper-ore,  0*50  ton  pyritic 
lead -ore,  1*40  ton  copper-matte,  1'60  ton  lead-matte  (comp. 
p.  83  on  the  composition  of  these  ores). 

In  1902  the  Rhenania  works  at  Stolberg  considered  200  kils. 
Westphalian  pyrites  per  superf.  metre  grate-surface  as  the  normal 
quantity ;  with  230  kils.  the  degree  of  desulphurization  was 
somewhat  less.  The  former  is  =  40  lbs.,  the  latter  =  46  lbs.  per 
superf.  foot. 

In  England  some  thirty  or  forty  years  ago  many  pyrites-burners 
were  made  about  33  inches  wide  and  26  inches  from  front  to  back 
at  the  fire-bars,  but  42  inches  square  at  the  level  of  the  bottom  of 
the  charging-door,  giving  a  slope  of  6  inches  back  and  9  inches 
sideways.  Later  on  burners  were  made  larger,  say  39  x  42  inches 
at  the  bars  and  48  X  51  inches  at  the  charging-doors,  many  going 
up  to  54  inches  wide  and  60  or  66  inches  from  front  to  back  at 
the  fire-bars.  The  smallest  sizes  burn  about  4  cwt.  of  Spanish 
ore  =  44  lbs.  per  square  foot  in  24  hours ;  the  largest  sizes  7  cwt. 
=  31  lbs.  and  upwards  per  24  hours.  The  most  usual  size  is 
about  16  to  18  square  feet  at  the  fire-bars  and  22  to  24  square 
feet  at  the  base  of  charging-doors,  burning  7  cwt.  daily  =37  to  41 
lbs.  of  ore  per  square  foot.  This  is  about  the  maximum  for  rich 
ores  consistent  with  proper  freedom  from  fluxing,  but  poor  ore 
may  be  burned  in  larger  quantity  (Thorpe's  Diet,  of  Applied 
Chemistry,  iii.  p.  719) .  With  the  very  well-burning  Agnas  Tenidas 
ore  Davis  (Chem.  Engineering,  ii.  p.  124)  states  the  proper  charge 
=  2*3  lbs.  per  square  foot  per  hour  =  55  lbs.  per  day,  in  which 
case  the  cinders  tested  1  per  cent.  S. 

It  is  hardly  necessary  to  say  that  the  pyrites-burners  are  always 
built  in  sets.  Usually  12  to  24  burners  are  served  by  the  same 
set  of  men  ;    and  they  must  be  worked  so  that  every  one  gets  its 


810  PRODUCTION  OF  SULPHUR  DIOXIDE. 

regular  turn,  as  is  evident  from  the  necessity  of  a  regular  evolution 
of  gas.  Frequently  the  burners  are  built  underneath  the  acid- 
chambers.  Not  only  must  they  in  any  case  be  protected  against 
rain  (if  not  underneath  the  chambers),  but  they  must  not  stand 
in  a  space  open  at  the  sides^  since  strong  winds  would  put  their 
draught  wrong,  and  cause  them  either  to  go  too  fast  or  to  blow  out 
at  the  doors.  It  is  best  to  protect  them  by  light  walls  or  by  a  brat- 
lire  with  shutters  adjustable  according  to  the  direction  of  the  wind. 
As  the  drawings  of  the  English  burners  (pp.  298  et  seq.)  show,  each 
burner  is  independent  of  the  other,  and  they  do  not  communicate 
one  with  another,  but  only  with  the  common  gas-flue.  Each 
burner,  then,  ought  to  have  its  own  damper,  which  is  not  always 
the  case.  On  the  Continent,  frequently  the  single  burners  are 
separated  merely  by  low  walls  ;  the  ore  in  this  case  lies  only  about 
18  or  20  inches  deep  on  the  grates,  and  the  whole  set  is  like  one 
large  burner  with  a  divided  grate  (p.  306).  It  is,  of  course,  not 
possible,  as  on  the  English  system,  to  treat  each  burner  individu- 
^^J>  to  give  it  more  or  less  draught,  to  isolate  it  for  repairs,  &c. 
Nevertheless  this  system  is  in  favour  with  some  of  the  more 
experienced  Continental  manufacturers,  who  say  that  18  inches 
depth  is  quite  sufficient  for  the  rich  ores,  now  universally  employed, 
and  that  the  connection  of  the  gas-space  of  all  burners  into  one 
whole  is  preferable  to  the  English  system,  because  one  burner  can 
aid  another  and  the  whole  is  visible  at  a  glance.  Evidently  this 
system,  of  which  good  illustrations  are  given  in  figs.  84  to  87,  p.  306, 
answers  its  purpose  as  well  as  the  English ;  and  in  a  special  case, 
in  which  I  saw  a  set  of  English  burners  working  alongside  a  set 
of  burners  of  the  kind  just  described,  the  manager  informed  mc 
that  he  preferred  the  latter,  because  it  was  easier  to  regulate  the 
draught  than  with  the  English  burners. 

In  Continental  works  possessing  no  Glover  tower  it  is  usual 
to  concentrate  the  chamber-acid  up  to  144°  Tw.  in  lead  pans^  which 
are  mounted  on  the  top  of  the  burners,  and  are  heated  by  their 
waste  heat.  Of  all  plans  for  concentrating  sulphuric  acid  this  is, 
as  we  shall  see  later  on,  the  cheapest,  only  excepting  the  Glover 
tower.  There  is  no  reason  why  such  pans  should  not  be  placed 
on  the  English  burners  as  well ;  but  even  before  the  Glover  tower 
did  away  with  most  lead  pans,  the  above  arrangement  does  not 
seem  to  have  been  practiced  in  England,  where,  however,  the  space 
on  the  fnrnace-ai'ch  is  otherwise  usefully  employed  for  drying 


FOTTING  SPECIAL  PYRITES-BURNERS.  311 

*^  balls  '^  from  pyrites-dust,  &c.  There  are  also,  as  we  shall  see 
m  Chapter  IX.,  sometimes  reasons  against  placing  the  pans  on  the 
top  of  the  burners. 

The  ^'poiting  "  of  the  mixture  of  nitric  and  sulphuric  acid  (liquid 
nitric  acid  is  not  used  in  England  for  this  purpose)  is  now  nearly 
always  done  in  such  a  way  that  the  burners  are  not  disturbed  by  it. 
Twenty  years  ago  the-  pots  were  frequently  put  on  pillars  between 
two  burners,  with  a  common  gas-space ;  these  were  provided  with 
special  potting-doors  in  the  burner-front,  and  cast-iron  dishes  as 
saucei*s  for  receiving  the  stuff  that  boiled  over;  these  saucers  were 
inclined  towards  the  doors,  so  that  the  nitre-cake  could  not  so 
easily  run  into  the  burners ;  but  it  got  out  of  the  doors,  which 
made  them  look  very  dirty ;  and  ultimately  it  also  got  into  the 
burners  themselves.  None  of  the  better  factories  have  this 
arrangement  now,  but  all  pots  belonging  to  a  set  of  burners  are 
placed  in  a  separate  ^'  nitre-oven/'  which  is  nothing  but  an  enlarge- 
ment of  the  gas-flue,  and  either  situated  over  the  burners  or  on 
pillars  outside  the  same.  The  latter  is  preferable ;  for  also  here 
there  is  always  a  metal  saucer  provided  for  catching  the  boiling- 
over  nitre-cake;  this  may  be  cracked  before  it  is  noticed,  and 
much  nitre-cake  may  get  into  the  burners,  doing  great  damage. 
If  the  arrangement  is  similar  to  fig.  74,  p.  298  (where,  by  the  way, 
the  nit  re- pots  are  replaced  by  a  better  contrivance  to  be  sub- 
sequently described),  no  risk  of  the  above-mentioned  kind  is  run. 

Favre  ('  Moniteur  Scientif.,^  1876)  reports  that  the  works  in  the 
south  of  Prance  use  pots  of  2  ft.  7^  in.  x  1  ft.  6  in.  x  12  in., 
standing  on  a  bridge  between  two  burners  ;  and  he  also  mentions 
the  drawback  of  boiling  over  into  the  burners.  This  would  show 
that  those  works,  even  in  1876,  were  in  a  backward  state. 

Special  kinds  of  Pyrites^umers. 

Addie  (E.  P.  180,  of  1886)  describes  a  peculiar  pyrites-burner. 
It  consists  of  a  cupola,  brought  to  a  white  heat,  in  which  the 
pyrites  is  charged  together  with  sandstone  or  other  slag-producing 
material,  and  is  burnt  by  a  hot  blast,  the  cinders  being  reduced  to 
a  molten  slag  which  is  run  off  from  time  to  time.  Unless  this 
apparatus  was  intended  for  some  very  special  purpose,  not 
apparent  at  first  sight,  it  must  be  pronounced  as  very  impracticable 
so  far  as  the  chemical  manufacturer  is  concerned* 

The  methods  described  in  the  patent  of  Hargreaves,  Robinson, 


812  PRODUCTION  OF  SULPHUR  DIOXIDE. 

and  Hargreaves  (E.  P.  no.  5681,  1886)  for  treating  pyrites  are 
evidently  less  intended  for  the  manufacture  of  sulphuric  acid  than 
for  the  recovery  of  arsenic,  antimony,  copper,  silver,  and  gold. 
A  whole  set  of  burners  is  combined  in  such  a  way  that  the 
air  or  the  gaseous  products  at  first  formed  can  be  successively 
passed  through  them  in  regular  rotation.  The  air,  previously 
heated  in  recuperators,  passes  downwards,  first  through  nearly 
exhausted  ore,  afterwards  successively  through  ore  containing 
more  sulphur.  The  residual  ore  is  treated  with  acid  gases,  in 
order  to  bring  the  metals  into  a  soluble  state.  For  details  we 
must  refer  to  the  patent  specification. 

Bvrners  for  roasting  copper-matte. — Haege  (Berg-  u.  Hiittenm. 
Zeit.  1893,  p.  883)  describes  the  process  introduced  by  him  at 
Britonferry,  near  Swansea.  The  copper-matte  produced  there 
could  not  be  roasted  in  Mansfeld  kilns,  nor  in  ordinary  pyrites- 
burners.  The  desired  result  was  obtained  by  increasing  the  heat, 
ill  the  first  instance  by  a  suitable  treatment  of  the  matte,  and  in 
addition  to  this  by  improving  the  construction  of  the  burners. 
The  matte  was  rendered  porous  by  tapping  it  on  to  a  sand-bed 
slightly  moistened  and  dusted  over  with  fine  coal.  It  was  then 
crushed  by  a  Blake's  stone-breaker,  in  which  one  of  the  corrugated 
faces  had  been  substituted  for  a  smooth  one,  so  that  flat,  more 
tightly  lying  pieces  were  obtained,  which  were  separated  from  the 
smalls  by  a  riddle  with  meshes  of  |  inch  width.  The  burners  are 
of  the  ordinary  shape  of  English  pyrites-burners,  described  above, 
but  of  slightly  different  dimensions : — Grate-surface  4  ft.  8  in.  by 
4  ft.  4  in. ;  area  at  the  level  of  the  upper  working-surface  5  ft. 
by  4  ft.  9  in.  ;  height  from  grate-bars  to  the  upper  working- 
surface  2  ft.,  to  spring  of  the  arch  8  ft.  4  in.,  to  the  crown  of  the 
arch  8  ft.  8  in. ;  smoke-flue  at  the  lowest  point  6  in.,  at  the 
highest  1  ft.  4  in. ;  total  outside  height  7  ft.  10  in.  The  heating- 
up  takes  place  from  the  top,  exactly  as  described  in  the  text ;  the 
burners  are  ready  for  work  in  two  or  three  days.  Each  burner 
then  receives  a  charge  of  from  6  to  7^  cwt.  of  crude  matte  every 
12  hours.  After  three  hours  everything  becomes  red-hot,  after 
six  hours  a  bright  cherry-red  heat  is  attained.  Now  the  interior 
of  the  burner  is  worked  up  through  the  middle  door  by  means 
of  a  steel  poker,  2^  in.  thick,  pointed  at  one  end ;  any  lumps 
formed  are  broken  up;  and  this  working  over  is  continued 
through  the  upper  door.     After  another  two  or  four  hours  the 


WORKING  PYRITES  LUMP-BURNERS.  318 

heat  is  at  its  maximum ;  the  upper  working-door  is  now  mostly  at 
a  dark-red  heat.  Then  the  heat  decreases.  11^  hours  after 
charging  the  grate-bars  are  turned  and  shaken,  in  order  to  remove 
the  roasted  matte,  and  after  12  hours  a  new  charge  is  made. 
There  is  no  picking  out  and  recharging  of  imperfectly  roasted 
matte,  since  everything  is  well  finished.  The  draught  must  be 
well  regulated ;  there  should  be  a  slight  plus- pressure  within  the 
burner.  In  this  way  mattes  containing  from  20  to  47  per  cent, 
copper  are  treated.  The  poorer  matte  yields  rather  hotter  and 
better  gas  and  more  sulphuric  acid  than  the  richer.  With  20.per- 
cent.  matte  the  roasted  product  contains  9  per  cent,  sulphur,  with 
rich  matte  it  contains  11  per  cent,  sulphur ;  both  are  at  once 
ready  for  the  concentrating  work.  From  40  per  cent,  matte  about 
47  or  48  per  cent,  of  the  weight  of  roasted  matte  is  obtained  in 
the  shape  of  chamber-acid  of  110°  Tw.,  with  consumption  of  0*8 
to  10  nitre  per  cent,  of  chamber-acid.  The  gases  are  hot  enough 
to  thoroughly  decompose  the  mixture  of  nitre  and  sulphuric  acid 
in  the  nitre-oven  and  to  denitrate  the  acid  in  the  Glover  tower ; 
the  acid  flows  from  this  with  a  temperature  of  140°  to  155°  C. 

Working  of  the  Pyrites-burners  for  Lumps, 

In  order  to  start  a  burner  it  is  first,  if  newly  built^  dried  by 
a  slow  fire  in  the  usual  way,  and  then  filled  with  burnt  ore  to 
within  3  inches  below  the  working-door.  If  no  burnt  ore  can 
be  procured,  ordinary  road-metal,  &c.,  may  be  takeu^  broken  suffi- 
ciently to  pass  between  the  grate-bars  when  they  are  turned.  The 
draught-hole  of  each  burner  is  closed  by  a  damper^  and  the  work- 
ing-door is  left  open.  Then  ordinary  fuel  (wood  or  rough  coals) 
is  heaped  on  the  ore  and  lighted.  After  twelve  or  twenty-foui 
hours  the  burner  and  the  uppermost  layer  of  the  ore  will  have 
reached  a  dull  red  heat ;  the  rougher  parts  of  the  fuel  still  present 
are  then  drawn  out  and  an  ordinary  charge  of  green  pyrites  is  put 
on.  By  the  heat  of  the  burner- walls,  that  of  the  ore  below,  and 
the  fuel  still  present,  the  fresh  ore  will  soon  be  lighted ;  when  it  is 
fully  burning,  the  working-door  is  closed,  the  damper  closing  the 
access  to  the  gas-flue  is  opened,  and  the  gas  allowed  to  go  to  the 
acid-chambers.  Care  must  be  taken  in  lighting  up  not  to  go  too 
far,  which  would  damage  the  burners. 

Thus  the  process  is  started ;  and  it  is  now  continued  regularly 


314  PRODUCTION  OF  SULPHUR  DIOXIDE. 

and  uninterruptedly  till  it  has  to  be  stopped  for  external  reasons. 
Repairs  are  very  rarely  necessary  in  pyrites-kilns ;  but  those  of 
other  parts  of  the  acid-making  apparatus  may  compel  their 
stoppage.  At  some  English  works  the  dampers  are  put  in  every 
Saturday  at  midnight^  and  are  opened  only  on  Sunday  at  midnight ; 
in  the  meantime  all  other  openings  are  well  closed;  and  the 
burner  thus  keeps  its  heat  so  well  that  the  new  charges  at  once 
take  fire  when  brought  in.  If  any  temporary  interruption  of  work 
does  not  last  beyond  four  or  six  days,  usually  the  burners  can  be 
kept  hot  enough  in  this  way  to  be  started  without  any  fresh 
lighting-up  by  means  of  fuel. 

The  regular  burning-process  has  a  double  object,  from  which 
follow  all  the  precautions  to  be  observed.  In  the  first  place,  the 
sulphur  contained  in  the  ore  is  to  be  burnt  as  far  as  possible ;  and, 
secondly,  a  just  sufficient  quantity  of  air  is  to  be  employed,  no 
more  and  no  less  than  is  required  for  the  chamber-process.  This 
means,  besides  the  air  necessary  for  burning  the  sulphur  to 
sulphur  dioxide,  as  much  more  air  as  is  required  for  oxidizing  the 
latter  to  sulphuric  acid,  and,  moreover,  a  certain  excess  of  air 
found  necessary  in  practical  work.  Anyhow,  therefore,  the  air 
will  be  more  than  just  sufficient  for  burning  all  the  sulphur  con- 
tained in  the  pyrites;  and  the  second  condition  seems  thus  to 
imply  the  first.  But  this  can  be  said  only  for  brimstone  and  for 
pure  pyrites  not  containing  any  zinc-blende  or  galena,  &c. ;  for 
only  the  former  can  be  desulphurized  completely  by  their  own  heat 
of  combustion.  The  sulphates  of  iron,  which  are  always  partly 
formed  as  intermediate  products,  arc  decomposed  again  at  a  com- 
paratively low  temperature  into  Fe203,  O,  and  SOj,  or  into  Fe203 
and  SO3,  for  which  the  heat  of  the  burners  is  quite  sufficient.  This 
is  a  little  more  difficult  with  the  sulphides  of  copper;  but  the 
temperature  of  decomposition  of  CuSOj  is  also  within  a  red  heat. 
Moreover  the  copper-extraction  works  do  not  want  all  the  sulphur 
to  be  burnt,  but  allow  a  residue  of  from  four  to  at  most  six  per 
cent,  sulphur  in  the  cinders.  If,  however,  the  ores  contain  blende 
or  galena,  which  on  burning  are  transformed  into  zinc  and  lead 
sulphates,  the  burner  cannot  possibly  effect  a  total  desulphurization; 
for  these  sulphates  are  only  decomposed  at  a  strong  white  heat, 
which  is  not  allowable  in  a  pyrites-burner,  and  they  must  thus 
remain  as  such  in  the  cinders.     Furthermore,  if  the  pyrites  contains 


WORKING  PYRITES  LUMP-BURNER?.  315 

calcium  sulphate  or  carbonate,  a  corresponding  quantity  of  CaS04 
will  remain  in  the  residue.  Any  barium  sulphate  present  would 
not  be  taken  notice  of  in  the  testing  of  the  pyrites  or  the  cinders, 
being  classed  among  the  '^  insoluble." 

In  the  case  of  the  usual  description  of  pyrites,  not  containing 
any  considerable  quantity  of  zinc  or  lead,  the  burning  of  ore  in 
lumps  will  reduce  the  sulphur  in  the  cinders  with  good  work  to 
3  or  4  per  cent.  Less  than  3  per  cent,  of  sulphur  rarely  occurs 
on  an  average  of  the  whole  year ;  but  with  very  good  ores  it  may 
go  down  to  2^  per  cent.  At  the  Rhenania  works,  at  Stolberg, 
even  pyrites  with  6  or  7  per  cent.  Zn  is  burnt  down  to  2  or  3  per 
cent.  S,  exceptionally  4  per  cent,  (information  received  in  1902). 
Most  frequently  the  limit  stated  above  for  good  work  is  exceeded ; 
some  works  leave  6  or  8  per  cent,  of  sulphur,  and  even  more,  in 
their  cinders,  whilst  their  neighbours  only  leave  4  or  5  per  cent, 
in  the  same  ore.  The  fault  of  this  may  be  due  either  to  the 
description  of  burner  employed  or  to  tlic  style  of  work.  If,  by 
the  construction  of  the  burner,  the  pyrites  lie  in  too  shallow  a 
layer,  and  this  is  let  down  too  soon  on  shaking  the  bars,  it  will 
easily  come  out  badly  burnt,  liut  even  if  the  burner  is  correctly 
built,  much  still  depends  upon  the  skill  and  care  of  the  burner- 
men. 

Excellent  results  are  obtained  with  some  of  the  very  rich  de- 
scriptions of  Spanish  non-cupreous  pyrites  recently  come  into  the 
market  (p.  56).  These  pyrites  can  he  burnt  down  to  0*5  percent, 
of  sulphur  in  the  cinders,  so  that  the  latter  can  be  sent  straight  to 
the  blast-furnaces.  But  if  this  degree  of  purity  is  to  be  obtained, 
the  place  in  front  of  the  kilns^  where  the  burnt  ore  is  drawn 
out,  must  be  kept  perfectly  clean,  so  that  no  green  ore  can  get 
mixed  among  the  cinders;  and  any  portions  of  these  which 
have  been  spilt  from  the  discharging  bogies  on  to  the  ground 
must  not  be  shovelled  back  into  them,  as  they  will  have  some 
admixture  of  dust  from  green  ore,  but  they  must  be  put  back  into 
the  kilns. 

How  much  depends  upon  employing  the  ore  in  neilher  too  large 
nor  too  small  pieces,  and  upon  keeping  the  pieces  of  as  uniform  a 
size  as  possible,  has  been  mentioned  on  p.  287.  Only  then  will  it 
be  possible  to  regulate  both  the  depth  of  layer  and  the  draught  in 
a  satisfactory  way. 


316  PRODUCTION  OF  SULPHUR  DIOXIDE. 

Whether  pyrites  is  properly  burnt  or  not  can  be  recognized  to  a 
great  extent  by  the  eye.  By  the  burning-process  the  pieces  swell 
out  and  burst  in  some  place ;  they  become  light  and  porous,  and 
assume  the  red  colour  of  ferric  oxide,  in  the  case  of  cupreous  pyrites 
a  more  blackish-red  colour.  The  burnt  ore  ought  therefore  to 
consist  of  light  porous  pieces  of  the  proper  colour,  apart  from  the 
powder  always  present  in  large  quantity,  which  is  generally  suffi- 
ciently burnt  off.  Already,  on  taking  up  the  larger  pieces,  their 
weight  will  allow  a  rough  judgment  of  the  state  of  the  burning ; 
and  this  can  l)e  more  distinctly  recognized  by  breaking  the  pieces 
and  observing  whether  they  contain  a  raw  core  in  the  centre.  Also 
the  presence  of  many  slags  (scars)  on  the  cinder-heap  is  a  proof  of 
bad  burning. 

Important  as  these  empirical  signs  are,  no  well-managed 
factory  will  be  satisfied  with  them,  but  will  from  time  to  time, 
daily  or  at  least  twice  a  week,  have  the  cinders  tested,  after  having 
drawn  a  large  sample  and  reduced  it  properly.  At  all  events 
the  above-mentioned  empirical  signs  have  hardly  any  value  for 
small  ore. 

The  chemical  testing  of  pyrites  cinders  (burnt  are)  can  take  place 
by  exactly  the  same  methods  as  described  in  the  second  Chapter 
for  the  analysis  of  pyrites  itself.  It  is  there  shown  that  in  the 
case  of  burnt  ore  more  expeditious  methods  may  be  used,  and  that 
among  these  that  of  Watson-Lunge  (igniting  with  sodium  bicar- 
bonate and  titrating  the  undestroyed  sodium  carbonate)  seems  to 
be  the  most  accurate  (p.  76). 

The  sulphur  contained  in  the  burnt  ore  is  no  longer  in  the 
shape  of  FeS2,  apart  from  any  quite  raw  cores  in  large  pieces. 
But  even  fine  or  quite  porous  cinders,  burnt  as  well  as  possible, 
also  those  from  pure  pyrites  free  from  lead,  zinc,  and  lime,  always 
contain  sulphur ;  and  as  this  cannot  be  in  the  shape  of  FeS^,  the 
question  can  only  be  whether  they  contain  FeS  or  sulphates  of 
iron  (most  probably  basic  ferric  sulphates),  or  both.  According  to 
Scheurer-Kestner  and  Rosenstiehl  (Bull.  Soc.  Chim.  1868,  ix.  p.  43), 
the  cinders  contain  essentially  FeS ;  they  give  two  analyses — 
(i.)  of  properly  burnt  ore^  (ii.)  of  an  operation  carried  on  too  hot, 
so  that  the  ore  bad  fluxed.  Both  are  from  Sain-Bel  pyrites, 
containing  46*1  per  cent,  sulphur  in  the  pieces  and  49*28  in  the 
smalls. 


PYRITES  CINDERS.  317 

I.  11. 

Moisture     1*0 

FeS     ',.     8-5  27-2 

Fe    5-4'>  17-31 

S  3-lJ  9-9J 

Oxide  of  iron 720  624* 

Fe    50-41  4101 

O .  21-6J  21-4/ 

tluarlz    18-5  10*4 


1000  1000 

From  these  analyses^  it  would  appear  that  there  would  be  no 
ferric  sulphate  whatever  in  the  residues^  which  is  very  improbable^ 
as  such  can  be  proved  by  washing  with  water  (comp.  Bode^ 
Dingler's  Journal^  ccxviii.  p.  327,  and  further  analyses  by  Phillips^ 
Gibb^  Brauniug,  Wedding,  and  Ulrich  in  the  Chapter  treating  of 
the  recovery  of  copper  from  the  cinders). 

According  to  Troost,  the  first  reaction  is  8FeS2  =  2S  +  Fe3S4. 
Uegnault  holds  that  the  sulphide  formed  has  the  formula  Fe^S^. 
Lemoine  (Fischer's  Jahresb.  1899,  p.  355),  from  observations  made 
in  a  Maletra  shelf-burner  (see  infra),  believes  that  in  the  upper 
layers  there  is  always  a  distillation  of  sulphur,  which  afterwaixls 
bums  with  a  blue  flame.  Lower  down  this  is  no  longer  the  case, 
either  because  here  most  of  the  pyrites  is  already  reduced  to  FeS, 
or  because  the  temperature  is  too  low  and.  the  supply  of  oxygen 
too  great  for  the  formation  of  free  S.  Ferric  oxide  appears  only 
after  roasting  for  2^  hours.  The  action  on  pyrites  seems  to 
proceed  from  the  outside,  where  there  is  combustion  into  FcsOj^ 
and  the  heat  acting  on  the  inner,  part  produces  a  decomposition 
into  FeS  and  S.  The  S  distils  and  burns  outside,  the  FeS  is 
oxidized  by  the  FejOg,  which  is  again  reformed  by  the  outer  air. 

Richters  (Dingl.  Journ.  cxcix.  p.  292)  gives  the  following 
analysis  of  burnt  ore  from  the  Silesia  works  at  Saarau : — 

Water    4*35 

Iron   43-36 

Manganese    0*16 

Silica 13-92 


Carried  forward    ,...     61*79 

*  The  calculation  does  not  agree  liere ;  62*4  Fe.p,  would  contain  43-68  Fe. 


318  PRODUCTION  OK  SULPHUR  DIOXIDE. 

Brought  forward  61 '79 

Alumina    4*84? 

Lime 0-02 

Zinc  oxide 8-83 

Sulphur  trioxide  4*35 

Sulphur 1-53 

Oxygen  and  loss   18*64 

Nickel  and  arsenic    traces 

10000 

Phipson  has  published  the  following  analysis  of  residue  from 
Irish  pyrites  ('Chemical  News/  vol,  xviii.  p.  29)  : — 

Zinc  oxide 5'50 

Cupric  oxide 2'86 

Manganese  oxide 1*60 

Nickel  and  cobalt  oxide  0*12 

Cadmium  oxide     0*01 

Lead  oxide    1-67 

Antimony  oxide    0*04 

Ferrous  oxide    1'17 

Alumina    3*25 

Sulphur 2-60 

Thallium    traces 

Indium  traces 

Gaugue 15-00 

Ferric  oxide  65*99 

Lime ! 0*11 

Magnesia  0'08 

100  00 

All  that  has  been  said  {cf.  p.  315)  respecting  the  maximum  of 
sulphur  in  the  cinders  to  be  aimed  at,  only  refers  to  the  burning  of 
pyrites  proper — that  is  to  say,  of  ores  containing  essentially  FeSj, 
and  got  exclusively  as  a  raw  material  for  vitriol-making,  in  which 
case  the  cinders  are  us  good  as  worthless.  Just  in  the  same  line  are 
those  cupreous  pyrites  (with  less  than  4  per  cent,  of  copper)  whose 
copper  can  only  be  extracted  by  the  wet  process ;  for  these  the 
above-mentioned  rules  for  the  sulphur  in  the  cinders  are  equally 
valid.  But  the  case  is  quite  different  with  a  number  of  ores  where 
the  residue  from  the  burning  is  regarded  as  by  far  the  most  important 


SUPPLY  OP  AlU  TO  PYRITEV-BUKNEKS.  319 

product,  and  where  the  gas  is  only  a  by-product,  often  only  con- 
verted into  sulphuric  acid  in  order  to  get  rid  of  it.  To  this 
category  belong  blende,  copper-pyrites,  coarse  metal,  &c.  Here 
the  burning-down  to  the  above-mentioned  minimum  of  sulphur 
is  partly  not  possible,  partly  not  even  desirable  (as  for  copper- 
pyrites)  ;  and  there  exist  for  each  case  definite  rules,  which, 
however,  do  not  belong  to  the  domain  of  acid-making,  but  to 
that  of  metallurgy.  Even  where  a  larger  percentage  of  sulphur 
is  required  for  further  metallurgical  operations,  it  is  more  rational, 
so  far  as  concerns  the  acid-maker,  in  order  to  save  labour, 
burner-space,  &c.,  to  bum  the  material  as  well  as  possible,  and  to 
supply  the  necessary  sulphur  afterwards  by  adding  a  little  green 
ore ;  thus,  for  instance,  the  copper-extraction  works  proceed  when 
they  receive  the  cinders  too  far  desulphurized.  The  case  of  zinc- 
blende  is  a  special  one  and  will  be  dealt  with  later  on. 

We  now  pass  on  to  the  second  fundamental  condition  of  proper 
work  in  the  pyrites-burners,  viz.,  that  neither  too  little  nor  too 
much  air  be  employed.  At  this  stage  we  leave  out  of  consideration 
the  absolute  quantity  of  air  required,  and  only  treat  of  the  prac- 
tical rules  and  of  the  appearances  observed  in  the  burners  them- 
selves. If  too  little  air  is  admitted,  whether  from  too  few  holes 
in  the  bottom  door  being  opened,  or  from  the  damper  in  the 
draught-hole  not  being  enough  drawn,  or  because  the  pipes  arc 
stopped  up  with  dust,  or  the  draught  in  the  whole  chamber  system 
is  insufficient  from  one  cause  or  another,  the  same  thing  will 
happen  as  with  sulphur-burners  when  they  get  too  hot :  sulphur 
will  sublime  as  such,  and  will  be  deposited  in  the  flues,  the  dust- 
chambers,  the  Glover  tower,  or  the  chambers  themselves.  It  is, 
however,  a  more  frequent  and  serious  consequence  that,  in  the 
case  of  insufficient  draught,  the  often-mentioned  slags  or  scars  are 
formed.  These,  as  Scheurer-Kestner  and  Rosenstiehl  have  shown 
(/.  c),  consist  mostly  of  iron  monosulphide,  PeS,  which  is  necessarily 
formed  when  FeSg  is  heated,  with  exclusion  or  insufficient  supply 
of  air,  along  with  free  sulphur.  It  is  easily  fusible,  and  fluxes  in 
the  burners  to  more  or  less  large  cakes  or  scars,  upon  which  the 
air  has  practically  no  action.  The  FeS  fluxes  all  the  more  easily, 
as  in  the  case  of  insufficient  supply  ^f  air,  where  no  cooling  by  the 
excess  of  air  takes  place,  and  more  heat  is  developed  in  certain  places 
than  when  the  supply  of  air  is  abundant.  The  scars  mostly  enclose 
some  green  pyrites,  and  in  this  way  cause  a  further  loss  of  sulphur. 
A  much  greater  loss  is  occasioned  by  their  stopping  the  passage  of 


820  PRODUCTION  OF  SULPHUR  DIOXIDE. 

air^  SO  that  the  ore  above  and  below  a  scar  is  very  incompletely  burnt. 
The  heat  is  locally  increased  and  driven  further  down  than  it  ought 
to  be ;  the  zone  of  combustion  is  removed  further  downwards ; 
and  on  letting  down  the  ore  the  pyrites  partly  comes  out  incom- 
pletely burnt.  If  scars  have  formed  in  the  burner^  they  naturally 
descend  as  the  cinders  are  let  down^  and  they  would  ultimately  lie 
immediately  on  the  grates  and  entirely  stop  them  up.  This^  how- 
ever^ must  be  prevented  by  all  means.  A  careful  workman  always 
breaks  up  the  surface  of  the  old  ore  before  putting  in  a  fresh 
charge;  and  thus  he  finds  out  whether  any  scars  have  formed, 
which  mostly  takes  place  near  the  surface :  they  can  then  be  easily 
brought  to  the  surface  by  means  of  hooks  and  pulled  out  at  the 
door.  But  if  they  have  been  overlooked  at  first  and  have  got  lower 
down,  in  doing  which  they  constantly  increase  in  size^  their  removal 
is  more  difficult.  Then  a  very  large  and  heavy  poker  of  the  best 
tough  iron  (these  are  made  up  to  12  feet  long  and  2  inches 
thick),  bent  in  the  way  shown  in  fig.  88,  is  introduced  into  the 

Fig.  88. 


burner  through  the  charging-hole,  and  the  men  work  it  till  they 
have  got  the  point  a  underneath  the  scar.  Several  men,  working 
at  the  end  i,  then  try  to  lift  up  the  scar,  in  spite  of  the  resistance 
of  the  superjacent  mass  of  pyrites.  This  labour  is  very  disagreeable, 
exhausting,  and  difficult.  The  middle  doors,  between  the  charging- 
door  and  the  grate,  found  in  all  pyrites-burners,  are  only  used  in 
extreme  cases. 

With  the  low  burners  mentioned  on  pp.  305  &  310,  where  the  ore 
lies  only  fit  a  depth  of  20  inches,  scarring  is  next  to  unknown,  at 
least  if  the  ore  is  very  carefully  sized,  so  that  all  passing  through  a 
^-inch  riddle  is  kept  out.  This  agrees  with  the  facts  which 
will  now  be  explained. 

Apart  from  other  causes,  the  supply  of  air  in  a  burner  may  be 
insufficient  because  the  ore  lies  too  deep.  As  the  depth  of  the  ore 
depends  upon  the  vertical  distance  between  the  grate  and  the 
working-door,  it  follows  that  for  ores  behaving  very  differently  in 


WORKIXO  PYRITES-BURNERS  FOR  LUMPS.  321 

this  respect  differently  built  burners  must  be  used.  Thus  the  deep 
burners  built  for  Irish  pyrites  had  at  once  to  be  given  up  when 
Spanish  pyrites  began  to  be  used.  With  the  same  height  of  pyrites 
which  was  just  right  for  the  poor  ore,  in  order  to  keep  the  heat 
better  together,  the  rich  cupreous  ore,  in  itself  more  fusible,  be- 
came far  too  hot,  and,  moreover,  the  air  could  not  pass  through 
quickly  enough  to  make  a  complete  burning  of  the  ore  possible  at 
every  point  ;  from  both  causes  combined  followed  this  effect  (easily 
comprehensible  after  what  has  just  been  said),  that  the  scarring 
became  excessive.  It  is  always  much  more  feasible  to  burn  poor 
ore  in  a  shallow  than  rich  ore  in  a  deep  burner. 

Insufficiency  of  draught,  if  very  considerable,  will  be  easily 
lecoguized  by  the  gas  blowing  out  of  all  the  joints  of  the  burners, 
and  especially  coming  out  in  force  whenever  the  working-doors  or 
the  bottom  door  are  opened.  On  the  other  hand,  the  draught 
should  not  be  so  strong  that  too  much  air  will  get  into  the  chambers ; 
the  gas  ought  to  be  kept  as  rich  as  possible,  as  will  be  shown  here- 
after. It  may  be  assumed  that  the  draught  is  just  right,  if,  on 
opening  the  small  slide  in  the  working-door,  neither  gas  nor  flame 
issues  from  it,  nor,  on  the  other  hand,  the  flames  inside  the  burner 
perceptibly  tend  towards  the  draught-hole.  They  ought  to  rise  up 
perpendicularly  and  quite  steadily ;  and  on  opening  the  door  they 
may  even  tend  slightly  towards  it.  As,  however,  the  exact  regu- 
lation of  the  draught  can  only  be  effected  by  regulating  the  holes 
in  the  bottom  door,  and  as  on  each  opening  of  the  doors  above  or 
below  the  grate  much  more  air  must  get  in  than  is  necessary,  of 
course  the  times  during  which  the  doors  are  opened  are  restricted 
as  much,  and  the  charging,  shaking  of  the  grates,  and  discharging 
are  managed  as  quickly,  as  possible.  It  is  very  advisable  to  close 
the  holes  in  the  bottom  door  completely  while  the  top  door  is 
open,  or  to  proceed  in  the  way  described  on  p.  303  et  seq.  If  the 
draught  is  not  very  copious,  whenever  the  door  is  opened,  there 
will  be  no  room  for  so  much  air  rushing  in,  in  consequence  of 
which  a  portion  of  the  gas  will  rush  out  and  get  into  the  burner- 
house  ;  this  is  both  a  loss  and  a  nuisance  to  the  workmen,  and, 
in  greater  quantity,  also  to  the  neighbours. 

For  regulating  the  snpjdy  of  air  several  plans  are  possible.  The 
regulation  takes  place  either  before  the  grate,  by  the  holes  in  the 
bottom  door,  or  behind  the  grate,  by  means  of  the  damper  in  the 
draught-hole  or  that  in  the  large  chimney  behind  the  chambers, 

VOL.  I.  Y 


322  PRODUCTION  OF  SULPHUR  DIOXIDE. 

or  else  by  fan-blasts  (comp.  Chap.  V.).  Regulation  behind  the 
burners  is  only  available  where  all  the  burners  have  a  common 
gas-space ;  otherwise  the  draught  through  the  chimney  or  fan  must 
be  equal  to  the  maximum  amount  required  for  all  the  burners^  and 
must  be  changed  according  to  the  atmospheric  conditions^  each 
burner  being  regulated  separately.  This  could  be  done  best  and 
most  safely  by  the  dampers  in  the  draught-holes  connecting  each 
burner  with  the  gas-flue  j  but  these  are  rarely  used  for  this  pur- 
pose ;  they  would  have  to  be  made  very  tight-fitting,  and  then 
would  easily  be  set  fast  by  flue-dust.  Therefore  here  also  the 
draught  is  made  suflScient  for  all  eventualities.  The  real  regula- 
tion of  the  air,  at  least  generally  in  England,  takes  place  by  means 
of  the  holes  in  the  ash-pit  door,  of  which  a  sufficient  number  are 
closed  by  plugs  or  otherwise.  Scheurer-Kestner  went  so  far  as  to 
pass  all  the  air  through  a  Combes^  anemometer ;  but  this  can  only 
have  been  done  for  isolated  experiments,  since  such  a  delicate 
instrument  can  hardly  have  been  kept  fit  for  use  for  any  length  of 
time  in  an  atmosphere  thus  exposed  to  acid  vapours  and  to  dust. 
It  is  therefere  left  to  the  burner-men  to  open  or  close  the  holes  in 
the  door  as  required.  At  the  Rhenania  works  (1902)  they  regu- 
late the  supply  of  air,  apart  from  the  exit  damper,  merely  by  a 
slide  damper,  shutting  off  the  flue  below  the  grates  in  which  the 
cinder-bogies  are  placed. 

The  supply  of  air  is  usually  regulated  by  the  following  practical 
rules : — At  the  beginning  (that  is,  immediately  after  making  a 
fresh  charge)  the  burner  does  not  require  very  much  air,  till  the 
ore  has  caught  fire,  which  will  take  half  an  hour  or  an  hour.  Then 
more  air  must  be  admitted,  always  with  the  above-mentioned 
restriction — that  the  flames  rise  perpendicularly,  and  tend  slightly 
towards  the  slide  when  this  is  opened.  When,  however,  the  prin- 
cipal portion  of  the  sulphur  is  burnt  and  the  flames  become  scarce, 
the  air  is  altogether  shut  ofiF,  and  further  action  is  left  to  the  heat 
of  the  burner.  About  two  hours  before  it  is  time  for  recharging, 
the  working-door  is  opened  and  the  ore  is  well  raked  and  turned 
over  by  means  of  a  hook  to  a  depth  of  3  or  4  inches,  and  any  small 
scars  are  removed.  If  herewith  blue  flames  appear  to  any  extent, 
this  proves  the  burning  not  to  have  been  sufficient,  and  a  little  air 
must  be  admitted.  When  the  whole  time  is  up,  be  it  a  twelve- 
hours'  or  a  twenty-four  hours'  turn,  the  air  is  entirely  shut  off^  at 
the  bottom,  the  small  doors  covering  the  grate-bars  are  opened,  and 
the  latter  are  turned  two  or  three  times,  leaving  each  alternate  one 


WORKING  FYRITB9-BURNEES  FOR  LUMPS.  323 

out.  During  this  the  workman  must  look  through  the  working- 
door,  to  see  whether  the  layer  of  ore  is  let  down  evenly  all  over ; 
he  can  easily  manage,  determined  by  the  eye,  not  to  let  the  ore 
down  too  much  or  too  little.  Then,  as  quickly  as  posible,  the 
new  charge  of  ore  in  pieces  (usually  with  a  little  dust),  which 
must  have  been  lying  ready  in  front  of  the  burner,  is  put  in,  and 
the  process  begins  again.  It  is  evident  that  there  must  be  a  regular 
rotation,  so  that  a  fresh  burner  comes  in  turn  every  hour  or  so ; 
this  is  both  indispensable  for  a  regular  evolution  of  gas,  and  con- 
venient for  distributing  the  labour  over  the  day. 

The  burner-men  ought  to  shake  the  grates  quite  equally  for  the 
purpose  of  discharging,  so  that  the  ore  does  not  come  down  more 
quickly  in  one  place  than  in  another,  and  to  take  care  that  only 
cold,  thoroughly  exhausted  cinders,  but  no  red-hot  ore,  comes 
down.  They  ought  then  to  work  up  the  ore  on  the  top  through 
the  doorway  with  their  pokers,  and  rake  the  surface  so  as  to 
make  it  even  again.  Then  they  must  charge  the  new  ore  equally 
all  over,  starting  about  two  inches  towards  the  door  from  the  back 
and  the  sides.  Two  men  can  attend  to  a  set  of  18  or  20  burners, 
consuming  from  6  to  8  cwt.  of  pyrites  each  every  24  hours, 
including  the  wheeling  away  of  the  cinders  and  the  potting. 

The  interior  of  a  burner,  after  the  throwing-in  of  a  fresh  charge, 
is,  of  course,  at  first  quite  black.  Gradually  small  blue  flames 
appear,  which  become  larger  and  more  lively  and  cover  the  whole 
mass.  After  a  few  hours  they  become  scarcer  again ;  but  the  mass 
in  the  meantime  has  become  red-hot.  Later  on  it  cools  again ; 
and  towards  the  end  of  the  period  there  is  no  glowing  visible  at 
the  surface ;  but  as  soon  as  the  mass  is  stirred  up  the  glowing 
appears  again. 

The  men  like  to  employ  a  practical  test,  to  convince  themselves 
that  the  burner  is  not  too  hot  for  recharging,  in  the  shape  of 
strokes  made  with  brimstone  on  the  burner-door :  so  long  as 
these  take  fire  at  once,  the  burner  is  still  too  hot ;  only  when  they 
remain  is  it  cold  enough  for  charging.  Frequently  it  is  necessary 
to  wait  a  short  time,  even  for  a  few  hours,  after  shaking  the  grate- 
bars  and  letting  down  the  burnt  ore,  in  order  that  the  burner  may 
cool  a  little  before  recharging  it;  this  has  the  advantage  that 
the  top  layer,  by  turning  it  over,  is  caused  to  burn  its  sulphur 
more  thoroughly  than  it  can  be  burnt  after  cold  pyrites  has  been 

thrown  in. 

y2 


324  PRODUCTION  OF  SULPHUR  DIOXIDE. 

Generally  it  takes  some  time  before  the  men  get  used  to  a  new 
kind  of  burner  or  of  pyrites.  If  even  skilled  men  are  taken  from 
other  places,  they  require  special  supervision^  and  still  more  if  a 
new  kind  of  pyrites  has  to  be  tried.  If  at  all  possible^  different 
kinds  ought  not  to  be  tried  mixed  up^  but  one  kind  adhered  to  for 
l^ome  time,  because  only  in  this  way  do  the  men  get  used  to  a 
thoroughly  proper  treatment  of  the  burner.  Each  kind  of  pyrites 
requires  a  little  different  treatment  as  to  supply  of  air,  breaking 
up,  &c. 

An  extremely  great  help  in  regulating  the  burning-process  is 
the  analysis  of  the  gas,  which,  however,  is  nearly  always  made  for 
a  whole  set  of  burners  together  in  their  common  flue.  We  shall 
enter  into  the  details  of  this  later  on. 

If  a  pyrites-burner  is  working  properly,  it  will,  if  touched  out- 
side, be  so  hot  in  its  upper  part  (say  6  inches  below  the  working- 
door)  that  the  hand  cannot  be  borne  upon  it ;  further  down  it 
must  be  cooler;  and  immediately  above  the  grates  it  ought  to  be 
cold,  or  at  most  hand-warm.  This  is  one  n>f  the  most  important 
practical  signs  of  the  proper  working  of  the  bulkier.  If  a  burner  is 
too  hot  below,  this  may  be  due  to  insufficient  draught,  or  (which 
in  the  end  comes  to  the  same  thing)  there  has  either  been  too 
much  pyrites  charged  or  there  is  too  much  dust  in  the  burner, 
which  has  stopped  up  the  interstices.  Too  much  dust  may  come 
from  bad  riddling,  from  too  much  having  been  added  on  purpose, 
from  the  falling  of  the  "  balls  ''  inside  the  burners,  or  from  the 
decrepitation  of  "  explosive''  ores  (comp.  pp.  55  &  77), 

In  any  case,  the  first  thing  to  be  done,  apart  from  removing 
the  cause  of  the  evil,  is  to  agaiu  cool  the  excessively  hot  burner. 
Above  all,  more  air  must  be  admitted;  and,  in  order  to  drive 
up  the  heat  more  certainly,  the  new  charge  must  be  kept  back 
a  little,  and  no  fresh  ore  put  in  the  middle,  but  only  along 
the  sides  and  the  back  of  the  burner.  It  always  takes  one 
or  two  days,  sometimes  longer,  before  a  burner  has  recovered 
its  normal  temperature.  In  specially  obstinate  cases  there  is 
nothing  for  it  but  making  very  small  charges  for  a  day  or  two, 
till  matters  have  come  right  again.  Some  manage  by  taking  out 
the  ignited  top  layer,  allowing  it  to  cool  a  little,  and  putting  it 
back  into  the  burner,  which  in  the  meantime  has  received  more 
draught,  owing  to  the  lower  depth  of  ore,  and  thus  has  become 
cooled. 


WORKING  TH£  PYRITES-BURNERS.  325 

If  a  kiln  is  allowed  to  go  too  hot  for  any  length  of  time, 
whatever  may  be  the  cause  (want  of  air,  too  large  charges, 
stopping  up  by  dust,  bad  breaking  up),  the  consequence  will 
always  be  the  same,  viz.,  increased  scarring,  with  all  its  un- 
pleasant accompaniments.  I  have  had  to  deal  with  cases  where 
the  scars  became  so  abundant  that  the  burner  had  to  be  put 
out,  the  grates  had  to  be  drawn,  the  whole  of  the  stone  taken  out, 
and  the  burner  freshly  filled  up. 

Of  course  it  also  sometimes  happens  that  a  burner  goes  too  cold 
and  the  fresh  charges  take  fire  too  slowly.  This  may  be  caused 
equally  by  a  want  of  draught  or  by  too  small  charges,  and  can  be 
easily  remedied  in  either  case.  If  it  has,  however,  got  so  far  that 
the  new  pyrites  will  not  take  fire  at  all^  nothing  remains  but  to 
put  in  very  hot  ore  from  some  of  the  other  working-burners  ;  in 
this  way  the  matter  may  always  be  put  right  with  some  patience, 
unless  large  scars  are  lying  on  the  grates,  or  there  are  other 
serious  faults,  which  must  be  removed  before  the  burner  can  be 
expected  to  work  properly.  A  frequently  used  but  objectionable 
remedy  against  cold  burners  is  to  put  live  coals  on  the  pyrites. 
Carbonic  acid  is  a  great  enemy  to  the  chamber  process,  probably 
not  so  much  by  diluting  the  gas  (for  its  injurious  action  is  far  too 
great  to  be  attributed  to  that  alone),  as  by  lying  in  the  lower  part 
of  the  chambers  and  preventing  contact  between  the  chamber-gas 
and  the  bottom  acid,  till  it  is  removed  by  diffusion.  This  point, 
however,  is  not  yet  cleared  up. 

A  pyrites-burner  may  also  go  too  cold  if  there  is  too  much 
draught — if,  therefore,  besides  the  air  required  for  its  intense  work- 
ing there  is  an  excess,  which  only  acts  as  inert  cooling  gas.  This 
is  a  very  great  fault ;  for  in  this  way  the  consumption  of  nitre  is 
increased  and  the  yield  of  sulphuric  acid  very  much  diminished. 
Long  before  the  burners  cool  from  this  cause,  an  excess  of  air  may 
become  injurious  in  this  way;  and  by  observing  the  flames  in  the 
burners  (much  better,  however,  by  the  analysis  of  the  gas),  it  must 
be  ascertained  whether  the  proper  proportion  of  air  is  present 
or  not. 

Balar^l  reports  (^  Rapports  du  Jury  International,'  1867,  vol.  vii. 
p.  29)  that  in  the  first  trials  of  Perret  and  Olivier  for  employing 
pyrites  in  manufacturing  sulphuric  acid,  thtyat  last  succeeded  in 
properly  conducting  the  combustion,  but  obtained  a  very  small 
yield  of  acid.      They  ascribed  this  to  an  insufficient  draught,  and 


326  PRODUCTION  OF  SULPHUR  DIOXIDE. 

applied  a  fan-blast ;  but  the  yield  instantly  became  minimaL 
Now  the  other  extreme  was  tried — the  air-channels  were  quickly 
stopped  up  with  boards  covered  with  sheep-skins  and  fastened  by 
stays.  At  once  the  chamber  process  became  regular,  and  the  key 
to  employing  pyrites  in  the  manufacture  of  sulphuric  acid  was 
found.  Probably  the  previous  endeavours  of  Cl^ment-Desormes 
in  this  respect  were  fnistrated  by  his  allowing  too  much  air  to  enter. 

Some  have  objected  to  the  employment  of  damp  pyrites  (Kerl- 
Stohmann's  '  Chemie/  3rd  ed.  vi.  p.  197),  because  in  this  case, 
on  burning,  more  sulphates  are  formed,  which  give  oflf  sulphur 
trioxide ;  this  takes  up  moisture,  and  condenses  as  sulphuric 
acid  before  getting  into  the  chambers,  destroying  the  flues  and  so 
forth.  Even  with  dry  ore  in  damp  weather  similar  phenomena  are 
said  to  be  observed,  and  a  smaller  yield  is  alleged  to  be  the  con- 
sequence of  the  moisture  in  the  air.  On  my  own  part,  I  have  never 
noticed  such  an  effect  of  damp  weather,  nor  have  I  been  able  to 
learn  anything  about  it  elsewhere,  in  spite  of  numerous  inquiries. 
It  is  very  desirable  that  this  point  should  be. specially  examined. 
The  formation  of  sulphur  trioxide,  as  well  as  the  occurrence  of 
liquid  sulphuric  acid,  in  the  connecting-tubes  has  certainly  been 
established  ;  but  it  has  not  yet  been  proved  that  the  moisture  of 
the  air  acts  in  a  way  to  increase  that  formation,  and  the  contrary 
is  more  than  likely  for  the  formation  of  SO3. 

He  who  has  no  practical  acquaintance  with  the  matter,  looking 
at  these  numerous  sources  of  mishaps,  may  be  inclined  to  think 
that  the  working  of  a  set  of  pyrites-burners  is  a  most  difficult 
task.  But  it  is  far  from  that.  If  once  the  burners  are  in  order, 
they  remain  very  long  so  if  the  burner-men  know  and  perform 
their  duty  to  any  considerable  extent,  and  if  proper  supervision 
is  exercised  over  them  ;  the  pyrites-buraers  then  give  even  less 
trouble  than  sulphur-burners.  Certainly,  when  they  do  get 
wrong,  it  takes  energetic  and  experienced  management  to  put  them 
right  again. 

It  will  now  hardly  be  necessary  to  explain  in  detail  why  there 
are  only  narrow  limits  for  each  given  burner  and  style  of  charging, 
within  which  the  quantity  of  pyrites  charged  may  vary  (comp. 
pp.  308  &  309).  If  too  much  is  charged,  the  burner  scars;  if 
too  little  is  taken,  it  gets  cold.  When,  therefore,  for  any  reason 
the  daily  quantity  of  pyrites  has  to  be  cut  down,  it  is  necessary  to 
put  out  a  corresponding  number  of  kilns  and  to  fully  work  the 


BVRNINO  PYRITES-SMALLS.  327 

remainder.  Only  in  the  case  of  brief  temporary  interruptions 
is  it  possible  to  charge  rather  less  than  usual  for  a  few  days; 
but  I  would  recommend  even  in  this  case  rather  to  allow  the  bulk 
of  the  burners  to  go  on  as  usual,  and  to  keep  the  necessary  number 
hot  without  fresh  charges  by  closing  all  openings.  Then  these 
kilns  will  be  much  more  easily  put  in  order  by  the  assistance  of 
the  other  burners  in  full  work  than  if  they  had  all  cooled  down. 

3.  Burning  Pyrites-smalls. 

We  have  seen  above  (p.  287)  that  the  fine  powder  which  passes, 
say,  through  a  ^-inch  or  at  most  a  ^-inch  riddle  must  be  kept  out 
of  the  ore  going  into  the  ordinary  pyrites-kilns.  The  '^  smalls," 
'^  fines,''  or  "  dust ''  produced  in  this  way,  whether  it  be  on 
breaking  the  ore  at  the  works  or  already  at  the  mine,  must  be 
dealt  with  separately. 

This  can  be  done  in  very  different  ways,  according  to  circum- 
stances. Where  pyrites-smalls  are  not  bought  as  such,  the 
question  is  only  about  the  dust  arriving  along  with  the  bulk  of 
the  ore  and  also  that  made  in  breaking.  Much  more  dust  is 
made  when  breaking  by  machine  than  by  hand — in  the  former 
case  up  to  20  per  cent,  with  middling  hard  ores,  and  even  more 
with  soft  ores.  Formerly,  before  rational  and  really  satisfactory 
contrivances  for  the  burning  of  smalls  were  known,  some  large 
works,  which  had  already  mounted  stone-breaking  machines,  went 
back  to  hand-breaking,  in  spite  of  its  costing  three  to  six  times 
as  much,  merely  in  order  to  avoid  the  excess  of  dust.  This  was 
especially  the  case  with  works  using  soft  ores,  such  as  the  Tharsis 
ore ;  with  Norwegian  ores  the  advantage  was  always  on  the  side 
of  the  mechanical  breaking,  because  these  are  much  harder  and 
make  less  dust.  If  the  quantity  of  dust  going  through  the  smaller 
riddle  does  not  exceed  1^  cwt.  to  the  ton,  it  can  be  got  rid  of, 
according  to  my  own  experience,  without  any  special  contrivance, 
in  the  following  way  : — ^The  dust  is  sifted  off  as  usual,  and  a 
certain  quantity  of  it  is  laid  down  for  each  burner  alongside  the 
pieces.  K,  for  instance,  the  whole  charge  is  7  cwt.,  6^  cwt.  of 
pieces  are  used  and  ^  cwt.  of  dust ;  if  more  than  this  is  used^  the 
burner  easily  gets  out  of  order.  First  the  coarse  ore  is  charged  as 
usual ;  and  then  the  man  throws  the  dust  with  his  spade  along  the 
sides  and  the  back  of  the  burner,  leaving  the  whole  central  part 


328  PRODUCTION  OF  SULPHUR  DIOXIDE. 

free.  Anyhow,  the  ore  ought  to  be  levelled  with  a  hook,  after 
throwing  in  the  charge,  in  such  a  way  as  to  make  it  higher  along 
the  sides  and  back  than  in  the  centre  of  the  burner.  The  reason  is 
this  :  the  air  entering  from  below  meets  with  much  less  resistance 
at  the  comparatively  smooth  walls  than  in  the  centre  of  the  layer 
of  ore,  and  it  will  preferably  rise  along  the  former ;  the  centre 
thus  will  get  less  air  than  the  parts  next  to  the  walls.  If,  bow- 
ever,  the  latter  lie  at  a  higher  level,  and  especially  if  the  passage 
of  air  is  obstructed  by  the  dust  lying  at  those  places,  the  draught 
will  be  more  nearly  equalized,  and  the  burning  will  take  place 
evenly  all  over  the  area  of  the  burner.  Of  course  it  is  not  well 
to  proceed  too  far  in  this  way ;  nor  can  it  be  expected  that  the 
result  is  as  good  as  when  lumps  and  smalls  are  each  treated  in 
the  best  way  suited  for  them. 

The  arrangement  just  described  does  not  answer  if  more  than 
l^  cwt.  o£  smalls  to  the  ton  of  pyrites  has  to  be  dealt  with ; 
and  special  arrangements  must  then  be  resorted  to.  Probably 
the  oldest  method,  now  almost  obsolete,  is  the  following : — The 
small  ore  is,  without  further  grinding,  mixed  with  sufficient  clay 
to  make  it  plastic,  made  into  a  puddle  with  water,  formed  into 
ballSy  and  dried  on  a  steam-boiler  or  pyrites-burner.  Rarely  less 
than  10  per  cent,  of  clay  will  be  required  for  this,  often  more,  up 
to  25  per  cent.  The  balls  are  then  charged  along  with  lumps  into 
the  ordinary  burners,  but  never  too  many  at  a  time  (at  most  one- 
sixth  part  of  the  whole  charge),  because  they  fall  to  powder  in  the 
burner  after  a  time,  and  if  used  in  a  greater  proportion  would  stop 
the  draught.  Only  locally  is  such  rich  clay  found  that  the  balls 
stand  pretty  well  in  the  burners  and  can  be  well  burnt  off.  The 
workmen  dislike  them  very  much,  because  they  disturb  the  working 
of  the  burners,  even  when  the  above-mentioned  restriction  of 
their  quantity  is  observed ;  if  a  burner  is  not  quite  warm,  they 
must  at  once  be  left  off.  Some,  in  order  to  get  rid  of  them  with- 
out disturbing  the  burners,  burn  them  by  themselves,  mixed  with 
"coal  brasses," — that  is,  the  pyrites  picked  out  of  coals,  which 
always  retains  some  of  the  latter,  and  therefore  burns  more  vividly 
and  gives  out  more  heat  than  pure  pyrites ;  but  then  it  sends  the 
injurious  CO3  to  the  chambers.  Usually  not  much  is  gained  by 
making  the  balls  with  clay,  since  they  so  quickly  fall  to  pieces  in 
the  burner ;  and  nearly  as  much  can  be  done  by  throwing  the 
dust  at  once  into  the  burner  and  saving  the  cost  of  making  the 


BURNING  PYRITES-SMALLS  IN  COAL-FIRED  FURNACES.  329 

balls.  Only  by  a  very  strong  admixture  of  clay  can  the  disinte- 
gration of  the  balls  be  prevented ;  but  then  the  loss  of  sulphur 
and  the  contamination  of  the  burnt  ore  is  all  the  greater.  In 
both  cases  the  sulphur  left  in  the  burnt  ore  rises  very  much^ 
from  6  to  8  per  cent,  and  more.  Where  the  cinders  go  to  copper- 
extraction  works^  the  use  of  clay  for  balls  is  quite  inadmissible. 

These  clay  balls  are  connected  with  so  many  drawbacks^  that 
something  else  was  soon  looked  for.  This  was  indispensable 
where  nothing  but  smalls  could  be  obtained^  or  where  they  could 
be  procured  so  cheaply  that  acid-makers  wished  to  dispense 
entirely  or  partially  with  using  lump  ore.  At  the  pyrites-mines 
there  were  formerly  enormous  heaps  of  smalls^  which  were  not 
saleable  at  all  and  would  sometimes  have  been  given  away  for 
nothing,  just  to  make  room.  In  other  places  pyrites  only  occurs 
in  a  loose,  roughly  crystalline  shape ;  and,  again,  in  others  it  is 
obtained  by  wet  preparation  altogether  in  the  state  of  smalls. 
Thus  there  was  great  encouragement  for  constructing  apparatus 
for  burning  small  pyrites  in  large  quantities. 

The  contrivances  for  burning  pyrites-smalls  may  be  divided 
into  three  classes,  namely,  those  working  by  external  heat,  those 
utilizing  the  heat  of  ordinary  burners  for  pyrites  in  lumps,  and 
those  arranged  for  burning  the  smalls  by  themselves  without  any 
extraneous  apparatus. 

(a)   Burning  Pyrites-smalls  in  Coal-fired  Furnaces. 

Apart  from  the  use  of  "  balls,"  the  oldest  plan  of  dealing  with 
pyrites-smalls  is  that  of  spreading  them  on  the  bed  of  a  furnace, 
heated  by  flues  underneath,  the  fireplace  being  arranged  at  one 
end  and  the  pyrites-dust  being  introduced  at  the  other,  and 
being  gradually  moved  forward  towards  the  fire  end,  as  room  is 
made  for  it  by  drawing  out  the  burnt  ore.  In  thus  being  turned 
over  many  times  on  its  way  from  one  end  of  the  furnace  to  the 
other,  the  sulphur  was  supposed  to  be  thoroughly  burnt. 
This  is,  however,  but  imperfectly  the  case,  even  if  the  furnaces 
are  made  100  feet  long.  Moreover,  the  cost  of  fuel  in  the  best 
case  is  very  heavy  (at  least  10  cwt.  of  coal  is  consumed  for  a  ton 
of  pyrites,  usually  much  more),  so  is  the  cost  of  labour ;  the  con- 
tinuous opening  of  the  working-doors  causes  very  much  false  air 
to  get  into  the  chambers,  even  fire-gases  sometimes  leak  through 


330  PRODUCTION  OF  SULPHUR  DIOXIDE. 

the  furnace-bottom^  and  therefore  the  consumption  of  nitre  and 
the  yield  of  acid  are  very  bad.  We  shall^  consequently,  not 
go  into  any  details  respecting  these  "  muflfle-furnaces,"  but  refer 
to  the  first  edition  of  this  work,  where,  on  pp.  186  to  190,  the 
Belgian  furnaces^  and  those  of  Spence,  of  Godin,  of  Imeary  and 
Richardson,  are  described  and  partly  illustrated  by  diagrams. 
Since  it  has  been  recognized  that  no  extraneous  heat  is  necessary 
for  burning  pyrites-smalls^  such  furnaces  must  be  looked  upon 
as  altogether  irrational,  and  they  are  practically  obsolete  now. 
This,  of  course,  has  nothing  to  do  with  the  fact  that  similar  fur- 
naces are  in  use  for  roasting  galena  and  other  ores  which  do  require 
external  heat  for  the  purpose. 

(b)  Burning  Pyrites-dust  by  the  heat  of  Burners  for  Lumps. 

This  was  considered  a  great  improvement  upon  the  older 
methods^  but  it  must  be* equally  pronounced  obsolete  now,  at  all 
events  in  the  case  of  ordinary  pyrites.  We  shall  therefore  treat 
these  processes  very  briefly,  referring  for  details  to  the  first 
edition  of  this  work. 

The  first  furnace  for  burning  pyrites-smalls  by  means  of  the 
heat  from  lump-burners  seems  to  have  been  that  patented  in 
France  by  Usiglio  and  Dony,  Jan.  24,  1852,  which,  however,  did 
very  imperfect  work.  Much  more  important  is  the  furnace  con- 
structed by  Olivier  and  Perret,  which  was  introduced  into  the 
majority  of  French  works  and  was  in  use  there  for  many  years, 
until  replaced  by  the  Maletra  burner  [vide  p.  334).  Olivier  and 
Ferret  placed  above  an  ordinary  him  p.  burner  a  number  of  shelves 
made  of  fire-clay,  and  charged  with  a  thin  layer  (not  above 
f  inch)  of  pyrites-dust  (for  exact  description  and  diagrams,  vide 
first  edition  of  this  work,  pp.  193  to  196).  In  this  way  it  is 
possible  to  bum  about  1  cwt.  of  dust  to  each  2  cwt.  of  lumps, 
the  sulphur  in  the  cinders  being  reduced  down  to  4  or  5  per 
cent.  The  whole  furnace  was  originally  about  20  feet  high,  which 
necessitated  a  second  working-stage  above  the  ground.  There  is, 
of  course,  a  good  deal  of  labour  connected  with  this  system. 
Later  on  it  was  made  lower,  and  so  arranged  that  all  the  doors 
were  on  one  side,  so  that  a  number  of  furnaces  could  be  grouped 
into  a  set. 

In  a  simpler  form,  namely,  that  of  a  single  cast-iron  plate  above 


BURNINO  PYRITES  WITHOUT  EXTERNAL  HEAT.  331 

ordinary  lump-burners,  this  system  was  introduced  into  some 
Tyneside  works,  first  by  MacCullocb,  but  was  soon  abandoned 
again  (comp.  1st  edition,  pp.  191  to  193). 

Another  way  of  carrying  out  the  same  principle  was  the  funiace 
of  Hasenclever  and  Helbig  (Ist  edition^  pp.  196  to  201).  Here, 
at  the  end  of  a  set  of  lump-burners,  a  tower-like  appiaratus  was 
arranged  with  eight  inclined  shelves  of  fire-clay,  over  which  the 
dust  was  gradually  to  slide  down  and  to  be  burnt  on  its  way. 
Thus  from  10  to  16  cwt.  of  smalls  were  to  be  burnt  for  each 
48  cwt.  of  lumps  ;  but  the  principle  of  automatic  sliding  down  did 
not  answer;  the  motion  of  the  dust  had  to  be  aided  by  hand- 
work^ with  much  introduction  of  false  air ;  and  although  a  large 
number  of  these  furnaces  were  erected,  principally  in  Germany, 
they  have  been  almost  or  entirely  abandoned  for  some  time  past, 
and  we  abstain  from  describing  them  in  this  edition. 

(c)   Burning  Pyrites-smalls  without  external  heat. 

We  must,  in  the  first  place,  mention  a  plan  which  does  with- 
out any  special  dust-burners,  and  only  represents  an  improvement 
in  making  "  balls/'  It  is  based  upon  the  fact  that  pyrites,  if  it 
is  in  the  shape  of  very  fine  powder  mixed  with  water,  coheres 
to  a  solid  mass  without  the  aid  of  any  plastic  substance.  The 
fine  pyrites-dust,  in  the  presence  of  water  and  air,  begins  to 
oxidize  very  soon,  even  at  the  ordinary  temperature ;  thus  basic 
ferric  sulphate  is  formed,  which  firmly  cements  together  the 
separate  grains  of  dust.  This  only  takes  place  to  a  sufficient 
extent  if  the  grains  of  dust  are  very  fine  and  the  mixture  with 
M  ater  very  perfect ;  and  this  can  never  be  attained  by  merely 
sifting  and  moistening  the  fine  ore.  The  ore  must  therefore  be 
ground  finely  with  water  in  a  mill,  for  which  purpose  usually  the 
so-called  pug-mills  are  used,  a  kind  of  vertical  mortar-mill,  some- 
times with  revolving  bottom  dish,  or,  if  the  dish  is  stationary, 
with  a  mechanical  arrangement  for  throwing  out  the  mixture  as 
soon  as  it  has  reached  the  proper  consistency.  The  pyrites-smalls 
are  thrown  into  the  mill,  water  is  run  on,  and  the  mill  is  run  till 
a  homogeneous  mixture  similar  to  fine  mortar  has  been  formed, 
Avhich  by  itself  has  somewhat  plastic  properties.  This  mass  is 
dried  in  layers  of  ^  inch  thickness  on  the  top  of  the  pyrites- 
burners,  often  in  cakes  about  1 8  inches  square ;  and  after  twenty- 
four  or  thirty-six  hours  it  has  hardened  sufficiently  for  use.     It  is 


332  PRODUCTION  OF  SULPHUR  DIOXIDE. 

broken  up  into  pieces  of  the  same  size  as  the  lump  ore,  and  charged 
along  with  this  into  ordinary  pyrites-burners.  In  this  it  is  not 
necessary  to  observe  a  certain  proportion  ;  for  the  balls  made  in 
this  way  are  so  hard  that  they  can  be  thrown  to  the  ground  with- 
out being  broken,  they  do  not  fall  to  powder  in  the  burners,  and 
burn  out  as  well  as  lumps ;  their  cinders  are,  of  course,  of  the 
same  value  as  those  from  lump  ore,  whilst  those  mixed  with  clay 
make  the  utilization  of  the  ferric  oxide,  at  last  obtained  at  the 
copper-extraction  works,  very  difficult. 

The  principal  drawback  of  the  process  is  this,  that  the  mills 
suffer  very  much  wear  and  tear  from  the  hard  pyrites.  In  spite 
of  this,  it  was  formerly  the  most  usual  in  the  large  English  works. 
The  labour  of  grinding,  carrying  to  the  top  of  the  burners  for 
drying,  taking  down,  breaking  up,  and  laying  down  in  front  of 
the  burners  amounts  to  I*.  4rf.  per  ton.  To  this  must  be  added 
6d,  for  coals  for  working  the  mill,  and  wear  and  tear  of  the  same, 
altogether  about  2*.,  apart  from  the  wages  for  the  burning  itself 
(another  2*.  per  ton). 

The  same  result  as  is  attained  by  the  ^^  pugging  ^^  process  is 
obtained  in  perhaps  a  more  complete,  but  decidedly  far  more  costly^ 
way  by  the  process  of  H.  Wurtz  (U.S.  Pat.  252,287).  He  mixes 
the  fine  ore  with  powdered  metallic  iron,  moistens  this  with  a 
solution  of  sulphate  of  iron,  and  allows  the  whole  to  agglomerate 
by  rusting. 

The  process  just  described  is  not  applicable  in  cases  where  the 
great  bulk  or  the  whole  of  the  pyrites  employed  is  in  the  shape  of 
dust.  In  such  cases  formerly  the  only  available  contrivance  was 
the  above-mentioned  muffle-furnace,  with  all  its  great  drawbacks. 
The  first  who  proved  that  the  heat  generated  by  the  combustion 
of  ferrous  bisulphide  is  sufficient  for  keeping  the  process  going 
without  any  external  aid^  quite  as  well  in  the  case  of  pyrites- 
smalls  as  in  that  of  lumps,  was  Moritz  Gerstenhofer,  whose  furnace 
is  described  at  length  and  shown  in  several  diagrams  in  the  first 
edition  of  this  work,  pp.  205  to  215.  We  here  give  only  one 
diagram,  fig.  89,  and  a  short  description.  It  consists  oE  a  shaft, 
17  feet  high,  2  feet  3  inches  long,  and  2  feet  7^  inches  \iide  inside, 
provided  with  a  large  number  of  prismatic  fire-clay  bars,  so  dis- 
posed that  the  intervals  of  each  upper  tier  are  covered  by  the  bars 
of  the  next  lower  tier.  The  pyrites-dust  is  fed  in  by  means  of 
fluted  rollers,  and  drops  from  tier  to  tier,  forcing  down  the  particles 


OBRSTENHOFFH  t 

Fig.  m. 


t 


334  PRODUCTION  OF  SULPHUR  DIOXIDE. 

previously  lying  on  the  bars  according  to  the  natural  slope  of  the 
ore.  Before  starting  the  feed  of  the  ore,  the  furnace  is  brought 
to  a  bright-red  heat  by  means  of  a  coal-fire.  Afterwards  the 
combustion  of  the  pyrites  by  means  of  the  air  entering  from 
below  is  quite  sufficient  for  keeping  up  the  heat. 

The  two  great  drawbacks  of  the  Gerstenhofer  burner  are :  the 
very  large  amount  of  flue-dust  produced  in  it,  and  the  very  in- 
complete desulphurization  of  the  ore  (8  or  10  per  cent.  S  in  the 
cinders).  Principally  for  these  reasons  this  ingenious  furnace  has 
been  abandoned  again  nearly  everywhere,  and  is  now  only  used  for 
roasting  ''  coarse  metal  '^  in  a  few  copper-works.  At  the  Freiberg 
works,  where  it  was  used  for  a  variety  of  mixed  ores  (25  to  36 
per  cent.  S),  it  has  also  been  replaced  by  the  Rhenania  furnace, 
to  be  described  below. 

According  to  Scheurer-Kestner  (Bull.  Soc.  Chem.  xlv.  p.  228), 
Perret  later  on  constructed  a  furnace,  resembling  Gerstenhofer's, 
but  free  from  the  defects  of  the  latter.  The  pyrites  was  stated 
to  be  thoroughly  utilized  and  the  cost  of  labour  reduced  to  one- 
half  as  against  Maletra's  "  shelf -burners  "  (see  below) .  At  the  time 
of  Scheurer-Kestner's  report  the  furnace  in  question  was  evidently 
still  in  the  experimental  stage;  and  as  nothing  more  has  been 
heard  of  it,  its  success  cannot  have  been  so  great  as  anticipated. 

The  object  but  imperfectly  attained  by  Gerstenhofer's  invention 
has  been  realized  by  a  very  simple  plan — so  simple,  indeed,  that  it 
was  not  thought  worth  patenting  at  the  time,  although  it  has  sub- 
ficquently  proved  to  be  of  immense  importance.  Mons.  Maletra, 
owner  of  the  works  of  Petit  Quevilly,  near  Rouen,  after  having 
for  some  time  burnt  his  smalls  by  means  of  an  Olivier-Perret  fur- 
nace, conceived  the  idea  of  separating  the  upper  part  of  this  furnace 
from  the  lower,  and  working  the  dust  by  its  own  heat  of  combustion 
without  any  aid  from  a  lump-burner.  This  idea,  which  was  worked 
out  about  1867  with  the  aid  of  M.  Tinel,  proved  entirely  success- 
ful; but  in  spite  of  this,  and  also  of  the  *^  shelf -burner*'  being  the 
jsimplest  and  cheapest  of  all  dust-burners,  it  became  comparatively 
slowly  known ;  but  since  1873,  when  it  became  better  known 
through  the  Vienna  Exhibition,  it  has  spread  on  the  Continent  with 
4Jxtraordinary  rapidity,  whilst  for  a  long  time  it  attracted  little 
Mtention  in  England.  The  first  burner  out  of  France  seems  to 
have  been  erected  at  the  works  of  Schnorf  Brothers,  at  Uetikon, 
near  Ziirich,  in  1870;  in  Germany  the  first  was  erected  at  Kun- 


\ 


halktra's  shelf-burner.  335 

helm's  vorks  in  Berlin.  Even  if,  as  it  would  seem,  some  form  of 
these  simple  shelf-burners  had  been  previously  in  use  here  and 
there,  their  successful  application  for  burning  pyritea-smalls  scema 
first  to  have  been  effected  by  MaMtra's  works. 

Fig.  90  gives  a  longitudinal,  iig.  91  a  cross  section,  the  latter 
through  two  furnaces.  Usually  a  whole  set  is  built  in  a  row.  In 
order  to  start  it,  a  coal-grate,  a,  and  fire-door,  b,  are  provided,  which 
are  walled  up  when  the  burner  has  got  up  to  a  white  heat.    During 

Fig.  90. 


this  time  the  top  working-door  remains  opeu,  Tlieu  the  five 
plates,  c,d,e,f,  g  are  charged  with  small  ore  through  the  doors  A,  i,k, 
whereupon  the  pyrites  takes  fire  at  once.  The  air  enters  through  /, 
and  is  regulated  at  will.  The  gas  travels  over  all  the  plates 
in  a  serpentine  mauner,  indicated  by  the  arrows,  escapes  through 
m  into  the  dust-chamber,  »,  and  through  o  into  the  acid-cham)>cr 
or  into  another  dust-chamber.  The  chamber  n  is  covered  by  u 
metal  plate,  p,  upon  which  lead  pans,  r,  r,  are  placed,  iu  which  ail 
the  chamber-acid  can  be  concentrated  from  113°  to  14i°Tw.    The 


336  FRODUCTION  OF  SULPHUR  DIOXIDE. 

acid  of  one  pan  commuaicates  with  that  of  another  (as  usual)  by 
siphons  or  by  simple  run-overs.  Each  of  the  shelves,  which  are 
8  feet  long  and  5  feet  wide,  consists  of  eight  plates  in  two  rows  of 
four  each ;  they  rest,  at  the  sides,  in  the  walls  of  the  burner,  in  the 
middle  on  fire-clay  bearers,  *,  g,  whose  shape  is  better  shown  in 
fig.  92.     They  are  not  equidistant,  as  can  be  seen  in  the  drawiug; 

Fig.  i).l. 


the  upper  shelves,  where  more  gas  is  evolved,  are  wider  apart 
than  the  lower  ones,  where  the  radiant  heat  of  the  shelves  is  all 
the  more  useful.  The  best  distance  for  the  upper  shelves  is 
4.^  inches.  In  order  to  burn  a  larger  quantity  of  pyrites,  it  is  not 
possible  to  leave  the  ore  lying  quietly,  as  in 
Olivicr-Perret's  burner :  since  here  the  ex-  ^'?'  "-■ 

tenia!  heating  hy  the  lump  ore  is  missing, 
the  combustion  would  be  too  incomplete, 
and  tiie  heat  would  soon  get  so  low  that  the 
burning  would  cease.  The  mass  must  there- 
fore be  moved,  which  is  done  in  the  follow- 
ing way : — Every  four  hours  the  contents  of  the  lowest  plate,  g,  are 


MALKTRA  S  SHELF-BURNER.  337 

drawn  through  the  door  k  on  to  the  arch  t  (which  is  level  at  the 
top,  but  slopes  behind),  after  the  burnt  ore  lying  on  the  arch  has 
first  been  pushed  through  the  door  k  to  the  opening  into  the 
pit  u.  Then  through  the  door  i  the  contents  of  /  are  pushed 
down  to  the  plate  g,  and  there  levelled  again.  Thus  the  higher 
plates  are  successively  treated^  till  the  highest  plate,  c,  is  emptied 
and  can  be  charged  with  fresh  ore.  If  four  furnaces  go  together, 
one  of  them  is  on  turn  every  hour.  The  contents  of  the  pit  u  are 
removed  once  a  day  by  the  door  v.  The  movement  of  the  ore  by 
removal  from  one  shelf  to  another  causes  its  thorough  combustion, 
and  thus  also  raises  the  heat.  Four  furnaces  of  the  above  dimen- 
sions burn  daily  3  tons  of  pyrites.  From  6^  to  7  lbs.  of  ore  are 
calculated  for  each  superficial  foot  of  shelving. 

Sometimes  the  shelves  are  made  in  the  shape  of  a  very  flat  arch, 
for  the  sake  of  greater  stability ;  or  at  least  the  bottom  is  arched, 
especially  in  the  case  of  wide  shelves.  Some  prefer  building  the 
furnaces  in  such  manner  that  the  fire-clay  slabs  forming  the  shelves 
are  nowhere  enclosed  within  the  brickwork  of  the  walls;  they  are 
then  more  easily  replaced  when  broken. 

The  Maletra  burners  have  recently  been  improved  by  making 
the  fire-clay  shelves  strouger  and  doing  away  with  the  middle 
bearers,  s,  s  (fig.  92),  which  give  much  trouble  in  working  the 
burner.  These  single  shelves  are  made  from  3  feet  3  inches  to 
3  feet  7  inches  inside. 

Maletra^s  burner,  which  has  obtained  general  acceptance  in 
Germany,  has  been  improved  there  by  Schaffner,  P.  W.  Hofmann, 
Bode,  and  others. 

Through  the  kindness  of  Dr.  Max  Schaffner,  of  Aussig,  I  was 
enabled  to  obtain  detailed  drawings  of  the  shelf-burners  as  modified 
by  him,  and  these  are  reproduced  and  described  in  our  second 
edition,  pp.  255  &  256.  This  furnace  has  seven  plates,  each 
served  through  its  own  door — three  on  one  side,  four  on  the  other. 
On  the  first  side  there  is  also  the  ash-pit  door,  18  inches  square, 
for  drawing  out  the  cinders,  which  is  thus  done  in  the  usual  way, 
not  by  the  rather  inaccessible  pit  of  Maletra.  The  doors  all  slide 
with  their  planed  margins  on  equally  planed  ledges  cast  on  the 
front  plates,  so  tliat  luting  or  plastering  is  not  necessary.  A 
certain  number  of  angle-pieces  are  bolted  to  the  front  plates; 
these,  between  their  outer  bend  and  the  planed  ledges,  leave 
sufficient  room  for  the  doors  t  to  slide  each  way  on  the  inclined 

VOL.  I.  z 


338 


PRODUCTION  OF  SULPHUR  DIOXIDE. 


Fig.  93. 


face  a  b ;  and  there  is  a  sufficient  number  of  such  pieces  present 
for  each  door  to  be  always  held  by  three  of  them  (fig.  93).  This 
style  of  work  is  evidently  much  cheaper  than 
casting  everything  in  one  piece,  because  the 
planing  is  much  easier  ;  it  is  also  cheaper  than 
the  English  style,  shown  on  pp.  298  and  299,  and 
quite  as  substantial  as  the  latter.  There  are 
no  special  openings  for  the  air,  as,  in  spite  of 
the  planed  surfaces,  sufficient  air  enters  to  sup- 
port the  combustion.  The  regulation  of  the 
draught  is  here  effected  entirely  by  the  chimney- 
damper. 

In  this  burner  diLst  and  peas  are  burnt  to-      *  ^ 
get  her,  and  the  sulphur  is  burnt  down  to  1  per 
cent. ;  thus  the  grinding  of  the  smalls,  which 
is  still  practiced  at  some  works,  is  done  away 
with. 

The  Aussig  or  Schaffner  dust-burner  has 
been  erected  in  many  works  from  the  plans  given  in  the  previous 
edition  of  this  book,  and  that  with  entire  success.  Of  course  at 
some  places  minor  modifications  have  been  introduced,  but  the 
principle  is  always  the  same,  also  in  the  plans  given  by  Falding 
in  'Min.  Ind.^  vii.  p.  668. 

Most  manufacturers  now  consider  that  burners  worked  from 
both  sides  allow  too  much  false  air  to  enter,  and  therefore  prefer 
arranging  two  rows  back  to  back.  I  am  enabled  to  give  full 
drawings  of  the  most  modern  dust-burners  from  the  designs  of 
Mr.  H.  H.  Niedenfiibr,  as  shown  in  figs.  94  to  96.  They  are 
clear  enough  to  require  no  further  description.  ' 

According  to  communications  from  Mr.  Benker,  he  still  (1902) 
builds  his  Maletra  furnaces  on  the  old  system  (p.  335),  all  the 
compartments  in  one  line.  On  the  top  he  places  a  collecting-flue 
and  dust-chamber,  5  feet  high ;  at  the  end  of  the  set  a  large  dust- 
chamber,  of  the  same  height  and  width  as  the  furnace  and  20  to 
30  feet  long,  according  to  the  description  of  ore.  One  man  serves 
two  compartments.  Each  of  these  burns  20  to  24  cwt.  of 
50  per  cent,  pyrites  per  24  hours,  but  up  to  32  cwt.  of  poor  ore, 
such  as  he  had  to  work  in  Italy,  containing  26  per  cent,  sulphur 
and  3  per  cent,  copper,  of  which  90  per  cent,  was  soluble  in  water 
and  95  per  cent,  soluble  in  dilute  sulphuric  acid  after  roasting. 


.4 


{ 


WORKING  SHELF-BURNERS.  339 

The  ore  is  spread  on  the  plates  by  means  of  a  tooth-rake^  pro- 
ducing an  undulated  surface  and  not  leaving  any  bare  places. 
From  such  poor  ores  Benker  obtained  gases  with  7 '7  per  cent.  SO2 
on  the  average^  and  produced  6*2  kg.  acid  of  106°  Tw.  per  cubic 
metre  (=0*39  lb.  per  cubic  foot)  in  24  hours^  with  a  consumption 
of  0-7  parts  nitric  acid  66°  Tw.  to  100  sulphuric  acid  106°  Tw. 

One  of  the  principal  advantages  of  the  shelf-burners  is  that 
the  ore  is  burnt  out  to  a  much  larger  extent  not  merely  than  with 
any  of  the  older  forms  of  dust-burners^  but  even  with  the  best 
lump-burners.  Even  without  grinding  the  smalls,  it  is  quite  easy 
to  keep  the  sulphur  in  the  cinders  down  to  1*5  per  cent.  At  many 
works,  e.g.  at  Uetikon,  the  average  amount  of  sulphur  in  the 
cinders  never  exceeds  1  per  cent.,  and  frequently  it  is  below.  At 
Mal^tra^s  own  works  they  get  down  to  0*6  or  0*8  per  cent.,  but 
this  can  be  done  only  by  crushing  the  smalls  down  to  an  almost 
uniform  fine  powder.  The  amount  passed  through  the  burner  also 
influences  this.  Sorel  states  that  a  set  of  burners,  charged  with 
34  or  35  kils.  of  ore  per  square  metre  every  24  hours,  was  regularly 
burnt  down  to  0*75  per  cent.  \  with  36  kils.  the  sulphur  in  the 
cinders  rose  to  1  per  cent.,  with  32  kils.  it  fell  as  low  as  0*42  per 
cent.  Jurisch,  in  his  '  Schwefelsaurefabrikation '  (p.  80),  quotes 
30  kils.  pyrites  per  square  metre  of  plates,  with  variations  from 
25-6  to  35-8  kils.  Stolzenwald  (Chem.  Zeit.  1901,  p.  22),  when 
burning  Hungarian  pyrites  (47  per  cent.  S),  was  not  able  to  burn 
more  than  24  kils.  per  square  metre  of  Maletra  plates,  in  order  to 
get  down  to  1*7  per  cent.  S  in  the  cinders. 

I  have  seen  in  Germany  shelf-burners  working  up  "  peas ''  of 
Spanish  ore  down  to  28  per  cent.  S,  and  even  real  '* lumps'' 
of  Westphalian  ore  down  to  35  per  cent.  S. 

Such  results  can,  of  course,  only  be  obtained  with  pure  ores, 
free  from  zinc,  lead,  &c.  Hence  the  cinders  from  shelf-burners 
are  readily  bought  by  iron-works,  both  for  blast-furnaces  and 
other  purposes. 

In  a  six-shelf  burner  there  ought  to  be  scarcely  any  purple 
flame  visible  when  pulling  the  charge  down  from  the  top  shelf  to 
^the  second  shelf.  The  second  shelf  is  at  a  bright  red  heat,  the 
bird  one  less  so,  and  so  forth ;  the  back  part  of  the  fifth  ought  to 
oe  visible  only  at  night  by  the  light  radiated  downwards  from  the 
fourth,  and  the  sixth  ought  to  be  perfectly  black.  Krutwig  and 
Dumoncourt  (Chem.  Zeit.  Rep.  1898,  p.  242)  found  the  temperature 

z2 


340  PRODUCTION  OF  SULPHUR  DIOXIDE. 

on  the  top  shelf  =680%  on  the  second  750°,  on  the  third  720%  on 
the  fourth  650°  C. 

Sorel  found  the  following  percentages  of  sulphur  on  the  diflFerent 
shelves  : — 

Sulphur  in  green  ore 50  per  cent. 

Firstshelf  32       „ 

Second  „    17       „ 

Third     „ 7       „ 

Fourth  „    5       „ 

Fifth     „    2       „ 

Sixth     „    0-75,, 

He  regularly  detected  half  of  the  sulphur  in  the  cinders  in  the 
shape  of  PeS,  the  other  half  in  that  of  sulphate. 

Crowder  (J.  Soc.  Chem.  Ind.  1891,  p.  298),  in  working  with 
shelf-burners  containing  seven  beds,  charged  once  every  eight 
hours  (so  that  the  charge  takes  7x8^8  56  hours  to  complete  the 
course),  found  the  following  percentages  of  sulphur  on  the 
different  shelves  (nearly  agreeing  with  SorePs  results  mentioned 
in  the  text)  : — 

Average  of  23  trials.       Ditto  of  26  trials. 

Ore  charged     50  50       per  cent.  S. 

No.  1  shelf 32-27  32*81 

2  „     21-41  17-55 

3  „     12-77  1109 

4  „     6-39                       505         „ 

5  „     4-08                       3-42         „ 

6  „     2-35                       2-56 

7  „     2-27                       1-96 

If  there  is  too  much  draught,  the  lower  shelves  cool  down  and 
the  upper  ones  get  hotter.  This  may  cause  the  process  to  appear 
as  going  on  very  well ;  but  it  soon  turns  out  bad.  If,  on  the  con- 
trary, there  is  too  little  air,  the  bottom  shelf  becomes  luminous 
and  the  sulphur  in  the  cinders  rises  rapidly.  In  both  cases  there 
is  incipient  fusion  on  the  second  shelf,  which  prevents  the  roasting 
from  being  carried  through.  This  can  be  remedied  by  admitting 
a  little  air  at  the  door  of  the  second  shelf,  or  even  mixing  a  little 


WORKING  SHELF-BURN  BBS.  341 

dead  ore  with  the  charge.  The  admission  of  air  to  the  inter- 
mediate shelves  serves  also  for  bringing  forward  any  burners 
wliieh  have  got  behind,  and  to  burn  any  sulphur  subliming  from 
the  first  shelf,  in  case  the  burners  are  going  too  hot^  or  from  damp 
pyrites  giving  off  sulphuretted  hydrogen ;  but  this  expedient^ 
useful  as  it  is  when  properly  handled,  must  be  employed  with 
caution  lest  the  bottom  shelves  get  too  cold  from  want  of  air. 

In  the  normal  style  of  working  all  the  air  required  for  convert- 
ing the  sulphur  into  sulphuric  acid  enters  at  the  bottom  shelf,  and 
this  large  quantity  of  cold  air  may  lower  the  temperature  of  the 
nearly  burnt-out  mass  to  such  an  extent  that  no  more  ferric 
sulphate  is  decomposed.  It  was  at  first  sought  at  Maletra's  works 
to  avoid  this  by  leading  the  burner- gas  downwards  underneath  the 
bottom  shelf,  thus  heating  tke  latter  and  employing  the  ground- 
space  as  a  dust-chamber ;  but  this  plan  did  not  answer  and  was  soon 
given  up  again.  It  has  even  been  tried  to  utilize  the  heat  of  the 
burner-gases  for  a  previous  heating  of  the  air  serving  for  the 
burning-process.  But  evidently  this  must  most  seriously  interfere 
with  the  draught,  and  will  hardly  answer  in  the  long  run.  The  same 
advantage  could  be  secured  more  easily  by  admitting  at  the  bottom 
only  the  quantity  of  air  absolutely  necessary  for  completing  the 
roasting  of  the  air,  and  allowing  the  remaining  air  to  enter  by  a 
regulating-slide  in  the  top  working-door.  In  this  case  the  bottom 
shelf  will  be  visibly  red-hot  in  the  dark.  This  plan  can  be  carried 
out  only  where  the  draught  is  very  good,  for  instance  by  making 
the  gas  to  rise  to  a  considerable  height  before  entering  the  chambers, 
and  never  leading  it  downwards  in  any  part  of  its  course.  The 
burner  walls  should  in  this  case  be  made  thick  or  hollow  to 
prevent  loss  of  heat  in  the  lower  part ;  on  the  contrary,  an  over- 
heating of  the  top  shelf  should  be  avoided  by  making  the  gas-flue 
rather  high  and  causing  the  heat  to  be  dissipated  there,  most 
rationally  by  means  of  evaporating-pans  for  sulphuric  acid. 
Another  plan  is,  introducing  the  requisite  excess  of  air  into  the 
first  chambers  by  means  of  an  injector. 

The  shelf -burner  answers  best  for  rich  ores.  With  50  per 
cent,  ore  good  results  are  obtained  when  burning  from  32  to  37 
kils.  of  pyrites  per  superficial  metre  (=  6*5  to  7*5  lbs.  per  square 
foot)  in  24  hours.  One  may  go  down  to  28  kils.  (=5*7  lbs.), 
but  only  exceptionally,  because  the  burners  cool  down  too 
much. 


342  PRODUCTION  OF  SULPHUR  DIOXIDE. 

For  poor  ores^  say  below  38  per  cent,  of  sulphur^  the  shelf- 
burner  does  not  answer. 

The  management  of  shelf-burners  is  really  easier  than  that  of 
lump-burners^  but  it  involves  a  little  more  labour.  It  is  generally 
assumed  that  one  man  can  charge^  burn^  and  withdraw  a  ton  of 
pyrites  every  day ;  but  it  is  possible  to  get  up  to  25  cwt.  It 
seems  best  to  give  five  burners  to  each  man^  so  that  each  burner 
is  charged  every  five  hours.  The  phenomenon  of  scarring  is 
hardly  ever  noticed  here.  The  working-doors  must  never  be  left 
open  any  longer  than  is  absolutely  necessary  for  the  work ;  in  this 
case  both  the  yield  of  acid  and  the  consumption  of  nitre  are  just 
as  favourable  when  working  dust  on  a  shelf-burner  as  with  the 
best  lump-burners.  This  is  the  uniform  testimony  of  the  many 
works  I  have  visited. 

In  order  to  start  a  new  burner  (which^  of  course^  must  have 
been  thoroughly  dried  first  in  the  ordinary  manner) ,  the  commu- 
nication with  the  chambers  is  stopped  and  a  fire  is  lighted  on  the 
shelves^  beginning  with  the  bottom^  sometimes  by  means  of  a 
temporary  chimney.  After  four  or  five  days^  when  the  burner  is 
moderately  red-hot  (it  is  unnecessary  and  even  injurious  to  get  it 
up  to  a  bright  red  heat),  the  remainder  of  the  fuel  is  cleared  away^ 
pyrites  is  charged  on  the  three  top  shelves^  and  communication  so 
made  with  the  chambers^  whereupon  the  regular  service  is  started 
as  previously  described. 

During  the  last  twenty  years  the  shelf-burners  have  also  beeti 
introduced  into  a  number  of  English  works,  and  everywhere  with 
great  success.  This  has  been  done  on  the  lai*gest  scale  at  the 
Newcastle  Chemical  Works  (AUhusen's),  where  129  shelf-burners 
on  Schafiner^s  plan,  described  in  this  book,  have  been  erected, 
which  consume  from  600  to  650  tons  of  pyrites-smalls  (Ma«on  and 
Barry's)  per  week.  Each  burner  is  charged,  once  in  8  hours,  with 
from  4^  to  4|  cwt.  of  smalls. 

The  objections  made  to  the  shelf-burner  in  its  employment 
for  sulphite  paper-works  by  Harpf  have  been  refuted  by  the 
author  in  Zsch.  angew.  Ch.  1896,  pp.  65  &  157. 

Combination  of  lump-burners  and  dust-burners  for  the  same  set 
of  chambers, — Such  a  combination  is  generally  avoided,  as  the 
conditions  of  draught  are  very  different  in  each  case.  I  have, 
however,  seen  a  combination  of  the  above-mentioned  kind  in 
excellent  operation   at   the  Stassfurt   potash- works  managed  by 


MECHANICAL  DUST-BURNERS.  343 

Dr.  Bemhardi^  the  good  result  being  brought  about  by  placing 
the  shelf-burners  so  low  that  the  top  shelf  is  on  a  level  with  the 
charging-door  of  the  lump-burners.  This  causes  an  upward 
draught  in  the  shelf -burners,  and  prevents  their  blowing  out,  even 
when  the  doors  are  opened. 

Other  Descriptions  of  Shelf -^burners. 

The  furnace  of  Finch  and  W.,  J.,  &  S.  Willoughby  (E.  P. 
2913,  of  1883)  diflfers  from  a  Maletra  burner  only  in  that  the 
shelves,  instead  of  being  placed  horizontally^  are  inclined  alter- 
nately in  opposite  directions. 

A  modification  of  the  Maletra  burner  has  been  patented  by 
Mactear  (no.  3701,  1878). 

A  furnace,  combining  some  of  the  features  of  the  Gerstenhofer 
and  the  Maletra  burners,  has  been  patented  by  Hasenclever  and 
Helbig  (description  and  diagrams,  1st  edition  of  this  work,  pp.  220 
to  222).  It  has  never  been  carried  out  in  practice,  and  is  not  likely 
to  be  so  now. 

E.  Bramwell  (G.  P.  no.  22,758)  has  constructed  a  somewhat 
complicated  pyrites-burner,  in  which,  contrary  to  the  ordinary 
dust-burners,  the  fresh  air  meets  with  the  green  ore,  the  products 
of  combustion  being  gradually  led  over  partially  roasted  ore, 
and  at  last  over  the  almost  spent  cinders.  This  is  effected  by 
placing  five  calcining-beds  in  a  row,  each  of  them  provided  with 
an  outlet  for  the  gas  connected  with  a  gas-main,  to  be  connected 
or  disconnected  by  means  of  a  throttle-valve,  so  that  the  current 
of  gases  can  be  directed  at  will.  The  last  burner  of  the  series 
communicates  with  the  first  by  means  of  a  flue  underneath,  so 
that  a  regular  rotation  can  be  kept  up,  as  is  done  in  lixiviating 
vats  for  black-ash. 

Mechanical  Dust-burners. 

The  necessity  of  frequently  opening  the  doors  in  Mal^tra's  and 
all  similar  furnaces  is  certainly  a  drawback  ;  it  necessitates  much 
labour  and  cannot  but  introduce  some  false  air.  These  drawbacks 
have  been  overcome  in  a  most  ingenious  way  in  the  mechanical 
pyrites-dust  burner  constructed  by  MacDougall  Brothers,  of 
Liverpool ;    but  unfortunately  fresh   troubles  have  arisen  there 


344  PRODUCTION  OF  SULPHUR  DIOXIDE. 

which  have  caused  these  humers  to  be  abandoned  again.  Still,  as 
in  theory  they  are  the  most  perfect  of  all  dust-burners,  we  will 
describe  them  here,  especially  since  the  drawbacks  connected  with 
them  have  been  overcome  by  later  inventions.  The  MacDougall 
burner  is  shown  in  figs.  97  to  99. 

The  burner  consists  of  a  metal  cylinder,  6  feet  in  diameter  and 
12   feet  high,  formed  of  seven  rings  (ad)  bolted   together,  and 
provided  with  a  solid  bottom,  but  open  at  the  top.     The  rings  are 
cast  in  such  a  way  that  the  lower  and  inner  edge  of  each  can  serve 
as  an  abutment  for  one  of  the  flat  arches  6^  to  b^,  which  divide  the 
inner  space  of  the  cylinder  into  seven  chambers,  the  uppermost  of 
which  is  open  at  the  top.      The  arches,  as  well  as  the  cast-metal 
bottom  of  the  cylinder,  are  pierced  in  the  centre,  and  allow  the 
passage  of  a  cast-iron  shaft,  c,  6  inches  thick,  which  is  turned  by 
means  of  the  toothed  wheel  rf,  the  pulley  e,  and  the  steam-engine 
/.     The  shaft  carries  at  top  and  bottom  the  lutes  f/  and  ffi,  into 
which  the  cups  h  and  Aj,  fixed  to  the  top  arch  and  the  cylinder- 
bottom,  enter ;  the  latter  are  fast,  whilst  the  lutes  g  and  gi  turn 
round  with  the  shaft,  and  a  hydraulic  joint  prevents  the  escape  of 
gas  at  the  places  where  the  shaft  enters  and  leaves  the  cylinder. 
To  the  shaft  are  fixed  the  cast-iron  arms,  t'l,  i^  .  .  .  «7,  provided 
with  teeth   along  their   lower    margin.      The   teeth   are    placed 
alternately  in  opposite  directions ;  so  that  the  arm  ij  moves  the 
ore-dust  from  the  centre  to  the  periphery,  (2  the  same  from  the 
periphery  to  the  centre;    h  acts  like  ii;  i^  like  i^,  and   so  forth. 
Corresponding  to  this,  the  arches  are  perforated  alternately — 61, 
is,  and  b^  near  the  margin,  b^,  ^4,  and  b^  in  the  centre.     The  latter 
have  a  large  central  opening,  1  foot  3  inches  wide,  lined  with  a 
metal  pipe,  which  gives  free  play  round  the  shaft  to  the  gas  and 
the  ore-dust ;    whilst  in  the  other  arches  the  shaft  is  so  tightly 
surrounded  by  a  metal  pipe  that  scarcely  any  dust^  and  still  less 
gas,  can  get  through.     The  small  ore  (which  need  only  be  passed 
through  a  1-inch  riddle,  and  therefore  contains  pieces  up  to  the 
size  of  a  walnut)    is  lifted  by  the  elevator  k  (also  moved  by  the 
engine/),  and  is  emptied  on  to  the  top  flat,  Ai,  where  the  arm  i^ 
takes    it  round  and    gradually  moves  it  towards  the  periphery. 
During  this  time  the  ore  is  completely  dried  by  the  heat  of  the  gas 
below.     The  ore  dropping  down  the  edge  at  /  from  the  open  top 
chamber  is  continually  pushed  into  the  first  closed  chamber  by  a  ram 
at  A,     The  ram  A  can  be  moved  reciprocally  either  by  the  rod  B 


[To  iaU  t-  344, 


MACDOUOALL^S  DUST-BURNER.  345 

or  C,  and  can  be  moved  more  or  less  quickly  ;  so  that  the  feed  of 
ore  can  be  regulated  to  a  nicety.  The  arm  1*2  moves  the  ore  towards 
the  centre  of  Jg,  where  it  drops  down  ;  tg  moves  it  towards  the 
periphery  of  b^,  where  it  drops  down  again,  and  thus  quite  gradu- 
ally and  constantly^  being  directed  by  the  teeth  of  the  arms^  arrives 
at  the  bottom^  and  is  emptied  out  through  the  pipe  m.  The  two 
slides^  n  and  0,  allow  the  contents  of  m  to  be  got  out  without  any 
loss  of  gas  or  any  air  entering  the  other  way.  As  the  furnace 
during  the  operation  is  in  full  heat,  most  of  all  near  the  top,  the 
ore  ignites  as  soon  as  it  arrives  on  the  bottom  of  the  first  closed 
chamber^  b^ ;  Rnd  in  its  gradual  zigzag  way  towards  the  bottom 
the  sulphur  is  completely  burnt  off.  The  air  is  continually  supplied 
by  the  air-pump  p  in  exactly  the  necessary  quantity ;  and  the 
gas  escapes  through  the  pipe  r  to  the  acid-chambers. 

An  apparatus  such  as  is  here  figured  is  sufiicient  for  burning 
3^  tons  of  ore  in  24  hours  ;  with  eight  closed  chambers  instead  of 
six^  it  can  bum  5  tons.  It  is  also  very  well  adapted  for  burning  the 
spent  oxides  of  gas-works;  but  then  it  must  have  only  four  cham. 
bers.  In  a  factory  on  the  Tyne,  where  this  apparatus  was  at  work 
for  a  while^  the  consumption  of  coals  for  driving  the  engine 
amounted  to  4  tons  per  week.  *A  two-horse-power  engine  and  a 
1^-inch  steam-pipe  are  said  to  suffice  for  the  largest  burner.  The 
wages  amounted  to  £4  os,  per  week ;  but  this  rather  high  amount 
was  explained  by  the  fact  that  two  other  furnaces  were  building, 
which  were  expected  to  be  served  by  the  same  men  who  attended 
the  first.  Of  course  this  apparatus  is  quite  independent  of  the 
skill  of  the  burner-men,  which  is  mostly  acquired  only  after  some 
years^  practice. 

For  heating  up,  the  engine  is  started  and  the  cold  furnace 
is  gradually  filled,  care  being' taken  to  regulate  the  thickness 
of  the  layers  of  ore  on  the  different  floors.  When  the  ore  has 
arrived  at  the  bottom,  the  engine  is  stopped,  and  the  flame  of  a 
temporary  fireplace,  built  against  the  cylinder,  is  allowed  to  enter 
it,  until  the  ore  lying  on  the  bottom  and  the  floor  &2  has  taken 
fire.  Then  the  engine  is  started,  the  temporary  fireplace  is  taken 
away,  the  man-hole  is  closed,  and  nothing  remains  but  to  see  that 
the  ore  arrives  at  the  bottom  properly  burnt.  If  this  should 
not  be  the  case,  the  speed  of  the  feeding-ram  A,  that  of  the 
air-pump,  or  that  of  the  agitating-shaft  is  altered  till  everything 
is  in  order.     It  is  easy  to  get  the  sulphur  in   the   burnt   ore 


346  PRODUCTION  OF  SULPHUR  DIOXIDE. 

down  to  1  per  cent. ;  in  forced  work  only  3  to  4  per  cent,  can  be 
attained. 

One  objection  will  at  once  be  made  to  MacDougall's  burner,  viz. 
that  the  machinery  in  its  interior  must  wear  out  very  quickly.  In 
order  to  obviate  this,  all  parts  of  the  machinery  are  made  of  thick 
cast-iron ;  and  when  one  of  the.  arms  is  worn  out  it  can  be  renewed 
through  the  man-holes,  s,  3,  without  allowing  the  apparatus  to  cool 
down.  That  otherwise  this  burner  has  many  very  great  advantages 
over  all  others  is  evident.  The  turning  of  the  small  ore  is  per- 
fect without  any  opening  of  the  doors  and  working  by  hand.  Not 
even  during  charging  and  discharging  does  false  air  enter  the 
burner;  and  by  means  of  the  air-pump  exactly  the  necessary 
quantity  of  air  can  be  admitted  (this,  however,  in  practice  was 
found  to  be  very  difficult).  This  work,  indeed,  is  done  under  such 
favourable  conditions  as  are  realized  by  no  other  burner,  whether 
for  pieces  or  for  smalls  ;  and  it  might  be  assumed  that  the  con- 
sumption of  nitre  would  thus  be  reduced  to  a  minimum,  and  the 
yield  of  acid  raised  to  a  maximum.  Nevertheless  MacDougall's 
burner  had  to  be  given  up  again  in  the  above-mentioned  factory, 
because  the  quantity  of  flue-dust  was  so  great  that  it  could  not  be 
managed  in  any  way,  and  the  chamber-process  was  seriously  inter- 
fered with.  Employment  of  the  Glover  tower  was  not  to  be 
thought  of.  It  does  not  appear  that  really  efficient  dust-chambers 
were  employed.  The  air-pump  acted  so  violently  that  the  dust 
was  carried  away  a  great  distance  *.  Probably  this  drawback  might 
have  been  counteracted  by  some  alteration  in  the  construction ; 
but,  altogether,  the  machinery  caused  endless  trouble,  continually 
requiring  repairs,  and  there  is  no  doubt  that  it  would  have  to  be 
altered  a  good  deal  before  it  could  become  a  real  success. 

The  drawbacks  ascribed  to  MacDougalFs  furnace  were  sought  to 
be  obviated  by  a  new  patent  of  the  same  inventor,  E.  P.  no.  3985, 
of  188a.  Dust-chambers  are  provided  with  perforated  baffle-plates 
for  the  interception  of  dust  carried  over  by  the  draught,  arrange- 
ments being  made  for  drawing  out  the  settled  dust  without  allowing 
gas  to  escape  or  air  to  enter.  The  shaft  and  rake-arms  are  con- 
structed of  cast-iron,  having  a  central  wrought-iron  tube  so  as  to 
obviate  warping  or  bending  from  the  eflFect  of  heat ;  and  in  order 
that  the  shaft  may  be  readily  withdrawn,  the  arms  or  rakes  are 

*  Davis  (*  Chemical  Engineering/  ii.  p.  120)  mentions  that  with  mechanical 
draught  out  of  25  tons  of  dust  burned  per  week  4  tons  were  carried  away  as 
flue-dust ! 


MACDOVOALL^S  DUST-BURNER.  347 

fixed  thereto  by  a  fork-shaped  end  and  cotter.  A  second  modifi- 
cation is  described^  which  is  to  avoid  the  dust  occasioned  by  the 
vertical  passage  from  floor  to  floor.  The  furnace  is  constructed  of 
an  oblongs  horizontal*  floor  or  chamber,  provided  with  a  series  of 
vertical  shafts,  having  rakes  similar  to  those  above  described  and 
revolving  in  opposite  directions.  The  teeth  are  so  placed  as  to 
draw  the  material  towards  each  shaft,  and  thus  pass  it  from  one  to 
the  other  and  from  end  to  end  of  the  furnace.  Where  prolonged 
roasting  or  burning  is  requisite,  a  similar  furnace,  or  the  first 
modification,  may  be  superposed  above  the  last  mentioned,  the 
material  being  first  passed  through  the  upper  furnace. 

A  further  improvement  was  patented  by  the  same  inventor  as 
E.  P.  no.  22,504, 1891.  Here  the  central  shaft  is  made  in  several 
lengths,  coupled  together  by  widening  one  end  of  the  shaft  to  form 
a  square  socket,  and  fitting  into  this  the  square  end  of  the  other 
shaft,  the  two  being  secured  by  a  square  key  wedged  between 
socket  and  square  end ;  a  tight-fitting  spring-clip  protects  the 
coupling  from  the  action  of  the  burner-gas.  The  furnace-rings 
are  joined  together  by  half  check-joints  secured  by  set  pans  and 
rust  jointing ;  the  ends  of  the  pins  are  not  exposed  to  the  corrosive 
fumes. 

The  subject  of  mechanical  furnaces  generally  has  been  treated 
in  detail  by  Bode,  Dingler's  Journal,  ccxix.  p.  55,  and  Wagner's 
Jahresb.  1876,  p.  296. 

A  furnace  very  much  like  MacDougalFs  was  patented  by 
Mr.  Perret  in  France,  on  June  23rd,  1875. 

A  mechanical  pyrites-kiln,  greatly  resembling  MacDougalPs  in 
principle,  has  been  patented  by  R.  Mackenzie  (E.  P.  no.  4418, 
1881).  It  is  provided  with  a  water-cistern  at  the  bottom,  in  the 
hope  of  promoting  the  process  by  the  presence  of  aqueous  vapour. 
Also  a  similar  furnace,  differing  only  in  details  of  construction, 
has  been  patented  by  Black  &  Larkiu  (E.  P.  no.  4456,  of  1881), 
and  another  by  Johnson  in  America. 

A  much  more  important  modification  is  the  burner  constructed 
by  Herman  Prasch,  which  avoids  most  of  the  difficulties  of  the 
above  system  by  the  introduction  of  water-cooling.  The  Frasch 
burner  has  been  described  by  me  in  Zsch.  f.  angew.  Ch.  1894, 
p.  15,  from  which  parts  of  the  drawings  are  reproduced  here  as 
figs.  100, 101, 102.  We  notice  the  hollow  shaft  C,  8  inches  outside 
diameter,  5  in.  bore.  Above  the  cylindrical  burner  it  is  connected 
with  the  fixed  water-pipe  D  by  means  of  a  stuffing-box.      As  we 


PRODUCTION  OF  SULPHUR  DIOXIDE. 

Pig.  ]00. 


see  from  fig.  102,  pipe  A'  takes 
the  water  from  the  cistern  E  to 
the  top  of  D,  and  pipe  k' ,  starting 
from  the  bottom  of  E,  reaches 
nearly  to  the  bottom  of  shaft  C. 
This  eauses  a  continuous  circula- 
tion of  water  from  E  thi-ough  k 
dowQwardSj  then  upwards  in  the 
annular  space  between  k'  and  C, 
and  back  through  k  to  E.  Braucli 
water-pipes  reaching  from  C  into 
the  hollow  stirrers  H  protect  these 
also  from  fusing  or  deformation. 
Shaft  C  is,  moreover,  protected 
on  the  outside  by  wire  gauze, 
covered  with  a  paste  of  fireclay. 
The  remainder  of  the  figure 
can  be  easily  understood  by 
reference    to     the    MacDougall 


HERKESHOFF  DUST-BURNER.  349 

furnace,  but  attention  must  be  drawn  to  the  very  efficient  dust- 
chamber  shown  in  sectional  elevation  fig.  100,  and  sectional  plan 
fig.  101. 

I  have  convinced  myself  by  personal  observation  of  the  excellent 
function  of  this  apparatus,  especially  also  of  the  fact  that  the 
protective-water  circulation  between  the  hollow  shaft  C  and 
the  hollow  side-arms  H  is  quite  sufficiently  effected  by  the  steam 
formed  in  the  latter. 

According  to  a  report  received  from  Mr.  Frasch  in  1902, 
his  furnaces,  which  are  now  regularly  made  16  feet  wide,  bave 
done  perfect  work  ever  since ;  thirty  of  them  are  in  operation  at 
eight  different  works  of  the  Standard  Oil  Company  for  the  purpose 
of  roasting  metallic  sulphides.  The  heat  produced  in  the  interior 
of  the  shaft  and  arms  is  utilized  by  attaching  a  steam-drum  to 
the  highest  portion  of  the  water  circulation,  and  the  steam  is  used 
under  two  atmospheres'  pressure  for  distilling  benzine  out  of  light 
petroleum  oils. 

Another  modification  of  the  MacDougall  burner  is  the  Herres- 
hoff  burner,  where  the  cooling  is  performed  by  air  (figs.  103 
&  104).  This  principle  had  been  carried  out  exactly  in  the  same 
manner  already  before  1883  by  the  blende-furnace  of  the  Societe 
Vieille  Montague  {vide  infra,  p.  364).  This  burner  and  its  working 
are  described  in  '  Mineral  Industry/  vi.  p.  236,  and  by  Gilchrist 
( Journ.  Soc.  Chem.  Ind.  1899,  p.  460) .  The  central  shaft  a,  fig.  103, 
is  hollow,  14  inches  outside  diameter  and  about  |  inch  thickness  of 
metal.  Above  every  shelf  there  is  a  cross  channel  or  socket  passing 
directly  through  the  shaft,  about  4  inches  wide  and  5  inches  high. 
Into  this  socket  the  side-arms  are  inserted.  In  the  top  ot  the 
channel,  at  the  centre  of  the  vertical  shaft,  is  a  pocket  running 
across  the  channel ;  into  this  a  rib  at  the  inner  and  top  edge  of  the 
ai*m  locks,  when  the  arm  is  forced  into  its  proper  position,  and  the 
weight  of  the  arm  keeps  it  locked  in  the  channel.  By  raising  the 
outer  end  of  the  arm  about  3  inches,  the  top  edge  of  the  rib  is 
brought  below  the  pocket  and  the  arm  can  be  pulled  out.  Each 
arm,  weighing  about  100  lbs.,  can  be  unlocked  and  removed  and  a 
new  one  inserted  in  about  one  minute.  The  greatest  strain  is  at 
the  point  of  contact  with  the  central  shaft ;  but  the  cooling  effect  of 
the  air  in  the  shaft  prevents  any  damage,  as  the  temperature  never 
exceeds  a  dark  red  heat.  About  six  of  these  arms,  at  a  cost  of  less 
than  £1  each,  cover  the  renewals  per  annum.     The  arms  are  hollow. 


PltOIIl'CTlOK  OF  8DLFUUK  DIOXIDE. 


MECHANICAL  DUST-BURNERS.  351 

of  a  rectaDgular  section^  and  are  made  of  cast-iron  capable  of 
resisting  the  heat. 

The  cross  channels  do  not  take  up  the  whole  area  of  the  shafts 
but  allow  the  air  entering  at  the  bottom  to  pass  up  the  shaft;  a 
light  steel  stacks  about  10  feet  high,  provides  the  draught. 

The  five  shelves  are  fire-brick  arches,  4^  inches  deep^  levelled 
off  with  ashes  or  similar  materials.  The  ore  is  fed  automatically 
from  the  hopper  c  by  means  of  the  plunger  d  moving  backwards 
and  forwards.  The  passage  down  the  shelves  takes  place  exactly 
as  in  the  MacDougall  furnace.  The  central  shaft  revolves  once 
in  two  minutes,  the  plunger  makes  one  stroke  per  minute.  There 
are  two  outlets  for  the  burnt  ore  at  the  bottom^  5x3  inches. 

The  furnace  is  about  10  feet  wide  and  10  feet  high.  The  outer 
casing  is  of  ^-inch  steel,  riveted  together,  with  a  red  brick  lining, 
8  inches  thick.  The  total  weight  is  about  7  tons;  the  heaviest 
piece  weighs  a  ton.  The  motive  power  is  practically  ^  H.P.  per  fur- 
nace. Each  furnace  roasts  6000  lbs,  of  44  per  cent.  Virginia  ore, 
or  49  per  cent.  Tharsis  ore,  in  24  hours.  The  amount  of  sulphur 
left  in  the  cinders  depends  upon  the  quality  of  the  ore,  may  be 
2  or  3  per  cent.,  or  down  to  1  or  1^  per  cent.  The  furnace  takes 
also  low-grade  ore,  with  30  or  even  25^  per  cent,  of  sulphur. 
With  magnetic  pyrites  (pyrrhotite)  the  grain  should  not  be  larger 
than  wheat,  with  proper  pyrites  it  may  run  from  pea-size  down  to 
dust.  When  some  sulphur  is  to  be  left  in  for  the  wet  copper 
extraction  process,  up  to  8700  lbs.  per  24  hours  can  be  treated. 
Spent  oxide  of  gas-works  can  be  also  worked,  but  it  is  best  mixed 
with  pyrites  fines. 

At  one  American  works  where  70  of  these  furnaces  are  in  operation 
only  two  men  attend  to  them.  A  prospectus  issued  in  November 
1901  enumerates  ten  American  and  fourteen  German,  French, 
Austrian,  and  Italian  factories  where  these  furnaces  were  intro- 
duced ;  four  furnaces  had  been  ordered  by  British  manufacturers. 
During  1902  I  heard  great  complaints  about  the  unmanageable 
quantity  of  dust  produced  by  these  burners  (comp.  p.  346) 

A.  P.  O'Brien  has  further  improved  the  HerreshofE  furnace 
(comp.  Falding,  Min.  lud.  ix.  p.  623),  but  no  details  or  definite 
results  can  as  yet  be  stated.  Utley  Wedge  (U.S.  P.  649,183  and 
654,335)  describes  a  similar  furnace. 

Other  mechanical  dust-burners.  —  Farmer  and  Hardwick's 
mechanical  pyrites-burner  (1878)  resembles  to  some  extent  Jones's 


352  PRODUCTION  OF  SULPHUR  DIOXID£. 

and  Walshes  mechauical  salt-cake  furnace.  It  is  automatically 
charged  and  emptied;  5^  tons  of  pyrites  are  said  to  be  burnt  off 
in  from  7  to  9  hours.  None  of  these  furnaces  seem  to  be  in 
practical  operation. 

The  mechanical  pyrites-burner  of  P.  Spence  (patented  in  Eng- 
land Dec.  24,  1878 ;  in  Germany  No.  9267 ;  in  America 
No.  248,521)  is  a  shelf-burner  provided  with  mechanical  stirring 
arrangement.  As  this  furnace  seems  to  be  constructed  on  rational 
principles,  and  as  it  has  met  with  practical  success  in  America, 
we  give  here  a  complete  description  of  it. 

Fig.  105  shows  an  exterior  side  view ;  fig.  106  a  plan ;  fig.  107  a 
cross  section  of  one  half  of  a  double  furnace^  the  other  half  being 
shown  in  outside  view ;  fig.  108  a  longitudinal  section  of  the  furnace- 
beds;  and  figs.  109,  110,  and  111  views  of  the  stirring  and  raking 
instruments.  The  construction  of  the  furnace-beds  is  best  seen 
from  fig.  108.  In  this  there  are  at  1  the  walls  of  the  furnace,  in 
which  are  fixed  projecting  fire-clay  slabs,  2.  Upon  these  are  placed 
tiles,  3,  reaching  from  one  side  of  the  furnace  to  the  other,  a  num- 
ber of  these  composing  the  length  of  each  furnace- bed.  In  figs. 
107  and  108  the  several  beds  are  shown  at  3,  3a,  3b,  3c;  alternate 
openings  in  these  beds  being  shown  at  4, 5,  6,  7.  The  pulverulent 
material  is  thrown  at  H  on  to  the  floor  3 ;  advancing  rakes  or 
ploughs  stir  it  and  carry  forward  a  portion  of  it  through  the  open- 
ing 4  on  to  the  second  bed  3a,  The  teeth  of  the  rakes  are  formed 
of  a  triangular  section,  as  shown  in  fig.  Ill,  the  apex  of  the  triangle 
being  in  the  direction  of  the  motion  of  each  rake  longitudinally 
from  end  to  end  of  the  furnace,  the  flat  sides  of  the  teeth  of  the 
rake  being  in  the  direction  in  which  it  is  desired  to  traverse  the 
ore  along  the  bed  of  the  furnace.  When  the  rake  is  advancing  in 
the  direction  of  the  pointed  part  of  the  teeth  of  the  rake,  the  ore 
will  be  only  turned  over;  but  when  the  rake  is  moving  in  an 
opposite  direction,  a  certain  quantity  of  the  ore  will  be  carried  by 
the  flat  side  of  the  teeth  along  the  floor  of  the  furnace.  Thus  the 
ground  material,  delivered  to  the  floor  3  at  the  point  H,  is  stirred 
and  subsequently  partially  carried  forward  till  it  is  delivered 
through  opening  4  on  to  the  second  bed,  3a,  where  the  same  opera- 
tions take  place,  the  material  now  passing  down  the  opening  5 
on  to  the  bed  3b,  and  so  through  all  the  beds,  until  it  is  at  last 
discharged  through  the  opening  7  into  the  receptacle  8.  Since  the 
openings  in  the  successive  beds  are  on  alternate  ends  of  the  furnace. 


SPISNCB  S  DITST-ltl/HNEK. 


PKOOnCTlON  OF  SULFHUK  DIOXIDE. 
Fig.  107. 


*rnTTT 


Fi^.  111. 

[A      ^     ^ 


tlie  stirring  and  couvcyirig  instrumeuts  must  be  reversed  as  regards 
their  faces  in  succeeding  beds.  The  teeth  of  the  rakes  are  mounted 
in  angle-iron  bars,  11,  provided  with  rollers,  11*,  wliich  run  upon 
rails,  12,  carried  by  the  projecting  supports  2,  To  eacli  of  these 
aiigle-biu's  are  connected  rods,  13,  attached  at  their  other  ends  to 
a  frame  or  carriage,  14,  provided  with  wheels,  15,  which  run  upon 
rails,  16,  on  the  floor,  the  said  rods  being  supported  and  guided  by 
grooved  pulleys,  17,  On  the  carriage,  14,  are  fixed  toothed  racks, 
18,  situated  outside  the  furnace,  and  supported  at  their  outwai-d 
ends  by  rollers,  19,  and  iu  gear  with  these  rods  are  piuions,  20,  on 
a  shaft,  21,  driven  by  motive  power.    Motion  being  communicated 


spence's  dust-burxer.  355 

to  the  shafts  21>  the  pinions^  20^  cause  the  racks^  18^  to  traverse 
the  frame^  14^  which,  as  stated,  travels  on  the  rails,  16,  and  thus 
the  rods,  13,  are  caused  to  traverse  the  rakes  or  conveyers  along 
the  several  beds  of  the  furnace.  According  to  the  positions  shown 
in  the  drawings,  the  carriage  14  is  in  its  outward,  or  nearly  out- 
ward, position,  and  the  flat  ends  of  the  instruments  will  have 
delivered  a  certain  amount  of  material  through  the  opening  4  on 
to  the  bed  3a,  the  same  operation  having  taken  place  with  regard 
to  the  opening  6  and  bed  3c.  The  carriage  now  running  inward, 
the  sharp  points  of  the  ploughs  will  simply  stir  the  material  on  the 
beds  3,  36,  while  the  blunt  ends  on  the  floor  3a  will  deliver  a 
certain  quantity  of  material  through  the  opening  5  on  to  the  bed 
36,  and  at  the  same  time  the  instruments  on  the  floor  3c  will  pass 
an  amount  of  completely  calcined  material  into  the  receptacle  8, 
to  be  removed  at  pleasure.  The  feeding  of  the  furnace  takes  place 
in  the  following  manner : — At  P  is  a  channel  leading  to  the  top 
floor  3,  and  above  this  channel  is  a  hopper,  20,  into  which  the 
ground  material  is  from  time  to  time  fed.  The  bottom  of  this 
hopper  is  provided  with  a  sliding  plate,  26,  having  a  ledge  at 
its  inner  end,  as  seen  in  fig.  107.  This  plate  is  connected  with 
rods,  22,  swung  upon  arms,  23,  and  each  having  two  stops,  24,  25. 
According  to  the  position  shown,  the  material  rests  upon  the  ledge 
of  the  plate,  26,  which,  when  the  carriage  runs  in,  is  pushed  for- 
ward by  its  arrival  in  contact  with  the  stops  24,  and  this  action 
delivers  a  certain  amount  of  material  through  the  channel  F.  On 
the  return  motion  of  the  carriage  the  stops  25  shift  the  plate  26 
back,  and  so  on.  Instead  of  plate  26,  there  may  be  a  winged 
bottom  to  the  hopper.  The  furnace  may  be  single  or  double,  the 
latter  (which  is  shown  in  the  drawings)  being  preferred.  The 
shaft  21  is  connected  by  means  of  suitable  gearing  to  any  source 
of  motive  power,  so  that  it  may  be  rotated  first  in  one  direction 
and  then  in  another,  and  thereby  traverse  the  rakes  alternately 
from  one  end  of  the  furnace  to  the  other.  The  rakes  may  move 
continuously ;  but  it  is  preferable  that  they  should  remain 
stationary  periodically  in  the  position  shown  in  the  drawings,  as 
they  are  then  clear  of  the  ore  and  out  of  the  direct  action  of  the 
heat,  thereby  sufiering  less  injury  from  corrosion. 

A  number  of  these  furnaces  have  been  put  up  by  the  Sulphur 
Klines  Company  of  Virginia,  at  Baltimore.  According  to  a  com- 
munication kindly  made  to  me  in  May  1888  by  the  President, 

2a2 


356  PRODUCTION  OP  SULPHUR  DIOXIDE. 

Mr.  Crenshaw,  three  double  furnaces  were  connected  with  a  set  of 
chambers  of  180,000  cubic  feet  capacity,  with  Glover  and  Gay- 
Lussac  towers,  and  two  other  furnaces  with  a  set  of  126,000  cubic 
feet.  The  5  furnaces  were  to  burn  14  tons  of  47/48  per  cent, 
pyrites  each  24  hours,  down  to  less  than  2  per  cent,  of  sulphur  in 
the  cinders. 

It  is  mentioned  as  a  drawback  of  Spence's  furnaces  that  at  the 
back  end  a  collection  of  dust  takes  place  by  which  the  rakes  are 
prevented  from  doing  their  work  properly.  Bartsch,  of  Bridgeport 
(Pischer^s  Jahresb.  1886,  p.  256),  consequently  applies  to  the 
furnace  ends  a  separate  set  of  broad  plates,  moved  by  a  second 
moving-frame  in  sucli  a  w^ay  that  the  dust  is  cleared  out  automatic- 
ally every  time  the  principal  frame  is  made  to  work. 

As  stated  in  Zsch.  f.  angew.  Ch.  1894,  p.  134,  I  have  met  with 
several  Spence  furnaces  at  work  in  America,  but  they  did  not  give 
general  satisfaction.  A  variety  of  this  furnace  has  been  patented 
in  America  by  A.  C.  Johnson,  of  Baltimore,  where  the  moving 
parts  are  protected  from  heat  (U.S.  P.  642,334). 

The  ordinary  shelf-burner  has  been  combined  with  a  mechanical 
arrangement  by  Hering  (G.  P.  9634),  who  feeds  the  top  shelf 
continuously  by  means  of  a  screen,  the  burnt  ore  being  removed 
from  the  bottom  shelf  by  another  screw. 

T.  Mason  (E.  P.  3196,  1880)  employs  a  furnace  with  a  bed 
slanting  slightly  downwards,  across  which  a  number  of  fluted 
rollers  (say  20)  are  lying,  made  of  cast-iron  or  stoneware,  moved  by 
means  of  gearing  outside  the  furnace.  The  pyrites-dust  is  fed 
mechanically  into  a  hopper,  situated  at  the  upper  end,  and  is 
gradually  moved  down  the  inclined  hearth  by  means  of  the  fluted 
rollers,  the  cinders  being  discharged  at  the  lower  end.  A  furnace 
placed  below  gives  additional  heat  in  the  case  of  poor  ores.  (It  is 
not  likely  that  such  an  arrangement  would  stand  the  wear  and 
tear  unavoidable  in  this  case.)  Modifications  of  this  furnace  are 
contained  in  the  patent  No.  1788,  of  1881,  and  No.  2831,  1882. 

Walker  and  Carter  (E.  P.  4000,  1883)  employ  for  roasting 
pyrites  a  set  of  eight  horizontal  cylindrical  retorts  (four  tiers  of 
two  each),  heated  outside  by  an  ordinary  coal  fire,  and  communis 
eating  by  openings  at  alternate  ends.  Hollow  shafts,  provided  with 
stirrers,  pass  through  each  retort ;  cooling-water  runs  through  all 
these  shafts  from  one  to  another  and  prevents  their  warping. 
Special  contrivances  prevent  the  stirrers  from  touching  the  sides  of 


MECHANICAL  DUST-BURNERS.  357 

the  retorts  in  spite  of  unequal  heating.  The  broken  ore  is  fed  into 
the  top  retorts  and  gradually  finds  its  way  into  the  three  following 
tiers ;  a  current  of  air  traverses  the  retorts  in  the  opposite  direc- 
tion. This  apparatus  is  stated  to  have  worked  well  for  roasting 
pyrites  containing  42*2  per  cent,  sulphur  (Engineering  and  Mining 
Journal^  xxxvii.  p.  29i),  but  it  does  not  convey  the  impression 
that  it  would  go  on  for  a  long  time  without  very  heavy  wear  and 
tear ;  and  the  necessity  of  an  outside  fire  also  militates  against  it. 
The  report  made  on  this  burner  by  W.  Martyn  (J.  Soc.  Chem. 
Ind.  1885^  p.  26)  is  not  encouraging. 

W.  Briiokner  (Engineering  and  Mining  Journal^  xxxvii.  p.  425; 
Fischer's  Jahresb.  1884,  p.  221)  employs  for  roasting  pyrites-smalls 
the  principal  of  a  horizontal  cylindrical  revolving  furnace.  As 
this  furnace  is  provided  with  internal  firing,  and  the  SO^  gets 
mixed  with  all  the  smoke-gases,  it  is  hardly  intended,  and  certainly 
not  adapted,  for  serving  in  the  manufacture  of  sulphuric  acid. 
This  is,  on  the  contrary,  the  aim  of  an  apparatus  patented  by 
R.  &  C.  Oxland  (E.  P.  No.  7285,  1885),  who  roast  the  pyrites  in 
a  revolving  cylinder  of  30  feet  length  heated  from  the  outside,  so 
that  the  SO2  is  kept  apart  from  the  smoke-gases.  At  the  lower 
end  of  the  rotating  tube  is  a  cast-iron  prolongation,  heated  exter- 
nally by  a  fire-grate  and  flues.  The  amount  of  air  admitted  to 
the  calciner  is  regulated  by  a  contrivance  in  the  end  plate  of  the 
prolongation,  which  is  also  fitted  with  a  door  for  the  removal  of 
the  cinders.  (This  apparatus  seems  to  be  more  intended  for 
roasting  arsenical  ores,  and  recovering  the  white  arsenic  in  the 
process.) 

K,  Walter  has  constructed  a  special  burner  for  '^peas/'  that  is, 
small  pieces  of  ore  between  the  size  of  a  hazel-nut  and  such  as 
pas:}  through  a  sieve  with  eight  holes  to  the  lineal  inch.  This 
apparatus  is  described  and  figured  in  the  1st  edition,  pp.  225  to 
229.  It  has  grate-bars  laid  sideways  across  the  burner,  cast  with 
projections  beneath,  through  which  a  bar  passes.  This  makes  it 
possible  to  turn  all  the  bars  at  the  same  time  and  exactly  in  the 
same  way.  The  spaces  between  the  bars  can  therefore  be  made 
very  small,  so  that  the  "  peas  '^  do  not  fall  through  without  the 
bars  being  moved ;  and  as  they  lie  only  6  inches  thick,  the  air  can 
pass  through  with  the  ordinary  draught.  Each  compartment, 
with  a  grate  surface  of  32  square  feet,  burns  from  14  to  20  cwt.  in 
24  hours. 


358  FBODUCTION  OP  SULPHUR  DIOXIDE. 

Walter's  burners  require  a  strong  draughty  and  must  be  worked 
for  a  separate  set  of  chambers ;  with  insufficient  draught  very  large 
scars  are  at  once  formed.  As  they  are  only  adapted  for  a  special 
size  of  ore,  they  have  not  met  with  any  extended  application. 

4,  Furnaces  for  Koasting  Zinc-blende. 

Zinc-blende  is  now  the  most  important  of  all  zinc-ores^  and  all 
of  it  must  be  converted  into  zinc  oxide  by  a  thorough  roasting. 
This  is  nothing  like  so  easy  as  with  pyrites,  as,  on  the  one  hand^ 
blende  contains  at  best  only  about  33  per  cent.,  sometimes  down 
to  18  per  cent.,  of  sulphur^  and,  on  the  other  hand,  it  is  much 
more  difficult  to  burn  out  than  iron  or  copper  pyrites,  zinc  sulphate 
being  formed,  which  is  very  difficult  to  decompose.  As  the 
manufacture  of  zinc  requires  nearly  all  the  sulphur  to  be  driven 
off,  and  as  the  burners  employed  for  pyrites  are  useless  in  the  case 
of  blende,  the  latter  was  formerly  roasted  in  reverberatory  furnaces, 
all  the  sulphur  dioxide  passing  away  with  the  furnace-gases.  This 
would  probably  be  done  even  now,  if  the  damage  produced  by  the 
acid  smoke  had  not  caused  the  sanitary  authorities,  both  in  Eng- 
land and  on  the  Continent,  to  impose  upon  the  manufacturers  the 
duty  of  doing  their  best  to  condense  the  acids  contained  in  the 
smoke,  the  damage  caused  by  which  has  been  described  svpra, 
pp.  154  et  seq. 

The  development  of  the  processes  for  abolishing  the  acid-smoke 
nuisance  and  utilizing  the  sulphur  in  connection  with  the  roasting 
of  blende,  at  least  in  one  of  the  most  industrial  parts  of  Germany, 
has  been  described  at  length  by  Robert  Hasenclever  (Zeitschr.  des 
Vereins  deutsch.  Ingenieure,  1886,  p.  83;  Fischer's  Jahresb.  1886, 
p.  257),  of  whose  paper  we  give  a  short  abstract.  Before  1855 
all  the  blende  consumed  at  the  large  Stolberg  zinc-works  was 
roasted  in  ordinary  open  furnaces  by  a  direct  coal-fire,  the  gases 
from  which  contained  only  about  0*75  per  cent.  SOj  by  volume 
and  escaped  into  the  atmosphere.  In  1855  the  Rhenania  chemical 
works  at  Stolberg  erected  a  furnace,  intended  to  utilize  the  larger 
portion  of  the  SO2.  This  furnace,  the  invention  of  Friedrich 
Hasenclever,  was  the  first  by  which  the  gases  from  roasting  blende 
could  be  utilized  for  the  manufacture  of  sulphuric  acid.  It  con- 
sisted of  a  long  muffle-furnace  in  which  the  ore  was  shifted  along 
the  hearth  from  back  to  front  by  manual  labour  (evidently  identical 
in  principle  with  Spence's  first  furnace,  supra,  p.  330) .     Thus  half 


MIEMDE-HTRNACES, 


tlic  sulphur  could  he  uHlizcd  for  the  manufacture  of  sulphuric 
aeiti,  but  with  great  waste  of  nitre.  Godiii  improved  this  furnace 
by  placing  a  series  of  muflBea  on  the  top,  which  the  ore  had  to  pass 
gmdatim  :  hut  this  apparatus  waa  given  up  again  for  the  Gersteu^ 
hiifcr  furnace  (siiprii,  p.  3^2).  By  this,  comparatively  rich  gases 
were  obtained,  but  the  immense  quantity  of  fine-dust  was  very 
trouhleaome,  and  it  proved  too  dilficiiit  to  combine  this  furnace 
ivitli  another  for  finishing  the  roasting.  After  this  several  orritnge- 
mciits  were  tried  by  Hasenelever  and  Helbig,  but  these  sho.ied 
various  drawbacks;  and  this  led  in  J874  tn  the  construction  of  a 

IV.  112. 


new  furnace,  which  has  been  fully  described  and  illustrated  in  the 
first  edition  of  this  work,  pp.  201  to  204  ;  we  describe  it  only 
briefly  here  {fig.  1 12) .  It  consisted  of  a  reverberatory  furnace,  y, 
on  the  top  of  which  was  placed  a  muffie,  c,  reaching  all  over  its 
length.     The  bottom  of  this  muffle,  forming  the  top  of  the  rever- 


360  PRODUCTION  OF  SULPHUR  DIOXIDE. 

beratory  furnace,  was  heated  directly ;  the  flame  of  the  furnace, 
passing  over  the  roof  of  the  mufl9e,  heated  this  as  well^  and  then 
passed  under  an  inclined  plane  at  an  angle  of  43°^  at  the  top  of 
which,  at  a,  the  fresh  (powdered)  blende  was  fed  in.  The  ore,  on 
sliding  down  this  plane  (partitions,  d,  d,  preventing  its  transit 
from  becoming  too  rapid),  underwent  a  preliminary  heating  by 
the  hot  gases  passing  underneath  ;  this  heating  was  continued  in 
the  muffle  c  c,  where  air  was  admitted  and  as  much  of  the  sulphur 
was  burned  away  as  possible.  At  last  the  semi-burnt  ore  was 
pushed  down  into  the  furnace  ff,  where  it  was  burned  completely 
by  the  fire  from  the  gas-producer  k.  The  sulphur  dioxide  formed 
here  is  certainly  lost,  and  it  constituted  no  inconsiderable  portion 
(generally  more  than  one  third)  of  the  whole ;  but  that  formed  in 
the  muffle  and  on  the  inclined  plane  is  strong  enough  to  be  carried 
into  lead  chambers  and  converted  into  sulphuric  acid,  certainly  at 
no  great  profit,  if  any. 

A  large  number  of  Hasenclever  furnaces  were  erected  on  the 
Rhine  and  in  Silesia,  but  they  were  found  to  utilize  on  an  average 
only  60  per  cent,  of  the  sulphur  as  sulphuric  acid.  The  remaining 
40  per  cent.  SO2,  being  mixed  with  the  fire-gases,  still  escaped 
into  the  atmosphere  and  were  blamed  for  even  more  damage  than 
they  actually  caused,  the  part  played  by  the  numerous  zinc- works, 
glass-works,  &c.  being  generally  overlooked  by  the  public  (comp. 
pp.  82  &  83).  We  shall  return  to  this  subject  in  the  7th  eectiou 
of  this  chapter. 

All  these  furnaces  have  become  obsolete  by  the  construction  of 
blende-roasting  furnaces,  which  permit  of  utilizitig  the  whole  of  the 
sulphur  of  the  ore  in  vitriol-chambers ,  and  thus  do  away  with  the 
extremely  troublesome  processes  for  absorbing  SO2  from  fire-gases. 
All  these  modem  furnaces  have  one  principle  in  common :  they 
combine  the  heat  produced  by  the  burning  of  the  blende  sulphur 
with  heat  applied  externally,  but  in  such  manner  that  the  fire- 
gases  are  kept  entirely  separate  from  the  roasting-gases.  It  has 
been  found  that  this  indirect  heat  suffices  for  completely  roasting 
the  blende. 

The  furnaces  which  first  realized  the  principle  of  utilizing  all 
the  sulphur  of  the  blende  in  vitriol-making,  by  completing  the 
roasting  by  means  of  indirect  fire,  were  invented  by  M.  Liebig,  who 
had  the  idea  of  constructing  a  sort  of  shelf-burner  with  shelves 
partially  hollow  and  heated  by  indirect  fire.     His  invention  (G.  P. 


ore  is  spread  in  layers  twice  as  thick  as  on  the  bottc 
small  gaps  between  the  charges,  to  prevent  their 
it  takes  three  or  four  days  before  a  hatch  chargf 
discharged   at  the  bottom.     The  raking  over  anc 


)f  the  blende  in  vitriol-making,  by  completing  the 
eaus  of  indirect  fire,  were  invented  by  M.  Liebig,  who 
of  constructiDg  a  sort  of  shelf-burner  with  ehelvea 
iw  and  heated  by  indirect  fire.     His  invention  (G.  P. 


RHENANIA  BLENDE-FURNACB.  361 

21032  of  Eichhorn  and  Liebig)  is  described  and  illustrated  (from 
the    patent  specification)    in  our   second   edition^  pp.  273-275 
Comp.  also  Eichhom's  report  in  Fischer's  Jahresb.  1889,  p.  332. 

We  omit  the  description  of  the  original  style  of  these  furnaces 

in  favourof  a  modification  known  as  '' Rhenania  furnaces/'  because 

they  were  constructed  at  the  Rhenania  Chemical  Works  at  StoU 

berg  (managed  by  R.  Hasenclever).     These  are  now  widely  used, 

not  merely  for  blende^  but  also  for  other  poor  sulphur-ores  in  the 

state  of  smalls  or  even  of  *'  peas ''  (pieces  up  to  ^-inch  diameter), 

and  for  metallurgical  products  (matte)  of  the  same  kind  (p.  363). 

The  Rhenania  furnace  is  shown  in  figs.  113  to  116,  in  a  shape  in 

which  it  has  been  used  for  several  years,  and  which  embodies  the 

same  principle  as  the  furnaces  actually  at  work  at  present^  which 

merely  differ  from  the  above  in  details,  to  be  mentioned  below. 

These  furnaces  require  two  men  per  shift,  and  roast  about  4  tons 

blende  per  24  hours,  with  a  consumption  of  16  cwt.  of  coal.     The 

temperature  of  the  top  muf9e  is  580°  to  690^",  that  of  the  following 

muffles  750°  to  900°.     The  progress  of  roasting  is  shown  by  the 

following  percentages  of  sulphur: — 

Raw  ore     19-2  268  26  5 

End  of  first  muffle    17-6  191     to  21'9     15-9     to  214 

„      second  „       120  112     „   14*3       99     „   12*4 

„     third     „       3-4       1-02  „     1*48     0  75  ,,     106 


99 


roasting     0*6       0-35  „     1*02 


In  the  case  of  richer  ores  the  second  muffle  does  not  require 
heating;  the  fire -gases  may  be  conducted  below  the  third  muffle 
without  a  partition,  and  then  at  once  over  the  second  roasting- 
bed. 

Jahne  (Zsch.  f.  angew.  Ch.  1894,  p.  305)  describes  some  ex- 
periments made  with  these  furnaces.  They  are  greatly  improved 
by  arranging  a  partition  cutting  vertically  through  all  three 
muffles  and  thus  dividing  the  furnace  into  two  parts^  without  any 
change  in  the  firing.  This  admits  of  roasting  30  per  cent,  more 
ore  down  to  the  same  percentage  of  sulphur  and  saves  labour.  It 
is  best  to  build  two  furnaces  back  to  back.  On  the  top  beds  the 
ore  is  spread  in  layers  twice  as  thick  as  on  the  bottom  beds,  leaving 
small  gaps  between  the  charges^  to  prevent  their  getting  mixed. 
It  takes  three  or  four  days  before  a  batch  charged  at  the  top  is 
discharged  at  the  bottom.     The  raking  over  and  moving  on  of 


362  PRODUCTION  OF  SULPHUR  DIOXIDE. 

the  batches^  following  upon  the  diBcharging  of  a  finished  batch, 
requires  4  hours.  The  most  careful  work  must  be  bestowed  upon 
the  finishing  of  the  batches  in  the  hottest  place ;  this  lasts  at 
best  1^  hours,  usually  3  to  4  hour?,  sometimes  7  to  8  hours. 
Tests  are  made  by  adding  hydrochloric  acid  to  a  sample^  and 
looking  for  any  evolution  of  HgS.  The  sulphur  can  be  brought 
down  to  0*1  or  0*2  per  cent. ;  it  ought  never  to  exceed  1  per  cent., 
except  in  the  case  of  blendes  containing  limestone,  which  may 
retain  2  or  3  per  cent.  S  in  the  shape  of  calcium  sulphate.  In 
regular  work  a  charge  of  9  to  12  cwt.  roasted  ore  is  drawn  every 
6  hours.  100  parts  of  raw  blende  average  85  of  roasted  ore,  and 
require  25  or  26  parts  of  good  coal.  The  furnaces  are  provided 
with  large  dust-chambers,  which  must  be.  cleaned  every  few  weeks. 
The  dust  consists  mainly  of  zinc  sulphate  and  calcium  sulphate. 
Lead  oxide  is  carried  farthest,  even  through  the  ten  cylinders  of  a 
Hargreaves  plant  connected  with  the  furnace  at  Stolberg,  right 
into  the  earthenware  receivers  of  the  acid-condensing  plant.  If 
the  blende  contains  mercury,  that  metal  is  found  in  the  mud  of 
the  vitriol-chambers  connected  with  blende-furnaces,  and  can  be 
recovered  from  it  by  distillation. 

In  Chem.  Ind.  1899,  p.  25,  Hasenclever  gives  some  more  details 
respecting  the  Rhenania  blende-furnaces,  which  now  roast  4700  kils. 
blende  in  24  hours  with  two  men  per  shift.  Only  for  poor  ores 
the  fire  plays  round  all  the  muffles ;  generally  the  ore  is  roasted  in 
three  superposed  muffles  and  the  fire  plays  only  round  the  top  and 
bottom  muffle.  Two  furnaces  are  built  back  to  back.  In  order 
to  avoid  annoyance  to  the  men,  there  is  a  space  of  25  feet  between 
two  opposite  tuniaces.  Six  furnaces  are  connected  with  one  set 
of  chambers,  their  flues  being  built  closely  together,  to  keep  the 
heat,  until  they  unite  just  in  front  of  the  Glover  tower. 

Pierron  (Mon.  Scient.  1900,  p.  562)  states  that  at  the  Vieille 
Montague  the  consumption  of  fuel  is  only  18  kils.  per  100 
blende  of  25-28  per  cent.  S  (with  hand-furnaces  or  mechanical 
furnaces?). 

Jensch  (Zsch.  f.  angew.  Chem.  189  A,  p.  50)  shows  by  analyses 
that  the  sulphur  in  roasted  blende  is  mostly  contained  therein  in 
the  shape  of  ferrous  sulphide ;  when  roasting  down  to  2  per 
cent.  S,  no  ZnS  is  present,  and  it  is  therefore  quite  unnecessary 
to  drive  the  roasting  down  to  0*5  per  cent.  S,  as  is  sometimes 
demanded. 


RHEXANIA  BLENDE-FURNACE.  363 

At  Oker  (1902)  all  " fines''  of  the  ores  used  there  (p.  85), 
passed  through  a  7  millim.  sieve^  are  roasted  in  Rhenania  blende- 
furnaces.  Each  furnace  roasts  from  3*55  up  to  5  tons  ordinary 
ores  or  matte^  according  to  whether  the  roasting  is  driven  to  3  or 
to  7  per  cent.  S  in  the  residue;  and  from  3  to  4*5  tons  regulus, 
according  to  whether  2  or  6  per  cent.  S  is  left  in  the  residue. 

At  Freiberg  the  Rhenania  furnace  is  used  (1902)  for  pyrites 
smalls  and  "  peas ''  down  to  5  millim.  size  (^  inch),  for  blende, 
recently  also  for  matte  and  speiss^  containing  about  20  per  cent.  S, 
25  per  cent.  Cu,  and  20  per  cent.  lead.  For  ores  containing  rather 
more  sulphur  the  furnaces  are  provided  with  three  mufSes  directly 
superposed.  The  fire-flue  passes  underneath  the  hearth  of  the 
bottom  muffle,  rises  up  at  the  end  of  this  and  along  the  ends  of 
the  second  and  the  top  muffle,  and  returns  along  the  roofing-arch 
of  the  latter,  so  that  the  fire-gases  heat  only  the  bottom  of  tlie 
lowest  and  the  top  of  the  highest  muffle.  For  poorer  ores  the 
furnaces  have  only  two  muffles,  the  fire-gases  passing  both  under 
their  top  and  over  their  bottom  and  between  both  muffles.  With 
such  furnaces,  whether  containing  two  or  three  muffles,  the  sulphur 
in  the  cinders  from  pyrites  ^'  fines ''  is  brought  down  to  2  per 
cent.,  from  pyrites  *'  peas ''  to  3  per  cent.,  from  blende  to  1  per 
cent.,  from  matte  and  speiss  to  5  per  cent.  Each  furnace  takes  3^ 
to  4  tons  ore  per  24  hours,  with  a  consumption  of  about  12  cwt. 
lignite  and  6  cwt.  coal ;  the  work  is  done  by  two  men  per  shift  of 
12  hours. 

At  Stolberg,  in  1902,  each  furnace  turned  out  8  tons  of  roasted 
blende  per  day,  with  four  men  per  shift,  two  on  each  side,  and  from 
14  to  18  per  cent,  coal  of  the  weight  of  roasted  ore.  The  blende  must 
be  crushed  to  pass  through  a  sieve  of  2  millim.  meshes.  The  product 
in  the  absence  of  lime  shows  0*5  to  1  per  cent.  S,  in  the  presence 
of  lime  correspondingly  more.  The  roasting  is  stopped  when 
a  sample,  treated  with  hydrochloric  acid,  does  not  stain  lead 
paper.  Sulphates  (apart  from  calcium  sulphate)  are  most  easily 
formed  when  the  furnaces  do  not  go  hot  enough,  e.  ff,  after 
stopping  for  Sundays ;  once  formed  they  are  never  completely 
decomposed. 

Bemelmans  (Germ.  pat.  7677o)  describes  a  furnace  for  roasting 
both  pyrites  and  blende  in  separate  compartments ;  the  sulphur 
vapour  obtained  from  pyrites,  sometimes  by  addition  of  coal,  is 
utilized  for  removing  from  the  blende  (which  must  not  be  mixed 


364  PRODUCTION  OF  SULPHUR  DIOXIDE. 

vfiih  coal)   arsenic^  antimony^  and  phosphorus  in  the  shape  of 
volatile  sulphides. 

Michel  Perret  (G.  P.  37842)  has  modified  his  well-known 
furnace  for  burning  fuel  in  the  shape  of  dust  so  as  to  roast  blende^ 
without  mixing  the  fire-gases  with  the  gases  evolved  by  the  burn- 
ing blende.  The  principle  is  very  similar  to  that  of  Eichhorn  and 
Liebig. 

Mechanical  blende-burners  are  the  following : — The  burner 
patented  by  J.  Haas  (G.  P.  23080)  is  very  similar  to  Mac- 
Dougall's  (comp.  p.  343),  but  the  single  chambers^  in  lieu  of 
having  simple  brick  bottoms^  are  separated  by  flues  through  which 
pass  the  fire-gases  from  a  coal-fire.  Mechanical  stirrers  move  the 
ore  from  the  top  shelf  over  three  others  and  ultimately  into  an 
open  hearth,  where  the  last  roasting  takes  place. 

Hegeler's  burner  is  a  combination  of  an  Eichhorn  and  Liebig's 
burner  with  a  stirring  arrangement  somewhat  similar  to  Spence's 
(p.  352),  but  difi^ering  from  it  in  some  important  practical  details. 
This  furnace  works  most  successfully  at  Mathiesen  and  Hegeler*s 
zinc-works,  La  Salle,  111.  It  treats  35  or  40  tons  blende  with  28 
per  cent.  S  in  24  hours. 

A  mechanical  blende-roasting  furnace  patented  by  the  Chemische 
Fabrik  Rhenania  (G.  P.  61,043)  has  not  been  actually  erected 
(Chem.  Ind.  1899,  p.  26).  Hitherto  in  Europe  no  other  but  the 
Yieille  Montague  mechanical  blende  furnaces  seem  to  be  at  work. 

The  burners  patented  by  the  Societe  Vieille  Montague  (G.  P. 
24,155  and  36,609)  are  mechanical  burners  in  which  the  flame  of 
the  coal-fire  is  not  separated  from  the  roasting-gases.  These 
burners  have  been  continuously  at  work  at  Oberhausen  since  1883. 
Their  construction  is  shown  in  fig.  117.  There  are  several  super- 
posed circular  calcining-hearths,  A,  A,  to  which  is  attached  a  square 
calciner  B.  The  ground  ore  is  charged  through  hopper  a  by  means 
of  feeding-rollers  and  flues  on  to  the  top  chamber  and  gradually 
finds  its  way  downwards  and  into  B.  The  fire  of  the  fuel  burning 
on  grate  T  first  passes  over  B,  then  over  the  circular  hearths  A,  A, 
into  the  dust-chamber  C  and  into  the  flue  S.  The  agitation  is 
procured  by  the  vertical  shaft  b  and  arms  e,  e,  the  stufBng-boxes 
being  packed  with  asbestos.  Shaft  b  is  contained  in  an  outer  pipe  ff^ 
and  the  air  rising  between  them  acts  as  a  cooling  medium.  The 
arms  carry  tooth-rakes  m  in  a  radial  position  for  the  purpose  of 
stirring,  and  slanting  solid  rakes  /  which  move  the  ore  from  the 


MECHANICAL  BLENDE-FURNACES.  365 

circumference  to  the  centre,  or  the  other  way,  as  is  required  for  the 
purpose  of  gradually  traosportiog  the  ore  downwards  and  ultimately 
on  to  hearth  B.  [These  furnaces,  which  had  to  be  frequently 
repaired  and  mode  much  flue-dust,  are  being  gradually  replaced  by 
hand-worked  mufBc- furnaces.] 

The  furnaccB  or  kilns  for  roasting  ordinary  copper-ores,  lead- 
ores,  and  ao  forth,  aa  far  as  they  are  not  mentioned  pp.  311,312,  and 
357,  cannot  be  described  in  this  book,  as  they  belong  to  tlie  domain 
of  metallurgy  proper,  and  in  these  cases  the  roas ting-gases  are,  if  at 
allj  sent  into  vitriol-chambers  merely  to  get  rid  of  them,  but  with- 
out the  expectation  of  profitable  work. 

We  merely  mention  a  few  modern  attempts  to  obtain  workable 
roast iug-gases  from  such  ores  by  new  methods. 
Fig.  117. 


Huntington  and  Heberlein  (E.  P.  8064,  1896;  3795,  1897) 
obtain  SO^  by  a  new  treatment  of  lead-ores,  but  in  such  a  way 
that  their  conversion  into  sulphuric  acid  seems  to  be  almost  im- 
possible. 

Sebillot  (13.  P.  21,6lt!,  1898)  charges  cuprous  or  other  sulphur- 
ores,  mixed  with  fuel,  into  a  furnace  provided  with  air-blast.  The 
gasea  are  taken  into  a  chamber  containing  coke,  pumice,  or  a 
suitable  metallic  oxide,  where  they  are  treated  with  air  and  steam, 
and  where  sulphuric  acid  is  formed  (comp.  Chap.  XI.}. 

Treatment  of  complex  ores  containing  blende. — Hart  (Journ.  Soc. 


366  PBpDUCTION  OP  SVLFHUR  DIOXIDE. 

Chem.  lud.  1895,  p.  544)  proposes  treating  Buch  o>es  with  sul- 
phuric acid  in  a  saltcake  pot,  and  when  tlie  mass  has  become  pasty 
transferring  it  to  a  blind  roaster  and  finishing  it  there,  all  the 
gases  going  into  vitriol-chambers.  The  zinc  remains  behind  as 
sulphate,  which  can  be  obtained  by  lixiviation  aad  crystallization; 
or  else  it  is  mixed  with  poor  zinc-ore  and  roasted,  in  which  case 
the  oxygen  of  the  sulphate  combiaes  with  the  sulphur  o£  the 
blende.     The  reaction  seems  to  be : 

ZnS  +  4SOa=ZnS04-|-4SOj. 

5.  Burners  por  the  Spent  Oxide  or  Gas-works. 
I'he  spent  oxide  is  now  generally  washed,  so  as  to  obtain 
ammonia  salts  therefrom,  and  is  also  frequently  treated  for  the 
ferrocyanide  or  sulpliocyanide.  At  all  events  the  sulphur,  which 
it  contains  in  the  free  state,  sometimes  up  to  50  per  cent.,  is 
ultimately  burnt  for  the  manufacture  of  sulphuric  acid.  This  is 
sometimes  done  in  ordinary  brimstone-burners,  as  shown  supru, 
p.  268  et  aeq. ;  but  in  this  case  it  is  difficult  to  bum  it  out  com- 
pletely, and  there  is  loss  of  sulphur  in  the  cinders.  Ordinarily  it 
is  burnt  in  apparatus  very  similar  to  "shelf-burners,"  as  shown 
in  f)g.  118  (Hill's  burner).     Each  chamber  in  this  case  is  about 

riy.  118. 


10  feet  long,  20  inches  wide,  and  9  inches  high.  MacDougall's 
and  Herreshoff's  mechanical  burners  (pp.  343  &  349)  have  also 
been  employed  for  this  purpose. 

Cowen's  burner,  figs,  119  and  120,  consists  of  a  row  of  fire-clay 
gas-retorts,*  and  requires  no  further  explauation.     Other  works 


BURNEHti  FUR  SPENT  UXIOB  AND  SULFDl 


ar3  said  to  burn   that  material  in  burners  with  very  narrowly- 
placed  grate-bars. 


Soiuttimcs  tlie  oxide  is  moulded  into  bricks  and  put  into  liimp- 
buiners ;  it  burns  off  very  well  and  the  cinders  fall  tliroujjli  the 
grate-bars  by  themselves :  in  fact,  the  bars  must  be  touched  as  little 
as  possible.     This  process  does  not  answer  so  well  as  shelf-burners. 

The  asfh  Alkali  Report,  p.  97,  recommends  not  to  discharge 
the  hot  residue  from  oxide  burners  through  the  front  working- 
doors,  as  this  causes  a  nuisance,  but  to  push  it  into  chambers 
placed  at  the  back,  where  they  can  cool  oflf.  The  f^ases  should  be 
led  through  loug,  heated  flues,  in  order  to  burn  the  tarry  substances 
and  ammonia  whieh  destroy  nitre. 

6.  Buhners  for  Svlphvhetted  Hydrouex, 

These  are  usually  of  a  very  simple  description.  As  shown  in 
tig.  121,  they  consist  of  a  brick  chamber  provided  with  sonic 
battling-walls  a,  a.  The  sulphuretted  hydrogen  gas  (which  is 
nearly  always  mixed  with  a  large  quantity  of  inert  gas,  chiefly 
nitrogen)  is  introduced  by  the  cast-iron  pipe  b,  the  supply  being 
regulated  by  an  inlet-valve  c.  Air  is  admitted  partly  round  the 
pi|>e  A,  partly  by  n  special  opening  d,  which  ought  to  be  provided 
with  a  slide  or  otiier  means  of  regulating  the  amount  of  air.  The 
licat  produced  by  the  combustion  of  the  sulphuretted  hydi-ogcn 


368  PRODUCTION  Of  SULPHUR  D10XID£. 

h  quite  sufficient  for  keepiug  the  temperature  of  the  chamber 
at  a  red  heat,  so  that  the  ga%is  always  lighted  again  if  by  chance 
the  flame  has  been  extinguished.  This  is  aided  by  the  baffliug- 
walls  a,  a,  which  serve  both  the  purpose  of  supplying  a  reservoir 
of  heat  for  the  just-mentioned  purpose,  and  of  mixing  the  gases  so 
as  to  insure  perfect  combustion.  The  grate  e  is  required  only 
for  irregularly  composed  gases,  like  those  formed  in  the  saturation 
of  the  gas  from  ammonia-stills  by  sulphuric  acid  ;  especially  for 
re-lightiug  the  gas  after  stoppages  over  Sundays,  and  so  forth. 
With   gases  of  regular  composition  and  comparatively  rich  in 


sulphurettcd  hydrogen,  like  those  given  off  in  Chance's  sulphur- 
recovering  process,  the  grate  e  is  quite  unnecessary,  as  these  gases 
are  as  easily  lighted  and  kept  burning  as  coal-gas.  The  doors  // 
serve  for  "  potting"  the  nitre,  where  it  is  not  preferred  to  employ 
more  rationally  constructed  apparatus  for  this  purpose  (comp. 
Chapter  V.).  The  size  of  the  whole  chamber  may  be  about  10  to 
12  feet  long,  4  or  5  feet  wide,  and  3  feet  high.  Pans  for  con- 
centrating sulphuric  acid  may  be  placed  upon  it,  and  even  in  this 
case  the  gases  will  issue  hot  enough  to  do  full  work  in  a  Glover 
tower.     Sublimation  of  sulphur  is  never  observed  with  ordinary 


BURNING  SULPHUBETTED  HYDROGEN.  369 

care  in  admittiug  the  air.  One  very  great  advantage  lu  burning 
sulphuretted  hydrogen  is  this :  that,  contrary  to  the  variations  in 
the  amount  of  SOg  in  burning  brimstone  or  pyrites,  even  when 
keeping  up  a  regular  rotation  of  the  burners,  there  is  in  this  case 
a  perfectly  continuous  process,  as  the  supply  of  HgS  from  the 
gas-holder  is  continuous ;  the  amount  of  air  need  never  be  varied 
when  once  regulated;  the  percentage  of  SOg  in  the  burner-gas 
is  altogether  uniform  ;  the  chamber  process  is  consequently  much 
more  regular  than  with  brimstone  or  pyrites,  and  the  consumption 
of  nitre  is  correspondingly  smaller.  All  this,  however,  holds  good 
only  if  the  percentage  of  HgS  in  the  gas  is  practically  constant, 
whilst  with  gases  of  very  varying  composition,  such  as  those  evolved 
in  ammonia-works,  the  very  contrary  is  the  case. 

It  must  be  remarked  that  at  some  works,  in  burning  the  sul- 
phuretted hydrogen  from  the  Chance  process,  an  increased  con- 
sumption of  nitre  has  been  noticed,  whilst  at  others  a  saving  in 
nitre  in  comparison  with  the  burning  of  pyrites  has  been  effected. 
Evidently  in  the  former  case  the  quality  of  the  sulphuretted 
hydrogen  has  not  been  as  it  ought  to  be ;  it  has  no  doubt  varied 
in  percentage,  and  may  even  have  contained  a  notable  quantity  of 
carbon  dioxide,  so  that  the  chamber-process  would  not  be  as  regular 
as  desirable.  Sometimes  it  has  been  noticed  that  the  combustion 
has  not  been  quite  perfect,  so  that  sublimed  sulphur  has  been  found 
in  the  Glover  tower  or  even  in  the  chambers ;  but  this  is  evidently 
owing  to  mistakes  and  careless  work,  and  should  not  occur  with 
ordinary  care. 

In  1886  E.  Lombard  (Monit.  Scient.  1889,  p.  1281)  described 
a  shelf-bumei*  for  sulphuretted  hydrogen,  consisting  of  two  separate 
compartments,  7  ft.  6  in.  deep  inside.  There  are  four  shelves, 
6  ft.  6  in.  long  and  1  ft.  4  in.  wide,  formed  of  four  fire-clay  slabs 
each.  The  top  shelf  is  perforated  with  many  holes,  and  occupies 
the  whole  length  and  width  of  the  furnace ;  the  other  shelves  are 
not  perforated,  and  leave  at  alternate  ends  a  passage  of  12  X 16  in. 
for  the  gases.  Each  furnace  is  provided  at  the  base  with  four 
burners  for  HgS  and  two  air-tubes,  disposed  in  two  tiers  of  three 
each,  the  air-tubes  occupying  the  central  places.  The  burners 
consist  of  fire-clay  tubes,  6  ft.  6  in.  long,  1^  in.  wide  inside,  and 
I  in.  thick,  projecting  two-thirds  of  their  length  into  the  furnace, 
and  provided  on  the  top  with  slits  or  holes  for  dividing  the  gas. 
They  are  connected  in  front  by  a  cast-iron  tube  with  a  stop-cock  for 

VOL.  I.  2  B 


370  PRODUCTION  OF  SULPHUR  DIOXIDE. 

regulating  the  flow.  The  air-tube  is  2^  in.  wide,  and  is  provided 
with  an  iron  thimble  for  regulating  the  quantity  entering.  The 
gaseous  products  of  combustion  pass  into  a  flue,  1  ft.  6  in.  x  2  ft., 
on  the  top  of  the  furnace,  then  into  a  small  dust-chamber,  and  then 
into  the  Glover  tower.  Total  height  6  feet.  The  pressure  of  the 
gas  is  =1^  inches  of  .water;  it  is  said  to  work  very  well. 

Simpson  and  Parnell  (E.  P.  14,711,  1886)  regulate  the  supply 
of  air  and  gas  in  any  desired  proportion,  so  as  to  obtain  either  free 
S  or  SO2,  by  employing  two  vessels,  each  of  which  is  provided  with 
an  inlet  and  an  outlet  valve.  Both  vessels  are  filled  and  emptied 
simultaneously  by  a  mechanical  arrangement,  the  two  vessels  acting 
in  conjunction,  so  that  the  gas  entering  and  leaving  one  of  the 
vessels  beai*s  a  constant  proportion  to  the  quantity  of  air  entering 
and  leaving  the  other  vessel.  [Such  an  arrangement,  very  useful 
as  it  undoubtedly  is  for  the  production  of  free  sulphur  from  HjS, 
seems  unnecessarily  complicated  when  the  object  is  that  of  burning 
the  H2S  with  an  excess  of  air  for  the  purpose  of  sulphuric-acid 
manufacture.] 

7.  Processes  for  Absorbing  Sulphur  Dioxide  contained  in 
Acid-smoke,  Fire-gases,  and  the  like. 

The  abatement  of  the  nuisance  caused  by  the  acid-smoke  given 
ofl^in  metallurgical  and  other  operations  presents  special  difficulties 
where  the  percentage  of  acids  is  so  slight  that  their  utilization  by 
condensation  or  by  conversion  into  sulphuric  acid  is  out  of  the 
question ;  that  is,  if  less  than  4  per  cent.  SO2  by  volume  is  present. 
The  damage  done  by  such  acid  gases  has  been .  described  in 
Chap.  III.  p.  154  et  seq. 

A  survey  of  the  processes  tried  a  number  of  years  ago  at 
Stolberg  for  dealing  with  acid-smoke  has  been  given  by  Hasen- 
clever  (Fischer's  Jahresb.  1881,  p.  173).  All  of  these  will  be 
mentioned  below ;  they  all  have  one  common  feature :  they  are 
very  expensive,  and  at  the  same  time  they  hardly  ever  attain  their 
purpose  completely. 

The  problem  of  dealing  with  the  enormous  quantity  of  sulphur 
dioxide  contained  in  ordinary  coal-smoke  has  been  hardlv  ever 
attacked  in  a  serious  manner,  as  the  expense  and  inconvenience 
of  any  imaginable  measures  for  this  purpose  have  hitherto  appeared 
to  be  quite  unbearable ;  and  it  does  not  seem  as  if  this  would  be 
diflferent  in  the  near  future.  The  only  practicable  remedy  in  this 
case,  as  well  as  in  some  cases  of  metallurgical  smoke,  is  to  dilute 


DEALING  WITH  SMOKE-GASES,  371 

the  gases  with  a  large  quantity  of  air,  by  erecting  very  tall 
chimneys  for  carrying  them  up  to  a  considerable  height  above  the 
surface  of  the  earth.  Such  chimneys  have  been  made  up  to  450 
feet  in  height.  In  the  case  of  hydrochloric  acid  they  have  entirely 
failed  in  their  object  (comp.  Vol.  II.),  but  in  that  of  sulphur  dioxide 
the  dilution  of  air  is  more  efficient.  Freytag  certainly  estimates 
(somewhat  arbitrarily)  that  smoke  is  harmless  only  when  it  does 
not  contain  beyond  0003  percent.  SOj  by  volume;  but  as,  for 
instance,  in  lead-works  the  percentage  of  SO2  in  the  main  flues, 
where  all  the  smoke  and  fire-gasses  are  mixed,  rarely  exceeds  O'l 
per  cent.,  it  is  very  likely  that,  if  these  gases  are  allowed  to  escape 
only  200  feet  or  more  above  any  vegetation,  they  get  sufficiently 
diluted  with  air  in  their  descent  to  become  harmless.  This  is 
owing  to  the  fact  that  sulphur  dioxide  diffuses  pretty  equally  in 
the  air,  whilst  hydrochloric  acid,  sulphuric  anhydride,  acid  salts, 
&c.,  which  form  visible  fumes^  generally  reach  the  bottom  in  a 
very  little  divided  stream,  and  cannot  therefore  be  made  innocuous 
by  very  tall  chimney-shafts.  In  fact,  this  is  the  only  explanation 
why  the  scores  of  tons  of  sulphur  dioxide  daily  belched  forth  in 
certain  localities  by  lead-works,  zinc-works,  glass-works,  &c.,  have 
not  ere  now  destroyed  all  vegetable  life  around  the  works,  which 
is  notoriously  the  case  only  in  a  few  isolated  instances.  But  as 
such  instances  do  occur,  and  as  altogether  the  requirements  of 
sanitary  authorities  are  constantly  becoming  stricter,  the  removal 
of  the  acid-smoke  to  a  high  level  by  means  of  chimneys  cannot  be 
pronounced  a  final  solution  of  the  difficulty,  even  where  only  SO2 
is  the  acid  concerned,  all  the  more  as  in  moist  weather  the  acids 
escaping  from  the  very  tallest  chimneys  are  brought  down  to  the 
ground  in  a  somewhat  concentrated  state. 

A  proposal  has  been  made  by  Wislicenus  and  Isaachsen  (G.  P. 
124,900)  to  dilute  smoke-gases  to  such  an  extent  that  the  amount 
of  acid  contained  in  them  becomes  innocuous.  This  is  to  be 
attained  by  building  within  the  chimney-stack  a  second  lower 
stack,  provided  with  pipes  carried  up  and  downwards.  Air  is 
introduced  into  the  inner  stack  and  escapes  partly  at  its  top, 
partly  through  the  up  and  down  pipes,  thus  intimately  mixing  it 
^vith  the  chimney  gases.  [It  is  not  likely  that  this  process  can 
be  carried  out  in  many  cases  as  prescribed  above,  but  it  is  stated 
in  the  38th  Alkali  Report,  p.  76^  that  bringing  down  the  per- 
centage of  acids  in  the  exit  gases  from  chemical  works  by  means  of 
diluting  them  in  the  chimney  with  air  is  not  contrary  to  the  law.] 

2b2 


372  PRODUCTION  OF  SULPHUR  DIOXIDE. 

O.  Schott  (Dingl.  Journ.  ccxxi.  p.  142)  has  proposed  to  utilize 
the  sulphur  dioxide  given  off  in  making  glass  from  sodium  sulphate 
for  the  manufacture  of  sulphuric  acid.  The  gas  is  to  be  made 
richer  in  sulphur  by  employing  for  the  glass-mixture  gypsum  in 
lieu  of  limestone.  Sulphate  of  soda,  gypsum,  and  coal  are  to  be 
mixed  in  proper  proportions,  and  brought  to  a  bright  red  heat  in 
muffle-furnaces  or  in  elliptical  glass  pots,  until  the  SO2  is  driven 
off.  The  fritted  residue  of  sodium  and  calcium  silicate  is  to  be 
powdered  and  used  by  glass-works;  the  gas  is  to  be  conducted 
into  lead  chambers  and  worked  for  sulphuric  acid.  This  process 
seems  entirely  impracticable  ;  especially  since  such  diluted  gas 
(mixed  with  a  great  deal  of  carbon  dioxide)  has  not  yet  been 
utilized. 

Thirion  (Fr.  P.  Feb.  28,  1874;  Wagner's  Jahresb.  1875.  p.  391) 
makes  a  similar  proposal  for  heating  sodium  sulphate  with  coal 
and  silica,  whereby  a  mixture  of  sulphur  vapour,  sulphur  dioxide, 
and  carbon  monoxide  is  cooled.  The  sodium  silicate  is  to  be 
decomposed  by  CO3  or  to  be  used  as  such.  [As  a  proposal  for 
manufacturing  sulphur  or  sulphuric  acid  this  process  is  evidently 
hopeless.] 

We  will  now  give  a  synopsis  of  the  various  methods  for  treating 
ordinary  acid-smoke,  with  special  reference  to  the  removal  of  SO2 
and  S.O3.  For  details  we  must  refer  to  the  sources  quoted  in  this 
work,  to  a  special  treatise  by  C.  A.  Hering,  '  Die  Verdichtung 
des  Hiittenrauches  ^  (Stuttgart,  1888),  and  to  one  by  Schnabel, 
*  Metallhiittenkunde,'  ii.  pp.  58  et  seq. 

Condensing  by  water  seems  to  be  the  simplest  and  most  obvious 
process,  looking  at  the  great  solubility  of  sulphurous  and  sulphuric 
acid  in  water.  But  this  process  is  in  reality  only  practicable  where 
the  percentage  of  acids  is  not  too  slight;  dilute  acid-smoke  is  not 
sufficiently  washed  without  employing  a  comparatively  enormous 
quantity  of  water ;  and,  surprising  as  it  is,  SO3  is  even  more  diffi- 
cult to  condense  in  this  way  than  SO2.  It  is  quite  certain  that 
condensation  by  water  can  be  made  to  pay  only  where  the  gases 
are  sufficiently  concentrated  to  convert  them  into  sulphuric  acid 
in  lead  chambers  ;  it  is  therefore  the  interest  of  smelting-works, 
&c.,  to  conduct  their  processes  in  such  a  manner  that  the  acids  are 
diluted  with  as  little  inert  gases  as  possible.  If  the  percentage  of 
SO2  reaches  4  per  cent,  by  volume,  they  may  be  submitted  to  the 
Scbroeder  and  Haenisch  process  {vide  infra),  or  they  may  even  be 
converted  into  sulphuric  acid,  although  this  will  hardly  leave  any 


ABSORBING  SO]  BY  WATER,  SULPHURIC  ACID^  OR  CAUSTIC  LIME.     373 

profit  at  that  percentage ;  but  it  is  enough  to  have  removed  the 
nuisance.  Where,  however,  there  is  less  than  4  per  cent,  of  SOg 
in  the  gases,  any  utilization  is  out  of  the  question;  the  thin  acid 
liquids  obtained  by  washing  the  smoke  must  be  run  to  waste  (which 
in  most  cases  means  a  fresh  nuisance,  and  is  not  permitted  by  the 
authorities) ;  nor  is  the  SO2  and  SO3  anything  like  completely 
taken  out  of  the  gases  j  and  the  nuisance  is  at  best  only  diminished, 
but  not  remedied. 

At  all  events  the  contact  of  the  absorbing-water  with  the  acid 
gases  must  be  made  as  intimate  as  possible.  The  condensiug- 
apparatus  used  for  hydrochloric  acid,  and  described  in  Vol.  II., 
act  only  for  somewhat  strong  gases ;  the  weak  gases  which  we  are 
here  treating  of  require  special  means,  such  as  paddle-wheels  or 
similar  spray-producing  apparatus,  costly  to  work  and  to  keep 
in  repair,  and  generally  imperfect  in  their  action.  Haworth 
(U.S.  P.  268,793,  of  1882)  proposes  to  condense  the  SOj  given  off 
in  lead-smelting  by  water,  boiling  it  out  of  the  solution  and  taking 
it  into  a  lead  chamber — an  economically  hopeless  process. 

In  lieu  of  water,  Freytag  (G.  P.  9969,  14,928,  15,546)  and 
Hasenclever  (ti.  P.  17,371)  employ  somewhat  concentrated  .ml- 
phuric  acidy  in  an  ordinary  coke-tower  of  large  size.  This  agent 
retains  the  SO3  much  better  than  water,  so  that  in  some  cases  the 
expense  of  working  the  process  is  paid  by  the  sulphuric  acid 
gained.  SO3  is  also  retained  to  some  extent,  but  only  if  the  gases 
have  been  well  cooled.  The  necessity  of  doing  this  and  of 
previously  removing  the  flue-dust^  which  is  sometimes  very 
difficult  to  perform,  is  a  great  drawback  to  this,  as  well  as  to 
all  corresponding  processes.  In  fact  Freytag^s  process  has  been 
abandoned  again  ;  at  the  best  it  could  remove  only  a  small  portion 
of  the  injurious  constituents  from  the  acid-smoke.  (Schroeder 
and  Haeuisch,  Chem.  Ind.  1881^  p.  118.) 

Absorbing  the  acids  by  caustic  limey  generally  in  the  shape  of  a 
cream  of  lime,  is  one  of  the  oldest  and,  if  properly  carried  out,  still 
one  of  the  most  efficient  ways  of  removing  the  acid-smoke  nuisance. 
Where  the  quantity  of  acids  is  but  slight,  and  the  manufacture  in 
question  is  sufficiently  profitable  otherwise,  this  process  is  even 
now  applicable,  and  if  properly  applied  it  does  remove  practically 
all  the  acids.  The  cream  of  lime  should  meet  the  gases  in  a  finely 
divided  state,  either  by  flowing  down  properly-constructed  towers, 
or,  still  better,  by  being  converted  into  a  spray  by  means  of  paddle- 
wheels  or  the  like  (comp.  Rayner  and  Crookes'  patent,  E.  P.  2678, 


874  FRODUCTION  OF  SULPHUR  DIOXIDE. 

]875).  That  this  leads  to  the  desired  effect,  even  with  the  large 
quantity  of  SOo  emitted  in  roasting  blende,  has  been  proved  by 
working  on  the  large  scale  in  Upper  Silesia  (comp.  Bernoulli, 
Fischer^s  Jahresb.  1880,  p.  184).  But  unfortunately  the  expense 
of  this  process,  where  large  volumes  of  acid  gases  are  concerned, 
is  very  serious,  more  especially  as  nothing  like  the  whole  of  the 
lime  can  be  utilized  for  absorption,  and  the  attempt  to  utilize  the 
product  as  bisulphite  of  lime  (Hasenclever,  G.  P.  10,710)  has 
failed  (comp.  Schroeder  and  Haenisch,  Chem.  Ind.  1884,  p.  118). 

According  to  Jensch  (Fischer's  Jahresb.  1889,  p.  321)  the 
deposit  forming  in  the  milk-of-lime  towers  contains  so  much  lime 
that  it  can  be  used  over  again,  and  at  least  a  product  is  obtained 
containing  37'7  per  cent,  lime,  38*4  SOj,  2*8  SO3,  4*1  CO2,  &c., 
which  is  very  useful  as  an  addition  to  animal  manure  for  the 
purpose  of  fixing  the  ammonia,  in  which  respect  it  is  equal  to 
gypsum. 

It  has  been  found  by  CI.  Winkler  and  other  observers  that  the 
SO2  in  smoke  is  much  more  injurious  to  vegetation  if  accompanied 
by  much  steam,  e.  g,  in  smoke-gases  from  brick-kilns.  Spitta 
(G.  P.  110,388)  proposes  to  absorb  SO2  and  steam  at  the  same 
time  by  passing  the  gases  up  and  down  several  flues,  into  which 
slaked  lime  in  the  shape  of  dust  is  injected  from  the  top.  The 
bisulphite  of  lime  formed  is  removed  from  the  bottom  of  the  flues 
by  means  of  special  doors. 

Egestorffs  Salzwerke  (G.  P.  70,396)  describe  a  very  efficient 
apparatus,  consisting  of  a  series  of  chambers  with  inclined  bottoms, 
connected  with  collecting-tanks.  The  alkaline  absorbing  liquid 
is  pumped  up  over  and  over  again  and  brought  into  contact  with 
the  gases  by  means  of  a  spray-producer. 

Limestone  is  very  much  cheaper  than  caustic  lime,  and  is  almost 
equally  efficient  if  employed  in  the  proper  way;  that  is,  if  a  very 
large  surface  of  limestone  is  exposed  to  the  acid  gases,  and  if  this 
surface  is  kept  from  being  covered  with  a  crust  of  sulphite  by 
being  constantly  washed  with  a  stream  of  water.  CI.  Winkler  has 
constructed  a  special  arrangement  for  this  purpose  (G.  P.  7174), 
which  completely  fulfilled  its  object  at  the  Schneeberg  ultramarine 
works.  It  consists  of  three  brick  chambers  filled  with  large  pieces 
of  limestone,  the  roof  being  formed  by  plank  covers  perforated 
with  many  holes,  through  which  water  is  kept  running  on  to  the 
limestone.     The  gases  pass  through  these  chambers  successively 


ABSOUBIXG  SO3  BY  LIMESTONE^  MAGNESIA^  ETC.  375 

and  in  regular  rotation.  The  absorption  of  SO2  is  excellent,  but  as 
each  cwt.  of  sulphur  requires  3  cwt.  of  limestone,  it  is  still  too 
dear  for  most  metallurgical  purposes,  especially  as  any  utilization 
of  the  sulphur  is  out  of  the  question. 

The  limestone  treatment  is  frequently  employed  at  sulphate-of- 
ammonia  works  for  getting  rid  of  the  SO2  formed  by  combustion 
of  the  HjS  escaping  from  the  saturators.  This  treatment  is 
frequently  mentioned  in  the  Alkali  Inspectors'  Reports,  and  in 
the  36th  Report  (for  1899),  pp.  25  &  26,  Mr.  R.  Forbes  Carpenter, 
the  Chief  Inspector,  states  the  following  conditions  as  being 
absolutely  necessary  for  success : — Ist.  There  must  be  sufficient 
draught  at  the  furnace,  and  the  suction  at  the  condenser  outlet 
must  be  adequate  to  supply  this  at  all  times,  to  avoid  sublimation 
of  sulphur.  Such  draught  might  be  supplied  by  injecting  air 
under  slight  pressure  in  the  furnaces.  2nd.  The  gases  must  be 
completely  cooled  before  and  behind  the  furnace.  If  they  enter  the 
limestone-tower  above  38°  C,  much  calcium  sulphate  is  produced, 
which  forms  a  protective  crust  on  the  limestone.  The  hot  gases 
are  to  be  cooled  first  by  cast-iron  pipes  until  some  condensation 
takes  place^  when  leaden  pipes  must  be  substituted  for  them. 
3rd.  The  limestone-tower  should  be  made  of  wood  planks,  tongued 
and  grooved,  or  of  brick  and  cement,  not  of  cast-iron.  [The 
latter  material  would  surely  not  be  dreamt  of  by  a  chemical 
engineer  in  such  a  case,  but  possibly  it  has  been  used  in  gas-works  !] 
4th.  The  supply  of  water  is  best  made  in  two  forms,  one  constant^ 
the  other  intermittent  (by  flushes),  especially  in  the  case  of  lime- 
stone, but  with  hard  chalk  the  intermittent  flush  only  may  be  used, 
at  not  too  long  intervals.  [Comp.  the  much  better  feeding  methods 
for  Gay-Lussac  and  Glover  towers  described  in  Chap.  VI.] 

Precht  (E.  P.  3443,  1881)  employs  for  absorbing  SO2  from 
gaseous  mixtures  either  magnesium  hydrate  or  aluminium  hydrate, 
especially  the  former.  It  is  either  spread  upon  trays  moistened 
with  water,  or  is  brought  into  contact  with  the  gases  (previously 
cooled  to  100°)  in  the  state  of  a  cream,  in  an  apparatus  provided 
with  a  mechanical  agitator,  or  in  columns  like  those  employed 
for  treating  sulphuric  acid  by  sulphuretted  hydrogen  (Chap.  X.). 
This  produces  a  crystalline  precipitate  of  magnesium  sulphite, 
besides  a  solution  of  magnesium  sulphate.  On  heating  the  mag- 
nesium sulphate  to  upwards  of  200°  the  SO3  is  split  ofi^,  and  can 
be  condensed   as  such  or  converted  into  sulphuric  acid,  whilst 


376  PRODUCTION  OF  SULPHUR  DIOXIDE. 

magnesia  remains  behind^  together  with  about  3  per  cent, 
magnesium  sulphate.  The  latter  is  heated  with  coals^  and  thereby 
converted  into  MgO^  remaining  behind^  and  a  mixture  of  SO2  and 
CO2,  which  is  utilized  in  vitriol-chambers  [?] .  M.  Lyte  (J.  Soc. 
Chem.  Ind.  1882^  p.  165)  gives  a  detailed  description  of  this 
process  with  diagrams.  It  has  been  tried  at  several  places^  but  has 
evidently  been  found  too  little  advantageous  for  most  purposes. 

Alumina  is  included  in  Precht's  patent^  but  is  less  efficient  than 
magnesia.  Sometimes  acid  gases  have  been  passed  through  layers 
of  clay-slate  (schist)^  whereby  sulphate  of  alumina  has  been 
formed^  but  this  process  is  evidently  only  practicable  under  special 
local  circumstances. 

Zinc  carbonate  or  omde  was  proposed  by  Schnabel  (Fischer's 
Jahresb.  1882,  p.  266),  who  had  previously  made  manifold 
attempts  at  the  Lautenthal  smelting- works  for  treating  the  acid- 
smoke,  all  without  any  sufficient  success.  Ultimately  a  process 
was  adopted  (G.  P.  16,860),  consisting  in  passing  the  gases  over 
basic  zinc  carbonate  moistened  with  water.  Zinc  sulphate  is 
formed,  which,  on  heating  (preferably  mixed  with  coal),  yields 
sulphur  dioxide,  to  be  converted  into  sulphuric  acid  in  lead 
chambers,  and  a  porous  residue,  consisting  of  a  mixture  of  zinc 
oxide  with  basic  zinc  sulphate.  SchnahePs  apparatus  is  rather 
complicated,  and  the  result  not  very  satisfactory ;  the  process  is 
very  troublesome  to  carry  on,  and  costs  much  more  than  the  value 
of  the  sulphuric  acid  obtained  (a  provisional  protection,  No.  5416, 
1881,  for  this  process  was  taken  out  in  England  by  M.  Lyte). 

Fleitmann  (G.  P.  17,397)  passes  the  sulphurous  gases,  together 
with  some  air,  through  a  kiln  containing  a  mixture  of  ferric  oxide 
and  coal.  The  latter,  in  burning,  yields  the  necessary  beat,  and 
at  the  same  time  reduces  the  Fe203  and  SO2,  so  that  FeS  collects 
at  the  bottom  (the  success  of  this  process  is  more  than  doubtful). 
Metallic  iron,  moistened  by  water,  was  employed  by  Winkler 
(G.  P.  14,425),  but  was  not  found  practicable  for  dilute  acid  gases. 
Thorp  (E.  P.  8862,  1889)  again  recommends  towers  filled  with 
scrap-iron,  and  kept  moist  with  water  or  a  solution  of  feiTOUS 
sulphate,  the  temperature  being  maintained  at  from  49°  to  71°  C. 
Metallic  copper  or  zinc,  in  very  finely  divided  form,  was  tried  at 
the  Frankfort  gold-parting  works,  but  without  sufficient  success ; 
but  at  the  same  works  the  following  interesting  process  was 
worked  out. 


TREATING  8O2  WITH  COPPER  OR  WITH  H28.  877 

Rossler  (Dingler's  Journal^  ccxlii.  p.  278;  Fischer's  Jahresb. 
188]^  p.  184)  showed  that  gaseous  mixtures^  containing^  besides 
a  large  excess  of  air,  far  too  little  SOg  and  SOg  for  being  treated 
in  vitriol-chambei  s  and  otherwise  not  treatable  in  any  efficient 
manner,  can  be  completely  deprived  of  both  the  above  acids  i)y 
forciDg  the  gases,  by  means  of  a  Korting's  injector  and  a  perforated 
coil  of  pipes,  underneath  a  column  of  water,  holding  some  copper 
in  suspension  or  some  cupric  salt  in  solution.  The  cupric  sulphate 
acts  as  a  carrier  of  the  oxygen  of  the  air  upon  the  SO3,  and  large 
quantities  of  sulphuric  acid  are  formed  in  this  way,  so  that  this 
process  might  even  be  employed  for  manufacturing  sulphuric  acid. 
At  Frankfort,  however,  it  is  carried  out  in  this  way,  that  the  tank 
into  which  the  gases  are  passed  is  always  supplied  with  precipitated 
copper,  from  which  by  this  process  cupric  sulphate  is  obtained 
without  any  expense.  Rossler  has  also  applied  this  principle  to 
the  treatment  of  ordinary  acid-smoke  (G.  P.  22,850),  by  combining 
a  whole  set  of  apparatus.  This  process  is  very  adversely  criticized 
by  Friese  (Chem.  Ind.  1895,  p.  137),  who  has  made  a  long  series 
of  experiments  with  it,  with  totally  negative  result.  No  oxidation 
of  SO2  with  air  to  SO3  by  the  catalytic  action  of  CaS04  could  be 
proved.  SO2  reduces  a  hot  solution  of  CuSO^,  with  intermediary 
formation  of  cupric  sulphite,  to  metallic  copper.  A  smooth  and 
easy  oxidation  of  the  cupric  sulphite  to  sulphate  does  not  take 
place.  Hence  this  process  would  be  useless  for  the  production  of 
cupric  sulphate,  and  still  more  so  for  that  of  sulphuric  acid. 

A  special  class  of  processes  utilizes  the  reaction  between  sulphur 
dioxide  and  hydrogen  sulphide,  either  both  being  in  the  state  of 
gases,  or  the  latter  being  in  the  nascent  state  as  evolved  frt  m 
sulphides.     The  reaction  in  its  simplest  form  is  : 

2HjS-l-SO2=2H30  +  3S; 

but,  apart  from  the  fact  that  polythionic  acids  are  formed  by 
secondary  reactions,  the  above  reaction  is  anything  but  complete 
with  very  dilute  gases.  Details  about  it  will  be  given  in  Vol.  II f. 
in  the  chapter  treating  of  the  recovery  of  sulphur  from  soda  waste ; 
in  this  place  it  may  suffice  to  mention  that  a  patent  founded  upon 
the  above  reaction  was  taken  out  by  Landsberg  (G.  P.  6364-)  in 
connection  with  the  roasting  of  blende. 

When  sulphides  are  employed,  the  reactions  are  even  more 
complicated,  but  the  absorption  of  SOj  can  be  made  more  complete. 


378  PRODUCTION  OF  SULPHUR  DIOXIDE. 

CI.  Winkler  (Fischer's  Jahresb.  1880,  p.  245  ;    more  details    in 
Chem.  Ind.  1880,   p.   126)  describes  a  very  interesting  process 
for  dealing  with  the  gases  from  an  ultramarine-works  containing 
much  SO^.     They  were  brought  into  contact  with  a  solution  of 
sodium  sulphide,  obtained  from  the  sulphate  going  to  waste  in  that 
manufacture,  by  reducing  it  with  coal.     The  SOj  is  completely 
absorbed,  with  formation  of  sodium  tbiosulphate,  or,  in  another 
modification,  with  formation  of  free  sulphur ;  but  on  the  large  scale 
sodium  tetrathionate  was  formed,  which  had  to  be  decomposed  by 
heating  into  sodium  sulphate,  SOo*  and  free  sulphur.    Theoretically 
nothing  was  consumed  but  coal,  but  evidently  a  very  large  amount 
of  fuel  must  have  been   used   in   the  various   evaporations   and 
furnace  operations,  with  an  amount  of  skilled  labour  out  of  propor- 
tion to  the  value  of  the  products  obtained.    After  having  been  used 
from  1868  to  1877,  the  process  just  described  was  abandoned  for  a 
simple  absorption  by  limestone  moistened  with  water  (p.  374). 
Even  before  Winkler,  in  1864,  Jacob  had  carried  out  for  some 
years  a  similar  process  to  that  just  described,  employing  either 
sodium  or  calcium  sulphide,  at  Miinsterbusch  (Fischer's  Jahresb. 
1881,  p.  181). 

Calcium  sulphide^  proposed  many  years  ago  by  Dumas,  forms 
also  the  absorbing  substance  in  Kosmann's  process  (6.  P.  13,123). 
By  reducing  calcium  sulphate  with  coal  and  lixiviating  a  solution 
of  calcium  sulphydrate  is  obtained  [?],  which  in  very  finely 
divided  state  is  brought  into  contact  with  the  gases  containing 
SOj.     The  result  is  the  formation  of  sulphur  and  gypsum : 

5S02  +  2CaH2S2  +  2H20=7S  +  2CaSO^,  2HoO. 

The  sulphur  is  extracted  from  the  mixture  by  superheated  steam- 
and  the  gypsum  returns  into  the  cycle  of  operations  [it  is  very 
doubtful  whether  this  would  succeed  !].  From  further  com- 
munications by  Kosmann  (Fischer's  Jahresb.  1882,  p.  270),  it 
appears  that  the  absorbing  medium  was  afterwards  prepared 
by  boiling  sulphur  with  milk  of  lime,  that  is,  as  the  ordinary 
''  liver  of  sulphur,'^  and  that  the  whole  process  was  entirely  in 
the  experimental  stage  (from  which  it  does  not  seem  to  have 
emerged) . 

Barium  sulphide,  which  was  experimentally  tried  at  Freiberg, 
proved  much  too  costly. 

Vegetable  charcoal  is  proposed  by  A.  H.  Allen   (B.  P.  189,  of 


SULPHUR  DIOXIDE  IN  THE  PURE  STATE.  379 

1879),  who  passes  the  gases,  freed  from  dust,  through  drying- 
towers  fed  with  sulphuric  acid  and  then  through  columns  filled 
with  charcoal,  previously  ignited  in  a  stream  of  nitrogen,  where 
the  SOg  is  retained,  whilst  the  nitrogen  passes  on.  By  a  vacuum 
or  by  heating  to  300°-400°,  or  by  a  combination  of  both,  the  SO2 
is  to  be  driven  out  and  utilized.  (This  process,  apart  from  the 
prohibitory  expense,  is  hardly  practicable,  because  the  gases  in 
question  contain  nearly  always  a  large  quantity  of  oxygen  which 
will  convert  the  SO2  to  a  great  extent  into  sulphuric  acid  within 
the  pores  of  the  charcoal.) 

A  totally  different  way  of  employing  coal  is  used  in  one  of  the 
oldest  processes  for  dealing  with  acid-smoke,  namely,  passing 
the  gases  through  red-hot  coals,  in  order  to  reduce  the  SO^  to 
sulphur.  This  has  already  been  mentioned  in  Vivian's  pamphlet, 
''  Proceedings  of  the  Subscribers  to  the  fund  for  obviating  the 
inconvenience  arising  from  the  smoke  produced  by  smelting  copper 
ores  ''  (London,  1833) ,  and  in  a  pamphlet  of  Reich's,  describhig  the 
experiments  made  at  Frankfort  in  1858,  and  it  has  been  proposed 
over  and  over  again,  with  the  same  negative  results.  A  new 
apparatus,  by  Schroeder  and  Haenisch  (G.  P.  33,100),  is  said  to 
give  good  results,  nearly  the  whole  of  the  SO2  being  reduced  to  S ; 
but  their  process  evidently  works  only  with  rich  gases,  and  does 
not  deal  with  those  poor  gases  which  concern  us  here. 

Bemelmans  (Germ.  pat.  77,335)  converts  the  SO2  by  reduction 
with  carbon  and  hydrogen  into  HgS,  dries  this  by  the  process  to 
be  described  below,  mixes  it  with  dry  SOj,  and  converts  them  into 
H2O  and  SO2. 

8.  Preparation  of  Sulphur  Dioxide  in  the  Pure  State  ♦. 

Formerly  pure  SO2,  free  from  nitrogen  and  excess  of  oxygen, 
was  required  only  in  very  few  cases  for  industrial  purposes.  The 
methods  employed  for  preparing  that  gas  were  various,  one  of  the 
commonest  being  the  action  of  concentrated  sulphuric  acid  upon 
copper  at  a  higher  temperature.  This  is,  of  course,  only  appli- 
cable where  there  is  a  sale  for  the  cupric  sulphate  formed,  and  is, 
moreover,  hardly  workable  on  a  large  scale.  Cheaper  and  easier 
is  the  process  of  heating  strong  sulphuric  acid  with  charcoal,  when 

*  A  special  treatise  on  the  preparation,  properties,  and  application  of  pure 
sulphur  dioxide  is  *  Tliisaiges  Schwefeldioxyd/  by  A.  Harpf  (Stuttgart,  1900). 


380  PRODUCTION  OF  SULPHUR  DIOXIDE. 

a  mixture  of  SOj  with  CO2  (and  CO)  is  obtained : — 

2  SO4H,  +  C  =  2  H2O  +  2  SO2  +  CO2. 

The  CO  and  CO2  are  harmless  in  many  applications  of  SO^.  Sul- 
phur dioxide,  quite  free  from  other  gases^  is  made  by  heating 
concentrated  sulphuric  acid  with  sulphur: — 

2S04H2  +  S  =  2H20  +  3S02; 

this  can  be  done  by  running  a  slow  stream  of  sulphuric  acid  on 
sulphur,  heated  to  about  400°  in  an  iron  retort.  It  should,  how- 
ever, be  noticed  that  melted  sulphur  acts  very  strongly  upon  cast- 
iron  ;  hence  another  process,  privately  communicated  to  me  frona 
a  trustworthy  source,  would  seem  preferable.  The  operation  is 
performed  in  a  cast-iron  pan,  widening  out  at  the  top  so  that  a 
lining  of  acid-resisting  bricks  can  be  put  in  it.  Concentrated 
sulphuric  acid  is  boiled  with  sulphur,  which  floats  on  the  top  and 
is  kept  by  the  brick  lining  from  coming  into  immediate  contact 
with  the  iron,  whilst  the  lower  part  of  the  pan  is  fully  exposed  ta 
the  heating  action  of  the  fire. 

Sulphur  dioxide  was  made  by  the  Compagnie  industrielle  des 
precedes  Raoul  Pictet  (G.  P.  No.  22,365),  and  was  purified  in  a 
special  apparatus,  utilizing  the  fact  that  the  hydrates  of  SOj  all 
crystallize  at  —10^,  and  that  gaseous  S02atthis  temperature  loses 
all  its  aqueous  vapour.  We  refrain  from  describing  this  (some- 
what complicated)  apparatus,  which  is  also  described  in  the 
Journal  of  the  Society  of  Chemical  Industry,  1883,  p.  413,  as 
the  condensation  of  liquid  SO2  is  performed  in  a  much  simpler 
way  by  the  Schroeder  and  Haenisch  process,  which  in  fact  has 
caused  the  above-mentioned  process  to  be  abandoned. 

P.  Hart  (E.  P.  13,950,  1885)  prepares  pure  sulphur  dioxide  by 
acting  with  strong  sulphuric  acid,  of  spec.  grav.  r750,  on  finely 
ground  iron  sulphide,  both  being  mixed  in  a  cast-iron  retort  and 
heated  to  over  200°  C,  when  a  steady  stream  of  nearly  pure  SO, 
is  evolved. 

An  old  and  well-known  process  for  obtaining  pure  SOgis:  heat- 
ing ferrous  sulphate  with  sulphur,  with  a  little  air,  the  reaction 
being : 

2FeS04  +  2S+3  0  =  Fe203  +  4S02. 

This  process  was  made  the  subject  of  a  new  patent  by  Terrell 
(B.  P.  5930,  of  1884),  who  evidently  lays   the  greatest  stress 


SULPHUR  DIOXIDE  IN  THE  PURE  STATE.  381 

on   the  ferric  oxide  remaining  behind^  which  famishes  a  good 
paint. 

Ford's  process  (Am.  Tat.  363,457;  Chem.  Zeit.  1887,  p.  721) 
consists  mainly  in  burning  sulphur  by  means  of  air  previously 
dried  with  sulphuric  acid^  and  passing  the  gases  through  a  worm, 
where,  by  cooling  and  pressure,  liquid  SO2  is  condensed.  It  is 
difficult  to  see  any  novelty  whatever  in  this  process. 

The  only  process  for  preparing  pure  liquid  sulphur  dioxide  on 
the  large  scale  is  at  present  that  of  Schroeder  and  Haenisch, 
which  allows  of  preparing  that  substance  in  a  cheap  way  from 
gases  containing  down  to  4  per  cent.  SO3.  It  is  unnecessary  to 
say  that  richer  gases  are  better  for  this  purpose.  This  process 
has  made  liquid  sulphur  dioxide  a  cheap  article,  manufactured  on 
a  large  scale,  and  has  rendered  it  possible  to  employ  that  substance 
for  many  purposes  for  which  formerly  only  the  ordinary  impure 
gaseous  SO3  was  available. 

The  process  of  Schroeder  and  Haenisch,  embodied  in  B.P.  2621, 
1883;  6404 &  6405,  1885,  was  first  taken  up  by  the  firm  Wilhelm 
Grillo  (afterwards  converted  into  the  Aktiengesellschaft  fiir  Zink- 
Industrie,  vormals  Wilhelm  Grillo)  at  their  zinc- works  at  Hamborn, 
Rhenish  Prussia,  where,  in  1885,  an  experimental  factory  was  erected, 
turning  out  about  12  cwt.  liquid  sulphur-dioxide  per  diem.  The 
gases,  testing  6  per  cent.  SO,,  were  taken  from  a  novel  kind  of 
blende-roasting  furnace,  similar  to  that  described  on  p.  361  (system 
Julius  Grillo,  G.  P.  28,458).  In  1886  four  such  furnaces  were 
combined  with  a  larger  plant  for  8  tons  SO3  per  diem.  Very  soon 
after  similar  factories  were  erected  at  Lipine  and  at  Chropaczow, 
in  Upper  Silesia,  and  about  1899  another  at  Bound  Brook,  N.J., 
U.S.A.  (The  factory  at  Chropaczow  has  since  been  converted  into 
an  ordinary  sulphuric-acid  works.) 

The  process  consists  in  absorbing  water  in  an  ordinary  coke- 
tower,  and  expelling  it  again  from  the  resulting  weak  solution  by 
the  action  of  heat,  in  such  manner  that  the  latent  heat  of  the  steaui 
carried  along  is  fully  utilized,  and  ultimately  a  very  small  amount 
of  coal  is  required.  It  is  described  by  the  inventors,  apart  from 
the  patent  specifications,  in  '  Chemische  Industrie,'  1881?,  p.  120; 
but  this  description  is  now  antiquated,  and  we  shall  here  go  by  later 
descriptions  (Paper  Trade  Journal,  1888  ;  Zsch.  f.  angew.  Ch. 
1888,  p.  488),  by  personal  observations  of  the  work  as  practically 
carried  out,  and  by  notes  received  from  the  inventors  in  1902. 


382  PRODUCTION  OF  SULPHUR  DIOXIDE. 

The  burner-gases  arrive  in  the  flue  a  a  (fig.  122),  and  after  having 
lost  part  or  most  of  their  heat  by  passing  underneath  the  lead 
pans  e  e,  they  pass  into  the  coke-tower  b,  where  they  are  treated 
with  such  a  quantity  of  cold  water  that  all  the  SO2  is  condensed 
(the  exit  gases  contain  only  0*05  per  cent.  SO,  per  volume),  and 
only  O  and  N  pass  out  at  c.  The  solution  of  sulphurous  acid, 
containing  about  10  kils.  SOg  per  1000  kils.  of  liquid,  is  run 
out  by  pipe  d,  and  first  passes  through  an  apparatus,  shown  sepa- 
rately in  fig.  123,  where  it  receives  a  previous  heating,  and  then 
successively  through  the  closed  lead  pans  e  e,  where  the  heating  is 
continued  by  the  action  of  the  hot  burner-gases  acting  in  the 
flue  a  a.  The  apparatus,  fig.  123,  serves  for  heating  up  the  cold 
acid  solution  by  the  heat  of  the  spent  liquor,  resulting  at  a  later 
stage  of  the  process.  It  is  built  up  by  superposing  a  number  of 
sheets  of  lead,  7  lbs.  per  superficial  foot,  of  considerable  surface, 
corresponding  to  the  quantity  of  acid  liquor  to  be  treated.  These 
sheets  are  combined  in  such  a  way  as  to  form  a  corresponding 
number  of  shallow  lead  chambers,  about  1^  inches  deep,  superposed 

Fig.  123. 


■!   J  I  I  I  I  III  IIIIUJIIIIII  X^ILg«X  1  I  I.I  T  T-r-m  d' 


[Li n  JE i ill n i  M  I  i  ii  i ii i  i i bCc? * i  rr 


<:>  «»  4»  «»  «i «  «  *  H»  «»  «ii 


j"{rTT  IirrtlTIIIlItliliMi'B  fWi  j  t  t  t  j 
d^.,       TTTt  I  m  1 1  f  1 1  1 1  I  M  n'f  T  '  '«'>  I  I  i  t  T  ¥  T 

one  over  another  and  connected  with  each  other  in  the  following 
way  : — The  acid  liquor  flows  through  d  into  the  bottom  chamber 
from  left  to  right;  through  a  side  connection  rf',  occupying  the 
whole  length  of  the  lateral  edge,  it  is  conveyed  into  the  third 
chamber,  from  here  through  Sf'  into  chamber  5,  and  thus  further 
cools  the  7th  chamber,  9th,  and  so  forth,  issuing  at  8'.  The 
chambers  Nos.  2,  4,  6,  8,  and  so  forth,  serve  in  the  same  way  for 
running  down  the  hot  spent  liquor  obtained  at  a  later  stage  of  the 
process.  This  liquor,  which  enters  at  q,  always  flows  in  a  direction 
at  right  angles  to  that  of  the  acid  liquor  rising  up  in  the  alternate 
chambers,  so  that  the  connections  for  the  spent  liquor  flowing  down 
are  situate  in  the  front  and  back  part  of  apparatus  fig.  123.     In 


SCHROEDER  AND  HAENISCH^S  PROCESS.  38S 

order  to  prevent  a  sagging  of  the  platen,  strips  of  lead  are  arranged 
in  each  chamber  as  stays,  running  in  each  chamber  in  the  direction 
of  the  current  of  liquor.  The  thin  sheets  of  lead  being  good  con- 
ductors of  heat,  the  cold  acid  liquor,  on  rising  through  chambers  1, 
3,  5,  7,  &c.,  is  gradually  heated  up,  whilst  the  hot  spent  liquor, 
descending  through  the  intermediate  chambers,  gives  off  its  heat. 
Of  course  there  must  always  be  a  certain  difference  and  loss  of 
heat,  depending  upon  the  duration  of  contact,  the  depth  of  the 
liquid,  and  the  speed  of  the  current.  With  chambers  of  1^  or 
2  inches  depth,  and  counter  currents  lasting  10  or  12  minutes, 
and  sufficiently  large  surfaces,  the  difference  of  temperature  will 
be  about  10° ;  that  is,  the  cold  acid  liquor  will  be  heated  up  from 
15^  to  85°  C,  whilst  the  hot  spent  liquor  goes  down  from  95°  to 
25°  C.  In  practice  the  heating  up  rises  to  95°,  and  the  cooling 
liquid  descends  to  50°.  The  cold  spent  liquor  is  run  to  waste 
through  X, 

Quite  recently  (1902)  the  flat  lead  chambers,  where  leaks  are 
not  easily  discovered  and  repaired^  are  replaced  by  a  set  of  small 
lead  cylinders  working  on  the  system  of  gradual  heat-exchange 
(counter- current) . 

The  heated-up  acid  liquor  now  travels  successively  through  the 
covered  lead  pans  e  e,  where  the  heating  is  continued  as  mentioned 
before,  so  that  the  boiling-point  is  attained.  The  gases  and  vapours 
here  evolved  are  conducted  through  pipe  /  into  the  water-cooled 
worm  g,  and  from  here  through  the  pipe  h  into  the  tower  i,  where 
the  last  remaining  admixture  of  moisture  is  taken  out  by  dry 
calcium  chloride  or  (preferably)  by  coke  moistened  with  strong 
sulphuric  acid.  From  here  the  dry  sulphur  dioxide  passes  through 
pipe  k  into  the  pump  /.  The  liquor  heated  to  boiling  in  the  pans 
e  e,  which  still  contains  some  SO^,  passes  through  pipe  m  into  the 
column  n,  where  the  steam  is  to  a  great  extent  condensed  by 
injection  of  cold  water,  whilst  nearly  dry  SOg  passes  up  in  p,  and 
thus  equally  gets  into  the  worm  ff  and  further  on  into  the  pump  /. 
The  column  n  is  shown  in  some  detail,  as  described  in  a  further 
patent  by  Schroeder  and  Haenisch  (G.P.  36,721),  which  refers  to 
the  separation  of  steam  from  its  mixture  with  SO^,  and  as  this  is 
a  matter  of  general  importance,  we  shall  give  their  statements  at 
some  length.  It  is  not  easy  to  separate  large  quantities  of  aqueous 
vapour  from  a  mixture  with  gaseous  SO^.  Indirect  cooling  by 
outward  application  of  cold  water  requires  a  very  large  leaden 


384  PRODUCTION  OF  SULPHUR  DIOXIDE. 

apparatus^  and  the  effect  is  but  partial^  as  the  vapours  pass  without 
hindrance  through  the  central  parts  of  the  worms  or  other  kind  of 
apparatus.  Moreover  the  condensed  water^  unless  the  temperature 
of  the  cooling-apparatus  is  kept  nearly  at  a  boiling  heat^  carried 
down  very  much  SO^,.  The  new  process  effects  the  removal  of 
the  steam  from  the  aforesaid  gaseous  mixture  by  direct  injection 
of  water,  which  certainly  at  first  condenses  a  good  deal  of  SO^. 
But  if  the  acid  solution  thus  formed  is  made  in  a  systematic 
manner  to  meet  the  hot  mixture  of  aqueous  vapour  and  SO^^ 
its  temperature  will  be  gradually  raised  and  will  ultimately 
attain  boiling  heat,  and  pari  passu  its  percentage  of  SO^  will 
decrease,  so  that  at  100°  it  is  nearly  at  zero.  The  following 
table  shows  the  diminution  of  the  percentage  of  SO9  with  the 
rise  of  temperature  : — 

Percentage  of  a  saturated  solution  of  SOj : — 

At  20°  C.  =  8-6  per  cent.  SO^. 
30°  C.  =  7  4  „  „  „ 
40°  C.  =  6-1  „  „  ,. 
50°  C.  =  4-9  „  „  „ 
60°  C.  =  3-7  ,,  „  „ 
70°  C.  =  2-6 


if       »       >} 
,   80°  C.  =  \-7 

,  90°  C.  =  0-9 

,  100°  C.  =  0-1 


>^         ii  y* 

yy         yy 


yi         y*         jy 

If  the  injection  of  water  is  so  adjusted  that  the  liquid  running 
off  is  at  a  temperature  of  95°  or  100°  C,  the  latter  cannot, 
as  shown  by  the  preceding  table,  carry  away  any  considerable 
quantity  of  SOo.  On  the  other  hand,  if  the  course  traversed  is 
long  enough,  the  steam  must  be  completely  condensed  by  the 
eold  water  injected. 

This  process  is  carried  out  in  the  apparatus  shown  in  fig.  124, 
viz.,  a  leaden  column,  filled  in  the  lower  part  with  stoneware 
diaphragms,  in  the  upper  part  with  coke.  The  mixture  of  steam 
and  SOg  enters  through  pipe  a  and  rises  in  the  tower.  Cold 
water  is  injected  by  the  rose  h,  condensing  both  water  and  SO^, 
and  flowing  down  as  an  aqueous  solution  of  sulphurous  acid.  On 
reaching  the  lower  parts,  it  meets  continually  fresh  quantities 
of  hot  gases  and  vapoui-s,  and  arrives  at  the  bottom  100°  C.  hot. 
It  there  yields  up  again  the  SOg  absorbed  higher  up,  and  at  the 


bottom  pipe  c  carries  off  botl 
the  injected  water  and  thai 
coudeiised  from  the  steam 
After  some  time  of  working, 
and  with  proper  regulation  of 
the  feed,  the  temperature  ol 
the  water  from  the  top  down- 
wards rises  regularly  to  a 
boiling  heat,  and  its  per- 
centage of  SO3  diminishes  at 
the  same  ratio;  but  the  quan- 
tity of  SOj  in  the  upper  region 
is  so  considerable  that  the 
injected  water  cannot  retain 
it  all,  and  pipe  d  carries  away 
a  continuous  stream  of  gaseous 
SO,  deprived  of  steam.  The 
dish  shape  of  the  stDueware 
parts  iu  the  lower  half  of  the 
tower  has  the  advantage  of 
retaining  the  deacendiug  liquor 
for  some  time,  and  exposing 
it  to  the  heat  of  the  rising 
steam;  but  instead  of  this, 
coke  may  be  used  all  over, 
if  the  tower  is  made  high 
enough. 

Returning  to  fig.  122,  we  see 
that  the  water  condensed  in 
the  worm  g  finds  its  way 
equally  into  column  n,  and 
is  deprived  of  its  SO^  there. 
The  hot  spent  liquor  runs  off 
at  the  bottom  by  pipe  q,  and 
is  utilizedj  as  explained  before, 
for  heating  up  the  cold  acid 
liquor  in  the  apparatus,  fig.  123, 
where  the  entrance  to  the  pipe 
g  is  visible.  In  order  to  regu- 
late   the   compression   of   the 


SCHHOEDEK  AND  HAEXISCH's  FROCESB. 


386  FRODUCTIOH  OF  SCLPHDK  DIOXIDE. 

gaseous  sulphur  dioxide  to  a  liquid,  a  taffeta  bag  (r)  is  interposed  in 
pipe  k,  and  the  motion  of  pump  I  is  r^ulated  according  to  the  siie 
of  this  bag.  The  compressed  gas  enters  throagh  » into  the  worm  t, 
and  ia  liquefied  there  by  cooling  and  pressure,  the  latter  depending 
upon  the  temperature  of  the  cooling-water,  e,  g.,  1-26  atm.  at  10°, 
2-24  atm.  at  20°,  3*51  atm.  at  30°,  &c.  From  t  the  liquid  runs 
into  the  wrought-iron  reservoir  u,  Jrom  which  it  is  drawn  off  into 
the  iron  bottles  v  or  into  tank-waggons.  In  order  to  get  rid  of 
the  carried-along  portions  of  oxygen  and  nitrogen,  the  boiler  «  is 
provided  with  an  outlet-pipe  w,  connected  with  u  by  a  valve  ;  the 
gases  from  here  are  conducted  back  into  the  absorbing-tower  b. 

Haenisch  has  also  described  an  improved  column  for  boiling 
the  solution  of  SO,  (O.  P.  52,025).  In  1899  a  foctory  in  Silesia 
produced  1266  tons  liquid  SO,  by  the  above  process  from  zinc- 
blende  gases;  the  production  of  the  other  works  is  not  known. 
The  cost  price  is  supposed  to  be  £2  per  ton  (on  somewhat  arbitrary 
data)  ;  the  selling  price  ia  £5  to  £5  10«.  at  the  works. 

Fig.  125. 


The  liquid  sulphur  dioxide  ia  sent  out  in  iron  cylinders  (bottles) 
holding  1  or  2  cwt.  each,  or  in  tank-waggons  of  10  tons  capacity. 
The  former  ave  shown  in  figs.  125  aud  126,  When  sent  out,  the 
outlet  valve  is  protected  by  a  cap  a.  Before  use  this  ia  removed, 
as  well  as  the  small  cap  fixed  on  the  neck  b.  If  now  the  plug  of 
the  screw-valve  c  is.  turned  by  means  of  a  key,  the  sulphur  dioxide 


SENDING  OUT  LIQUID  SULPHUR  DIOXIDE.  387 

escapes  in  gaseous  form  through  the  opening  in  b.  The  stuffing- 
box  or  the  whole  valve  must  not  be  removed.  After  a  time  the 
evaporation  of  SO^  lowers  the  temperature  to  —  lO*'  C,  so  that  no 
more  gas  is  given  off  till  the  apparatus  has  taken  up  heat  from 
without. 

If  the  sulphur  dioxide  is  to  be  got  out  in  the  liquid  form^  the 
vessel  is  put  on  its  side  (fig.  126)  in  such  a  position  that  neck  b  is 
at  the  top  side.  The  pressure  of  its  vapour  now  forces  the  SO^ 
out  of  b.  The  bent  tube  within  the  vessel  admits  of  emptying  it 
entirely  of  liquid  SO2.  This  substance  can  be  conveyed  away  by 
a  lead  pipe,  screwed  on  to  b,  or  even  by  an  india-rubber  pipe.  The 
bottles  are  tested  to  50  atmospheres  pressure,  so  that  there  is  no 
danger  whatever  in  their  transit,  as  the  vapour-tension  of  SO, 
amounts  to : — 

0        atmosphere  overpressure  at  — 10°  C, 
0-53  „  „  „  0° 

1-26  „  „  „       +10° 

2*24  atmospheres    „  „  20° 

3-51  ,,  „  „  30° 

515  ,,  „  „  40° 

Still,  it  is  advisable  not  to  keep  the  liquid  in  a  place  whose  tem- 
perature may  rise  upwards  of  40"  C. 

To  prevent  over-filling,  in  view  of  the  expansion  by  heat,  the 
bottles  should  not  be  filled  more  than  nine-tenths,  which  is  ascer- 
tained both  by  weighing  them  and  by  prolonging  the  outlet-tube 
inside  to  one-tenth  of  the  depth  of  the  vessel ;  when  opening  the 
valve  only  gas,  no  liquid,  should  escape.  These  bottles  are  usually 
made  to  hold  100  kils.,  exceptionally  500  kils.  Besides,  tank- 
waggons  are  used  for  10  tons  liquid  sulphur  dioxide,  contained  in 
three  wrought-iron  welded  cylinders,  about  23  feet  long  and  2  feet 
3  inches  diameter,  tested  for  30  atmospheres. 

Boake  and  Roberts  (Engl.  pat.  19,789, 1892)  find  that  liquid  SO^ 
does  not  act  on  tin  or  soft  solder,  and  that  therefore  these  can  be 
employed  in  the  manufacture  of  carrying-vessels. 

Soy  (Engl.  pat.  12,276,  1893)  patents  the  process  of  sending  out 
liquid  SO3  in  glass  vessels  sealed  by  the  blowpipe,  to  be  broken  by 
a  hammer  in  the  rooms  to  be  disinfected. 

The  principal  uses  for  liquid  sulphur  dioxide  are  for  refrigerating- 
machines  (Pictet's  and  others),  for  wood-pulp  manufacture  (to 

2c2 


388  PAODUCTION  OF  SULPHUR  DIOXIDB. 

bring  the  calcium  bisulphite  liquors  up  to  strength),  for  the 
purification  of  beet-root  juice,  for  disinfecting^  for  bleaching,  for 
the  manufacture  of  glue  and  gelatine. 

Recently  liquid  sulphur  dioxide  has.  been  applied  by  Behrend 
and  Zimmermann  as  a  means  for  increasing  the  efficiency  of  steam* 
engines  by  utilizing  the  heat  of  the  exhaust  steam  for  evaporating 
SOj.  The  high-pressure  vapours  thus  produced  are  utilized  in  an 
auxiliary  cylinder  for  generating  motive  power,  and  are  afterwards 
again  condensed  to  liquid  SO^.  Hitherto  this  system  does  not 
seem  to  have  fulfilled  its  expectations. 

The  formerly  rather  extensive  use  for  bringing  calcium  bisulphite 
liquor  (for  the  manufacture  of  wood-pulp)  up  to  strength  has  very 
much  decreased,  since  the  factories  have  improved  their  plant  for 
the  direct  preparation  of  strong  sulphite  liquor. 

The  employment  of  the  strong  SO3  obtained  by  the  Schroeder 
and  Haenisch  process  for  manufacturing  sulphuric  anhydride 
(fuming  O.V.)  will  be  mentioned  in  the  11th  Chapter. 

The  analysis  of  liquid  sulphur  dioxide  is  described  in  my 
'  Chemisch-technische  Untersuchungsmethoden/  vol.  i.  p.  269. 

9.  Draught-pipes  and  Flubs. 

The  fines  leading  the  burner- gases  from  the  kilns  into  the 
chambers  or  into  the  Glover  towers  may  be  constructed  of  brick- 
work only  so  far  as  the  gases  keep  hot  enough  not  to  allow  any 
moisture  whatever  to  condense,  that  is  especially  in  upright  flues 
and  flue-dust  chambers.  From  this  point  they  must  be  made  of 
cast-iron,  and  further  on,  when  they  have  got  cooler,  of  lead. 

The  gas,  which  goes  away  red-hot  from  the  burners,  must 
necessarily  be  cooled  down  to  the  temperature  of  the  chambers^ 
say  60°  or  80°  C. ;  otherwise  the  first  chamber  would  be  very 
quickly  destroyed.  This  cooling  was  formerly  effected  by  con- 
veying the  burner-gas  in  very  long  fiues  of  cast-iron,  or  partly  of 
cast-iron,  and,  when  partially  cooled,  of  lead.  Such  cooling-flues 
were  made  up  to  300  feet  long. 

The  cast-iron  pipes  are  suitably  shaped,  as  shown  in  fig.  127, 
in  order  that  the  upper  half  may  be  replaced  independently  of  the 
lower,  or  taken  away  for  cleaning;  the  latter  can  also  be  done  by 
means  of  man-holes.  For  a  set  of  from  12  to  18  burners  a  pipe 
of  2  feet  diameter  is  sufficient ;  but  they  are  now  and  then  made 


DRADOHT-PIPES  AXD  FLUES. 


Upwards  ot  3  feet  in  diameter.  Sometimes  they  are  lined  with 
fire-bricks,  as  shown  in  fig.  128;  the  cooling  in  this  case  is  very 
imperfect  and  the  cost  higher.     Occasionally,  in  very  large  works. 


square  or  oblong  fluca  of  wrought-  or  cast-iron  are  found.  Brick 
flues  (for  perpendicular  shafts  or  for  ffne-dust  chambers)  are  made 
of  bricks  boiled  iu  tar,  and  set  with  tar  and  snnd.  Earthenware 
pipes  mostly  crack  too  quickly. 

Perpendicular  stacks  and  pipes  act  as  a  sort  of  chimney,  and 
they  are  therefore  carried  up  nearly  to  the  top  of  the  chambers 
where  there  is  no  Glover  tower.  These  pipes  were  sometimes 
outwardly  cooled  by  water,  and  even  very  complicated  contrivances 
were  met  with  for  this  purpose.  It  has  long  been  recognized  that 
the  only  rational  way  of  cooling  the  burner-gas  is  this:  taking 
away  its  heat  for  some  useful  purpose,  and  this  is  almost  everywhere 
done  in  the  Glover  tower  (Chap,  VI.).  Apart  from  this,  the  heat 
of  the  bumer-gas  is  occasionally  utilized  for  concentrating  acid 
in  lead  pans  (Chaps.  IV.  &  IX.^  Sometimes  other  ways  of  dis- 
posing of  this  heat  are  employed.  Thus  at  the  manure-works  of 
Messrs.  H.  &  E.  Albeit,  at  Biebrich-on-tbe-Rhine  (see  fig.  129), 
each  pyrites-kiln  A  is  surmounted  by  a  gas-chamber  B ;  the  burner- 
gases  enter  by  the  holes  a,  provided  with  shut-off  valves,  and 
through  similar  openings  {6)  get  into  the  pipe  d,  leading  to  the 
Glover  tower  C ;  a  third  opening  (c)  permits  sending  the  gas 
direct  into  d  and  C.  In  each  of  the  chambers  B  there  are  hori- 
zontal cast-iron  pipes  [e),  branching  off  from  a  main  pipe/,  into 
which  air  is  forced  by  a  fan-blast.  This  air,  being  exposed  to  the 
hot  burner-gases,  becomes  hot  itself  and  leaves  the  chamhers  in 
order  to  be  carried  away  by  the  main  pipe  h.  This  heated  air  is 
then  conveyed  to  drying-stoves,  where  the  superphosphate  is  dried 


390  PRODUCTION  OF  SULPHUR  DIOXIDE. 

by  its  action.  At  Albert's  works  the  temperature  of  the  air  is 
brought  to  100*  C,  but  it  may  be  kept  cooler  or  hotter  (up  to  135°) 
by  regulating  the  speed  of  the  fan-blast.  The  burner-gas,  entering 
through  d  into  the  Glover  tower  C,  is  still  hot  enough  to  do  all  the 
concentrating  and  denitrating  work  required  ;  the  Glover  towers 

Vig.  120. 


are  not  so  overheated  and  require  less  repairs  than  formerly;  the 
acid  flows  from  them  only  at  115°-120°,  against  140°  as  before 
the  new  arrangement,  and  requires  leas  cooling  for  the  Gay-Lussac 
towers.  The  saving  in  coals  for  the  drying-stoves  is  5  tons  ppr 
diem  (comp.  the  description,  with  further  diagrams,  in  Zeitschr.  f. 
angew.  Chemie,  1889,  p.  287;  also  E.  P.  of  Albert,  FeUner  and 
Ziegler,  No.  15,980,  of  18H8}. 

Flue-dusi. 

In  the  gas-flues  and  draught-pipes  ^ue-tfusf  is  always  deposited, 
much  more  when  smalls  are  burnt  than  with  lump  ore,  especially 
in  furnaces  where  the  small  ore  is  moved  about.  In  such  oases 
special  dust -chambers  are  indispensable,  as  haa  been  remarked  iu 
the  description  of  those  furnaces.  Even  with  large  lumps  the 
flues  and  pipes  must  be  cleaned  out  from  time  to  time,  as  they 
would  otherwise  be  stopped  op  entirely.  At  some  factories  this  is 
done  monthly,  at  others  more  rarely.  If  the  deposit  is  allowed  to 
remain  too  long,  it  hardens  into  a  stone-like  mass,  which  cannot  be 
got  out  without  stopping  tbe  process. 

The  composition  of  this  deposit  varies,  of  course,  very  much; 
and  even  its  external  aspect  varies  from  that  of  a  dry,  light  dust, 
to  that  of  a  thick,  strongly  acid  mud.     Clapham  analysed  such  a 


7LUE-DUST.  391 

deposit^  from  a  source  not  mentioned  (Richardson  and  Watts^ 
Chem.  Technol.  i.  8,  p.  70),  and  found : — 

Sand,  &c 2-833 

Lead  oxide    1*683 

Ferric  oxide  3-700 

Cupric  oxide trace 

Zinc  oxide trace 

Arsenious  acid  58'777 

Sulphuric  acid  25-266 

Nitric  acid trace. 

Water    8000 


99-759 


D.  Playfair  (Chem.  News,  xxxix.  p.  245)  has  examined  flue-dust 
from  pyrites-kilns,  in  which  he  found  chiefly  arsenic,  antimony, 
lead^  copper,  and  iron  ;  of  thallium  0*002  to  0*05,  of  tellurium  and 
selenium  0*001  per  cent,  was  present.  He  describes  in  detail  the 
analytical  methods  employed. 

Reich  (^Erdmann's  Journal/  xc.  p.  176)  found  in  the  Mulden 
Works  a  crystallized  deposit  consisting  of  equal  molecules  of 
arsenious  and  sulphuric  anhydride.  Similar  deposits  have  been 
frequently  observed  since. 

In  other  cases  the  deposit  is  dry  dust,  mostly  consisting  of 
mechanically  conveyed  pyrites-dust,  better  burnt  than  that  within 
the  burner  itself  (Bode,  'Beitrage,'  p.  41),  and  nearly  always  con- 
taining so  much  arsenic  than  its  crystals  can  be  seen  with  the 
naked  eye. 

H.  A.  Smith  ('  Chemistry  of  Sulphuric- Acid-making^)  found  in 
the  dust  46*36  per  cent,  of  As^Og,  along  with  a  large  quantity  of 
sulphur  in  the  pasty  condition — the  latter,  of  course,  formed  by 
sublimation  from  pyrites. 

The  flue-dust  is  also  a  principal  source  of  thallium,  as  we  shall 
see;  and  when  selenium  occurs  in  the  pyrites  it  is  found  in  the 
flue-dust. 

The  flue-dust  from  the  roasting  of  blende  is,  of  course,  quite 
differently  composed  from  that  formed  in  burning  pyrites.  Such 
flue-dust  contains  (Fischer's  Jahresb.  1882,  p.  273)  : — 


392  PRODUCTION. OF  flULPHUR  DIOXIDE, 


}^«-2^   12'?S}'^''« 


I.  IL 

Zinc  oxide  insoluble 8-401  o/j.on  8*^ 

Ditto  in  soluble  combination    17*80 

Ferrous  oxide,  soluble  2'  16  .  2-52 

Ferric  oxide,  ditto 2-40  4-20 

Lead  oxide 3-38  4-26 

Sulphuric  acid,  insoluble  6*46 1  24'89  ^'^"^"l  26*88 

Ditto  soluble 20-43  J  18-84  J 

Water 6-59  9-00 

Residue  (chiefly  ferric  oxide)    31-80  32-42 

99-42  99-48 

Flue-dust  from  the  St.  Mardy  Tinto  Santarossa  pyrites  (com p. 
Lunge  and  Banziger,  supra  p.  55)  contained  sulphur:  sulphur 
free  0-13  per  cent. ;  ditto  as  sulphide  1-48;  SO3  as  free  sulphuric 
acid  and  sulphates  16-31;  AsA  6907;  SbgOa  1*68;  CuO  O'U; 
FcaOs  2-03;  sand  265  ;  water,  traces  of  other  substances  and  loss 
6-51. 

Bellingrodt  (Chem.  Zeit.  1886,  p.  1039)  has  found  in  the  flue- 
dust  from  roasting  blende  at  Oberhausen  (Rhenish  Prussia)  a 
sufficient  quantity  of  mercury  to  make  its  recovery  profitable. 

Krause  (G.  P.  55,676)  washes  the  flue-dust  from  blende-furnaces 
and  tries  to  recover  the  zinc  from  the  washings  by  precipitation 
with  alkaline  carbonates. 

Where  the  quantity  of  flue-dust  is  very  large,  as  is  generally 
the  case  with  arsenical  ores,  and  with  some  of  the  burners  for 
pyrites-smalls,  the  ordinary  dust-chambers,  which  form  simply 
enlargements  of  the  gas-flue,  are  not  sufficient,  and  special  contri- 
vances must  be  adopted  here.  This  matter  has  been  thoroughly 
worked  out  in  the  lead-smelting  works  and  other  metallurgical 
establishments,  and  a  large  number  of  apparatus  has  been  con- 
structed for  this  purpose.  A  very  complete  synopsis  of  this  is  given 
in  the  pamphlet  by  C.  A.  Hering  :  '  Die  Verdichtung  des  Hiitten- 
rauchs '  (Stuttgart,  1888) ,  pp.  8  to  36.  Many  of  the  contrivances 
employed  at  lead- works,  &c.,  are  unsuitable  for  pyrites  on  account 
of  being  made  of  iron.  But  the  general  principles  remain  the 
same:  the  flue-dust  must  be  made  to  deposit  by  cooling,  by 
retarding  the  speed  of  the  gaseous  current  and  by  offering  to  it 
large  surfaces  to  which  it  can  attach  itself.  All  these  conditions 
are  more  or  less  fulfilled  by  making  the  gas-flues  adequately  long 


FLUE-DUST  CHAMBERS.  OUA 

and  wide,  but  this  ib  not  aiifficient  for  "  bad  cases,"  especially 
for  arsenical  ores.  The  case  is  here  complicated  by  the  fact  that 
the  cooling  of  the  gas  may  be  injurious  to  the  chamber  process, 
and  that  the  long  flues,  especially  those  carried  in  ii  zigzag  way 
or  provided  wit!i  "baffle-wails,"  interfere  very  seriously  with  the 
draught.  The  latter  disadvantage  has  been  greatly  lessened  since 
it  has  been  recognized  that  it  is  unnecessary  to  carry  the  gases  in 

Vig.  l:». 


flues  like  those  skeV^hed  in  figs.  130  and  131  (in  the  former  the 
diagram  may  be  taken  either  as  plan  or  elevation),  where  the 
current  of  gas  is  constantly  checked  by  meeting  solid  surfaces, 
but  that  the  snrfaces  may  be  disposed  in  the  direction  of  the 
current  itself,  where  they  cause  the  dust  to  be  deposited  on 
tfaem  without  interfering  with  the  draught.  Fig.  132  shows  how 
this  can  be  done  in  such  a  way  that  the  flue-dust  can  be  removed 
without  interfering  with  the  process.  The  gases  arriving  through 
a  are,  by  means  of  dampers,  sent  either  through  chamber  A  or  B. 
In  the  present  case,  the  dampers  i  b  being  closed,  the  gases  travel 
through  A.     Each  chamber   is  divided  into  several  longitudinal 


394  PRODVCTION  OF  SULPHTTB  DIOXIDE. 

channels  by  tbin  partitions  d  d,  made  of  masony,  fireclay  slabs, 
lead,  or  other  suitable  material.  The  gas  thus  travels  id  parallel 
streams,  without  any  check  than  t)iat  of  the  indispensable  friction, 
and  the  streams  collect  again  into  one,  issuing  at  e.  Wheo 
chamber  A  is  too  much  choked  up  by  dust,  the  dampers  b  b  are 
opened,  the  dampers  c  c  are  shut,  and  the  ga^es  now  travel  through 
B,  giving  an  opportunity  to  clean  out  chamber  A  by  means  of 
suitable  man-Iiulcs. 

rig.  132. 


In  very  bad  cases,  as,  for  instance,  with  mechanical  dust-bumers, 
longitudinal  partitions  are  not  sufficieHt,  and  real  baffle-platea 
must  be  employed,  as  shown  in  figs.  130  and  131,  and  very  much 
multiplied  in  figs.  100  and  101  (p.  347).  In  such  cases  the  loss  of 
draught  must  be  sometimes  compensated  by  mechanical  means. 

In  many  cases,  nhcre  very  large  quantities  of  flue-dust  have  to 
be  dealt  with,  the  gases  must  be  cooled  artificially.  This  was 
done  at  the  Freiberg  works  by  a  special  kind  of  lead  flue,  cooled 
by  water,  as  sketched  in  figs.  133  and  134,  where  the  first  represents 
a  longitudinal  section  on  the  line  A  B,  the  second  a  sectional 
plan  uu  the  line  C  D.  The  sides  of  the  flue  are  formed  by  a 
number  of  oblong  pipes,  a  a,  joined  together  at  their  narrow 
ends.  On  the  top  there  is  a  shallow  trough,  h,  supplied  with  a 
constimt  stream  of  water,  which  trickles  down  through  holes,  shown 
in  the  diagram,  into  the  space  a  a,  and  from  these  through  other 
holes  into  the  common  channel  c,  running  lengthways.  The 
bottom  of  the  flue  is  not  water-cooled,  but  as  it  rests  on  the  small 
pillars  d  d  '\i  \&  exposed  to  the  action  of  the  air.  These  flues  are 
very  expensive  to  build,  hut  they  have  been  found  to  do  their 
work  lery  well  indeed,  and  they  need  next  to  no  repairs  (detailed 
in  the  'Freiberger  Jahrbuch/  1879,  p.  151,  table  xii.).     Of  the 


FLUE-DUST  CHAUBEH8.  305 

2  or  2|  per  cent,  of  arsenic  contained  in  the  Freiberg  ores,  by  far 
the  greatest  portion  (97  per  cent.)  is  condensed  in  these  long  flues, 
where  the  gases  are  nltbnately  cooled  down  to  the  temperature  of 
the  outer  air. 

Kg.  133. 


Bauer  {Jalirb.  f.  Berg-  u.  Huttenw.  189i,  p.  39)  states  that 
the  nine  sets  of  chambers  connected  with  the  Freiberg  smelting- 
works  (containing  <{0  lead  chambers)  possess  8037  metres  of  flues, 
of  3'8  square  metres  section.  The  flue-dust  in  1893  contained 
1137  kils.  silver,  1656  tons  lead,  and  917  tons  arsenic,  valued  at 
j613,600.  Eighty  per  cent,  of  the  dust  was  recovered,  20  per  cent, 
has  hitherto  been  lost.  The  damages  to  be  paid  had  diminished 
from  £3050  to  £180.  In  that  year  new  flues  on  the  Monier- 
Freudenberg  system  were  built  for  recovering  the  last  20  per  cent, 
of  (lust.  The  rate  of  cooling  of  the  gases  was  1°  C.  per  8'3  metres 
length  In  closed-in  Monier  flues,  per  4*5  metres  in  freely  exposed 
Monier  flues,  per  3  metres  in  leaden  flues,  and  per  6  metres  in 
brick  flues. 

In  1902  I  am  informed  that  the  water-covered  flues  have  been 
abandoned  at  Freiberg  as  being  too  costly,  and  have  l>een  replaced 
by  simple  lead  tunnels.  Where  the  beat  is  too  great  for  the  stability 
of  the  latter,  brick  tines  are  employed. 


396  PRODUCTION  OF  SULPHUR  DIOXIDE. 

Falding  (Min.  Ind.  ix.  p.623)  describes  adust-catcher,  constructed 
by  A.  P.  O'Brien,  of  Richmond,  Va.,  on  the  well-known  centri- 
fugal principle.  It  works  in  connection  witli  the  cast-iron  fan  of 
the  same  inventor,  described  in  Cliap.Vl .,  and  receives  the  gas  from 
five-Herreshoff  fines  furnaces,  retaining  75  per  cent,  of  the  dust. 
At  the  same  time  it  does  very  efficient  service  as  a  metre-oven.  As 
shown  in  figM.  1 35  &  136,  it  consists  of  a  tapering,  hopper-shaped 
Fig.  135. 


iron  shell,  8  feet  wide  in  the  cylindrical  part  and  12  feet  high,  with 
a  6-in.  opening  in  the  bottom  for  the  discharge  of  flue-dust.  It  is 
lined  with  4  inches  fire-brick.  The  gas  enters  through  the  top  pipe 
at  a  high  rate  of  speed  from  the  fan  and  strikes  the  cylinder  tan* 
gentially ;  it  leaves  the  apparatus  through  a  central  pipe.  The  gas 
takes  a  rotary  motion  and  deposits  all  the  heavy  dust,  which  is 
automatically  discharged  through  the  6-in.  opening.  Six  tubular 
metre-pots  are  arranged  iu  the  manner  shown,  so  that  they  can  be 
charged  from  the  top  and  discharged  sideways. 

Sulphur  Dioxide  for  the  Manufacture  of  Wood-pulp  ought  to  be 
as  free  as  possible  not  merely  from  flue-dust  but  also  from  sulphuric 
acid  (or  sulphur  trioxide,  comp.  next  Chapter).     For  this  purpose 


BURNER-GAS.  397 

very  efficient  diist-chambers  must  be  provided ;  the  gas  must  also 
be  specially  cooled,  e,  g.  by  perpendicular  cast-iron  pipes,  2  feet 
6  inches  diameter,  running  up  for  a  height  of  50  or  60  feet  and 
down  again ;  they  end  in  a  lead-lined  pipe  provided  with  a  man- 
hole and  filled  with  iron  borings.  Here  the  sulphuric  acid 
which  is  condensed  by  the  cooling,  collects,  and  is  taken  up  by 
the  iron  borings.  Provision  must  be  made  for  removing  the 
solution  of  ferrous  sulphate  formed,  and  for  renewing  the  iron 
borings  as  they  waste  away.  (A  description  of  such  an  apparatus 
is  found  in  '  Papier-Zeitung/  1894,  pp.  2099  &  2130.)  A  more 
efficient  removal  of  the  SOg  and  H2SO4  is  effected  by  the  apparatus 
of  Nemethy,  G.  P.  48285,  of  1889,  in  which  the  gases  from  the 
burner  pass  through  a  large  bos.  containing  iron  borings  &c. 
before  entering  the  cooling-apparatus  (comp.  p.  283). 

10.  The  Burner-gas. 
(1)    Composition  of  the  Burner-gas  from  burning  Brimstone. 

Atmospheric  air  contains,  roughly  speaking,  28  per  cent,  by 
volume  of  oxygen,  and  79  per  cent,  nitrogen  *;  If  it  were  possible 
to  convert  all  the  oxygen  into  sulphur  dioxide,  the  volume  would 
not  be  changed,  since  1  mol.  O2  furnishes  1  mol.  SOg. 

In  the  case  of  making  sulphur  dioxide  for  the  manufacture  of 
wood-pulp,  we  want  to  render  it  as  free  as  possible  from  a  surplus 
of  oxygen.  But  for  the  manufacture  of  sulphuric  acid  we  must 
introduce  into  the  burner  sufficient  oxygen  for  later  on  forming 
SOs,  and  a  further  excess  practically  necessary  in  the  process. 
For  the  former  object  we  must  at  once  increase  the  oxygen  by 
50  per  cent.,  as  2SO2  require  O2  for  the  formation  of  SOg,  and 
the  theoretical  maximum  of  SO2  in  the  burner-gas  would  therefore 
be  14  per  cent,  together  with  7  per  cent,  oxygen  and  79  per  cent, 
nitrogen.  Practically  we  must  have  an  excess  of  oxygen  equal 
to  5  per  cent,  of  the  exit-gases  from  the  system,  together  with 
95  per  cent.  N. 

If  we  call  the  unknown  volume  in  the-burner-gas  of  this  excess 

79 
oxygen = a?,  it  must  carry  along  — a?  vols.  N.     To  this  are  added 

*  Of  course  this  item  "nitrogen"  comprises  argon,  helium,  and  ^11  other 
indifferent  gases  recently  discovered  in  atmospheric  air.  To  simplify  matters, 
we  shall  throughout  this  book  omit  the  special  mention  of  these  gases,  which  in 
sulphuric-acid  making  play  exactly  the  same  inert  part  as  elementary  atmospheric 
nitrogen. 


398  FttODUCTION  OF  SULPHUR  DIOXIDE. 

79  vols.  Ny  entering  along  with  the  21  vols.  O  required  for  forming 
14  vols,  of  SO2  and  converting  them  into  SO3.  The  volume  of 
the  total  N  and  of  the  excess  oxygen  required  in  practice  for  each 
14  vols,  of  SO2  introduced  into  the  chambers  thus  amounts  to 

^n  .79  ^^  .  100 

X  was  stated  to  form  5  per  cent.  =  ^^  of  this  volume. 
We  have  thus  the  equation : 

^_  1/79  + 100  \^79J^ 

From  this  follows  : 

5         16  _n 
*~2l'"°'^2l'^~20' 

79x21     .-„      , 
•"=2()^l(i='^'^^^'°^^-' 

that  isj  besides  the  theoretical  quantities  of  gas  mentioned  above^ 

another   5*18  vols,   of   oxygen^   along    with  the   corresponding 

79 
5*18  XoT= 19*50  vols,  of  nitrogen^  are  necessary.     The  gaseous 

mixture  formed  in  the  sulphur-burner  accordingly  ought  to  con- 
tain upon  each 

14       vols,  of  SO2, 
7-h   5-18=1218       „       O,  and 
79+19-50=98-50      „       N. 


121-68  vols. 

From  this  the  following  composition  for  1  litre  of  this  gaseous 
mixture  is  computed : — 

01 123  litre  SO3 
00977     „     O 
0-7900    „     N 


1-0000 


ii 


That  is  to  say  :  The  normal  quantily  of  SO2  in  burner^gas  from 
irimstone-burners  is  11*23  per  cent,  by  volume. 

This  normal  quantity  can  be  attained   by  proper  care,  but  is 
frequently  not  reached. 


BUKNER*OAS.  399 

(2)   Composition  of  the  Burner-gas  in  burning  Pyrites, 

The  proportion  of  air  required  in  this  case  differs  very  much 
from  the  preceding.  We  shall  calculate  this  for  pure  iron 
disulphide.  This  body  consists  of  46*66  per  cent.  Fe  and  53'33 
per  cent.  S. 

Although  on  burning  dense  pyrites  sometimes  the  iron  is  not  all 
oxidized  up  to  Fe^Os^  and  a  little  magnetic  oxide^  Fe304,  is  formed^ 
we  must  suppose  the  complete  conversion  of  iron  into  Fe203  as  the 
normal  state  to  be  aimed  at  for  complete  utilization  of  the  sulphur. 
Consequently  2  mols.  or  240  pts.  of  FeS^  require  3  atoms =48  pts. 
O  for  oxidizing  the  iron^  and  another  8  atoms=128  pts.  O  for 
burning  the  S  into  SOj.  Altogether  11  atoms=176  pt<.  oxygen 
arc  necessary  for  burning,  and  another  4  atoms  of  oxygen  =  64  pts. 
for  changing  the  formed  4  mols.  =  256  pts.  of  SO2  into  SO3.  From 
this  we  calculate  that  for  each  thousand  parts  of  FeS2, 

200  pts.  oxygen  are  required  for  oxidizing  the  iron, 

533J  „  „  „  forming  SO2, 

^^^1  V  7>  t*  oxidizing  this  to  SO3. 


1000  ..       in  all. 


}i 


Now  here  also  an  excess  of  oxygen  must  be  used^  even  larger 

than  in  the  case  of  brimstone,  which  we  will  assume  to  amount 

to  6*4  per  cent,  by  volume  in  the  gas  leaving  the  chambers.     If 

we  call  the  unknown  volume  of  oxygen  in  excess  to  be  introduced 

for  each  kilogram  of  S  employed  as  FeS,,  x  litre,  the  volume  of 

79 
nitrogen  accompanying  it  is  ^  ^  litre.     Both  together  and  the 

4933*3  liti*e  N  introduced  along  with  the  O  requisite  for  combustion 
and  formation  of  SO3  form  the  gaseous  mixture  escaping  at  the 
end,  the  volume  of  which  is  therefore 

79  100 

4933-3  +  ^ -h^  a: = 4933-3 +;^.r. 

As  A*  is  TTTTL  of  this  volume,  we  have 

a? =454-1, 
Accordingly  for  each  kilogram  of  S  burnt  as  FeSo,  apart  from 


400  PRODUCTION  OP  SULPHUR  DIOXIDE. 

the  theoretical  6244*7  lit.  air,  another  454*1  lit.  oxygen  along  with 
4D4ax79_jyQg.^  nitrogen— that  is,  2162-5  lit.  air— altogether 

8407*2  lit.  air  at  0^  and  760  millims.  pressure,  have  to  be  introduced. 
Now  each  kilogram  of  free  sulphur  (brimstone)  requires  6199 
litres  air  at  0°  and  760  millims. ;  consequently  a  certain  quantity 
of  sulphur,  burnt  as  FeSg,  requires 

8407-2     ,  „^«  ^. 
-^^  =  1*356  times 

as  much  air  as  if  burnt  in  the  free  state« 

This  is  not  quite  the  proportion  of  the  gas  as  it  enters  the 
chambers.  For  on  burning  FeS2  a  portion  of  the  oxygen  remains 
behind  with  the  iron,  whilst  on  burning  brimstone  the  whole 
quantity  of  air  gets  into  the  chambers,  and  at  equal  temperature 
and  pressure  retains  its  volume,  since  oxygen  on  combining  with 
S  to  SO2  does  not  change  its  volume. 

The  8407*2  litres  air  entering  the  burner  for  each  kilogram  of 
sulphur  burnt  as  FeS^  furnished  the  following  quantities  of  gas, 
calculated  for  0°  and  760  millims. : — 

699*4  lit.  SO2  generated  from  the  same  volume  of  O, 
349*7   „   O  required  for  transforming  SO2  into  SO3, 
454*1    „   O  as  excess, 
4933*3   „    N  accompanying  the  theoretically  necessary  oxygen, 
1708*4   „   N  „  ,,         excess  of  oxygen. 

81  44*9  ht.  containing  699*4  lit.  SO2, 

803*9  „   O, 
6641*7  „   N. 

8144*9 
For  a  certain  quantitv  of  sulphur,  burnt  as  FeS2,  -^tt^ft  times 

6199 

=  1*314  times  as  much  gas  must  enter  the  chambers  as  if  the 

sulphur  were  burnt  in  the  free  state. 

Consequently,  in  the  case  of  burning  pyrites,  100  volumes  of  the 

normal  gaseous  mixture  on  entering  the  chamber  ought  to  consist  of 

8*59  vol.  SO2, 
9*87    „    O," 
81-54    „    N. 

In  many  factories  the  sulphur  dioxide  is  much  below  8*59  per 


COMPOSITION  OF  GAS  FROM  BLENDE-FUBNACES.  401 

cent.,  sometimes  not  above  6  per  cent,  of  the  volume  of  the 
gas.  In  that,  ease  so  much  les^acid  is  made  in  the  same  chamber- 
space^  unless  the  formation  of  sulphuric  acid  is  increased  by  a 
larger  consumption  of  nitre.  We  shall  return  to  this  subject  in 
Chap.  VII. 

Sulphur  Dioxide  for  manufacturing  Calcium  Bisulphite  {in  the 
manufacture  of  wood-pulp,  ^c). — In  this  case  the  conditions  are 
different  from  those  just  described.  There  is  no  question  of  having 
to  provide  the  oxygen  for  forming  H2SO4  from  SOj  and  the  excess 
of  oxygen  practically  necessary  in  the  lead  chambers ;  and  the 
formation  of  SO3  in  the  burners  should  be  avoided  as  much  as 
possible.  The  operation  should  be  conducted  so  as  to  exceed  as 
little  as  possible  the  amount  of  osfygen  demanded  by  the  equation  : 
2FeS2  +  ll  0=Fe203  +  4S02,  which  corresponds  to  a  theoretical 
maximum  of  16  per  cent.  SO2  by  volume  in  the  burner-gas. 
Practically,  however,  11  per  cent,  should  not  be  exceeded,  because 
otherwise  the  burners  get  too  hot,  which  causes  the  sublimation  of 
sulphur  and  the  formation  of  scoria  in  the  burners. 

Harpf  (Wochenbl.  fiir  Papierfabr.,  Biberach,  1901,  nos.  23, 
25,  &  27)  gives  some  calculatious  referring  to  this  special  case, 
containing  nothing  of  importance. 

(3)   Composition  of  the  gas  from  Blende- furnaces. 

For  burner-gas  from  zinc-blende  the  following  calculation  has 

been  made  by  Hasenclever  (Chera.  Ind.  1884,  p.  79) : — Zinc-blende 

(in  the  pure  state),  ZnS,  consists  of  63  parts  Zn  +  32  parts  S. 

For  burning  it  into  ZnO  +  S02,  3x16=48  parts  O  are  required, 

for  converting  the  SO2  into  SO3  another  16  O  ;  therefore  for  95 

ZdS,  containing  32  S,  altogether  64  O.     This  means  that  each 

kilogram  S  in  zinc-blende  requires  2  kilograms  O,  or  1398*7  litres 

at  0°  and  760  millims.,  together  with  5258*0  litres  nitrogen =665(5 

litres  air.     In  order  to  make  allowance  for  the  6*4  volume  per  cent. 

of  oxygen  required  to  be  in  excess  in  the  exit-gas,  we  find  this  by 

the  formula : — 

6*4 /._^^  100  \ 

'*=iooV^2^^+^i^> 

n=  484-0  litres  oxygen,  corresponding  to 
1820*7    „     nitrogen 

2304*7     „      air, 

VOL.  I.  2 1> 


402  PRODUCTION  OF  SULPHUR  DIOXIDE. 

Consequently  the  normal  gaseous  mixture  in  roasting  1  kilo^. 
blende  consists  of : —  *• 

699-4  litres  SO,, 

3497     „     0  for  forming  SO3, 

484'0     „     O  in  excess^ 
5288*0  .    „     N  entering  with  the  theoretically  necessary  oxygen, 
1820*7     „     N        „  „       excess  oxygen, 


864r8  litres  of  gases. 

This  means  that  100  volumes  of  the  gas  should  contain : 

8*12  vols.  SO2 
9*69    „     O 
8219    „     N. 

According  to  information  received  in  1902  the  blende-gases 
contain  only  exceptionally  less  than  6  per  cent.  SO2 ;  ordinarily 
6  to  7*5  per  cent.  SO2  apart  from  SO3  (see  below). 

So  far,  as  we  see  from  Hasenclever's  calculation,  theory  would 
show  that  the  strongest  obtainable  burner-gas  from  blende  is  not 
much  inferior  to  that  obtainable  from  pyrites  (p.  400) .  But  apart 
from  the  fact  that  here,  as  well  as  in  the  case  of  pyrites  and  to  some 
extent  even  of  brimstone,  the  theoretical  figures  are  undoubtedly 
interfered  with  by  the  formation  of  sulphuric  anhydride,  there  is, 
at  least  with  all  the  older  blende-furnaces,  a  far  more  potent  reason 
why  the  practical  percentage  of  SO2  in  blende-gases  should  be  far 
below  the  theoretical  one.  Seeing  that  in  those  furnaces  only  ^  or 
at  most  §  of  the  sulphur  was  liberated  as  SO2  [and  SO3] ,  that  the 
other  ^  or  J  remained  behind  in  the  state  of  ZuSOi,  and  that  the 
nitrogen  corresponding  to  the  four  atoms  of  oxygen  contained  in 
ZnSO.1  dilutes  the  burner-gas,  it  is  easily  understood  why  formerly 
it  was  considered  good  work  if  blende-gases  contained  5  or  at 
most  6  per  cent,  of  SO2.  The  modern  furnaces  (p.  360  et  seq.) 
undoubtedly  yield  better  gases,  not  much  inferior  to  the  burner-gas 
from  pyrites. 

(4)  Sulphuric  anhydride  in  Burner-gas. 

In  the  pyrites-burner,  besides  sulphur  dioxide,  there  is  always 
sulphuric  anhydride  formed  during  the  burning.     This  fact  has 


SULPHURIC  ANHYDRIDE  IN  BURNER-GAS.  408 

long  been  known^  and  was  explained  in  1852  by  Woehler  and 
Mabla^  and  again  in  1856  by  Plattner  (^Die  metaUurgisehen 
Robtprocesse ')  after  many  experiments^  in  this  way — that  many 
substances,  one  of  which  (ferric  oxide)  is  present  in  large  quantity 
in  the  pyrites-burner,  dispose  sulphur  dioxide  to  combine  with  the 
oxygen  of  the  air  to  form  sulphuric  anhydride.  We  have  already 
seen,  and  in  Chapter  XI.  the  subject  is  fully  detailed,  that  this 
reaction  can  be  used  for  the  production  of  sulphuric  anhydride 
itself.  Another  plausible  explanation  is,  that  in  the  cooler  parts 
of  the  pjnrites-burners  sulphates  of  iron  are  formed,  which  in  the 
hotter  parts  again  split  up  into  FcaOa  and  SOs.  This  explanation, 
however,  is  not  sufficient  for  Fortmann's  experiments  (Dingl. 
Journ.  clxxxvii.  p.  155),  according  to  which  the  whole  of  the 
fumes  of  anhydride  appear  the  moment  the  pyrites  take  fire. 
Scheurer-Kestner  (Bull.  Soc.  Chim.  1875,  xxiii.  p.  437)  explained 
the  matter  from  the  well-known  fact  that  ferric  oxide  can  act  as  an 
oxidizing  agent  by  successively  giving  up  and  absorbing  oxygen. 
It  is,  however,  established  that  even  on  burning  pure  sulphur 
a  little  anhydride  is  formed,  as  we  shall  see. 

In  Fortmann's  experiments,  made  on  a  small  scale,  on  burning 
pyrites  far  more  SOg  than  SOo  was  formed,  viz.  in  one  experiment 
4  times  as  much,  in  another  as  5  :  3.  His  results  were  evidently 
altogether  wrong,  in  consequence  of  a  faulty  analytical  method. 
Scheurer-Kestner  [loc,  cit.)  only  found  2  or  3  per  cent,  of  all  the 
SO2  converted  into  SO3,  but  a  larger  deficiency  of  oxygen  in 
the  gas  than  corresponds  to  this  amount ;  and  the  later  discussion 
between  Bode  (Dingl.  Journ.  ccxviii.  p.  325)  and  Scheurer-Kestner 
(ib.  ccxix.  p.  512)  did  not  clear  up  the  matter. 

In  order  to  decide  the  question  of  the  formation  of  SOy  on 
burning  pyrites  by  more  exact  methods  than  those  hitherto  used, 
especially  by  Fortmann,  I  made,  together  with  Salathe,  a  series  of 
experiments  (Deutsch.  chem.  Ges.  Ber.  x.  p.  1824).  It  was  found 
that  SO2  cannot,  as  Scheurer-Kestner  had  supposed,  be  absorbed 
and  estimated  by  barium  chloride,  because  even  chemically  pure 
SO2  with  BaCl2  in  the  presence  of  O  or  atmospheric  air  at  once 
gives  a  precipitate  of  BaSO^.  Check  tests  proved  that  exact  results 
were  obtained  by  conducting  the  gas  through  an  excess  of  standard 
iodine  solution,  retitrating  the  latter  by  sodium  arsenite,  and  esti- 
mating the  total  sulphuric  acid  formed  in  another  portion  of  the 
liquid  by  precipitation  with  BaCL.     By  retitration  the  quantity 

2  D  2 


404  PRODUCTION  OF  SULPHUR  DIOXIDE. 

of  SO2  absorbed  was  found,  and  by  subtracting  this  from  the  total 
sulphuric  acid  that  of  the  SO3  was  obtained.  Two  experiments 
with  burning  Spanish  cupreous  pyrites,  containing  4862  per  cent, 
of  sulphur,  in  a  glass  tube  in  a  current  of  air  gave 

I.  II. 

Sulphur  obtained  as  SO,, 88'02  88-78  p.  c. 

SO3 5-80  605     „ 


;:  ;::::::::::;::::;:;  iT.}    ->'  ■■ 


in  the  residue 3'43 

lost 2 


Of  the  sulphur  of  the  burner-gas  itself  there  were  present 

I.  II. 

As  SO.  93-83  93-63  p.  c. 

„  SO3  617  6-37    „ 

Two  other  experiments  were  made  in  this  way : — In  the  glass 

tube  50  grams  of  cinders  from  the  same  pyrites,  in  pieces  about  the 

size  of  a  pea,  were  completely  freed  from  sulphur  by  ignition,  and 

fresh  pyrites  burnt  as  before,  the  gas  passing  through  the  cinders^ 

Pound : — 

III.  IV. 

SurphurasSOa    79-25  7690  p.  c. 

SOa    16-02  16-84    „ 

Residue  and  loss 4-73  6-26    „ 

Of  the  sulphur  of  the  burner-gas  itself  there  werejpresent : — 

in.  IV. 

AsSOg  83-18  82-00  p.  c. 

„  S0»  16-82  1800    „ 

On  the  large  scale  the  formation  of  SO3  will  hardly  be  as  much  as 
in  the  last  two  experiments,  because  in  the  burners  the  gas  passes 
through  much  less  ignited  ferric  oxide  than  in  our  experiments. 

By  later  experiments  in  my  laboratory  (Chemiker-Zeitung, 
1883,  p.  29)  it  was  found  that  in  roasting  pyrites  by  itself  5"05 
per  cent.,  when  passing  the  gases  through  a  layer  of  red-hot 
pyrites- cinders  15-8  per  cent,  of  the  total  sulphur  reappeared  as 
SOa,  which  entirely  confirms  the  above  results.  On  burning 
brimstone  it  was  found  that  even  here  2*48-2-80  per  cent,  of  the 
sulphur  was  converted  irito  SO3 ;    and  this  quantity  was  increased 


SULPHURIC  ANHYDRIPE  IN  BUBNER-GAS. 


405 


to  9*5-13*1  per  cent,  if  the  gases  were  passed  through  red-hot 
pyrites-cinders. 

Hempel  (Ber.  d.  deutsch.  chem.  Ges.  1890^  p.  1455)  found  that, 
on  burning  brimstone  in  oxygen  at  the  ordinary  atmospheric 
pressure,  about  2  per  cent,  of  it'  was  converted  into  SO3  (which 
agrees  with  my  results,  as  given  above);  but  when  effecting  the 
combustion  under  a  pressure  of  40  or  50  atmospheres,  about  half 
of  the  sulphur  was  converted  into  SO3. 

Further  experiments  were  m^e  by  Scheurer-Kestner  (Bull.  Soc. 
Chim.  xliii.  p.  9,  xliv.  p.  98)  with  the  gases  from  pyrites-kilns  as 
given  off  in  actual  manufacturing.  We  quote  here  a  series  of 
his  results,  obtained  with  samples  of  burner-gas  taken  at  various 
times — A,  from  a  lump-burner;  B,  from  a  Maletra  dust-burner. 


Volume  per 
cent  of  bOj. 

Sulphur  converted 

into  SOg  per  cent. 

of total  S. 

A.  Lump-burner. 

7-3 

2-8" 

7-5 

5-8 

6-5 
G-6 
8-3 

1-2 
10 
00 

Average 
"     81 

9-9 

2-8 

6-2 

8-4 

•J 

B.  Dust-burner, 

8-2 

30" 

90 

6-8 

7-6 

0-4 

11-3 

7-7 

0-8 
10 

Average 
"     8-5 

8-7 

2-5 

8-7 

9-3 

7-6 

41 

The  quantity  of  SOs  formed  is  here  found  to  be  very  irregular, 
varying  from  0  to  9*3  per  cent,  of  the  SO2 ;  the  average  is  decidedly 
less  than  in  our  laboratory  experiments  with  pyrites. 

F.  Fischer  (Dingl.  Journ.  cclviii.  p.  28)  obtained  the  following 
results,  which  at  the  same  time  give  an  idea  of  the  difference  in 
the  composition  of  the  gases  on  the  various  shelves  of  a  Maletra 
dust-burner : — 


1 


406  PRODTTCTIOX  OF  SULPHUR  DIOXIDE* 

SOa  SO,  O 

per  rent.       per  cent.       per  cent, 

A.  First  test  (shelf-burner). 

Second  shelf  from  below 096  0*44  184 

Fourth         „         „            1-52  068  16-6 

Sixth           „         „           3-81  0-97  12-5 

Main  flue  8-26  1-34  59 

„       „     7-53  1-27  7-5 

B.  Second  test  (shelf-burner). 

Sixth  shelf  from  below     8-43  3-17  3-9 

„       4-92  068  10-7 

Second  shelf  from  below 2*48  1-42  14-8 

Fourth         „          „         2-62  0*78  160 

Main  flue  580  0-65  10*6 

C.  Lujnp'buriier  up  to     9*3  2*1  50 

These  tests  were  made  by  an  expeditious  method  which  cannot 
compete  as  to  accuracy  with  that  employed  by  me  or  by  Scheurer- 
Kestner.  The  much  larger  quantity  of  SOg  in  proportion  to  SOg 
is  perhaps  explicable  in  this  way  *. 

Blende-roasting  gases, -when  tested  by  my  method  at  the  Rhenania 
works  at  Stolberg,  yielded  up  to  25  per  cent,  of  the  total  S  as  SO3. 

If  the  burner-gases  are  not  passed  hot  into  a  Glover  tower,  but 
are  cooled  in  the  old  way,  most  of  the  SO3  condenses  in  the  shape 
of  sulphuric  acid,  more  than  enough  water  for  this  purpose  being 
contained  in  the  air  and  the  pyrites.  Where  the  gases  go  into  a 
Glover  tower,  this,  of  course,  retains  all  the  SO3  previously  formed, 
also  in  the  shape  of  SO2H4  (Scheurer-Kestner,  loc.  cit,).  We 
shall  further  on  consider  this  fact  in  detail  when  speaking  of  the 
Glover  tower  and  the  formation  of  sulphuric  acid  generally. 

The  constant  presence  of  sulphuric  anhydride  in  various  pro- 
portions in  the  burner- gas  is,  of  course,  a  source  of  inaccuracy  in 
the  testing  process  according  to  Reich  (see  below),  which  indicates 
only  the  sulphur  dioxide,  as  we  shall  see  later  on ;  it  causes,  more- 
over, a  deficiency  of  oxygen  and  an  excess  of  nitrogen  in  the 
composition  of  the  gases.  Hitherto  no  satisfactory  relation  has 
been  found  between  the  amount  of  SO2,  SO3,  O,  and  N  in  the 
many  analyses  of  burner-gases,  as  is  apparent  from  the  disputes 
between  Scheurer-Kestner  and  Bode  (vide  supra  p.  403;   comp. 

*  Harpf  (Dingler's  Journ.  ccci.  part  2)  haa  grossly  misinterpreted  Scheurer* 
Kestner^s  results,  as  shown  by  me,  ibid,  part  4. 


t 
PERCENTAGE  OF  SULPHUR  DIOXIDE  IN  BURNER-GAS.  407 

also  Ber.  d.  deutsch.  Chem.  Ges.  vii.  p.  1665)^  as  irell  as  from 
Fischer's  tests  just  quoted. 

(5)  Actual  Percentage  of  Sulphur  Dioxide  in  Burner^gas. 

Another  source  of  dilution  of  the  burner-gas^  likewise  not  trace* 
able  quantitatively,  is  this — that  the  burnt  ore  does  not  contain 
pure  Fe203,  but  sulphates  of  iron,  which  must  always  retain  more 
oxygen  than  FcaOa,  and  the  nitrogen  corresponding  to  this  excess 
of  oxygen  must  be  found  in  the  buroer-gas.  On  the  other  hand, 
a  little  nitrogen  will  have  to  be  deducted  if  in  the  burnt  ore  FeS 
is  present ;  but  this  amounts  to  very  little  indeed. 

Lastly,  in  the  factories  working  with  nitrate  of  soda  decom- 
posed immediately  behind  the  burners,  the  dilution  of  gas  caused 
thereby  must  be  accounted  for.  The  calculated  density  of  NO3H 
is  2' 17823  ;  we  need  only  take  this  into  account,  as  the  NO3H 
forms  the  largest  portion  of  the  gas  given  off  by  the  nitre  mixture. 
It  differs  so  little  from  that  of  SO2  (viz.  2'21126),  that,  looking 
at  the  small  quantities  in  question,  we  can  take  the  two  as  equal 
without  any  sensible  error.  Now  in  normal  working  order,  and 
using  a  Gay-Lussac  tower,  certainly  not  above  5  per  cent,  of  nitre 
on  the  burnt  sulphur  is  consumed  (corresponding  to  3*7  per  cent. 
of  NO3H),  or  1*85  upon  the  SO2.  Thus  a  gaseous  mixture  which, 
without  the  nitric  acid,  contains  8*59  per  cent,  of  SO2,  contains 

1*85  X  8*59 
besides r        -  nitric  acid  vapour,  which  increases  its  volume 

to  100' 1589:  and  diminishes  the  percentage  of  SO2  in  the  total 
volume  to  8*576 — a  diminution  too  slio:ht  to  be  traceable  by 
analysis.  Even  if  the  nitric  acid  is  not  calculated  as  such,  but 
as  NO2  or  N2O3,  it  has  no  sensible  influence  upon  the  analyses, 
even  if  the  sample  of  gas  is  taken  in  a  place,  where  the  nitrous 
vapours  coming  from  the  Gay-Lussac  tower  have  already  entered 
into  the  process. 

Still  all  the  above-mentioned  causes  unite  in  somewhat  dimin- 
ishing  the  percentage  of  SO2  in  the  burner-gas :  so  that  the 
percentages  stated  above : — 

11*23  per  cent,  by  volume  in  burning  sulphur, 
8-59       „  „  „  pyrites, 

must  be  looked  upon  as  the  maximum,  which  in  practice  can  only 
be  approached,  but  hardly  ever  reached,  and  which  ought  never 
to  be  exceeded. 


t 
408  PRODUCTION  OF  SULPHUR  DIOXIDE. 

I£  the  sulphur  dioxide  in  the  burner-gas  be  estimated,  this  will 
sufficiently  test  the  style  of  burning,  since  the  oxygen  of  the  gas 
must  necessarily  be  in  inverse  proportion  to  its  sulphur  dioxide — 
although  not  exactly,  as  the  sulphuric  anhydride  comes  into  play. 
In  practice,  usually  from  11  to  13  per  cent,  of  oxygen  is  found  ia 
good  burner-gas. 

The  innumerable  observations  made  upon  the  percentage  of 
burner-gas  in  chemical  works  during  recent  years  have  proved 
that  with  very  good  pyrites  the  above  maximum  figures  can  be 
very  nearly  approached,  whilst  with  other  ores,  badly  burning  or 
containing  unfavourable  metallic  sulphides,  only  7  to  7^  per  cent. 
SO2  in  the  burner-gas  is  attained  {e.  g.  Biichner,  Dingl.  Jourii. 
ccxv.  p.  557).  Of  course,  looking  at  the  difficulty  of  keeping  the 
evolution  of  gas  exactly  equal,  the  different  observations  made  in 
the  coiirse  of  a  day  will  frequently  yield  less  than  the  above  figures 
{e,g,  Scheurer-Kestner,  in  Dingl.  Journ.  ccxix.  p.  117,  in  one  day 
found  6'5,  6*5,  6*0,  8*0,  9*0,  8*7 ;  even  greater  differences  occur  in 
his  tests  quoted  supra^  p.  405} ;  and  they  only  signify  the  average 
percentage  of  the  burner-gas.  As  a  minimum,  below  which  the  gas 
of  real  pyrites  ought  never  to  fall,  6 — as  ordinary  average,  7  to  8  per 
cent.  SO2  by  volume  can  be  assumed.  If  less  is  found,  the  draught 
should  be  cut  off;  if  more,  more  air  should  be  admitted. 

Crowder  (J.  Soc.  Chem.  Ind.  1891,  p.  298)  quotes  the  following 
observations  on  the  volume-percentage  of  burner-gas  (details  in  the 
original;  no  account  is  taken  of  the  SO3  present)  : — 

SO^.  O. 

Lump-kilns from  4*97  to  6-83  960  to  11*21 

Old  dust-kilns  (shelf -burners)     „     603  „  7'02  9*10  „  10*00 

Ditto,  another  ore „     6-34  „  7-43  7-  78  „    8-82 

New  dust-kilns „    4'86  „  7*03  8*98  „  1068 

The  temperature  of  the  gas,  where  it  enters  the  Glover  tower, 
in  the  case  of  lump-burners  is  between  the  melting-points  of  zinc 
(412°  C.)  and  antimony  (432°).  The  gas  from  dust-burners,  which 
has  first  to  traverse  a  series  of  dust-chambers,  is  generally  hot 
enough  to  melt  lead  (  =  326°),  but  it  is  sometimes  rather  less. 

In  the  case  of  the  Rhenania  blende-furnaces  (p.  361)  the  gases 
arrive  at  the  Glover  tower  above  300°  C,  sometimes  up  to  400°  C. 

All  the  above  calculations  refer  only  to  pyrites  proper — that 
is,  containing  merely  a  few  per  cent,  of  other  metallic  sulphides. 


C0MPABI80N  OF  BRIMSTONE  AND  PYRITES.  409 

If  the  latter  have  to  be  roasted  by  themselves  (for  instance, 
preparatory  to  their  metallurgical  utilization)^  only  poor  gas  can 
be  obtained,  partly  because  more  sulphates  remain  in  the  residue, 
for  which  the  corresponding  nitrogen  is  found  in  the  gas,  partly 
because  they  must  be  roasted  altogether  with  a  larger  excess  of  air. 
Bode  states  ('  Gloverthurm,^  p.  88)  that  at  Oker  poor  ores  with 

27  per  cent,  sulphur,  of  which  only  22  per  cent,  was  combined 
with  iron,' the  remainder  being  present  as  blende  and  barium  sul- 
phate, yielded  gas  with  5*5  per  cent.  S02*  Lead-matte  yields  gas 
with  5  to  5"5  per  cent. ;  coarse  copper  metal  (with  34  per  cent.  Cu, 

28  per  cent.  Fe,  and  28  per  cent.  S),  5*5  per  cent.  SO2. 
According  to  Wunderlich  (Zeitschr.  f.  d.  chem.Grossgew.  i.  p.  74), 

the  gas  at  Oker  contains  5  to  7  per  cent.  SO2 ;  its  temperature  in 
the  case  of  ores  rich  in  sulphur  reaches  360°,  in  the  case  of  poorer 
ores  about  280°. 

Attention  must  be  drawn  to  a  circumstance  frequently  over- 
looked in  analyses — that  for  technical  purposes  very  rarely  a  reduc- 
tion of  the  volumes  of  gases  to  QP  and  760  mms.  is  effected.  This 
matters  less  in  ordinary  gas-analysis  than  in  tests  like  that  of  Reich, 
where  the  gases  are  compared  with  a  fixed  quantity  of  SO2  assumed 
to  be  at  QP  and  760  mms.  This  causes  most  tests  made  by  Reich's 
method  to  indicate  less  than  the  real  percentage  of  SO3  present. 

Usually  4  per  cent.  SO2  in  the  gases  entering  the  chambers  is 
considered  the  minimum  at  which  it  is  possible  to  make  sulphuric 
acid  without  actually  losing  money  by  the  process.  Locally,  of 
course,  this  may  be  modified  to  some  little  extent.  At  Freiberg 
4  to  3^  per  cent.  SO2  is  stated  as  the  minimum  at  which  the 
manufacture  of  sulphuric  acid  can  be  carried  on  without  pecu- 
niary loss.  The  average  at  those  works,  where  a  great  variety 
of  poor  ores,  all  arsenical,  and  ^'  matte  '^  is  roasted,  preparatory 
to  the  smelting  process,  is  from  5  to  7  per  cent.  SO2  in  the 
burner-gas. 

(6)  Comparison  of  Brimstone  and  Pyrites  as  Material 

for  Sulphuric-acid-makinff. 

We  have  seen  above  that  the  burner-gas  from  brimstone  is 
richer  than  that  from  pyrites  in  the  proportion  of  1  to  1*314;  that 
is  to  say,  under  equal  conditions,  the  gas  generated  in  burning 
pyrites  occupies  1*314  times  as  much  space  as  if  the  same  quantity 
of  sulphur  had  been  employed  as  brimstone.     From  this  it  directly 


410  PRODUCTION  OF  SULPHUR  DIOXIDE. 

follows  that  the  gas  will  also  require  much  more  chamber- 
space;  thus^  for  an  equal  production  of  sulphuric  acid^  the 
chambers  must  be  about  one  third  larger  if  working  with  pyrites 
than  if  working  with  brimstone.  Usually  it  is  assumed  that  the 
consumption  of  nitre  has  to  be  increased  in  a  similar  ratio ;  this^ 
however,  is  not  the  case,  as  a  properly  constructed  Gay-Lussac 
tower  retains  almost  the  whole  of  the  nitre-gas,  and  the  excess 
volume  of  air  is  not  of  great  importance.  At  the  present  day, 
indeed,  in  well-managed  works,  less  nitre  is  used  with  pyrites 
than  has  ever  been  used  with  brimstone. 

Leaving  the  nitre  out  of  consideration,  the  advantages  of  using 
brimstone  are: — a  somewhat  higher  yield  of  acid  (see  Chap.  X.); 
rather  less  cost  of  plant,  and  less  trouble  with  the  burners  if  any 
thing  goes  wrong;  and,  above  all,  much  greater  purity  of  the 
sulphuric  acid,  especially  from  iron  and  arsenic  (this  is  important 
only  for  sale  acid,  not  for  use  in  manure-works,  alkali-works,  &c.) . 
If  brimstone  could  be  had  at  the  same  price  as  the  sulphur  in 
pyrites,  nobody  would  hesitate  for  a  moment  to  employ  the  former; 
and  even  a  moderately  higher  price  would  not  deter  from  this ; 
but  where  the  pyrites-sulphur,  as  is  the  case  in  most  industrial 
countries,  only  costs  half  the  price  of  brimstone,  or  even  less,  the 
latter  cannot  be  employed,  except  for  pure  acid ;  and  even  this, 
when  the  difference  in  price  is  very  large,  can  be  more  cheaply 
made  from  pyrites  than  from  brimstone. 

Owing  to  this  cause,  the  manufacture  of  brimstone-acid  in 
Europe  is  confined  to  small  factories  which  make  specially  pure 
acid  for  bleach-works,  for  manufacturing  articles  of  food,  &c. 
A  somewhat  considerable  number  of  such  factories  still  exist  in 
England,  whilst  very  few  are  found  in  other  European  countries. 
But  it  should  be  noticed  that  sometimes  acid  is  sold  in  England 
as  *' brimstone-acid''  which  is  in  reality  made  from  pyrites  and 
purified  from  arsenic,  or  else  acid  made  from  spent  oxide  of 
gas-works,  which  is  also  practically  free  from  arsenic. 

In  America  formerly  all  sulphuric  acid  was  made  from  Sicilian 
brimstone ;  but  the  notes  given  above  (p.  58)  as  to  the  consumption 
of  pyrites  in  America  show  that  this  is  rapidly  gaining  ground. 

It  is  frequently  asserted  that  sulphuric-acid  chambers  worked 
with  brimstone  last  very  much  longer  (up  to  three  times)  than  with 
pyrites.  It  is  not  impossible  that  there  is  some  difference  in  this 
respect ;  but  even  this  is  not  certain,  and  at  all  events  the  difference 


ESTIMATION  OF  SULPHUR  DIOXIDE  IN  BURNER-GAS.  411 

in  the  duration  of  the  chambers  is  nothing  like  so  great  as  was 
formerly  supposed^  and  forms  no  item  in  a  comparison  of  costs 
(comp.  Chap.  V.). 

(7)  The  Quantitative  Estimation  of  Sulphur  Dioxide  in  Burner-gas, 

This  is  usually  effected  by  Reich's  process,  which  consists  in 
aspirating  the  gas  through  a  measured  quantity  of  a  solution  of 
iodine,  to  which  a  little  starch  has  been  added.  This  is  carried 
on  till  the  blue  colour  of  the  solution  disappears ;  the  amount  of 
gas  aspirated  in  proportion  to  the  constant  quantity  of  iodine 
employed  admits  of  calculating  the  percentage  of  SOo  in  the  gas. 

The  reaction  taking  place  is  as  follows : 

2I  +  S02  +  2H20  =  2HI  +  H2S04. 

The  operation  is  carried  on  with  the  apparatus  shown  in  fig.  137. 
A  is  a  wide-mouthed  bottle  of  about  200  or  300  c.c.  capacity, 
provided  with  a  three-times  perforated  india-rubber  cork.  Through 
one  perforation  passes  the  glass  tube  a,  which,  by  means  of  the 
elastic  tube  b,  serves  for  introducing  the  gas ;  for  this  purpose  a 
hole  is  drilled  in  some  convenient  part  of  the  burner- pipe,  and 
the  india-rubber  cork  c  exactly  fitted  into  it.  The  second,  some- 
what wider  perforation  is  closed  by  the  small  plug  d;  through 
the  third  the  elbow  tube  e  passes,  which  is  connected  with  the 
corresponding  tube  /  of  the  bottle  B,  holding  2  or  3  litres.  The 
latter  serves  as  an  aspirator — the  glass  tube  g,  reaching  to  its 
bottom,  being  continued  into  an  elastic  tube  h,  closed  by  the 
pinch-cock  i,  the  whole  when  once  filled  serving  as  a  siphon.  The 
graduated  cylinder,  C,  holds  250  cub.  centims. 

When  the  sulphur  dioxide  in  any  gaseous  mixture  has  to  be 
estimated,  the  cork  c  is  inserted  into  a  hole  6f  the  pipe  conveying 
the  gas. 

The  vessel  A  is  filled  up  to  about  half  of  its  capacity,  through  rf, 
with  water;  and  B  is  filled  almost  entirely.  A  small  quantity 
(usually  10  c.c.)  of  standard  iodine  solution  (12'65  grams  I  in  1  litre 
of  water)  is  added  to  the  water  in  A,  along  with  a  little  starch,  by 
which  the  water  assumes  an  intensely  blue  colour.  The  pinch-cock 
on  the  elastic  tube  b  is  shut  so  that  no  air  can  enter  into  A ;  t  is 
opened,  so  that  water  runs  out  until  the  air  in  A  and  B  is  so  far 
expanded  that  the  column  of  water  in  B  is  supported.  The  water 
then  ceases  to  run,  provided  that  everything  closes  air-tight ;  if 


412  PRODUCTION  OF  SULPHUR  DIOXIDE. 

not,  the  water  will  continue  to  run.  When  the  apparatus  has 
been  thus  tested^  i  is  shut  and  b  opened  ;  then  i  is  opened  so  that 
the  water  runs  out  slowly^  the  gas  to  be  tested  entering  through  a 
in  single  bubbles  and  rising  through  the  coloured  water.  As  soon 
as  the  SO2  contained  in  the  gas  gets  into  the  water^  it  converts  the 
free  iodine  into  hydriodic  acid ;  and  after  a  certain  time  the  liquid 
will  be  decolorized^  which  at  last  happens  very  suddenly  and  can 
be  very  accurately  observed.  Directly  this  happens^  the  cock  t 
is  closed.  By  this  preliminary  operation  the  whole  of  the  inlet- 
tube  is  filled  with  the  gas  to  be  tested. 

Now  d  is  opened,  and  a  measured  volume  (say,  n  cub.  centims.) 
of  standard  iodine  solution  is  put  into  the  vessel  A^  by  which,  of 
course,  a  blue  colour  is  again  produced;  d  is  closed  again  ;  t  is 
cautiously  opened,  and  water  is  run  out  till  the  liquid  in  a,  which, 
on  opening  d,  had  risen  to  the  level  of  the  outer  liquid,  has  been 
depressed  to  the  point  of  the  tube,  in  order  to  expand  the  gas  in  A 
up  to  the  degree  of  pressure  at  which  the  following  observation 
is  made ;  then  i  is  quickly  shut,  all  the  water  that  runs  out  is 
poured  away,  and  the  empty  graduated  vessel  C  is  put  back 
into  its  place.  Now  i  is  opened,  and,  by  the  running-out  of  the 
water,  gas  is  slowly  aspirated  through  A,  till  the  liquid  is  decolorized 
again,  whereupon  i  is  closed,  and  the  volume  of  the  water  run 
out  into  the  graduated  cylinder  is  measured.  We  will  call  it  m  cub. 
centims..  In  this  process  no  sulphur  dioxide  escapes  anabsorbed  if 
the  bottle  A  is  constantly  shaken;  it  is  best  to  do  this  with  one  hand^ 
holding  the  pinch-cock  i  open  with  the  other  hand,  and  letting  this 
go  the  moment  the  colour  has  vanished,  or  even  when  it  is  but 
faint,  as  it  generally  disappears  on  shaking  a  little  longer. 

It  is  advisable  to  add  to  the  iodine  solution  a  little  sodium  bi- 
carbonate, which  will  facilitate  the  absorption  of  SO2  (C.  Winkler). 

If  a  second  testing  is  to  be  made,  without  any  further  alteration 
a  fresh  quantity  of  iodine  solution  can  be  put  in  and  the  process 
recommenced.  When  this  has  been  repeated  a  few  times,  the 
decolorized  liquid  in  A,  after  a  short  time,  again  turns  blue, 
because  then  its  percentage  of  HI  has  become  so  large  that  it 
decomposes  on  standing  and  liberates  iodine.  This  liquid  must 
then  be  poured  away,  and  replaced  by  fresh  water  and  a  little 
starch  solution. 

The  calculation  of  the  result  is  as  follows  : — ^The  n  cub.  centims. 
of  iodine  solution,  provided  it  contains  12*65  grams  per  litre,  by 


ESTIMATION  OF  SVLPHDK  DIOXIDE  IN  RURNER-OAS.  413 

Fi^.  137. 


its  I  decolorizatioQ  bIiows  0-0032  gram  SOj,  whicli,  at  0°  C.  and' 
a  barometrical  pressure  of  760  millims.,  oceupies  a  volume  of 
1*114>  X  R  cub.  centims.    If  the  barometer  shows  b  millims.,  and  the 


414  PRODUCTION  OF  SULPHUR  DIOXIDE. 

thermometer  /°  C,  and  the  difference  of  water-level  in  the 
aspirator  is  =A  millims.^  equal  to  Yq:^;  naillims.  of  mercury,  the 
exact  volume  of  0*0032  x  n  gram  SOj  is 

1-114 xnx      ^^^     X  (1+0003665/)  cub.  centims. 

*"I3^ 

As  the  water  run  out,  and  thus  also  the  gas  aspirated  through  A, 
amounts  to  m  cub.  centims.,  the  volume  of  the  aspirated  gaseous 
mixture,  before  the  absorption  of  the  SO2  contained  therein,  must 
have  been 

i«+l-114xnx T-  X  (1  +  0*003665  x^  c^b.  centims., 

*-T36 
and  the  percentage  of  SO3  in  volumes  of  the  gaseous  mixture 

100xlll4x»x      —  -  X  (1+0003665  x  t) 

^-Wa 

»n+lll4xnx  -  -^V  X  (1+0003665  x  0- 

*-13^ 

In  many  cases  a  correction  for  the  barometrical  and  thermome- 
trical  changes  will  not  be  required ;  and  the  formula  is  then  simply 

lll*4x«  .     ,   ^^ 

".  1  i  1 7~     per  cent.  SO9. 
//i  +  l"114x /i^ 

If  the  percentage  of  SO2  in  the  gas  is  very  small,  and  thus  m 
very  large  in  proportion  to  n,  the  formula  may  be  simplified  into 

111-4X 
m 

If  10  cub.  centims.  of  a  decinormal  iodine  solution  ( =  12*65  grams 
in  1000  cub.  centims.)  have  been  put  into  A,  this  quantity,  accord- 
ing to  the  above-given  formula,  will  correspond  to  0*032  gram,  or 
11*14  cub.  centims.  SOo,  at  0°C.  and  760  raillims. ;  and  this  number 
need  only  be  multiplied  by  100,  and  divided  by  the  number  of  cub. 
centims.  of  water  collected  in  C,  plus  11,  in  order  to  find  the  per- 
<;entage  of  SOo  in  the  gas.     The  barometrical  and  thermometrical 


ESTIMATION  OF  SULPHUR  DIOXIDE  IN  BURNER-GAS.  415 

ijorrections  are  in  this  case,  of  course,  neglected.  The  subjoined 
Table  will  save  this  calculation.  On  employing  10  cub.  centims. 
of  decinormal  iodine  solution,  the  following  number  of  cub. 
centims.  collected  in  the  graduated  cylinder,  C,  show  : — 

Gub.  cenlims.  Volume  percentage  of  SO.^. 

82  120 

86  11-5 

90  11-0 

95  10-5 

100  10-0 

106  9-5 

113  9-0 

120  8-5 

128  80 

138  7-5 

148  7-0 

160  6-5 

175  G-0 

192  5-5 

212  50 

Even  if  the  gas  to  be  examined  is  taken  at  a  point  where  it  is 
already  mixed  with  nitre  gas,  this  will  not  exercise  any  practically 
important  influence  upon  the  result.  We  have  already  seen  that, 
in  ordinary  work,  for  each  100  parts  of  SO2  only  1*85  NHOy,  or  its 
equivalent  as  NjOg  or  NO2,  exists  in  the  gas.  In  such  dilute 
aqueous  solutions  as  come  into  question  here  nitric  acid  hardly  at 
all  oxidizes  sulphurous  acid ;  this,  however,  is  done  by  nitrous  and 
hyponitric  acids.  Even  if  we  assume  that  only  XO2  is  formed 
(which  is  going  much  too  far),  this  could  at  most  oxidize  its 
equivalent  in  SO2,  according  to  the  formula 

N02+H20  +  S02=S04H2  +  NO. 

46  NO3  thus  oxidizes  64  SO3,  or  1-35  NO2  (the  equivalent  of 
1*85  NO3H)  only  1*88  SO2 ;  in  other  words,  in  the  worst  case,  never 
happening  in  practical  work,  of  100  parts,S02  188  part  would  be 
oxidized  by  nitrogen  acids  instead  of  iodine.  Even  this  maximum 
error  would,  say,  at  10  per  cent.,  only  amount  to  a  deficiency  of 
0*188  per  cent. ;  but  this  is  certainly  reckoning  it  much  too  high. 


416  PRODDCTION  OF  SULPHUR  DIOXIDE. 

(8)  Lunge's  Test  for  total  Acids  in  the  Burner-gas. 

CoDsidering  the  inaccuracy  peculiar  to  Reich's  teat,  owing  to  the 
constant  presence  of  sulphuric  anhydride  in  the  burner-gas  (comp. 
supra,  p.  402  et  seg.),  the  question  arises  whether  it  would  not  be 
better  to  substitute  for  it  a  test  showing  the  total  acidity  of  the 
burner-gases.  There  is  no  difficulty  in  doing  this,  either  by  the 
method  indicated  for  testing  the  exit-gases,  or  in  a  more  expe- 
ditious way  by  employing  in  the  apparatus  (fig.  138)  a  caustic-soda 
solution  tinged  red  by  phenol ph thai eiu  (litmus  is  not  suitable  ia 
this  case,  nor  is  methyl-orange,  which  acta  differently  upon  sul- 
phurous and  sulphuric  acid,  comp.  p.  160).  I  have  shown  this 
method  to  be  quite  practicable  and  accurate,  and  it  is  carried 
out  at  many  works  for  the  regular  control  of  the  process.  A 
decinormal  solution  of  caustic  soda  ia  employed,  of  which  10  c.c. 
are  tinged   red  with  phenolphtbalein  and  diluted  to  about  100 

Fig.  138. 


or  200  c.c.  The  gas  is  aspirated  through  it  slowly,  exactly  as  in 
Keich's  test,  with  continuous  shaking.  Especially  towards  the 
end  the  shaking  must  be  continued  for  a  while  {say  ^  minute; 
each  time  after  aspirating  a  few  c.c.  of  gas  through  the  liquid, 
till  the  colour  has  been  completely  discharged,  which  is  best 
ascertained  by  putting  a  white  piece  of  paper  or  the  like  under- 


ESTIMATION  OF  OXYOEN  IN  CHAMBER-OASES.  417 

neath  the  bottle.  The  calculation  is  made  exactly  as  \vith  the 
iodine  test^  counting  all  the  acids  as  SOj.  A  large  number  of 
practical  tests  made  in  this  manner  have  shown  that  the  percentage 
of  total  acids  calculated  as  SO2  is  always  larger  than  the  figures 
found  by  the  iodine  test,  owing  to  the  presence  of  SOs,  and  that 
the  results  of  the  former  test  agree  with  those  of  gravimetrical 
estimations. 

The  absorption-bottle  used  by  me  differs  from  Reich's  in 
having  an  inlet-tube  for  the  gas,  closed  at  the  bottom,  and 
perforated  with  many  pin-holes,  through  which  the  gas  rises  in 
many  minute  bubbles,  instead  of  one  large  bubble,  as  shown  in 
fig.  138.     Experience  proves  this  to  be  greatly  superior  to  fig.  137. 

The  otherwise  excellent  absorbing-bottle  described  in  No.  34 
of  the  Alkali  Inspectors'  Reports,  p.  22,  is  not  available  in  this 
case,  as  it  contains  india-rubber  rings,  which  act  upon  iodine. 

(9)  Estimation  of  Oxygen  in  Burner-  and  Chamber -gases. 

Although  burner-gas  is  not  generally  tested  for  oxygen,  this 
test  being  reserved  for  the  exit-gases,  we  will  here  describe  the 
methods  employed  for  estimating  oxygen  in  any  of  the  gases 
occurring  in  the  manufacture  of  sulphuric  acid. 

Oxygen  is  for  technical  purposes  always  estimated  by  means  of 
an  absorbent,  observing  the  contraction  of  volume  produced. 
Some  of  these  absorbents  are  not  now  employed,  as  nitric  oxide 
(used  by  Priestley  and  recently  by  Scheurer-Kestner,  Compt.  Rend. 
Ixviii.  p.  608;  also  lately  recommended  by  Wanklyn),  ferrous 
hydrate  (Vogt,  Dingl.  Joum.  ccx.  p.  103),  and  others.  Cuprous 
chloride  in  ammoniacal  solution  may  be  employed  for  absorbing 
oxygen,  but  it  has  no  advantages  over  pyrogallol  or  phosphorus, 
and  several  drawbacks,  so  that  it  cannot  be  recommended.  The 
choice  really  lies  between  the  two  agents  just  mentioned. 

Of  these  pyrogallol  must  be  used  in  an  alkaline  solution,  and  it 
acts  very  promptly  indeed*.  Its  use  for  this  purpose  was  proposed 
by  Chevreul  as  early  as  1820,  but  it  became  general  only  through 
Liebig  many  years  after.  It  is  true  that  this  reagent  in  the 
presence  of  pure  oxygen  forms  some  carbon  monoxide  (Grace 
Calvert,  Proc.  Manch.  Lit.  &  Phil.  Soc.  1863,  p.  184)  ;  but  this 
never  happens  with  gaseous  mixtures  containing  no  more  oxygen 
than  atmospheric  air  (Poleck,  Zeitschr.  f.  aualyt.  Chemie,  1869, 

VOL.  L  2  E 


418  PRODUCTION  OF  SULPHUR  DIOXIDE. 

p.  451).  It  is  therefore  altogether  reliable  in  the  present  case^  and 
is  very  much  employed.  Its  drawback  is  that  the  solution  (25 
grm.  potassium  hydrate  and  10  grm.  pyrogallol  to  400  c.c.  water) 
gradually  thickens  and  becomes  useless  long  before  this  somewhat 
expensive  reagent  has  been  used  up. 

Phosphorus  is  one  of  the  oldest  absorbents  for  oxygen^  and  it  has 
again  come  into  use^  since  the  manner  of  employing  it  has  been 
properly  studied^  and  as  it  is  now  found  in  trade  in  very  thin 
sticks^  offering  a  great  surface.  Of  course  it  must  be  kept  under 
water^  and  must  be  exposed  only  to  the  gas  to  be  analyzed.  It 
acts  only  at  a  temperature  of  at  least  \&^,  better  a  little  above; 
this  is  the  first  condition  to  be  observed  in  its  use^  but  it  is 
easy  to  attain  if  the  apparatus  is  kept  in  a  somewhat  warm  place 
(near  an  acid-chamber)  •  The  action  of  phosphorus  on  oxygen  is 
interfered  with  by  traces  of  tarry  matters  and  the  like ;  but  such 
do  not  occur  in  chamber-gas.  As  it  is^  the  gases,  both  for  the 
pyrogallol  and  the  phosphorus  test,  are  often  previously  washed 
and  freed  from  acids  by  passing  them  through  a  solution  of  caustic 
potash  j  but  there  is  generally  no  great  error  made  by  omitting 
this  treatment.  The  action  of  the  oxygen  on  the  phosphorus  is  at 
once  indicated  bv  the  formation  of  a  white  cloud,  and  it  is  necessarv 
to  wait  a  few  minutes  till  that  cloud  has  completely  disappeared, 
when  the  absorption  of  oxygen  will  be  complete.  Once  charged, 
such  an  apparatus  may  serve  for  hundreds  of  tests,  but  it  should 
be  kept  from  daylight. 

The  apparatus  employed  for  estimating  oxygen  in  gaseous  mix- 
tures may  be  of  various  descriptions.  Those  most  used  are  Orsat^s 
apparatus  (comp.  Lunge  and  Hurter's  Alkali -Maker^s  Pocket- Book, 
p.  74,  and  Winkler- Lunge's  Technical  Gas- Analysis,  2nd  edition, 
p.  87),  Lindemann's  apparatus  (ibid.  p.  92),  and  M.  Liebig's 
apparatus  (Dingl.  Journ.  ccvii.  p.  37,  and  ccxxxiii.  p.  396)  ; 
Younger^s  apparatus  (J.  Soc.  Chem.  Ind.  1887,  p.  348)  is  a  slight 
modification  of  the  latter.  The  two  former  can  be  used  for 
phosphorus  or  pyrogallol,  the  latter  for  pyrogallol  only. 

Of  course  Hempel's,  Bunte^s,  or  any  other  apparatus  for  general 
technical  gas-analysis  may  be  employed  as  well. 

Instead  of  taking  only  single  samples  of  the  escaping  gas,  it  is 
advisable,  along  with  these,  to  collect  an  average  sample  (say,  for 
24  hours)  by  aspirating  a  certain  quantity  (say,  about  50  litres)  by 
means   of  a   large   aspirator  with   the  outlet»cock  very  slightly 


ESTIMATION  OF  NITROGEN  OXIDES  IN  OASES.  419 

opened.  Owing  to  the  slowness  of  the  aspiration^  the  gas  stand- 
ing over  the  water  in  the  aspirator  will  be  thoroughly  mixed  up, 
and  by  taking  a  sample  from  the  aspirator  the  average  percentage 
of  oxygen  can  be  estimated  with  some  degree  of  accuracy.  We 
shall  treat  this  matter  more  in  detail  in  the  7th  Chapter,  when 
describing  the  testing  of  the  exit-gases. 

(10)  Estimation  of  the  Oxides  and  Acids  of  Nitrogen  in  Gaseous 

Mixtures. 

Burner-gas  will  contain  the  above  acids  if  the  ^^  potting ''  has 
been  done  either  within  or  close  to  the  burners,  as  is  usual  in 
England.  The  acids  and  oxides  of  nitrogen  are,  however,  but 
exceptionally  estimated  in  burner-gas,  and  not  very  often  even  in 
chamber-gas ;  the  latter  is  not  indispensable^  because  the  colour 
of  the  chamber-gas  on  the  one  hand,  and  the  testing  of  the 
"  drops  '^  on  the  other,  which  we  shall  describe  in  the  5th  Chapter, 
are  sufficient  for  guiding  the  manufacturer  in  his  work. 

In  well-conducted  works,  however,  the  chamber-exits  are  tested 
not  merely  for  total  acidity,  but  also  for  nitrogen  acids  separately. 
For  this  purpose  the  prescriptions  formulated  in  1878  by  the 
British  Alkali-Makers'  Association  mav  be  observed,  which  we 
shall  give  in  detail  later  on  (Chap.  VII.) ,  These  do  not  extend  to 
nitric  oxide,  but  we  shall  see  that  it  is  easy  to  estimate  this  at  the 
same  time.  In  this  place  we  shall  give  a  short  outline  of  the 
methods  employed  by  Lunge  and  Naef  for  their  extended  experi- 
mental investigation  of  the  vitriol-chamber  process  (^  Chemische 
Industrie,'  1884,  p.  5)  for  estimating  nitrogen  oxides  and  sulphur 
dioxide  at  the  same  time.  The  pipe  bringing  the  gas  from  the 
chambers  is  continued  into  a  Y-pipe,  both  branches  of  which  are 
connected  with  sets  of  absorbing- tubes.  One  branch  is  connected 
with  three  U-tubes  containing  concentrated  pure  sulphuric  acid 
(for  retaining  H^^^  &^d  N2O4)  and  a  fourth  tube  containing  an 
acidulated  solution  of  potassium  permanganate  (for  retaining  NO). 
The  other  branch  of  the  Y-pipe  first  leads  into  a  long  glass  tube 
filled  with  cotton-wool  or  glass-wool,  where  any  drops  of  mechani- 
cally carried-over  sulphuric  acid  are  retained,  and  then  into  two 
U-tubes  containing  pure  caustic-soda  solution  (for  estimating 
SO3).  At  the  end  of  both  sets  of  tubes  there  is  an  aspirator,  con- 
sisting of  a  large  glass  bottle,  holding  about  20  litres,  divided  into 

2e2 


420  PRODUCTION  OP  SULPHUR  DIOXIDE. 

single  litres^  with  a  tap  or  tap^siphon  leading  into  a  similar  bottle, 
so  that  the  quantity  of  water  run  out  indicates  the  quantity 
of  gas  passed  through  each  set  of  tubes.  The  gas  remaining  in 
the  aspirators  is  tested  for  oxygen  by  absorption ;  nitrogen  by 
difference.  Sulphur  dioxide  is  found  by  oxidizing  the  caustic-soda 
solution  with  bromine- water  and  precipitating  the  sulphuric  acid 
formed  by  barium  chloride.  In  the  sulphuric  acid  nitrogen  trioxide 
and  tetroxide  are  estimated  in  the  way  indicated  in  Chapter  III. 
(p.  253  et  seq.),  by  testing  both  with  permanganate  and  with  the  ni- 
trometer. The  tube  filled  with  potassium  permanganate  must  have 
retained  the  nitric  oxide,  which  is  found  by  adding  titrated  ferrous 
sulphate  solution  and  re-titrating  with  permanganate.  Where  the 
quantity  of  SO9  in  the  gas  is  considerable,  this  method  cannot  be 
employed ;  in  this  case  it  is  not  possible  to  separate  the  'Nfiz  and 
Ns04,  and  the  method  otherwise  used  for  the  chamber-exits  must 
be  employed  (Chapter  VII.). 

Nitrous  oxide  has  never  yet  been  actually  proved  to  exist  in 
chamber-gases  ;  but  it  probably  does  occur  there  in  very  slight 
quantities.  The  former  methods  of  its  detection  and  estimation 
were  very  inadequate  and  failed  entirely  in  the  presence  of  other 
nitrogen  oxides.  It  may  be  possible  to  apply  the  method  proposed 
by  Enorre  (Berl.  Ber.  xxxiii.  p.  2186)|  viz.  burning  with  excess  of 
hydrogen  in  a  Drehschmidt's  platinum  capillary  (comp.  Winkler- 
Lunge's  Technical  Gas-Analysis^  2nd  edition,  p.  162),  or  else 
PoUak^s  method  (described  in  his  inaugural  dissertation^  Prag,  1902, 
p.  52,  and  in  Treadwell's  '  Lehrbuch  der  analyt.  Chemie,'  2nd  ed. 
ii.  p.  538)  of  burning  in  a  bright  red-hot  Drehschmidt^s  capillary 
with  pure  carbon  monoxide,  measuring  the  contraction  and 
estimating  the  CO2  formed.    The  contraction  in  burning  for  NO  is 

NO 

;  for  N2O  there  is  no  contraction  at  all ;    the  volume  of  the 

absorbed  COj  is  equal  to  !N0  +  N2O.  Hence  the  volume  of  N2O  is 
obtained  by  deducting  twice  the  volume  of  the  first  contraction 
from  the  volume  of  COj  found.  This  is  made  clear  by  the 
following  equations : — 

2  vol.  NO  +2  vol.  C0=1  vol.  N2  +  2  vol.  CO3. 
1  vol.  NjO  +  l  vol.  C0  =  1  vol.  N2  +  I  vol.  CO2. 


NECESSITY  OF  LEAD  CHAMBERS.  421 


CHAFTER  V. 

CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

We  have  already  seen,  p.  8  et  seq.,  through  how  many  stages  the 
construction  of  that  apparatus  has  gone  in  which  formerly  all 
sulphuric  acid,  other  than  fuming  oil  of  vitriol,  was  made  and 
up  to  now  is  still  made  for  the  most  part,  viz.  the  lead  chambei*. 
The  reader  already  knows  that  sulphuric*  acid  is  fonned  by  the 
oxygen  of  the  air  being  transferred  to  sulphur  dioxide  through  the 
intervention  of  the  acids  of  nitrogen  and  with  the  aid  of  a  molecule 
of  water,  thus  : 

SO2  +  0  +  H20  =  S04H2. 

All  the  substances  entering  into  the  process  are  in  the  state  of  a 
gas  or  vapour,  except  the  water  which  is  sometimes  introduced  as 
a  spray  or  mist.  The  reaction  takes  a  certain  time,  as  the 
nitrogen  compounds  which  serve  as  carriers  of  oxygen  have  to  be 
frequently  reduced  and  reoxidized,  and  as  the  gases  and  liquids 
are  only  gradually  mixed  so  intimately  that  they  can  actually 
enter  into  reaction.  There  must  therefore  be  a  space  provided  in 
which  large  quantities  of  gas  can  remain  for  some  time. 
According  to  the  calculations  given  on  pp.  397  and  399,  for  each 
kilogram  of  sulphur  in  the  state  of  brimstone  6199,  or  in  the 
state  of  pyrites  8145  litres  of  gas,  reduced  to  0°  and  760  millims. 
pressure,  must  enter  into  reaction ;  and  these  figures  are  a  good 
deal  increased  by  the  higher  temperature,  the  steam,  &c.  In  order 
to  harbour  such  vast  quantities  of  gas,  very  large  spaces  must 
be  provided.  Since  the  strongest  acids  have  to  be  dealt  with, 
both  in  the  liquid  and  the  gaseous  form,  most  materials  other- 
wise used  in  building  are  out  of  the  question ;  and  since,  of 
those  suitable,  glass,  earthenware,  &c.  are  excluded  by  the  large 
size  of  the  apparatus,  practically  only  one  material  remains  which 
is  sufficiently  cheap  and  suitable  for  the  purpose,  viz.  lead.  The 
disadvantages  of  this  metal,  such  as  its  great  weight,  its  softness 


422  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

and  lack  of  rigidity^  its .  easy  fusibility^  its  comparatively  high 
price,  cannot  outweigh  the  advantages  which  none  of  the  base 
metals  share  with  it  for  our  purpose,  viz. : — the  great  chemical 
resistance  to  the  acid  gases  and  liquids ;  its  ductility,  which  per- 
mits rolling  it  into  large  sheets ;  its  extraordinary  pliability  and 
toughness,  in  consequence  of  which  it  can  easily  be  shaped  in 
every  possible  way ;  and,  lastly,  even  its  easy  fusibility,  which  per- 
mits the  edges  of  two  sheets  to  be  so  completely  united  by  melting 
together  with  a  strip  of  lead,  that  they  form  a  whole  for  all  prac- 
tical purposes,  so  that  it  is  possible  to  make  vessels  of  indefinitely 
large  size  and  any  shape,  provided  care  be  taken  to  support  the 
walls  of  the  vessel  on  the  outside,  lest  they  collapse  by  their  own 
weight. 

A  special  advantage  of  lead  is  this,  that  even  after  a  number  of 
years,  when  the  chambers  have  become  quite  worn  out,  the  greater 
portion  of  its  value  can  be  recovered  by  remelting  the  material ; 
even  the  mud  containing  lead  can  be  utilized. 

The  attempts  to  make  sulphuric-^cid  chambers  from  other  materiaU 
than  lead  have  completely  failed.  To  this  class  belongs  the  proposal 
of  Leyland  and  Deacon  (patents  of  September  10th  and  December 
2nd,  1853)  to  make  them  of  hard-burnt  firebricks,  slate,  sandstone^ 
basalt,  &c.,  set  with  a  mixture  of  melted  sulphur  and  sand.  VuU 
canized  india-rubber  or  gutta  percha  are  just  as  useless ;  Krafft 
(Wagner's  ^  Jahresb/  1859,  p.  137)  found  that  gutta  percha  in  an 
acid-chamber  loses  six  times  as  much  weight  as  lead,  and  half  as 
much  again  of  its  surface.  It  would  be  absolutely  impossible 
to  use  it,  because  it  softens  at  the  temperature  of  the  chambers, 
and  in  that  state  is  even  more  easily  acted  upon  by  the  gases. 
Simon's  zeiodelite  (Dingler's  ^  Journal,'  civ.  p.  100),  a  mixture  of 
1 9  sulphur  with  42  pounded  glass,  to  be  employed  in  slabs  of  ^  inch 
thickness,  has,  no  doubt,  never  been  so  much  as  tried  for  this 
purpose,  no  more  than  the  sheets  of  glass  proposed  by  Wilson  and 
others. 

We  will  now  describe  the  erection  of  lead  chambers. 

The  chambers  are  always  placed  at  some  elevation  above  the 
ground- level.  At  the  present  day  chambers  are  probably  nowhere 
found  placed  on  the  ground  itself,  or  on  such  low  foundations  that 
one  cannot  at  least  walk  underneath ;  mostly  their  bottoms  are 
much  higher  than  this.  The  first  object  of  this  is  to  give  the 
opportunity  of  ascertaining  whether  the  chambers  are  tight.     If 


FOUNDATION  ANB  PILLARS.  423 

their  bottoms  are  not  easily  accessible,  large  quantities  of  sul- 
phuric acid  may  get  lost  in  the  ground  before  any  loss  is  detected. 
And  this  means  not  merely  a  loss  of  the  acid,  but  still  more :  the 
foundations  get  corroded  and  undermined,  and  the  whole  structure 
may  collapse.  The  expense  of  building  the  chambers  on  pillars 
&c.  is  not  thrown  away,  as  the  whole  space  underneath  can  be  used 
as  a  warehouse  which  in  winter  time  has  always  a  moderately  high 
temperature ;  or  it  may  even,  if  high  enough,  be  utilized  for  the 
pyrites-kilns  &c.,  although  this  course  is  not  to  be  recommended. 
In  the  latter  case  it  should  be  from  17  to  20  feet  high.  At  some 
works,  which  are  pressed  for  space,  even  the  saltcake-furnaces, 
ball-furnaces,  &c.  are  built  underneath  the  chambers;  but  the 
space  below  them  must  then  be  at  least  30  feet  high. 

In  any  case  the  soil  must  first  be  examined  to  ascertain  whether 
it  affords  a  spfe  foundation ;  for  if  it  settles  more  in  one  place  than 
in  another,  the  chamber  gets  out  of  plumb  and  its  bottom  out  of 
level,  which,  owing  to  the  acid  lying  on  the  latter  and  to  the  insta^ 
bility  of  the  chamber-sides,  causes  great  inconvenience.  A  rocky 
or  pebbly  ground  is  best;  next  to  this,  sand  or  clay;  marl  or  lime- 
stone are  bad,  because  sometimes  acid  will  run  over  accidentally, 
which  acts  upon  it;  and  this  may  happen  even  with  clayey  soil. 
In  such  cases  the  whole  soil  underneath  the  chambers  must  be 
protected  by  a  layer  of  asphalt. 

The  pillars  upon  which  the  chamber  is  erected  must,  of  course, 
go  down  to  the  "  rock,''  as  in  auy  ordinary  higher  building.  If 
the  accumulation  of  made  ground  or  loose  earth  is  so  deep  that  it 
would  be  too  costly  to  excavate  and  raise  the  pillars  from  below, 
piles  must  be  driven  in,  according  to  well-known  building-rules, 
and  the  pillars  built  upon  these. 

The  pillars  themselves  can  be  made  of  brickwork,  stone,  cast- 
iron,  or  wood.  Sometimes,  instead  of  single  pillars,  two  longi- 
tudinal walls  are  erected,  connected  by  cross  joists  and  interrupted 
by  doo«8,  windows,  &c.,  as  shown  in  the  sketch,  fig.  139.  Such 
long  walls  take  much  material  and  make  the  room  underneath  the 
chambers  dark,  in  spite  of  the  windows.  They  are  only  suitable 
where  the  chambers  are  placed  unusually  high  in  ordei:  to  build 
furnaces  underneath.  Up  to  a  height  of  about  26  feet  metal 
pillars  seem  preferable. 

The  cheapest  pillars  are  those  made  of  wood  or  bricks  ;  very 
rarely  they  are  made  of  stone — much  more  frequently  of  the  dearer 


424  CONSTRUCTION  OF  THE  LEAD  CHAMHERS. 

but  much  stronger  and  more  durable  material,  cast-iron.  If  made 
of  wood,  round  or  canted  balks  of  at  least  10  inches  (better  12 
inches)  thickness  must  be  employed.     Mostly  fir-  or  pine-wood  is 

Fig.  139. 


used,  especially  Scotch  fir;  but  the  American  pitoh-pine  or  yellow 
pine,  Bucli  as  is  used  for  ship-building,  is  preferable  (on  account  of 
its  much  greater  durability)  in  spite  of  its  higher  price.  This 
applies  not  merely  to  the  foundation  pillars,  but  even  more  to  the 
frame  of  the  chamber  itself.  The  pillars  must  vary  in  their  thick- 
ness, mutual  distance,  and  manner  of  being  stayed,  according  to 
their  height  and  the  weight  resting  upon  them  (which  may  be  taken 
at  150  lbs.  per  superficial  foot  of  the  total  chamber-area,  for  the 
lead,  timber,  and  acid,  the  latter  alone  in  a  full  chamber  amounting 
to  120  lbs, per  superficial  foot};  but  for  an  average  height  of  10 to 
13  feet,  which  will  not  often  be  exceeded  with  wooden  pillars,  they 
ought  not  to  be  further  apart  than  10  to  at  most  13  feet  from 
centre  to  centre.  In  any  case  they  are  put  into  a  stone  socket 
projecting  from  the  ground,  lest  the  bottom  of  the  pillar  be 
damaged  by  any  moisture  or  acid ;  the  stone  has  at  the  top  a 
hollow  of  ^  to  1  inch  depth,  into  which  the  foot  of  the  pillar  fits 
exactly ;  at  first  a  little  tar  is  poured  into  it.  Wooden  pillars  do 
not  last  for  ercr ;  they  are  not  to  he  trusted  very  much,  and  are 
rarely  found  now  in  larger  works,  at  any  rate  as  principal  pillars, 
except  where  wood  is  very  cheap. 

Frequently  brick  piUara  are  employed .  These  also  are  not  often 
made  above  13  feet,  at  most  15  feet  high;  they  ai«  at  least 
18  inches  (better  2  feet)  square.  They  are  made  of  common 
bricks  with  a  mortar  very  poor  in  lime. 


The  brick  pillars  io  many  works  have 
been  replaced  by  cast-iron  ones,  because 
they  are  not  very  durable,  especially  at 
the  top,  where  the  beams  rest.  Even 
the  bricks  themselves  become  rotten 
by  contact  with  the  acid,  and  only 
stand  better  if  previously  soaked  in 
hot  tar ;  but  they  take  the  mortar  very 
badly  after  that.  They  may  also  be 
painted  with  hot  tar  afterwards. 

On  the  Continent,  where,  in  con- 
sequence of  the  colder  winters  and 
hotter  summers,  the  chambers  have  to 
be  placed  in  a  closed  building,  the 
pillars  may  be  built  in  a  piece  with  the 
main  walls  of  this  building;  but  it 
is  even  then  best  to  keep  them  seiia- 
rate,  as  their  settlement  is  different 
from  that  of  the  main  walls. 

Chambers  20  feet  and  upwards  in 
width  are  sometimes  built  with  mixed 
pillars — viz.  brick  pillars  for  the  two 
long  sides,  and  wooden  pillars  for  the 
centre  row. 

Stone  pillars  are  not  often  used  for 
acid-chambera.  Alade  of  rough  stones, 
they  would  be  extremely  clumsy ;  and 
hewn  stone  in  most  places  is  too  dear. 
On  the  other  hand,  of  course,  stone 
pillars  of  the  latter  kind  are  very  sub- 
stantial, and  last  almost  for  ever, 
unless  the  stone  be  very  soft  and 
rotten. 

In  the  larger  works  in  England  ca»l- 
iri/n  pillars  are  almost  exclusively 
employed,  iu  spite  of  their  higher  cost. 
These  can  be  made  30  or  even  36 
feet  high;  they  take  very  little  space, 
and  are  almost  imperishable  if  painted 
from   time   to   time.       They   can   be 


426  CONGTRDCTION  OP  THE  LEAD  CBAMBEBS. 

■weighted  a  good  deal  more  than  any  other  pillars,  unless  these  are 
made  very  thick;  and  they  can  be  used  as  supports  for  many  other 
purposes  by  means  ot  cast-on  brackets  or  even  of  pieces  bolted 
on  subsequently.  A  brick  or  stone  foundation  must  be  made  for 
them  up  to  the  level  of  the  grouod  or  a  little  higher;  the  top 
stone  is  made  with  a  socket  to  receive  the  foot  of  the  pillar,  as  in 
the  case  of  wooden  ones ;  or  holes  are  drilled  into  the  stone, 
corresponding  to  other  holes  in  the  base  of  the  column;  and  the 
joint  is  made  by  iron  cramps,  fastened  by  pouring  in  melted  lead, 
or  in  some  other  way. 

The  cast  metal  columns  are  now  frequently  made  of  an  H- 
shiiped  section  and  a  little  tapering  upwards.  Fig.  140  will 
show  this  more  distinctly  tc^ether  with  a  bracket  on  each  side  for 
receiving  a  wooHen  stay  for  the  timber  above.  Another,  cross- 
shaped  section  is  shown  in  fig.  141.  These  constructions  are 
better  adapted  for  brackets,  &c.  than  round  columns.  If  higher 
than  shown  in  the  figures  (15  feet),  they  must  be  correspondingly 
stronger — for  instance,  for  20  or  24  feet  height,  12  inches 
diameter  at  the  base.  Such  columns  can  be  placed  at  20  feet 
distance  from  centre  to  centre,  if  the  beams  resting  upon  them 
are  strong  enough. 

Sometimes  the  columns  are  made  of  wrought  iron,  of  the  section 
shown  in  fig.  142.  They  are  a  little  dearer  than  cast-iron 
columns,  but  more  durable  and  reliable. 

The  pillars  are  in  most  works  placed  so  that  F'g-  1-li 

they  stand  directly  under  the  side  frame,  which 
has  to  carry  the  weight  of  the  chamber  sides,  and 
in  the  English  systt^m  also  the  whole  weight  of 
the  chamber  top.     This,  however, in  anycasesuf- 
(ices  only  for  very  narrow  chambers ;  for  chambers 
ot  ordinary  width  (from  20  feet  upwards)  a  centre  row  of  pillars 
must  be  added  to  prevent  sagging  of  the  joints.      But  as  the 
weight  of  the  acid  in  a  full  chamber  may  be  up  to  four  times  as 
much  as  that  of  the  frame  and  lead  combined,  it  seems   more 
rational  to  place  the  pillars  more  inside,  in  wjiich  case  two  rows 
suffice  even  for  a  chamber  of  ordinary  width.   - 

Above  the  pillars  there  are  generally,  in  England,  longitudinal 
sleepers.  If  there  is  a  continuous  wall  in  the  place  of  pillars,  to 
cover  this  with  a  2-inch  plank  will  be  sufficient ;  but  if  there  are 
separate  pillars,  the  sleepers  must  be  strong  enough  to  support  the 


SLEEPERS  AND  JOISTS.  427 

whole  structure  of  the  chambers^  both  wood  and  lead  ;  and  their 
strength  will  then  depend  on  the  distance  between  the  pillars.  With 
chambers  of  20  feet  height^  and  distances  between  the  pillars  of 
20  feet  from  centre  to  centre,  the  longitudinal  sleepers  should  not 
be  less  than  12  to  14  inches  high,  and  ought,  besides^  to  be  sup- 
ported by  stays,  as  shown  in  fig.  143.  With  the  pillars  at  shorter 
distances  (say  10  or  13  feet),  timber  of  9  by  12  inches,  always  on 
edge,  suffices  for  the  longitudinal  sleepers.  The  joints  of  the 
beams  of  which  they  consist  ought  to  be  well  connected,  as  shown 
in  fig.  148,  and  should  be  placed  between  the  pillars,  where  they 

Fig.  14:3. 


JL 

20 

are  supported  from  below  by  the  stays.  The  upper  face  of  the 
sleepers  must  be  levelled  as  well  as  possible  from  one  end  of  the 
chambers  to  the  other.  Above  these  the  cross  joists  are  placed, 
running  from  side  to  side,  and  made  long  enough  to  carry  the  side 
frames,  and  to  leave,  moreover,  a  passage  round  the  chambers. 
For  the  latter  object  only  every  third  or  fourth  joist  need  project 
about  5  feet  on  each  side.     The  joists  are  mostly  planks  on  edge. 

If  chambers  are  much  less  than  20  feet  wide,  which  rarely 
happens  now,  no  centre  longitudinal  sleeper  is  needed,  and  the 
cross  joists  should  have  9  by  3  inches  section  and  corresponding 
length.  Wider  chambers  require  a  centre  row  of  pillars  and 
sleepers;  and  iu  this  case,  as  such  long  planks  are  not  easy  to  get, 
the  joists  can  be  made  in  two  lengths,  resting  on  a  side  and  on  the 
centre  sleeper.  The  horizontal  distance  of  the  floor-joists  is 
usually  12  inches  from  centre  to  centre.  Some  works  have  them 
3  by  11  inches.  The  length  of  the  joists  is  equal  to  the  width  of 
the  chambers  j9/ti«  the  chamber- frame,  plus  the  width  of  the  passage. 

The  joists  are  covered  with  a  1 -inch  ^oor,  laid  quite  level  in  all 
directions.  As  the  flooring-boards  might  easily  warp  afterwards 
from  the  heat  of  the  chambers,  this  must  be  prevented  by  the 
well-known  methods  of  carpentry.  The  edges  of  the  boards  are 
planed  so  as  to  form  a  perfectly  smooth  floor  without  any  chinks. 


428 


CONSTRUCTIOX  OF  THE  LEAD  CHAMBERS. 


Another  system  of  building  is  more  in  favoar  on  the  Continent. 
Firsts  from  pillar  to  pillar  strong  sleepers  are  laid  across  the  width 
of  the  chamber;  upon  these  a  large  number  of  longitudinal  joists 
are  laid^  and  the  flooring-boards  on  the  top  of  these,  running  from 
one  side  of  the  chamber  to  the  other. 

Upon  the  whole  the  frame  of  the  chamber  is  erected^  which  serves 
for  supporting  the  lead.  It  consists,  for  each  side  of  the  chamber^ 
of  a  sole-tree  (sill)  and  a  crown-tree  (capping),  connected  by 
uprights  or  ^'  standards/^  and  further  tied  by  cross  rails  or  stays. 
The  sole-  and  crown-trees  and  uprights  are  either  of  square  section 
(say  6  inches  square  for  a  chamber  up  to  20  feet  high)  or  oblong 
(say  7  by  3  inches).  The  Sole-  and  crown-trees  lie  on  the  flat 
side;    and  the  uprights  are   mortised  into  them  so  that  their 

Fig.  144.        Fig.  14.5. 


,-5 


longer  side  just  covers  the  trees.  In  the  corners  the  trees  project 
over  and  are  rabbeted  into  each  other.  If  no  cross  rails  are 
employed,  the  uprights  are  placed  3  feet  3  inches  apart  from  each 
other ;  if  they  are  connected  by  cross  rails,  they  can  be  placed 
4  feet  apart.  The  cross  rails  are  3  inches  by  2  inches  ;  they  are 
only  partly  let  into  the  uprights,  in  order  not  to  weaken  these  ; 
and  are  placed  at  vertical  distances  of  4  to  5  feet  from  each  other. 
The  chamber-lead  is  kept  a  little  away  from  the  woodwork  in 
order  to  expose  the  lead  always  to  the  cooling  action  of  the  air. 
If  this  is  not  done,  the  lead  is  found  to  be  quickly  corroded  in  the 
parts  protected  against  radiation  of  heat  by  the  wood  ;  it  has 
even  been  observed  that  insects  from  the  wood  have  bored  through 
it"^.  It  is  becoming  more  and  more  the  fashion  to  shape  the 
woodwork  so  as  to  present  the  least  possible  contact  with  the  lead, 
as  shown  in  figs.  144  and  145.  Almost  the  same  effect  is  obtained 
by  using  round  timber  for  uprights. 

The  best  kind  of  timber  for  this  purpose,  as  well  as  for  all  others 

*  1  have  described  such  a  case,  where  the  beetles  in  question  belonged  to  the 
gpecies  Tetropium  luridum  and  Hiflotrupes  bq/olus  (Zsch.  ang.  Chem.  1897^ 
p.  527).  *  ^  ■ 


TIMBER-FRAME.  42U 

where  acids  are  concerned,  is  American  yellow-pine  or  pitch-pine ; 
but  as  this  is  frequently  too  expensive,  ordinary  red-wood  is  also 
very  much  in  use.  It  is  beneficial  to  protect  it  against  the  action 
of  the  acids  by  a  coating  of  whitewash,  which  is  at  the  same  time  a 
slight  protection  against  the  risk  of  fire.  Another  kind  of  pro- 
tection from  the  former,  although  not  from  the  latter,  risk  consists 
in  painting  the  woodwork  with  coal-tar,  or  preferably  with  a  sort 
of  tar-vamish,  made  by  dissolving  coal-tar  pitch  in  heavy  tar-oils, 
and  known  as  "prepared"  or  "refined"  tar  (Lunge's 'Coal-Tar 
and  Ammonia,'  3rd  edition,  p.  374).  The  latter  enters  better  into 
all  the  pores  of  the  wood  and  on  drying  does  not  leave  so  many 
crevices;  it  is  altogether  preferable  to  raw  coal-tar  for  painting 
wood,  iron,  or  brickwork,  and  is  not  much  dearer. 

The  painting  of  the  woodwork  is  best  done  twice,  and  before  the 
lead  is  put  on,  so  that  all  parts  can  be  reached  by  the  brush. 

Special  care  must  be  taken  lest  any  acid  gets  into  the  mortise- 
boles,  where  the  uprights  are  joined  to  the  sole-trees,  8sc.  No 
empty  space  should  be  left  here  where  any  acid  could  lodge,  but 
all  interstices  should  be  filled  up  with  coal-tar  pitch  or  the  like. 
It  seems  also  another  good  plan  to  cut  out  the  bottom  of  the 
upright,  and  make  it  fit  on  to  a  corresponding  saddle-shaped  part 
of  the  sole-tree,  as  shown  in  fig.  146.     Two  small  lead  pipes  drain 

Fig.  146. 


away  any  liquid  collecting  in  the  low  corners,  so  that  no  acid  can 
ever  lodge  there  and  cause  the  wood  to  decay. 

In  France  sometimes  the  bottoms  of  the  uprights  are  not  at  all 
mortised  into  the  sole-tree,  but  rest  flatly  upon  them,  being  kept 
in  their  places  by  pressure  and  friction  only. 

Whether  cross  rails  are  used  or  not,  in  any  case  there  should  be 
diagonal  stays,  to  give  more  stability  to  the  frame.     II.  is  not  of 


430  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

much  consequence  how  the  stays  are  put^  so  long  as  this  is  done 
according  to  the  well-known  rules  of  carpentry. 

If,  as  is  usual  in  England^  the  chambers  are  in  the  open  air^  one 
side  of  the  frame  is  made  about  a  foot  higher  than  the  other,  so 
that  the  rain-water  and  melted  snow  can  run  off^  and  on  the  lower 
side  a  water-spout  is  arranged  so  that  the  rain-water  cannot  run 
along  the  chamber-side  down  into  the  acid  at  the  bottom. 

At  some  places  the  chamber-frames  are  made  of  angle-iron. 
This  plan  has  the  advantage  of  presenting  an  extremely  durable 
and  clean  erection  and  of  avoiding  overheating  of  the  lead  in  any 
part.  Such  frames  may  be  constructed  in  the  following  manner. 
The  side-frames  consist  of  thin  angle-irons  crossing  each  other  at 
right  angles^  the  uprights  9  ft.  6  in.  and  the  horizontals  7  feet 
distant  from  each  other.  No  iron  nails  are  employed  at  all;  the 
lead  straps  are  simply  bent  round  the  angle-irons.  The  roof  i& 
suspended  from  angle-irons  in  exactly  the  same  way.  Of  course 
iron  frames  are  more  costly  than  wooden  and  must  be  kept  in 
order  by  painting  from  time  to  time,  preferably  with  coal-tar 
varnish  (p.  429). 

Now  the  chamber  itself  can  be  erected,  and  we  shall  therefore 
now  speak  of  the  lead  to  be  employed.  For  this,  sheet-lead  as  wide 
as  the  rolling-mills  can  supply  it,  and  of  convenient  length,  is  used, 
so  as  to  have  as  few  seams  as  possible.  The  usual  thickness  in 
England  is  6  lbs.  to  the  superficial  foot,  sometimes  7  lbs.,  especially 
for  the  ends  and  the  top,  or  for  the  first  chamber  of  a  set. 

This  thickness  is  sufficient  for  a  chamber  to  last  upwards  of 
ten  years ;  the  bottom  lasts  longest,  because  it  does  not  get  so 
hot  as  the  sides  and  the  top,  and  it  is  also  more  protected  by 
the  mud  of  lead  sulphate  which  collects  upon  it ;  only  in  cases  of 
gross  neglect  (for  instance,  if  nitric  acid  gets  to  it)  it  is  quickly 
worn  out,  whether  the  lead  be  thick  or  thin.  But  where  ctTic- 
blende  is  used,  the  mercury  contained  in  it  may  have  a  different 
effect,  especially  since  the  blende-furnaces  are  driven  at  a  higher 
temperature,  so  that  more  mercury  gets  into  the  chambers. 
According  to  information  received  from  Dr.  Hasenclever  in  1902, 
it  has  been  noticed  at  Stolbergthat  the  mercury  acts  most  strongly 
at  the  lateral  parts  of  the  bottom  w  hich  are  less  protected  by  the 
sulphate-of-lead  mud,  and  where  the  joint  between  the  side  sheet 
and  the  bottom  sheet  causes  the  double  layer  of  lead  to  collect  acid 
and  mercury  between  the  two  sheets.  Here  sometimes  mercurv 
is  visible  in  globules,  and  that  part  is  worn  out  in  less  than  three 


QUALITY  OF  LEAD.  431 

years.  Hence  they  make  the  whole  bottom  of  stronger  lead,, 
rolled  extra  strong  at  the  part  next  to  the  sides,  which  is,  moreover, 
protected  by  a  covering  of  acid-proof  flags. 

In  America  the  usual  thickness  of  lead  is  only  5  lbs.  per  super- 
ficial foot,  and  even  4  lbs.  lead  is  sometimes  used  (Journ.  Soc. 
Chem.  Ind.  1885,  p.  27);  but  this  seems  very  bad  economy  indeed,, 
and  it  can  only  be  done  when  burning  brimstone.  In  the  best 
American  works  I  have  found  6  lbs.  lead. 

On  the  other  hand,  at  some  of  the  best  English  works  not 
only  is  7  lbs.  lead  used  throughout  for  the  chambers,  but  in  the 
most  exposed  places,  such  as  the  front  and  back  ends  of  the 
leading  chamber  and  several  feet  of  the  sides  adjoining  these,  9  lbs. 
is  used.  Sometimes  the  side  sheets  are  rolled  so  that  the  upper 
and  lower  two  feet  are  made  stronger  than  the  remainder,  because 
these  parts  are  more  quickly  worn  out.  Chambers  built  in  this 
careful  way  last  upwards  of  20  years. 

The  quality  of  the  lead  is  certainly  not  indifferent.  Opinions 
were  formerly  not  altogether  agreed  as  to  the  point  whether  pure  or 
impure  lead  better  resists  the  action  of  sulphuric  acid  ;  and  in  the 
present  case  it  is  no  doubt  not  so  much  this  acid  as  the  nitrous 
compounds  to  which  the  attack  of  the  lead  is  due.  Most  manu- 
facturers formerly  inclined  to  the  belief  that "  hard  ''  lead  is  better 
adapted  to  vitriol-chambers  than  *'  soft  lead/'  A  test  sometimes- 
performed  consists  in  trying  which  of  several  samples  of  lead  in 
contact  with  sulphuric  acid  gives  off  more  hydrogen  from  a  given 
surface  in  a  given  time ;  but  this  test  is  very  apt  to  mislead,  and 
there  is  really  no  good  test  known  as  yet  (comp.  Journ,  Soc.  Chem. 
Ind.  1884,  p.  230). 

This  subject  has  been  fully  discussed  before,  p.  206  et  seq.,  where 
the  conclusion  was  come  to  that  for  vitriol-chambers  the  purest  and 
softest  lead  is  the  most  suitable  material.  In  Zsch.  ang.  Ch.  1892, 
p.  643,  I  have  given  the  following  analyses  of  lead  specially  suited 
for  vitriol-chambers: — 1.  Soft  lead  of  the  Mulden  lead-works: 
0001  per  cent.  Cu,  0-044  Bi,  0-0004  S  b,  00005  Fe,  00004  Sn,  0-0005 
Ag,  no  As.  2.  Soft  lead  from  W.  Leyendecker  &  Co.,  Cologne  : 
00034  Cu,  00019  Bi,  00029  Sb,  trace  of  Fe,  00047  As,  0*00025 
Cd,  trace  of  Ni  &  Co,  0 0010  Ag,  00002  Zn,  00024  O. 

G.  E.  Davis  ('Chemical  Engineering,'  i.  p.  142)  quotes  the 
following  analyses  of  "  chemical  lead  '^  (from  what  source  or  by 
whom  made  is  not  stated)  ;  the  figures  indicate  milligrams  per 
kilogram  (I  omit  the  decimals)  : — 


432  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

A.  B.  C.  D. 

Antimony  17  19  64  32 

Copper    21  13  14  19 

Silver 22  14  39  16 

Iron     3  2  12  2 

Cadmium    1  1  1  2 

Bismuth 4  2  22  4 

Zinc    2  12  3 

Sulphur 12  2  1 

According  to  Eng.  &  Min.  Journal,  March  8,  1902  (Journ. 
Soc.  Chem.  Ind.  1902,  p.  510),  a  special  brand  of  lead  is  designated 
in  Missouri  '^chemical  hard  lead^'  and  is  sold  at  5  cents  per 
100  lbs.  above  the  price  of  common  Missouri  lead.  It  is  supposed 
to  contain  a  little  copper  and  antimony,  but  no  attempt  is  made  to 
keep  the  composition  within  precise  limits.  MUhlhauser,  in  Zscfa. 
angew.  Ch.  1902,  p.  758,  quotes  an  analyses  of  soft  chamber-lead 
from  Chicago  and  St.  Louis. 

Leyendecker  (B.  P.  2756,  1901)  prepares  a  special  quality  of 
chemical  lead  by  adding  either  0' 1-0*5  per  cent,  copper  or  O'l- 
0*5  per  cent,  copper  and  0*l-0'3  per  cent,  antimony.  (Such  a 
patent  could  hardly  be  maintained  in  the  face  of  my  researches, 
p.  206  et  aeq.y  published  a  long  time  ago,  for  the  purpose  of 
benefitting  chemical  manufacturers  generally.) 

The  analysis  of  such  lead,  which  1  have  obtained  from  the 
Rhenania  Chemical  Company,  as  compared  with  ordinary  soft  lead, 
gives  the  following  results  : — 

Ordinary  Leyendecker'a 

soft  lead.  special  quality. 

Bi  percent 0*00501  0-00605 

Cu      „         001787  006683 

Cd       „         000004  000003 

As       „         0  0-00002 

Sb       „         000039  005025 

Fe      „         0-00089  0*00074 

Zn       „         0-00082  0-00122 

We  notice,  in  the  ''  special  quality,*'  besides  a  certain  amount 
of  copper  and  antimony  (the  latter  in  such  small  quantities  a^ 
not  to  counterbalance  the  useful  effect  of  the  copper)  also  an 
extraordinary  small  amount  of  bismuth,  being  only  1/100  of 
that  present  in  the  '' ordinary  soft  lead.'*     The  firm  using  both 


JOINING  LEAD  BY  BURNING.  433 

had  not  had  a  sufficiently  long  experience  with  them  to  judge  of 
any  difference  in  behaviour. 

Another  ^^  special  quality/^  particularly  recommended  for  KrelPs 
concentrating  apparatus  (comp.Chapt.IX.)^  is  supplied  by  Graffweg 
&  Co.j  Diisseldorf.  It  is  probably  something  very  similar  to 
Leyendecker's  lead. 

All  sheet-lead  before  being  used  should  be  '^  mangled,''  in  order 
to  beat  out  all  inequalities  and  indentations  casually  produced  in 
transit  &c.  For  this  purpose  it  is  tightly  rolled  round  a  wooden 
roller,  about  6  inches  thick,  and  is  beaten  all  the  time  with  a 
plumber's  mallet. 

The  sheets  of  lead  were,  in  the  infancy  of  acid-making,  joined 
together  by  the  ordinary  soft  solder ,  which  is  very  convenient  for 
use,  but  is  soon  corroded  by  the  acid.  Places  soldered  thus  are 
also  much  more  brittle  than  pure  lead.  So  long  as  the  chambers 
had  to  be  put  together  in  this  way,  there  was  occasion  for  innumer- 
able repairs. 

Another  plan  (which  is  far  better  in  this  respect,  but  takes 
much  lead,  and  is  only  easily  applicable  for  straight  seams)  is  the 
rabbet'^omi.  The  edges  of  two  sheets  of  lead  are  turned  over  in 
the  way  shown  in  fig.  147,  placed  one  into  the  other,  and  beaten 

Fig.  U7, 


down  on  a  smooth  surface.  Such  joints  are  gas-tight,  and  have 
been  used  here  and  there  in  England  till  within  the  last  few  years. 

The  kind  of  joint  now  generally  cm  ployed  is  that  made  by  burning, 
with  the  lead  itself — that  is,  by  melting  it  with  a  hydrogen  flame 
fed  by  compressed  air.  In  this  way  the  two  sheets  are  joined  so 
tightly,  that  with  good  work  the  joint,  being  thicker  than  the 
sheets,  is  actually  stronger  than  they  are.  If  the  work  is  rough 
and  uneven^  foreign  substances  will  easily  be  deposited  in  the  rough 
parts,  by  which  the  lead  may  be  damaged. 

This  mode  of  joining  was  invented  by  Debassayns  de  Richemond 
in  1838.  Two  apparatus  are  required  for  this,  whose  construction  is 
seen  in  figs.  148  &  149.  Fig.  148  shows  the  '' plumbers' machine" 
— that  is,  the  hydrogen  apparatus — quite  similar  to  an  ordinary 
laboratory  gas-holder,  but  made  of  lead,  often  with  a  wood  casing. 
The  lower  vessel.  A,  contains  a  lead  grating,  KL,  upon  which 

VOL.  I.  2  F 


^34  CONSTRUCTION  OF  THE  LEAD  CHAHBERS. 

granulated  or  scrap  zinc  ia  put.  The  upper  veasel  contains  dilute 
sulphuric  acid.  The  counecting-tube  with  a  cock /allows  the  gas 
to  pass  out  of  the  opening  (',  after  it  has  first  been  washed  in  a 
water-vessel.  Often  there  is  a  plain  outlet  just  above  the  cock  /, 
The  outlet  is  connected  with  a  long  india-rubber  tube,  by  means 
of  which  the  gas  can  be  conducte<i  to  a  distance.  The  tube  G 
serves  for  running  sulphuric  acid  from  B  to  A,     It  can  only  run 

Kg.  U-.  Fig.  140. 


in  as  gas  is  allowed  to  escape  by  opening  the  cock  /;  aiid  thus 
a  continuous  current  of  gas  is  obtained.  The  openings  D,  E, 
and  F  serve  for  introducing  acid  and  zinc,  and  for  running  off  the 
solution  of  zinc  sulphate. 

The  second  part  of  the  apparatus,  which  is  shown  in  fig.  149,  is 
siraply  a  portable  smith's-bellows  of  cylindrical  shape,  the  lever  of 
which,  0  a  c,  a  buy  works  with  his  foot.  The  air  is  forced  through 
the  valve  D  from  C  to  the  closed  air-vessel  B,  and  escapes  through 
the  opening  /,  likewise  connected  with  a  long  elastic  tube.     The 

Fig.  l-iO. 


two  tubes  are  united  by  a  blow-pipe,  tig.  150 ;  and  the  mixture 
is  ignited.  Each  limb  of  the  blow-pipe  is  provided  with  a  stop- 
cock,  by  turninj;  which  the  plumber  may  admit  moreair  or  hydrogen 


BURNING  THE  LEAD  TOGETHER.  435 

at  will,  and  thus  can  produce  a  flame  of  any  size,  which,  however, 
should  never  be  an  oxidizing  one. 

The  mouth-piece  of  the  blow-pipe  itself  is  sometimes  connected 
with  the  fork-shaped  piece  by  a  short  elastic  tube,  to  make  it  more 
mobile.  Besides  the  ordinary  mouth-piece,  ending  in  an  aperture 
of  about  2^5  of  ail  iiich  diameter,  the  plumber  also  carries  another, 
provided  with  a  small  brass  shield,  to  obtain  a  steady  flame  in  windy 
weather.  The  gases  unite  only  immediately  before  escaping;  and 
thus  the  flame  cannot  strike  back.  By  means  of  this  machine  a 
pointed  and  very  hot  hydrogen  flame  is  produced,  which,  at  the 
place  where  it  touches,  melts  the  lead  immediately  down  to  a 
certain  depth  ;  and  the  art  of  burning  consists  in  touching  and 
melting  parts  of  two  sheets  at  the  same  time^  which,  on  cooling, 
solidify  to  a  whole. 

It  has  happened  that  plumbers  have  been  poisoned  by  arseni- 
uretted  hydrogen,  produced  by  impurities  in  either  the  zinc  or 
the  sulphuric  acid.  The  hydrogen  can  be  freed  from  this  by 
washing  it  with  a  solution  of  cupric  sulphate,  by  which  the  arsenic 
is  precipitated.  Hydrochloric  acid  should  not  be  employed  for 
evolving  the  hydrogen,  even  when  free  from  arsenic,  as  the 
workmen  are  injured  by  gas  thus  made. 

The  burning  itself  is  a  kind  of  work  requiring  much  practice, 
because  the  plumber  must  not  allow  the  flame  to  act  a  moment 
too  short  or  too  long.  If  he  does  the  former,  the  fusion  is  not 
perfect  and  the  seam  is  not  tight ;  if  the  latter,  he  burns  a  hole 
in  the  lead.  Wherever  it  is  possible,  one  sheet  is  laid  about 
2  inches  over  the  edge  of  the  other,  as  shown  in  fig.  151.      The 

Fig.  lol. 


^^rMtM,a^*/MrMf,y  '. 


1(y/.  '.  MP".' 


seam  is  made  with  the  help  of  a  strip  of  lead,  about  f  by  ^  inch 
thick,  which  the  plumber  holds  in  one  hand  whilst  he  guides  the 
blow-pipe  with  the  other.  He  works  in  this  way  : — He  touches 
with  the  flame  the  place  a  (fig.  151),  where  the  edge  of  one  sheet 
lies  upon  the  other,  so  that  the  surface  of  the  lead  (previously 
scraped  clean)  just  melts,  but  the  back  part  of  the  lead  does  not 
melt.  At  the  same  time  he  holds  the  above-mentioned  strip  in 
the  flame,  so  that  drops  fall  from  it  on  to  the  just-melted   part 

2f2 


436  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

of  the  sheets,  and  the  whole  is  united  into  a  seam,  b,  all  fusing 
together  into  one  mass.  By  a  slight  motion  of  the  wrist  the 
plumber  removes  the  flame  for  a  moment,  and  the  lead,  which  has 
only  just  been  melted,  at  once  solidities ;  in  another  second  the 
flame  ia  again  directed  upon  the  lead,  and  a  new  drop  flows  partly 
over  the  firBt  one ;  so  that  at  laat  the  whole  seam  takes  the  shape 
shown  in  fig.  152. 

Although  all  this  is  much  more  easily  described  than  carried  out 
successfully,  still  the  burning  of  horizontal  seams  is  learned  in  a 
comparatively  short  time,  and  can  be  done  very  quickly  by  a  prac- 
tised workman.  In  windy  weather  it  is  certainly  much  more 
difficult,  and  in  rainy  weather  it  is  not  possible  at  all. 
Fig.  162. 


The  burning  of  perpendicular  (upright)  joints  is  much  more 
difGcult,  and,  even  in  the  hands  of  the  most  experienced  workmen, 
takes  at  least  three  times  as  long  for  the  same  length  of  seam 
as  horizontal  buroiug,  without  ever  being  as  strong  as  the  latter. 
This  ia  easily  understood;  for  the  melted  lead,  which  quietly  remains 
lying  on  a  horizontal  sheet,  iu  upright  burning  at  ouce  runs  down; 
anil  this  can  ouly  be  prevented  in  one  way  :  the  lead  must  be  heated 
exactly  up  to  the  melting-point,  and  the  tlame  instantly  removed 
till  the  seam  has  solidified ;  and  the  burning  must  always  be  done 
from  the  bottom  upwards,  so  that  to  a  certain  extent  the  seam  will 
retain  the  drops  of  lead.  In  this  case  not  much  use  can  be  made 
of  strips  of  lead  for  strengthening  the  seam. 

A  practised  plumber  can  burn  as  much  as  10  fee't  upright  or 
25  feet  horizontal  joints  in  an  hour;  but  such  figures  are  only 
reached  in  piece-work. 

Recently  the  burning  of  lead  has  frequently  been  effected  by  a 
pure  oxykydrogetijlame,  both  oxygen  and  hydrogen  being  applied  in 


ERECTING  A  LEAD  CHAMBER.  437 

the  compressed  state^  contaiued  in  steel  cylinders.  The  burning  in 
this  way  is  done  much  more  rapidly.  Suitable  burners  are  sold 
by  the  Sauerstoff  Fabrik,  Berlin,  O. 

Water-gas  can  be  employed  for  lead-solderiug  without  a  blast 
of  air  (or  oxygen),  but  its  poisonous  properties  must  not  be 
forgotten. 

7'he  way  of  erecting  a  lead  chamber  in  England  is  usually  as 
follows  : — The  commencement  is  made  with  the  sides,  for  which  the 
sheets  are  made  as  wide  as  possible  (most  lead-rolling  mills  supply 
them  up  to  7  feet  9  inches,  some  even  wider),  and  so  long  that  they 
extend  4  inches  beyond  the  height  of  the  chamber,  of  course 
taking  into  account  that  one  side  of  the  chamber  is  a  foot  higher 
than  the  other.  6  inches  are  reckoned  to  turn  over  the  crown-tree; 
but  2  inches  are  saved  at  the  bottom,  because  the  lead  afterwards 
expands  by  the  heat  of  the  chamber. 

Now,  on  the  wooden  floor  before  mentioned  a  wooden  table  (the 
''  sheet-board '')  is  constructed,  held  together  at  the  back  by  battens, 
but  quite  smooth  on  the  upper  surface.  It  has  the  width  of 
two  or  three  sheets  of  lead  (that  is,  15  feet  6  inches,  or  23  feet 
3  inches)  and  the  height  of  the  chamber — which,  of  course,  can 
only  be  done  when  (as  is  generally  the  case)  the  chamber  is  at  least 
as  wide  as  it  is  high.  On  this  table  the  sheets  of  lead  are  rolled 
out  flat,  placed  side  by  side,  so  that  one  overlaps  the  other  2  inches, 
and  burned  together ;  at  the  same  time  all  the  straps  (of  which  we 
shall  speak  directly)  are  burnt  to  the  lead,  which  can  be  done 
because  the  upper  surface  will  afterwards  be  the  outer  one.  The 
upper  edge  is  bent  round  the  sheet-board,  so  as  to  hold  it  fast ; 
and  when  everything  is  finished  this  end  is  wound  up  by  a  set  of 
pulleys,  so  that  the  sheet-board  is  raised  along  with  the  sheets  of 
lead,  and  lies  flat  against  one  side  of  the  chamber-frame.  Now  the 
upper  edge  of  the  lead  is  at  once  bent  over  the  crown-tree  and 
nailed  down,  as  well  as  all  the  straps.  For  this  no  cut  or  wire 
nails  are  ever  used,  but  wrought  nails  with  broad  heads  (^'  plate- 
nails^^),  about  1^  inch  long,  whose  heads  are  all  protected 
against  the  acid  by  dipping  a  few  at  a  time  into  melted  lead. 
When  the  lead  has  been  completely  fastened  to  the  frame,  the 
sheet-board  is  lowered  down,  moved  forward  its  own  width,  and 
another  piece  of  the  chamber-side  made  upon  it,  till  in  this  way 
the  chamber-sides  and  ends  have  been  finished  all  round.  Only 
iu  the  corners  it  is  preferable  to  use  single  sheets,  which  form 


438  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

a  rounded  corner :  this  is  much  stronger  than  a  sharp  edge. 
The  object  of  the  described  process  is  this,  to  reduce  the  upright 
burning  to  a  minimum.  It  is  much  better  than  the  former 
plan  of  hoisting  up  each  single  sheet,  turning  its  margin  over  the 
crown-tree,  and  unrolling  the  sheet  by  its  own  weight.  In  this 
case  every  single  sheet  had  to  be  joined  to  its  neighbour  by  upright 
burning,  and  the  straps  had  to  be  burnt  on  in  an  equally  incon- 
venient manner.  If  at  all  possible,  the  seams  ought  not  to  be 
behind  the  uprights,  so  as  to  be  better  accessible  for  repairs ;  and 
for  this  reason  also  it  is  to  be  recommended  to  make  the  chamber- 
frame  as  shown  in  figs.  144,  145,  or  153,  where  the  uprights  do 
not  touch  the  lead  at  all. 

The  straps  of  the  sides  must  be  arranged  according  to  the  style 
of  the  frame.  If  this  only  consists  of  uprights  mortised  into  the 
crown-  and  sole-trees,  without  any  cross  rails,  the  straps  consist  of 
perpendicular  pieces  of  lead  nailed  sideways  to  the  uprights  with 
five  leaded  nails  each.  The  strap  ought  to  be  long  enough  to  turn 
over  the  edge  of  the  upright,  so  that  two  of  the  nails  come  to  the 
front  (fig.  155,  upper  part).  Such  straps  are  placed  alternately  on 
one  and  on  the  other  side  of  the  upright,  one  about  every  4  feet. 
These  straps  do  not  allow  the  chamber-lead  to  follow  the  changes 
of  temperature  by  extension  or  contraction.  This  easily  leads  to 
deformation  of  the  sides  and  tearing  off  of  the  straps;  and  it  is 
therefore  better  to  avoid  this,  which  can  only  be  done  by  nailing 
down  the  top  strap  in  this  way.  For  the  lower  straps  longer 
pieces  of  lead  are  burnt  to  each  side  of  the  upright,  which  meet  on 
its  front,  and  are  there  joined  by  rabbeting  (see  fig.  155,  lower  part, 
and  fig.  156).  There  are  no  nails  used  here ;  so  that  the  lead  walls 
may  move  up  and  down  the  upright,  whilst  at  the  same  time  they 
are  all  the  more  stiffened  by  being  held  fast  in  two  places.  This, 
of  course,  takes  more  lead  and  labour  than  simple  straps.  In  each 
case  the  straps  are  about  8  inches  in  depth. 

The  object  of  keeping  the  lead  clear  of  the  wood,  and  of  giving 
it  scope  for  expanding,  is  well  attained  in  the  form  of  strap  shown 
in  figs.  153  and  154.  The  upright  a  is  placed  with  one  of  its  edges 
pointing  towards  the  chamber.  The  strap  b  turns  round  the  edge 
of  a,  and  is  fastened  to  it,  not  by  ordinary  nails,  but  by  a  broad- 
headed  pin  c,  which  passes  through  a  slit  2  inches  in  height.  This 
arrangement  allows  the  strap  to  work  up  and  down,  as  the  chamber- 
side  expands  and  contracts. 


440  CONSTRUCTIO.V  OF  THE  LEAD  CHAMBERS. 

If  the  frame  is  provided  with  horizontal  cross  raib,  odIt  b 
few  upright  straps  are  used — sometimes  oooe,  ooiy  horizontal 
ones,  turned  down  over  the  rail,  and  nailed  * 

to  it  (fig.  157),  two  o£  6  inches  length  for 
each  rail.  This  kind  of  straps  protects  the 
chamber-sides  much  better  against  defor- 
mation than  the  upright  straps,  and  carries 
the  weight  better  upon  the  frame  {this 
is  confirmed  by  information  from  Stolberg  in  1902)  ;  it  nlso 
permits  the  lead  to  he  kept  further  apart  from  the  wood,  since  the 
straps  may  leave  about  \  inch  (not  more)  space  between  tlie  lead 
and  the  rails.     The  diagram  shows  this. 

The  chamher-sides  can  also  {as  at  the  Tbanu  Works)  be  made  of 
horizontally  disposed  sheets  of  lead.  The  overlap  in  this  case  is 
nailed  to  the  horizontal  cross  rails  in  lieu  of  straps,  as  shown  in 
fig.  158 ;  but  first  the  whole  height  of  the  cbamber-sido  is  fiDished, 

Kiji.  157. 


the  whole  is  rolled  upr»n  a  ivooden  roUei-,  and  allowed  to  unwind 
itself  by  its  own  weight  from  the  fop.  In  this  way  there  is  not  so 
much  pull  upon  tiie  seams  as  if  the  chamber  were  made  of  sheets 
hanging  down  by  their  length,  since  each  sheet  is  supported  just 
in  the  place  where  ihei-e  would  be  a  pull.     This  plan,  indeed,  seems 


to  be  worthy  of  general  recommenda- 
tioQ ;  for  it  saves  the  lead  and  lahour 
of  all  the  straps,  and  supports  the 
chamber  very  well. 

At  least  as  substantial  is  the  plan  used 
at  Aussig.  There  are  no  side-straps  at 
all ;  but  to  each  upright  of  the  frame 
corresponds  a  strip  of  lead  burnt  to  the 
chamber-side  along  its  whole  height, 
probably  the  lap  turned  outside.  This 
is  nailed  sideways  to  the  upright.  Be- 
tween this  and  the  lead  there  is  a  wooden 
lath,  to  increase  the  contact  of  air  with 
the  chamber-lead  as  much  as  possible. 
Fig.  159  shows  this  in  horizontal  sec- 
tion. 

FifT.  150. 


Mr.  Benker  ascribes  great  advantages  to  his  pefforated  straps, 
sliown  in  figs.  160  to  162.  Fig.  160  is  a  plan,  showing  the 
chamber-side  a,  the  uprights  b,  the  cross-bars  c,  the  small  wooden 
bars  d,  and  the  straps  e.  The  same  parts  are  seen  in  vertical 
section  in  fig.  IGl.  The  chamber-lead  is  kept  2  or  2^  inches  apart 
from  the  cross-bars;  the  perforations  of  the  straps  (which  may 
extend  the  whole  width  of  tl)c  cross-bars,  as  in  fig.  1G2)  cause  a 
strong  curreut  of  air  to  rise  upwards  and  cool  the  lead,  without 
allowing  any  quantity  of  dust  to  accumulate  on  the  straps.  This 
system  is  especially  good  for  chambers  which  are  driven  hard  for 
"  forced  work." 

lu  the  first-described  case,  now  generally  used  in  England,  at 
first  only  about  a  yard  of  the  scams  is  burned,  and  that  at  the  top, 
so  that  the  chamber  can  be  covered  in  and  the  remainder  can  be 
done  at  leisure  in  bad  weather.  The  next  thing,  therefore,  is  the 
chamher-top.     For  this  we  need  a  temporary  scaftbldiug,  movable 


CnXSTRDCTlON  OF  THE  LEAD  CHAMBERS. 


on  wooden  rollers,  made  of  high  trestles  joined  together  at  the  top, 
equal  in  height  and  width  to  the  chamber,  and  in  length  to  at 
least  two  (or,  better,  three)  sheets  of  lead.  This  scaffold  is  put 
together  within  the  chamber  itself,  its  separate  parts  being  got  in 
by  bending  back  one  of  the  side  sheets.  It  is  covered  on  the  top 
with  a  flooring  of  boards ;  and  upon  this  the  sheets  serving  for  the 
chamber-top  are  flattened  out.  I'^ese  are  a  little  wider  than  the 
chamber,  so  that  they  project  3  inches  on  each  side.     Thus  they 


do  not  project  quite  as  far  as  the  overlap  of  the  side  sheets 
(6  inches),  and  there  remains  a  joint  Buitable  for  burning 
(fig.   163,  fl),  which  is  burned  very  strongly.     Now  the  sheets 


themselves  are  joined  by  burning,  and  all  the  top  straps  are  burnt  on. 
The  latter,  in  England,  serve  for  fixing  the  chamber-top  from  above 
to  the  top  joists  carrying  it.  The  latter,  for  a  chamber  20  to  26  feet 
wide,  are  3  to  4^  inches  thick  and  10  to  12  inches  high,  and  are 
placed  at  distances  of  14  to  18  inches  from  centre  to  centre.  Their 
length  is  at  least  suflBcient  to  reach  to  the  outside  of  the  crown- 
trees;  it  is  better  if  they  even  project  a  little  beyond,  to  have  a 
good  Bupport.  The  straps  themselves  are  made  ^  indies  square, 
and  stand  alternately  on  both  sides  of  the  top  joists,  about  3  feet 
apart  ou  each  side.  At  other  works  there  are  fewer  but  longer 
straps.  They  are  bent  up  and  nailed  to  the  top  joists  laid  above 
them  on  edge,  with  five  leaded  nails  each.  When  all  this  has  been 
done,  the  top  joists,  by  the  help  of  the  straps,  carry  the  lead  of 
the  chamber-top,  and  the  joists  themselves  rest  upon  the  side 
frames,  but  separated  from  them  by  the  overlap  of  the  chamber- 
sides.  The  joists  should  be  well  clear  of  the  chamber-top  (farther 
than  is  shown  in  the  figure),  so  that  air  can  circulate  between 
lead  and  wood. 

The  top  joists  are  protected  from  canting  over  by  a  few  boards 
nailed  across  them,  which  at  the  same  time  serve  as  a  passage  on 
the  chamber-top.  Where  the  chambers  are  roofed  in,  longitudinal 
sleepers  may  be  laid  on  the  top,  joined  to  the  top  joists  by  iron 
clamps,  and  the  whole  suspended  from  the  timber  of  the  roof 


441  CONSTRUCTION'  OF  THE  LEAD  CHAMBERa. 

v'hici)  must  be  made  strong  enougli  for  this  purpose ;  but  some 
hold  thnt  even  with  roofed-in  chambers  it  is  sftfer  to  keep  the 
chamber-top  independent  of  any  movemeat  of  the  roof- 
Where  the  cliamljer  is  too  wide  for  any  single  cross  joists,  two 
lengths  of  these  must  be  joined  together  and  trussed,  accordiDg  to 
the  rules  of  carpentry  ;  in  this  case  trussed  girders  may  rua  across 
the  width  of  the  chamber,  and  the  proper  joists,  to  which  the  top 
lead  is  fastened  by  straps,  mn  parallel  with  the  long  sides  of  the 
chambers ;  they  are  either  mortised  into  the  girders,  or  (which  is 
the  stronger  plan)  they  rest  in  cast-iron  shoes  bolted  to  the  girders. 
This,  however,  is  only  required  for  chambers  standing  in  the  open 
air ;  it  is  not  very  convenient,  as  the  side  frames  have  to  be 
weighted  very  much.  Such  wide  chambers,  as  we  shall  see  below, 
have  not  altogether  turned  out  well. 

Fifi.  104. 


Quite  different  from  tlie  just-described  chamber-tops  are  ihose 
found  in  many  continental  works.  There  are  no  wooden  top  joists, 
but,  in  the  place  of  these,  thin  iron  rods  about  J  in.  thick,  fastened 
to  the  chamber-top  by  a  lead  covering  burnt  on  each  side  to  the 
chamber-lead.  These  horizontal  rods  themselves  are  suspended  from 
the  roofing  by  means  of  J-inch  rods  placed  at  short  distances  from 
each  other.  This  system  cannot  be  employed  for  chambers  standing 
in  the  open  air,  as  it  makes  the  chamber-top  dependent  upon  the 
beams  of  the  roof ;  it  is  shown  in  fif;.  IGJ-. 

Another  system,  which  may  or  may  not  be  connected  with  the 
roofing,  is  the  following  (fig.  165): — The  chamber-side  a  is  carried 


CHAMBER-TOP  AND  -BOTTOM.  445 

somewhat  higher  up,  aud  bends  round  an  iron  rod,  b,  |  inch  thickj 
the  part  coming  back  over  the  iron  being  burnt  to  the  other  lead. 
Here  and  there  holes  are  left  for  the  passage  of  the  iron  hooks,  c, 
which  are  bolted  to  BtroDg  joists,  d.  The  latter  may  form  part  of  the 
roof,  or  they  may  be  supported  quite  independently  on  the  crown- 
tree  e.    The  straps  //  hold  up  the  cliamber-top  (/,  aud  prevent  it 


from  sagging  ;  the  clear  space  between  g  and  d  is  about  8  inches. 
The  object  of  this  arrangement  is  to  prevent  all  contact  between 
lead  and  wood  even  at  the  top  edges  of  the  chambers. 

At  the  Grieeheim  works,  in  Germany,  the  following  very  rational 
plan  of  erecting  lead  chambers  is  followed : — On  a  staging  of  the 
whole  area  of  the  chamber-bottom,  but  raised  over  its  top,  first  the 
chamber-ends  are  made;  over  these,  without  removing  the  ends, 
the  chamber-sides  are  made,  firat  one,  then  the  other,  and  last  of 
all  the  sheets  composing  the  top  are  laid  down  and  burnt  together. 
Thus  ultimately  five  layers  of  lead  are  lying  on  the  staging  one 
above  auotlier.  Then  the  top  straps  are  burnt  on  and  are  joined 
to  the  top  joists,  which  are  put  in  their  respective  places.  The 
whole  lead-work  is  now  hung  from  sis  differential  pulleys,  and  the 
staging  is  removed.  As  this  is  done,  tlie  ends  and  sides  drop  down 
into  their  places,  and  need  only  be  joined  iu  the  corners,  where 
they  are  bent  in  at  an  obtuse  angle.  This  mode  of  procedure 
causes  nearly  all  the  burning  to  be  horizontal,  so  that  the  work  is 
done  more  quickly,  cheaply,  and  substantially. 

The  chamber-bottom  is  left  to  the  last ;  and  it  happens  no  doubt 
very  rarely  (in  England  probably  never)  that,  according  to  older 
prescriptions,  the  bottom  is  laid  down  first  aud  protected  by  straw 
and  boards  while  the  remainder  of  the  chamber  is  being  made. 


416  coNsinircTioN  op  the  lead  ci 

It  is,  on  the  coutrary,  made  last  of  all,  but  not  always  in  the  same 
way.  Id  some  works  the  side  sheets  are  burned  to  it  all  round, 
and  openings  are  left  iu  a  few  places  for  drawing  off  the  acid,  for 
taking  sample.",  &c.  In  the  majority  of  works  the  bottom  is 
independent  of  the  sides,  and  forms  an  enormous  tank  with  turned- 
up  sides,  into  which  the  chamber-sides  bang  down,  dipping  into  the 
bottom-acid,  and  thus  forming  u  hydraulic  joint.     This  allows  the 

Fig.  166. 


chamber-sides  to  expand  and  contract  with  the  temperature,  and 
also  makes  the  bottom-acid  accessible  from  all  sides,  so  that  it  is 
generally  preferred  in  spite  of  the  larger  expenditure  of  lead  ;  but 
recently  a  good  many  works  have  adopted  tlie  first-mentioned  plan 
of  making  the  chamber  as  a  closed  box,  which  saves  both  lead  and 
the  trouble  unavoidably  connected  with  the  second  system.  Often 
the  upstand,  or  "lag,"  which  should  not  be  less  than  14  inches 


CHAMBER-BOTTOM. 


447 


high,  so  as  to  afford  a  good  deal  of  room  for  acid^  is  made  from  a 
narrow  sheet  of  lead  of  douhle  width,  by  bending  up  one  half  and 
leaving  the  other  half  to  form  a  portion  of  the  chamber-bottom  ; 
the  latter  is  then  finished  by  burning  it  together  with  other  sheets^ 
of  lead.  This  is  more  convenient  for  the  plumber  than  taking 
sheets  equal  in  length  to  the  width  of  the  chamber^  along  with 
the  height  of  the  upstand  on  each  side.  The  latter  must  not  be 
left  loose,  because  it  is  easily  bagged  out  by  the  side  pressure  of 
the  acid ;  but  a  1-inch  board  is  placed  all  round  the  chamber- 
floor,  over  the  edge  of  which  the  upstand  is  turned  round  and 
nailed  down.  This  is  shown  in  fig.  166.  Instead  of  a  solid  board, 
it  is  preferable  to  employ  merely  a  number  of  perpendicular  or 
horizontal  rails,  which  admit  the  cooling-action  of  the  air  upon 
the  lead.  At  Stolberg  the  ^'  lag  ^'  is  made  up  to  2  ft.  6  in.  high, 
wdth  a  correspondingly  strong  plank  to  resist  the  side  pressure  of 
the  acid. 

Fig.  167. 

UUUUUUUUUUUUUULILJUUUUUUUUDnL? 


In  some  works  the  bottom  is  divided  into  two,  three,  or  four 
parts  by  partitions  the  whole  height  of  the  upstand.  The  object 
of  this  is,  not  to  empty  the  whole  chamber  in  case  of  repairs ; 
but  it  is  very  rarely  done,  as  this  arrangement  prevents  a  free 
circulation  of  the  acid,  and  as  the  bottom  mostly  suffers  less  than 
any  other  part  of  the  chamber — excepting  through  gross  neglect, 
by  the  formation  of  nitric  acid,  which  ought  not  to  happen  at  all. 


448  CONSTRUCTION  OV  THE  LEAD  CHAMBERS. 

Palding  (Min.  Ind.  vii.  p.  679  et  seq.)  gives  details  of  chamber 
construction  which  refer  to  the  usual  English  plau^  mostly  followed 
in  America  as  well.  Fig.  167  shows  part  of  the  chamber-side 
in  elevation.  The  pillars  (posts)  a  a  are  of  14  x  14  inches  wood  ; 
corbels  bb  14x14x5  in.;  stringers  c  14x14  in.;  joists  d 
3x15  in.,  16  in.  centre  to  centre,  3  x  2  in.  herringbone-strutting; 
gangway-floor  e  with  2  x  12  in.  joists.  Of  the  chamber-Arame 
itself,  the  sill  /is  6  x  10  in.,  with  a  dowel-pin  at  each  post  and 
toe-nail  to  each  intermediate  upright.  The  strong  uprights  (posts) 
^y  6x6  in.,  13  ft.  9  in.  from  centre  to  centre;  the  intermediates 
hh  6x2  in.,  33  in.  centres;  the  bracing  ii  6x2  in.,  with 
lag-screw  to  each  post  and  spike  to  each  intermediate.  Crown- 
tree  k  6  X  10  in.,  with  lag-screw  at  each  post  and  toe-nail  to  each 
intermediate  upright.  Top  joists  II  3x15  in.,  14  in.  centres, 
with  three  lines  of  solid  2x12  in.  board- bridging. 

Fig.  168  represents  a  portion  of  chamber-ceiling,  seen  from 
above,  and  fig.  169  the  same  in  sectional  elevation  on  a  larger 
scale,  which  clearly  shows  how  the  chamber-lead  m  at  the  top  ib 
joined  to  the  sides  n  and  turned  over  the  crown  k,  and  how  the 
straps  0  0  (24  inches  centre)  suspend  the  top  from  joists  /  /. 
Fig.  170  makes  this  clearer  by  a  side  elevation,  and  fig.  171  shows 
the  way  the  straps  are  cut  from  a  strip  of  rolled  lead. 

Fig.  172  gives  a  plan-section  of  a  chamber-corner,  and  fig.  173 
a  sectional  elevation  of  the  lower  part  of  a  chamber,  showing  how 
the  straps  r  r  are  fastened  to  the  uprights  g,  hy  and  how  the  lead 
side  m  and  the  saucer  p  stand  off.  Lastly,  fig.  174  shows  how  the 
upstand  p  of  the  saucer  is  turned  over  ledge  *  (2  X  1  in.),  and  held 
at  the  bottom  by  another  strip  /  (3x2  in.),  spoked  to  the  sill. 

In  England,  where  the  winters  are  not  severe,  lead-chambers 
are  hardly  ever  roofed  in,  but  are  only  built  so  that  the  rain-water 
can  run  off  as  described  above.  But  even  then  the  space  between 
each  two  chambers  must  be  covered  by  a  light  roof,  and  the  whole 
set  must  be  surrounded  by  a  wooden  shed,  because  a  gale  might 
tear  the  lead  off  the  frames,  or  even  throw  down  a  chamber 
altogether.  These  wooden  houses  have  windows  or  Venetian 
blinds,  changed  according  to  the  wind.  In  windy  places  they  are 
always  made  first,  as  soon  as  the  foundations  and  the  frame  are 
finished,  but  before  the  lead  has  been  fastened  to  the  latter, 
because  during  the  building  the  incomplete  chamber  is  even  more 
exposed  to  being  thrown  down  by  a  gale  than  after  completion. 


EMGLISH  CHAUBEB-PLANT. 

rig.  IGrt. 


D 


mr^v 


[Ly^^J- 


M 


g  Pig.  i;o. 


450  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

Thus  the  chamber-tops  are  exposed  in  England  to  the  heat  of 
the  sun  in  summer  and  to  the  snow  in  winter  ;  this  is  tolerable, 
because  neither  of  them  occurs  to  an  excessive  d^ree.  In  the 
less  windy  places  even  the  chamber-sides  are  sometimes  left  without 
protection  against  the  weather,  but  never  so  in  well-arranged  works. 
In  the  south  of  France,  on  the  other  hand,  the  chamber-tops  are 
always  protected  against  the  sun  and  the  rain  by  a  roof;  but  the 
sides  are  generally  exposed,  which,  on  account  of  the  heat  of  the 
sun  there,  is  certainly  very  wrong.  In  the  north  of  France,  in 
Belgium,  and  in  Germany  the  chambers  are  always  completely 
enclosed  in  buildings^  usually  of  a  very  light  construction,  and  it 
must  be  said  that  this  would  be  decidedly  preferable  also  in  the 
English  climate. 

Niedenfiihr  recommends  placing  the  chambers  on  brick  pillars, 
and  filling  up  the  spaces  between  these  on  the  outside  with  a  light 
wall.  The  chamber-sides  are  surrounded  by  a  wooden  shed  and  a 
light  roof,  employing  roofing- felt  as  a  cover  for  this.  He  reckons 
a  square  foot  of  such  a  building,  including  the  chamber-frame,  to 
cost  from  3*.  to  4*.  6d. 

Renewal  of  the  Chambers. — ^The  greatest  wear  and  tear  is 
experienced  in  the  first  chamber,  more  especially  at  the  front  end, 
and,  as  some  assert,  even  more  so  at  the  back  end  and  the 
immediately  adjoining  parts  of  the  sides.  Hence  the  first  (leading) 
chamber  is  often  made  of  stronger  lead  than  the  others.  Besides, 
it  must  be  noticed  that  any  angular  parts  of  a  chamber  wear  out 
more  quickly  than  round  or  straight  portions.  The  upright 
corners  are  therefore  always  broken  or  rounded  off ;  but  this  is 
not  easily  managed  with  the  horizontal  top  corner.  Hence,  at 
some  w^orks  they  make  the  lead  stronger  in  that  place  (p.  431). 
The  plan  of  making  the  roof  partly  slanting  (p.  454)  may  do 
some  good  in  this  respect  as  well,  as  this  avoids  a  sharp  corner. 
The  "curtain,^^  or  part  dipping  in  the  acid,  and  alternately 
subjected  to  this  and  to  the  action  of  the  air,  is  also  liable  to 
quicker  wear.  There  is  general  agreement  on  the  point  that  any 
part  of  a  chamber  which  gets  hotter  than  the  remainder  will  wear 
out  much  more  quickly ;  and  this  should  be  guarded  against  in  the 
construction  of  the  chamber-frame  {supra,  pp.  438,  441,  &  453). 

We  have  constantly  laid  stress  on  the  fact  that  the  lead  should 
be  clear  of  the  woodwork  at  all  points,  both  because  it  is  thus 
longer  preserved  by  the  cooling-action  of  the  air,  and  because  it 


RENEWAL  OF  CHAMBERS.  451 

is  accessible  to  the  plumber.  But  this  condition  can^  of  course^ 
be  realized  only^  for  the  sides  and  top^  not  for  the  bottom. 
Fortuimtely  the  latter  suffers  leasts  being  protected  by  the  acid 
itself  and  by  a  layer  of  sulphate  of  lead.  If,  however,  a  leak 
occurs  here  after  all,  it  is  very  awkward  to  repair.  Sometimes 
this  can  be  done  by  measuring  its  distance  from  the  sides,  cutting 
a  hole  in  the  chamber-top  and  dropping  down  a  bucketful  of 
plaster  of  Paris  or,  preferably,  of  a  mixture  of  fresh  and  burnt 
pyrites-dust,  which  quickly  hardens  into  a  cake  and  may  stop  the 
leak  for  years.  But  if  this  does  not  succeed,  there  is  nothing 
left  but  to  stop  and  empty  the  chamber^  and  to  enter  through  the 
manhole  in  order  to  get  at  the  bottom. 

A  chamber  will  last  very  much  longer  if  the  frame  be  substan- 
tially made,  and  the  straps  be  well  burnt  on  and  nailed  down  and 
numerous  enough,  so  that  they  will  not  be  readily  torn  off.  Should 
this  happen,  the  mischief  must  be  repaired  at  once :  nowhere  does 
the  saying  come  more  true  ^'that  a  stitch  in  time  saves  nine.'' 
If  the  repair  is  put  off  too  long,  the  chamber-lead,  pulled  by  its 
own  weight,  wrinkles  irregularly,  and  the  chamber  becomes  unfit 
for  work  much  too  soon.  Especially  those  parts  of  the  frame 
most  exposed  to  the  action  of  the  acid  must  be  carefully  looked 
after,  and,  in  case  of  need,  at  once  repaired,  before  the  parts  of 
the  lead  sides  dependent  upon  them  have  lost  their  support  and 
have  collapsed.  This  is  most  necessary  at  the  junctions  of  con- 
necting-pipes, at  the  places  where  the  acid  is  siphoned  off,  &c. 
The  wind  must  also  be  kept  off,  and  any  loose  pieces  in  the  brat- 
ticing  round  and  between  the  chambers  promptly  put  right;  a 
gale  of  wind  may  tear  off  the  straps  of  a  whole  chamber-side  at 
once  or  force  the  frame  to  one  side.  The  gangway  round  the 
chambers  ought  to  be  wide  enough  (say  5  feet)  to  admit  of  easy 
control  and  repair. 

It  used  to  be  reckoned  that  with  6  lbs.  lead  in  normal  circum- 
stances a  chamber  would  generally  last  from  eight  to  ten  years,  but 
with  many  repairs  during  the  latter  years.  But  since  the  art  of 
building,  and  more  particularly  of  managinff,  vitriol-chambers  has 
become  better  understood,  they  have  been  made  to  continue  much 
longer  in  use.  On  the  Continent,  where  they  are  not  (or  formerly 
were  not)  so  much  strained  as  is  frequently  the  case  in  England, 
vitriol-chambers  generally  last  much  longer  than  the  above  term, 
viz.,  30  or  even  30  years ;  but  even  in  England  this  is  found  to 

2q2 


452  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

be  the  case  at  some  works  where  the  chambers  are  built  with  more 
regard  to  durability  than  to  economy  in  first  cost. 

There  is  no  doubt  whatever  that^  all  other  things  being  eqiial^ 
a  chamber  lasts  longer  in  proportion  as  it  is  less  heated ;  it  is 
not  so  much  the  heat  itself^  but  the  intensity  of  the  chemical 
reactions  going  on  within  the  chambers  which  produces  the  heat, 
and  moreover  the  increase  of  the  action  of  all  chemicals  by  the 
elevation  of  temperature  brings  about  the  same  result.  It  is 
only  another  way  of  stating  this  fact^  if  we  say  that  a  chamber 
lasts  all  the  less  time  the  more  nitre  is  sent  into  it  and  the  more 
acid  is  made  in  it. 

In  the  case  of  chambers  without  a  roof  the  top  generally  wears 
out  firsts  then  the  parts  dipping  into  the  bottom-acid  and  the 
ends ;  the  bottom  remains  good  up  to  the  last^  unless  nitric  acid 
gets  to  it,  which  most  easily  happens  in  the  last  chamber,  if  its 
strength  is  allowed  to  run  down  too  much. 

When  a  chamber  requires  so  much  repairing  aud  patching  that 
it  does  not  seem  likely  to  pay,  and  when,  after  all,  the  escape  of 
the  gas  from  the  too  numerous  chinks  and  rents  can  no  longer  be 
kept  down,  it  is  very  bad  economy  not  to  pull  it  down  at  once ;  for 
the  yield  of  acid  must  fall  off  very  much.     In  this  case  a  temporary 
connexion  is  made  between  the  two  apparatus  on  either  side  of  it, 
the  acid  contained  in  the  chamber  is  worked  down  as  long  as  it 
will  run,  a  hole  is  cut  into  its  side,  and  men  provided  with  india- 
rubber  boots  are  sent  in  to  shovel  up  the  mud  lying  at  the  bottom 
into  a  heap,  from  which  a  good  deal  of  acid  is  still  obtained  by 
draining.     The  mud  must  now  be  removed ;  if  the  space  under- 
neath is  free,  a   receptacle   is   formed  by  low  banks  of  clay,  a 
hole  is  cut  in  the  chamber-bottom,  and  the  mud  pushed  down. 
If  this  is  not  possible,  it  must  be  removed  in  a  much   more 
troublesome  manner,  by  thickening  it  with  sawdust  and  washing 
with  water.     In  either  case  it  is  dried  in  a  reverberatory  furnace, 
sometimes  with  the  addition  of  a  little  lime  in  order  to  prevent 
the  escape  of  acid  vapours.     Notwithstanding  this,  the  operation 
usually   causes  a  very   disagreeable   stench,  probably  owing  to 
arsenic,  selenium,  &c.     The  dried  mud,  principally  consisting  of 
lead  sulphate,  is  either  smelted  for  lead  in  a  small  cupola  heated 
by  coke,  or  simply  sold  to  the  lead-workers. 

After  taking  out  the  lead-mud,  the  chamber-lead  is  detached 
from  the  frame,  and  the  good  whole  pieces  rolled  up  for  use  as 
sheet-lead  ;  the  others  are  melted  in  an  iron  pan^  the  dross  is 


RENEWAL  OF  CHAMBERS.  453 

scummed  off^  and  the  lead  cast  in  the  usual  pig -moulds;  at  the 
lead-rolling  mills  this  lead  is  much  liked  for  other  chemical 
purposes  (see  p.  431).  Including  the  pig-lead,  the  dross,  and  the 
lead  sulphate,  usually  nine  tenths  or  upwards  of  the  original  weight 
of  the  chamber  is  recovered ;  the  remainder  has  disappeared  in 
one  shape  or  another  \rith  the  acid  made. 

If  the  frame  has  been  substantially  made,  it  stands  a  second, 
sometimes  a  third  lead  chamber,  with  a  few  repairs,  putting  in  odd 
beams  &c.  Of  course,  in  case  of  any  doubt,  it  would  be  extremely 
bad  economy  to  run  the  risk  of  having  to  stop  a  chamber  because 
its  frame  would  not  hold  out  as  long  as  the  lead. 

Mr.  G.  E.  Davis  has  sent  me  the  following  observations: — 
A  set  of  three  chambers  (20  x  18  x  120  feet)  had  been  at  work  at 
high  pressure  for  seven  years,  when  the  first  two  chambers  were 
pulled  down.  They  were  built  of  7  lbs.  lead  ;  at  the  end  of  the 
time  the  top  was  still  between  5  and  6  lbs.,  the  bottom  between 
2  and  3  lbs.,  the  sides  were  almost  nil.  In  the  first  chamber 
sulphate  of  lead  equal  to  19  tons  metallic  lead  was  found,  in  the 
second  16  tons  metallic  lead.  The  chamber-top  had  not  been 
repaired  all  this  time,  the  sides  had  had  new  lead  all  round,  and 
the  bottom  had  been  repaired  in  places. 

Special  observations  on  the  wear  and  tear  of  lead  chambers  have 
also  been  made  by  Burgemeister  (Chem.  Zeit.  1889,  p.  1633) .  A  set 
of  two  chambers  was  observed  after  23J  years,  during  which  time 
the  larger  chamber  had  been  at  work  with  brimstone  for  32  months, 
with  pyrites  (first  Westphalian,  then  Rio  Tinto)  for  178  months, 
idle  for  75  months.  The  thickness  of  the  lead  was  originally 
2*57  mm.,  at  the  end  of  the  period  on  an  average  only  1*88,  that 
is  a  loss  of  0*69  mm.  or  26*8  per  cent.  The  part  dipping  into  the 
bottom-acid  was  most  worn ;  next  the  places  where  the  lead  was 
double  or  where  it  was  protected  against  cooling  by  the  wooden 
frame.  For  this  reason  it  is  best  to  burn  the  joints  outside,  because 
the  inner  part  of  the  lap-joint  is  then  eaten  away  first  without 
injuring  the  joint ;  if  the  joint  is  burned  inside,  the  lap  is  loose 
on  the  outside,  and  as  soon  as  the  inner  part  is  eaten  away  the 
chamber  must  leak.  The  bottom  of  the  chamber,  which  is  pro- 
tected by  the  acid,  suffers  least.  A  small  chamber  which  was 
placed  between  the  Glover  tower  and  the  large  chamber,  and  which 
was  kept  at  a  higher  temperature  (from  65°  to  90P  C),  had  lost  in 
120  working  months  as  much  as  17*65  per  cent,  of  the  thickness 
of  lead. 


■W*  CON8IEOCTIOX  OP  THE  LEAD  CHAMBERS. 

Shape  of  Lead  Chancers. 

Tlie  sAape  of  the  chaiDbers  is  nearly  always  that  of  a  long  bos 
of  square  or  approximately  square  transverse  section.  At  some 
places,  in  order  to  save  lead,  the  chambers  have  been  made  up  to 
60  feet  wide;  but  this  is  not  to  be  recommeoded  on  any  account. 
It  causes  difScuIties  in  coustmcting  the  wood  frame,  and,  what  is 
more  serious,  the  yield  of  acid  in  such  large  chambers  is  not  so  good 
as  in  those  of  ordinary  shape,  say  between  20  and  30  feet  wide. 
This  is  easily  understood,  as  in  such  very  large  sections  the  gases 
do  not  get  properly  mised,  and  there  are  too  few  surfaces  offered 
for  contact  and  cooling  (comp.  Chap,  VII,), 

For  the  purpose  of  saving  lead,  the  chambers  belonging  to  the 
different  works  of  the  Rhenania  Chemical  Company  are  constructed 
in  the  way  illustrated  in  fig.  176 — that  is,  with  the  top  comers  cut 

Fig.  176. 


off,  to  suit  the  slope  of  the  roof.  This  admits  of  putting  the 
largest  possible  height  of  chamber  into  a  roofed  building;  and 
Mr.  Hasenclever  also  contends  that  the  "  dead  corners  "  of  square- 
sectioned  chambers  are  thereby  avoided.     There  is  also  less  wear 


SHAPE  OF  LEAD  CHAMBERS.  455 

and  tear  than  in  the  sharp  corners  of  chambers  of  the  ordinary 
square  section  (comp.  p.  450), 

The  usual  width  of  vitriol- chambers  is  rarely  below  20  or  above 
30  feet ;  their  height  varies  from  16  to  25  feet,  or  exceptionally  a 
few  feet  more.  Their  length  (always  speaking  of  the  principal 
•chambers,  not  of  the  small  chambers  or  ''  tambours  "  arranged 
before  and  behind  these  in  the  French  system)  is  rarely  below 
100  feet,  but  may  attain  200  or  even  300  feet. 

H.  A  Smith,  in  a  pamphlet  on  the  Chemistry  of  Sulphuric-acid 
Manufacture  (1873),  endeavoured  to  prove  that  the  upper  space  of 
the  vitriol-chambers  did  no  work  at  all,  and  that  chambers  of  3,  6, 
or  at  most  8  feet  in  height  would  be  most  suitable.  His  experi- 
ments (described  and  refuted  in  detail  in  our  first  edition,  p.  285 
et  seq,)  were  decidedly  inconclusive,  and  a  practical  test  of  his 
theory  at  the  Oker  works  led  to  its  entire  rejection. 

E.  and  T.  Deplace  (E.  P.  5058,  1890)  describe  an  annular 
chamber,  in  which  the  gaseous  current  is  continually  changing 
its  direction,  owing  to  that  shape.  Siphon-shaped  tubes  placed 
on  each  side  of  the  chamber  produce  a  circulation  and  mixture  of 
the  gases.  These  chambers  occupy  less  space  than  the  usual  form, 
and  are  stated  to  produce  up  to  6  kils.  acid  of  52°B.  (=3*7  kils. 
H2SO1)  per  cubic  metre  =  1  lb.  sulphur  to  13*2  cub,  feet  per 
24  hours.  A  few  sets  of  this  kind  have  been  erected  in  France 
and  England.  According  to  the  28th  Alkali  Report,  p.  55,  the 
shape  of  chamber  actually  built  differs  a  good  deal  from  that 
described  in  the  patent.  According  to  information  received  from 
manufacturers,  the  production  from  these  chambers  per  cubic  foot 
does  not  exceed  those  of  ordinary  chambers. 

Th.  Meyer's  ''tangential  chambers''  (E.  P.  18,376,  1898) 
are  also  devised  as  a  means  for  inducing  a  better  mixture  of 
the  chamber-gases.  The  chambers  should  have  a  circular  or 
polygonal  section,  and  the  gas  inlet-pipes  be  placed  tangentially 
on  the  upper  part  of  their  sides,  the  outlet-pipes  in  the  centre  of 
the  bottom  ^,  This  imparts  a  spiral  motion  to  the  gases,  rapid  at 
the  circumference,  slower  towards  the  centre,  and  thus  causes 
them  to  travel  through  a  greater  distance  and  to  get  much  better 
mixed  than  in  ordinary  chambers.    The  inventor  gives  more  details 

*  The  patent  specification  speaks  of  the  centre  of  tlie  ceiling j  but  in  practice 
ihe  gas-exit  is  from  the  centre  of  the  chamber-6o^^om. 


456  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

concerning  his  system  in  Chem.  Zeit.  1899,  p.  296 ;  Zsch.  augew. 
Ch.  1899,  p.  656,  and  ibid.  1900,  p.  739.  His  system  has  been 
carried  out  at  the  Norddeutsche  Chemische  Fabrik,  Harburg,  and 
at  the  Chemische  Dungerfabrik,  Rendsburg.  The  chambers  are  10 
metres  in  diameter  and  8  metres  high,  in  a  set  of  three,  with  Glover 
and  Gay-Lussac  towers.  The  draught  is  very  good,  the  yield  from 
92-5  to  95-2  of  the  theory  (291  H2SO4  per  100  S  burned) ;  per 
cubic  metre  the  production  is  from  366  to  3*87  kils.  H2SO4, 
with  a  consumption  of  1*34  to  1-44  nitric  acid  36°  B.  (  =  1*0  to  1*07 
nitrate  of  soda)  for  100  H2SO4,  or,  say  3  NaNO»  to  100  S  burned. 

[This  production  is  good,  but  still  inferior,  not  merely  to  French 
*'  forced  work  '^  with  ordinary  chambers,  but  also  to  that  of  some 
of  the  German  works,  comp.  p.  468.] 

Recently  (Zsch.  ang.  Ch.  1900,  p.  742)  Meyer  has  improved  his 
chambers  by  arranging  in  the  first  (and  hottest)  chamber  a  cooling 
system,  consisting  of  43  lead  pipes,  2  to  2^  inches  wide,  suspended 
in  water-lutes  from  the  chamber-top  all  round  the  circumference 
and  reaching  8  to  10  feet  down  into  the  chamber.  They  are 
closed  at  both  ends ;  through  their  tops  enter  thin  lead  pipes, 
reaching  nearly  to  the  bottom  of  the  larger  pipes,  for  introducing 
the  cooling- water,  as  shown  in  fig.  177.  The  whole  offers  a 
cooling-surface  of  23  square  metres  (  =  250 square  feet),  i.  c.  7  per 
cent,  of  the  heat-radiating  surface  of  the  chamber  sides  and  ceiliog. 
The  water,  of  which  8^  tons  is  used  per  day,  issues  at  a  temperature 
of  67°  C.  The  heat  evolved  by  the  process  of  converting  SO*, 
O,  and  H2O  into  H2SO4,  as  far  as  it  goes  on  in  that  chamber,  is 
calculated  =2^  millions  metrical  heat-units  per  24  hours,  of  which 
500,000  are  removed  by  the  cooling-water  =20  per  cent.  This 
is  not  shown  by  the  chamber  thermometers,  as  the  loss  of  heat  is 
made  up  by  that  newly  generated  by  the  chemical  process,  and  it 
is  manifested  by  the  increased  production  of  sulphuric  acid 
(according  to  the  theories  of  Lunge  and  Sorel,  comp.  later  on). 
The  pipes  last  a  long  time  and  can  be  immediately  renewed  by 
taking  them  out  of  the  hydraulic  seals.  The  hot  water  is  used  for 
feeding  the  steam  boilers. 

I  have  shown  in  Zsch.  f.  angew.  Ch.  1902,  pp.  151  et  seq.,  that 
the  advantages  to  be  realized  by  Meyer's  proposals  by  his  own 
showing  are  not  very  considerable.  It  is  very  doubtful  whether 
for  equal  weights  of  lead  his  tangential  chambers  produce  any 
more  than  even  moderately  well-managed  ordinary  chambers. 


MEVER  a  TAKGENTIAL  CHAMBERS. 


Ill  another  paper  (Zsch.  augew.  Chem.  1901,  p.  1245),  Meyer 
acknowledges  the  "  Lunge  towers  "  as  the  best  solution  of  the 
problem  of  bringing  the  misty  particles  floating  in  the  chamber  to 

Fig.  177. 


act  upon  each  other,  and  he  advises  to  combine  such  intermediate 
towers  with  his  "  tangential  "  chambers. 

I  am  informed  that  in  1903  seiious  attempts  had  been-made  to 
introduce  circular  chambers  into  England,  but  after  inquiry 
and  consideration  this  plan  was  given  up. 


458  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

Combination  of  chambers  to  sets. — Sometimes  the  whole  working- 
space  is  contained  in  one  chamber.  Scheurer-Kestner  (Wurtz, 
Diet.  iii.  p.  147)  mentions  a  single  chamber  of  142,000  cubic  feet 
<;apacity,  and  quotes  the  experience  of  different  works,  according 
to  which  it  is  quite  unnecessary  to  divide  the  set  into  several 
chambers.  More  frequently,  however,  several  chambers  are  com- 
bined to  form  a  set,  which,  to  begin  with,  affords  this  advantage 
—that  for  repairs  it  is  not  necessary  to  stop  the  whole  set. 

A  great  diversity  of  opinion  exists  as  to  how  the  single  chambers 
are  to  be  combined  to  form  sets.  Among  the  hundreds  of 
vitriol. works  very  few  will  be  exactly  alike  in  this  respect ;  and 
frequently  even  in  the  same  works  different  combinations  are 
found.  We  may,  however,  consider  it  as  established  that  it  is 
almost  indifferent  in  which  way  the  chambers  are  combined,  if  they 
are,  in  the  first  instance,  properly  built  (that  is,  not  too  high  or 
wide),  and  if,  secondly,  they  possess  a  certain  cubical  capacity  for 
the  quantity  of  sulphur  or  pyrites  to  be  consumed.  Within  these 
limits  those  combinations  are  best  which  require  least  lead^  and 
which  are  laid  out  so  as  to  afford  the  greatest  facility  for  super- 
vision. Of  course  there  is  also  an  extreme  limit  to  the  capacity 
of  the  whole  set ;  but  opinions  differ  upon  this  point  also.  At  some 
works  a  set  consists  of  nine  or  eleven  chambers  of  35,000  cubic 
feet  each;  at  others,  equally  large,  it  is  limited  to  three  chambers 
of  42,500  cubic  feet  each,  &c.  Thus  at  Hebburn-on-Tyne  several 
sets  of  three  chambers  each  are  employed,  each  chamber  20  feet 
wide,  125  feet  long,  17  feet  high  on  one  side,  18  feet  on  the  other; 
each  set  serves  for  18  burners,  burning  7  cwt.  daily.  At  Gates- 
head there  are  several  sets  of  three  large  chambers^  each  so 
arranged  that  two  of  them  communicate  separately  with  a  set  of 
kilns  (''working-chambers'^),  and  both  of  them  are  connected 
with  the  third  chamber ;  the  whole  set  has  a  capacity  of  about 
200,000  cubic  feet.  More  usually  the  gas  passes  through  all  three 
chambers  in  succession.  Very  often  four  chambers  are  combined, 
each  of  them  about  20  x  20  x  130  feet, — or  five  chambers,  two  of 

them  working-chambers,  thus,   ^     4/^9 — o'  even  six  chambers. 

In  America  (Zsch.  f.  angew.  Cliem.  1894,  p.  133)  I  found  at 
one  place  a  set  of  twelve  chambera  of  equal  size,  each  24  feet 


SETS  OF  CHAMBERS.  459 

long,  which,  it  was  asserted,  combined  very  good  yield  with  small 
oonsuroption  of  nitre.  At  another  place  they  had  three  chambers, 
60,  50,  and  40  feet  in  length,  with  plate-columns  between. 

The  chamber-set  described  by  Hasenclever  (Chem.  Ind.  1899, 
p.  26)  consists  of  two  very  large  and  two  small  back  chambers 
of  a  total  capacity  of  7250  cub.  met.  =267,C00  cub.  feet.  He 
mentions  the  existence  of  sets  comprising  12,000  cub.  met. 
=420,000  cub.  feet,  which  form  decidedly  a  very  undesirable 
exception. 

At  one  of  the  most  modern  German  works  I  found  sets  con- 
sisting of  three  chambers,  all  of  them  10  metres  wide  and  7  metres 
high ;  the  first  had  a  length  of  41,  the  second  of  31,  the  third  of 
10  metres.  They  produce  2*8  kils.  H2SO4  per  cub.  metre  (equal 
to  about  18  cub.  feet  chamber-space  per  lb.  of  sulphur  burnt  in 
24  hours). 

The  Rhenania  Chemical  Co.  prefers  throughout  sets  of  two 
equally  large  chambers,  followed  by  two  small  back  chambers 
(1902). 

In  France  it  is  usual  to  combine  three  chambers  in  a  set, 
exceptionally  four  or  five.  The  total  capacity  of  a  set  hardly  ever 
exceeds  6000  cub.  metres  (=210,000  cub.  feet). 

According  to  Mon.  Scient.  1900,  p.  563,  Benker  has  for  a 
number  of  years  built  chambers  (in  France)  on  the  following 
plan : — Besides  the  Glover  tower  he  employs  a  dry  filtering  chamber 
in  order  to  retain  flue-dust  and  arsenic.  His  chambers  are  three 
in  number,  of  a  total  capacity  of  only  2000  to  3000  cub.  met. 
(70,000  to  105,000  cub.  feet).  Into  the  last  of  these  he  introduces 
SO2  (burner-gas) ;  then  comes  a  small  intermediate  chamber  and 
then  two  Gay-Lussac  towers.  The  draught  is  produced  by  a  fan- 
blast.  Benker  claims  to  produce  6  to  7  kils.  acid  of  52°  B. 
(  =  3'7  to  4*3  kils.  H2SO4)  per  cubic  metre  (  =  1  lb.  sulphur  burnt 
upon  13*2  to  11*3  cubic  feet !),  with  a  consumption  of  0*8  to  I'O 
nitric  acid  36°  B.  per  100  acid  of  52°  (  =  3  to  37  lbs.  NaNO^  per 
100  S  burned).  The  chambers  are  fed  with  a  water-spray  in  lieu 
of  steam  (vide  infra),  and  he  always  injects  some  SOj  (burner-gas) 
into  the  last  chamber  (G.  P.  88,368  &  91,260 ;  comp.  later  on). 

Benker,  according  to  direct  communications  received  from  him 
in  1902,  employs  only  narrow  chambers,  say  18  to  20  feet 
wide,  and  from  25  to  33  feet  high.  Such  chambers  are,  in  the 
first  instance,  better  adapted  for  water-spraying,  but  they  also 


460  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

afford  a  better  mixture  of  the  gases,  especiallj  if  the  sides  are 
cooled,  by  employing  an  open,  bratticing  for  the  side  passages 
(2^  in.  laths  with  1^  in.  clear  spaces)  and  a  roof -rider.  The 
cold  gases  descending  along  the  sides  must  rise  again  iu  the 
centre  ;  but  in  the  case  of  very  wide  chambers  a  dead  space 
remains  where  the  velocity  is  very  slight,  and  where  the  mist  of 
nitrous  vitriol  sinks  down  without  acting  on  the  gaseous  con- 
stituents. This  cannot  produce  '^high-pressure  work''  (comp. 
later  on).  Benker  objects  to  Meyei-^s  tangential  chambers  that 
there  is  no  question  of  tangential  action,  that  in  the  centre  of 
these  circular  chambers  gases  of  very  different  concentrations  get 
mixed  up,  and  that  they  would  be  too  expensive  if  the  only 
proper  way  was  followed,  viz.  building  many  small  circular 
chambers  in  a  set.  We  shall  later  on,  when  describing  the 
system  of  water-spraying,  give  a  complete  diagram  of  Benker's 
chambers. 

The  size  of  the  chambers  varies  very  much.  Apart  from  the 
''  tambours "  of  the  French  system^  the  proper  chambers  are 
made  with  as  little  as  10,000  and  as  much  as  110,000  cubic  feet 
capacity.  Such  small  chambers  are  no  longer  built  as  main 
chambers ;  the  usual  capacity  of  these  may  now  be  taken  as 
ranging  from  25,000  to  70,000  cubic  feet,  more  frequently  nearer 
the  upper  than  the  lower  limit.  Smaller  chambers  cost  ranch 
more,  comparatively,  than  large  ones,  and  it  is  doubtful  whether 
they  afford  any  corresponding  advantages. 

The  different  chambers  of  a  set  are  either  placed  on  the  same 
level,  or,  more  suitably,  each  following  chamber  is  placed  1  or  2 
or,  better,  3  inches  higher  than  the  preceding  one,  so  that  the 
acid  of  the  back  chambers  can  be  run  more  easily  into  the  working- 
chamber.  In  the  first  chamber  the  acid  is  both  strongest  and 
most  free  from  nitre ;  and  it  is  therefore  preferable  to  draw  off  any 
acid  from  this,  whether  it  be  for  sale,  for  use,  or  for  concentration. 
The  acid  drawn  off  is  replaced  partly  by  that  newly  formed  in  the 
same  chamber,  partly  by  the  weaker  acid  run  over  from  the  other 
chamber.  If  there  is  only  one  long  chamber,  the  acid  is  always 
found  strongest  near  the  entrance  ol*  the  gas. 

In  England,  all  the  chambers  of  a  set  are  generally  of  equal  size^ 
apart  from  local  circumstances ;  and  this  plan  is  now  more  fre- 
quently found  on  the  Continent  as  well  than  formerly,  when  the 
French  system,  even  now  the  more  usual,  was  the  only  one  to 


SIZE  OF  CHAMBERS. 


461 


be  met  with.  In  this  system  there  is  a  "large  chamber/'  C 
(fig.  178),  placed  at  the  lowest  level,  combined  with  a  few  small 
chambers  at  a  higher  level,  both  before  and  behind  the  large  one. 
Thus  the  first  small  chamber  or  '' tambour" A,  serves  for  deni- 
trating  the  nitrous  vitriol  by  hot  water ;  the  second  one,  B,  for 
introducing  fresh  nitric  acid ;  the  third  and  fourth  tambours,  E 
and  F,  for  finishing  the  reaction. 

In  the  south  of  France  (Favre,  '  Monit.  Scient.'  1876,  p.  272) 
there  is  mostly  a  large  chamber  of  135x26x20  feet,  or  of 
100  X  16  X  22  feet,  combined  with  two  small  chambers,  together 


¥\ 

i«?-l 

78. 

A 

B 

about  140,000  cubic  feet.  At  Aussig  each  large  chamber  is 
200  feet  long  and  24  feet  wide,  and  is  combined  with  a  small 
tambour  for  catching  the  fine  dust,  and  two  small  end  chambers, 
not  receiving  any  steam,  but  only  serving  for  cooling  the  gas  pre- 
viously to  its  entering  the  Gay-Lussac  tower. 

Some  manufacturers  reject  all  preliminary  chambers  (tambours)^ 
because  the  chamber  process  is  carried  on  best  if  a  large  space  is 
afibrded  at  once  for  the  mutual  reaction  of  the  gases.     Thus  in  a 


462  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

large  French  works  two  thirds  of  the  whole  chamber-space  are 
occupied  by  the  first  chamber,  two  ninths  by  the  second,  and 
one  ninth  by  the  third ;  this  system  is  also  adopted  at  Uetikon. 
At  the  Government  works  at  Oker  (official  commanication, 
1902)  there  are  five  sets  of  chambers,  the  best  working  of  which 
have  the  following  dimensions  : — 

Chamber  I.  35  met.  long,  800  m.  wide,  6*50  m.  highs 2800  cub.  met. 
„        II.  30        „         8-00       „        6-50        „       =1560        „ 
„       Ur.  3015    „         5-49       „        6-25        „       =  869 

5289 

The  chambers  communicate  by  pipes  1  met.  wide,  entering 
about  f^  of  the  height  and  leaving  1*20  above  the  bottom.  Small 
front  and  back  chambers  have  been  designedly  left  out  in  this 
system,  but  small  back  chambers  exist  by  chance  at  the  older  sets. 

Small  chambers,  of  course,  require  more  lead  and  space  than 
large  ones  of  equal  capacity.  A  preliminary  chamber,  however,  is 
serviceable,  where  no  Glover  tower  is  present,  for  catching  the  dust 
and  cooling  the  gas,  so  as  to  save  the  large  chamber.  For  the 
same  reason  the  nitric  acid  was  once  usually  introduced  into 
a  special  tambour ;  but  it  is  best,  as  we  shall  see,  to  run  it  down 
the  Glover  tower.  • 

A  small  chamber  at  the  exit  end  is  certainlv  serviceable  for 
drying  the  gases  previously  to  their  entering  the  Gay-Lussac 
towers  in  cases  where  there  is  no  long  tube  or  tunnel  for  the 
above-named  purpose. 

The  waste  of  lead  in  small  chambers  is  more  easily  understood  by 
a  definite  example  : — A  chamber  of  100  X  20  X  20  feet  has  a  cubical 
capacity  of  40,000  cubic  feet  and  a  surface  of  8800  square  feet.  A 
tambour  of  16  X 10  x  10  feet  has  a  capacity  of  1600  cubic  feet  and 
a  surface  of  840  square  feet.  Its  contents  are  therefore  ^,  but 
its  surface  almost  ^^  of  that  of  the  large  chamber;  and  conse- 
quently its  surface  is  nearly  2^  times  as  large,  in  comparison  with 
its  capacity,  as  that  of  the  large  chamber. 

Whilst,  of  course,  there  is  no  doubt  that  a  given  cubic  space 
of  chamber-room  is  more  cheaply  obtained  with  a  few  large  than 
with  a  greater  number  of  small  chambers,  it  is,  on  the  other  band, 
very  easy  to  overstep  the  mark  in  this  direction.  We  have  seen 
above  that,  in  the  case  of  chambers  of  an  excessive  section,  the 
gases  do  not  get  properly  mixed  ;    but  the  same  principle  applies 


SIZE  OF  CHAMBERS.  463- 

evea  to  the  division  of  the  chamber-space  in  the  direction  of  its 
lengthy  since  every  time  the  gas  has  to  be  compressed  into  a 
comparatively  narrow  connection-tube  in  order  to  pass  from  one 
chamber  to  another^  this  must  bring  about  a  good  mixture  supe- 
rior to  that  produced  in  the  same  length  of  undivided  chamber- 
space.  For  this  reason,  to  begin  with,  it  seems  expedient  to 
subdivide  the  chamber-space  by  multiplying  the  number  of  cham- 
bers ;  and  we  shall  further  on  meet  with  another  strong  reason 
for  the  same  purpose,  namely,  that  the  cooling  down  of  the  con- 
tents of  the  chamber,  essential  for  the  reaction  among  them,  is 
promoted  by  their  contact  with  the  comparatively  cool  end-walla 
of  the  chambers. 

In  England  it  is  taken  as  a  practical  rule  that  for  every  cubic 
foot  of  chamber-space  there  should  be  about  0*2  foot  of  total 
surface  (top,  bottom,  sides,  and  ends).  A  chamber  20  x  25  x  100 
feet  would  contain  50,000  cubic  feet  and  have  a  total  surface  of 
10,000  square  feet,  which  is  exactly  the  above-stated  proportion. 
Sets  of  chambers  in  England  are  rarely  made  larger  than 
200,000  cubic  feet  ;  if  more  is  required,  the  whole  is  broken  up 
into  two  or  more  sets. 

When  speaking  here,  and  elsewhere,  of  '^  chamber-gases,"  we 
always  comprise  in  them  not  merely  the  vapours  of  water,  nitrous 
anhydride^  &c.,  but  also  the  misti/  particles  of  liquid  sulphuric 
acid,  uitrosulphuric  acid,  &c.^  floating  about  in  the  atmosphere  of 
the  chambers. 

Schertel,  in  fact,  starting  from  the  principle  adduced  by  my 
experimental  and  theoretical  basis,  to  which  he  agrees,  proposes  to 
multiply  the  number  of  chambers,  keeping  them  rather  short 
(Chem.  Ind.  1889,  p.  80).  Bode  (Zeitsch.  f.  angew.  Chemie,  1890> 
p.  11),  on  the  same  principle,  proposes  chambers  of  half  the  usual 
length,  but  twice  the  ordinary  width — say  40  feet.  This  would 
involve  some  difficulties,  although  not  insuperable,  in  constructing 
the  chamber-frames.  Later  on  (Sachs.  Jahrb.  1890,  p.  148) 
Schertel  described  practical  experiments  bearing  out  the  theo- 
retical considerations  just  mentioned ;  and  further  experiments  on 
the  manufacturing  scale^  entirely  confirming  my  own  results  and 
conclusions,  have  been  made  by  Retter  (Zeitsch.  f.  angew.  Chem. 
1891,  p.  4). 

In  the  usual  case,  where  a  set  of  several  chambers  is  combined 
to  form  the  acid-making  apparatus,  the  question  arises  how  the 


464  CONSTRUCTION  OF  THB  LEAD  CHAMBERS. 

single  chambers  of  the  set  are  to  be  connected.  One  thing  about 
this  is  certain  :  that  the  connecting-tubes  must  be  placed  at  the 
small  ends^  so  that  the  gas  shall  travel  right  through  the  length 
of  the  chambers,  and  no  dead  corners  are  left.  But  the  next  question 
is^  at  what  part  of  the  section  the  connecting-tubes  are  to  leave  or 
enter  the  chambers.  There  is  general  consent  as  to  this^  that  the 
gas  should  enter  the  first  chamber  near  its  top.  Some  proceed  in 
this  wa^ :  they  take  the  gas  away  at  one  end  near  the  bottom 
and  introduce  it  into  the  next  chamber  near  its  top.  Others  main- 
tain just  as  strongly  that  this  is  wrongs  and  that;  on  the  contrary^ 
the  gas-pipe  ought  to  leave  each  chamber  near  its  top  and  enter 
the  next  chamber  near  its  bottom.  Others^  RgRin,  contend  that 
it  matters  very  little  where  the  gas  enters  and  leaves^  and  that 
it  is  therefore  the  simplest  plan  to  make  straight  connecting- 
tubes  about  midway  in  the  height  of  the  chamber.  This  last 
view  seems  to  be  borne  out  by  the  practice  of  several  practical 
men  of  very  large  experience,  and  it  agrees  very  well  with  the 
investigations  of  Lunge  and  Naef  {vide  infra),  who  found  that  the 
composition  of  the  chamber-gases  in  any  given  cross-section  of  the 
chambers  does  not  diflFer  very  materially  between  top  and  bottom,  so 
that  it  must  be  indifferent  where  the  connecting-tubes  are  placed. 
This  is  confirmed  by  information  from  the  Rhenania  works  in 
1902. 

The  connecting-tubes  may  be  round  pipes  or  angular  flues 
(tunnels).  The  former  are  preferable,  because  they  can  be  made 
without  a  frame,  and  because  they  stand  better.  They  must, 
however,  be  made  of  strong  lead,  say  9  to  12  lbs.  per  square  foot, 
and  bound  here  and  there  with  iron  hoops,  between  which  and 
the  lead  wooden  staves  are  placed  in  order  to  keep  the  pipes  in 
shape ;  but  if  the  weight  of  the  lead  amounts  to  15  lbs.  per  square 
foot,  no  staves  are  needed.  Figs.  179  &  180  will  make  this 
clearer. 

The  iron  hoops  serve  also  for  suspending  the  pipes  from  beams 
&c.  The  width  of  the  pipe  introducing  the  gas  into  the  first 
chamber,  whether  it  comes  from  the  Glover  tower  or  from  the 
burners,  must  be  adapted  to  the  quantity  of  gas  conveyed.  For  a 
combustion  of  7  tons  pyrites  daily  a  pipe  of  2  feet  diameter,  for 
9  tons  one  of  2^  feet,  upwards  of  that  one  of  3  feet  diameter  will 
do ;  more  than  10  tons  are  rarely  consumed  for  a  single  set  in 
twenty-four  hours.     Since  the  volume  of  the  gas  decreases  in  its 


CONNECTINQ-PIPES.  465 

onward  journeyj  the  eounecting-pipes  between  the  single  ehatnbers 
may  be  successively  a  little  smaller;  but  it  is  not  well  to  grudge 
any  thing  here,  since  no  harna  is  done  if  the  pipes  are  too  large, 
but  very  much  if  they  are  too  small. 

Fiy.  179. 


At  Griesheim  several  coiiucctiug- tubes  are  introduced  between 
the  cliambers  instead  of  one.  This  seems  very  rational,  and  at 
the  same  time  serves  for  partially  cooling  the  gases  in  their  transit, 
which  we  shall  find  further  on  to  be  an  important  feature.  "  Dead 
corners  "  are  most  easily  avoided  by  this  plan. 

The  total  cubical  contents  of  a  set  of  chambers  must  bear  a  certain 
proportion  to  the  quantity  of  acid  to  be  produced,  several  special 
circumstances  modifying  that  proportion.  Thus  it  is  certain  that 
for  pyrites  more  chamber-space  is  needed  than  for  sulphur;  wc 
have  seen  above  (p.  400)  tliat  the  relative  proportion  may  be  stated 

VOL.  I.  2  b 


466  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

as  1  :  1*314.  But  now  the  question  is.  What  is  the  absohite  amount 
of  space  needed  ?  Properly  speaking,  the  connecting-pipes,  if  they 
are  of  great  length,  and  the  Glover  and  Gay-Lussac  towers  should 
also  be  included  in  the  calculation,  and  that  to  a  larger  extent 
than  coiTCsponds  to  their  cubical  contents. 

The  consumption  of  nitre  also  influences  the  chamber-space ; 
within  certain  limits  a  larger  consumption  of  nitre  may  compensate 
for  a  smaller  space. 

Partly  from  this  the  widely  divergent  views  on  this  point  may  be 
explained,  but  not  entirely ;  for  some  manufacturers  obtain  about 
the  same  yield  as  their  neighbours  possessing  half  as  much  more 
chamber-space,  although  both  the  pyrites  and  the  general  con- 
struction of  the  plant  and  their  consumption  of  nitre  are  as  nearly 
as  possible  the  same.  In  the  following  remarks  we  shall  reduce  all 
measures  to  cubic  feet  of  chamber-space  required  for  burning  1  lb. 
of  sulphur  daily,  taking,  in  the  case  of  pyrites,  the  sulphur  bought, 
not  that  actually  burnt. 

For  some  particulars  concerning  older  methods,  comp.  2ud  edition 
of  this  work,  pp.  371  &  372;  for  recent  ones,  pp.  456  &  458. 
From  sundry  English  alkali-works  I  can  state  the  following  pro- 
portions (1879): — 

I.  II.         III.         IV.         V. 

28  25  20  18  16  cubic  feet. 
I.  and  II.  were  considered  too  high  by  the  chemists  of  the  respective 
works  themselves ;  but  it  should  be  stated  that  the  same  space  was 
employed  in  1864,  when  30-per-cent.  Irish  pyrites  was  used,  for 
which  it  was  more  suitable.  III.  (viz.  20  lb.)  is  a  proportion  era- 
ployed  at  many  large  works ;  but  IV.  and  V.  are  found  in  works 
having  as  good  a  yield  of  acid  (270  to  288  o.v.)  and  no  larger 
consumption  of  nitre  (3^-  to  4  per  cent.).  In  all  cases  rich  Spanish 
or  Norwegian  ore  was  burnt,  and  both  Gay-Lussac  and  Glover 
towers  were  used.  From  this  it  follows  that  under  the  same  con- 
ditions 20  cubic  feet  per  lb.  of  sulphur  charged  is  amply  sufficient, 
and  18,  or  even  16,  will  do;  but  the  latter  certainly  is  generally 
assumed  to  be  the  lowest  allowable  limit.  This  agrees  with  a 
statement  of  Wright's  (Chem.  News,  xvi.  p.  94),  who  demands  16 
to  19*2  cubic  feet. 

From  the  Inspectors'  Alkali  Reports  it  will  be  seen  that  the 
amount  of  chamber-space  actually  employed  at  English  works 
varies  in  a  most  extraordinary  way,  and  not  merely  in  consequence 


TOTAL  CHAMBER-SPACE. 


467 


of  the  fact  that  very  small  works  generally  employ  an  excessive 
chamber-space.  It  is  also  seen  from  the  same  source  that  the 
usual  assumption  that  less  chamber-space  is  used  with  brimstone 
than  with  pyrites  is  altogether  erroneous.  We  will  here  give 
merely  a  few  figures  obtained  by  taking  averages  of  the  single 
works  enumerated,  leaving  out  those  burning  both  pyrites  and 
brimstone,  or  coal-brasses,  or  "  oxide.^' 

In  the  20th  Report,  pp.  48  &  49,  we  find  the  average  of  18 
works  burning  pyrites  to  be  23"1  cubic  feet  of  chamber-space 
(minimum  15*5,  maximum  38*4) ;  the  average  of  10  works  burn- 
ing brimstone  29*7  cubic  feet  (min.  21*7,  max.  44*8).  In  the  21st 
Report,  pp.  20  &  21,  21  works  burning  pyrites  average  26*6  cubic 
feet  (16-40) ;  15  works  burning  brimstone  average  26*2  cubic 
feet  (21-48).  On  pp.  64  &  65,  22  works  burning  pyrites  average 
29*2  cubic  feet  (17*3-43'2)  ;  18  works  burning  brimstone  average 
31'4  cubic  feet  (19*3-46*2).  But  as  the  great  majority  of  these 
works  are  too  small  to  afPord  a  real  guidance  in  this  respect,  we 
will  quote  in  detail  (from  21st  Report,  p.  81)  the  figures  of  fifteen 
medium  and  large-sized  works  in  the  Widnes  district,  comprising 
some  other  interesting  information  :— 


1 

1 

Pyrites  burnt 

per  week. 

Tonp. 

175 
52 

Oubio  feet  oham- 
ber-spaoe  per  lb. 

1 

i  Nitrate  of  soda 

per  cent,  of 
sulphur  burnt. 

1 

Capacities  of  Gay- 
Lussac  towera  per 

TotAl  acidity  of 
waste  gases  as 

of  S  burnt  in 
24  hours. 

ton  pyrites  used 
per  week.  Cub.  ft. 

grains  SO,  per 
cub.  ft. 

210 

3-50 

360 

180 

500 

65-8            [            0-87 

i            210 

17-8 

4-70 

18-7 

2-10 

i            125 

28-0 

4-00 

361 

0*65 

98 

17-8 

4-20 

32-4 

2-88 

240 

210 

426 

24-0 

1-71 

250 

28-3 

3-75 

15-7 

2-34 

150 

21-0 

37-8 

0-79 

250 

19-3 

6-00 

20-5 

1-90 

60 

22-3 

27-5 

389 

260 

22-0 

3-30 

33-7                       1-60 

117 

210 

400 

53-5           i            1-30 

183 

200 

21-5                       2-94 

70 

17-5 



79-6 

0-70 

Total    1 

. 

and        2590 

21-0 

417 

44-4 

1-82 

averages 

The  usual  proportions  in  the  south  of  France  were  stated  by 
Favre  (Monit.  Scient.  1876,  p.  271)  as  follows : — Each  square 

2h2 


468  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

metre  of  grate-surface  in  the  pyrites-burners  daily  receives  270 
kilograms  of  40-per-cent.  pyrites^  and  corresponds  to  180  cubic 
metres  of  chamber-space.  This  means  1*66  cubic  metre  for  each 
kilogram  of  sulphur  charged^  or  26*5  cubic  feet  per  lb. 

In  the  north  of  France  1  found,  in  1878,  about  8  cubic  feet 
per  lb.  of  pyrites,  or  about  17  cubic  feet  per  lb.  of  sulphur  chained, 
with  good  yields  and  low  consumption  of  nitre,  but  only  for  low 
or  medium  temperatures;  in  summer  ^  to  ^  more  chamber-space 
is  required. 

Recently  a  new  style  of  working  has  been  introduced  into  several 
French  works,  called  '^production  intense/*  say  "  forced  or  high- 
pressure  work.''  It  consists  in  supplying  the  chambers  with  a 
greatly  increased  stock  of  nitre,  without  losing  any  of  it,  by  means 
of  largely  increased  Gay-Lussac  and  Glover  towers ;  in  this  way 
the  production  may  be  increased  to  almost  twice  the  usual  amouut^ 
so  that,  in  winter  at  least,  a  maximum  of  yield  and  a  minimum 
consumption  of  nitre  are  attained  with  the  extremely  small  chamber- 
space  of  0*7  cubic  metre  per  kilogram,  or  11*2  cubic  feet  per  lb. 
of  sulphur  burnt.  We  shall  have  frequent  occasion  in  later  parts 
of  this  book  to  speak  of  this  ''  forced  style,''  which  at  the  time  of 
writing  is  nowhere  practised  in  England  or  Germany. 

In  1 900  Pierron  (Monit.  Scient.  1900,  p.  367)  stated  as  a  minimum 
production  in  24hours,2"34  kils.  H2SO4=0'78  kils.  sulphur  burned 
per  cub.  met.=:l  lb.  S  per  19  cub.  feet,  but  at  Euhlmann's  works 
the  normal  production  is  2*9  kils.  H2SO4,  and  Benker  (p.  459) 
claims  obtaining  3*6  to  4"2  kils.  H2SO4  with  ordinary  chambers. 
The  ordinary  production  can  be  increased  by  the  use  of  artificial 
draught  (fan-blasts),  by  ^^  tangential  chambers  "  (corap.  p.  456),  by 
'^  plate  columns,"  and  by  other  means  described  in  their  places. 

For  Germany,  Niedenfuhr  (1902)  states  the  usual  cubic  space 
=  1*2  cub.  met.  per  kil.  of  sulphur  =  19  cubic  feet  per  lb.,  which 
is  just  the  same  as  the  maximum  space  allowed  in  France,  but 
decidedly  more  than  the  average  employed  in  that  country,  even 
where  no  *'  intense  production  "  is  aimed  at.  But  Niedenf  iihr's 
statement  is  decidedly  not  valid  for  the  most  carefully  managed 
German  works,  which,  according  to  direct  information,  manufacture 
3*5  H2SO4  per  cubic  metre  of  chamber-space,  which  is  about  0*85 
€ub.  metre  per  kil.  of  sulphur  burnt  or  about  14  cubic  feet 
per  lb. 

For  the  Bhenania  works,  producing  their  SO3  from  zinc-blende, 


J 


TOTAL  CHAMBER-SPACE.  469 

Dr.  Hasenclever  states  as  the  normal  production  2*5  kils.  of 
60°  B.  per  cubic  metre  in  24  hours,  with  a  consumption  of  0*5  to 
1*0  per  cent,  nitre  per  100  acid  of  60°  B. 

The  following  (hitherto  unpublished)  data  have  been  kiudly 
supplied  to  me  by  Mr.  6.  E.  Davis  respecting  the  results  obtained 
in  a  set  of  three  chambers,  each  120  x  20  x  18  feet,  with  a  Glover 
8^x22  feet  and  Gay-Lussac  12x12x60  feet.  This  set  was 
worked : — A.  One  month  without  the  towers :  pyrites  burned 
135  tons,  potted  96  ewt.,  25  cb.  ft.  chamber-space  per  lb.  of  sulphur 
in  24  hours ;  79  lbs.  nitrate  of  soda  sent  into  the  chambers  per 
ton  of  pyrites.  B.  One  month  with  the  towers  in  full  operation  : 
pyrites  burned  180  tons  (19  cb.  ft.  chamber-space  per  lb.  sul- 
phur), 101  cwt.  NaNOa  introduced  by  Gay-Lussac  acid,  56*2  cwt. 
nitrate  potted,  98  lbs.  nitrate  introduced  into  chambers  per  ton 
of  pyrites.  C.  One  month  with  towers :  240  tons  pyrites 
(  =  144  cubic  feet  per  lb.  sulphur),  205*6  cwt.  NaNOs  in  Gay- 
Lussac  acid,  86  cwt.  nitrate  potted,  135  lbs.  nitrate  in  gases  per 
ton  of  pyrites.  D.  One  month  with  towers :  302  tons  pyrites 
(  =  11*5  cub.  ft.  chamber-space  per  lb.  S),  277*3  cwt.  NaNOg  in 
Gay-Lussac  acid,  135*1  cwt.  potted,  152  lbs.  total  nitrate  per  ton 
of  pyrites.  Lastly,  E.  One  month  with  towers :  380  tons  pyrites 
(^8*1  cb.  ft.  chamber-space  per  lb.  S),  394  cwt.  NaNOs  in  Gay- 
Lussac  acid,  203  cwt.  nitrate  potted,  total  nitrate  176  lbs.  per 
ton  of  pyrites.  Under  the  last  conditions  the  chambers  were 
worked  for  nearly  a  year;  oxygen  at  burners  10  per  cent.,  at 
dust-burner  12  per  cent.  Average  acidity  of  gases  going  into 
Gay-Lussac  5*5  grains  H2SO4  per  cubic  foot,  and  gases  leaving 
the  tower  1*4  grains  H2SO4. 

The  yield  varied  very  little  in  all  these  cases,  viz.  from  40*2  cwt. 
acid  of  123°  T.  per  ton  of  pyrites  in  A  to  39*8  cwt.  in  B.  (The 
above  quoted  consumption  of  nitre  is  very  high,  even  for  easy 
work,  let  alone  for  high-pressure  work.) 

Mr.  Davis  states  the  general  opinion  of  English  acid-makers 
as  follows  : — "  If  you  go  on  in  the  old  way,  working  with  25  cubic 
feet  of  space  per  lb.  of  sulphur  per  24  hours,  the  process  goes  on 
absolutely  by  itself.  Decrease  your  chamber-space  to  15  cb.  ft., 
and  you  want  a  chemist  and  clever  foreman,  while  with  8  cb.  ft. 
neither  foreman  nor  chemist  knows  what  peace  is  either  by  night 
or  day.^* 

The  preceding  statements  refer  to  ordinary  pyrites,  but  when 


472  CONSTRDCTION  OF  THE  LEAD  CHAMBERS. 

acid  in  a  given  chamber- space  than  usual  is  the  employment  of  a  very 
large  quantity  of  nitre  {intense  production^  or  high-pressure  work) . 
This  means  providing  the  chambers  with  unusually  large  Gay- 
Lussac  and  Glover  towers,  which  absorb  a  considerable  portion 
of  the  saving  in  the  size  of  the  chambers  themselves.  Still,  this 
style  of  work  has  obtained  much  favour  in  France,  where  it  has 
led  to  a  sensible  reduction  of  the  chamber-space  at  some  works, 
as  already  mentioned  (p.  468).  But  it  is  evident  that  the  limit  of 
reduction  by  that  means  is  soon  reached. 

A  third  way  of  increasing  the  production  of  acid  for  a  given 
chamber-space  is  by  contrivances  for  a  better  mixture  of  the  gases 
within  the  chambers.  Some  of  the  proposals  in  this  direction  are 
combined  with  the  cooling  action  demanded  by  the  theories  to  be 
explained  in  Chap.  VII. 

Most  proposals  for  manufacturing  sulphuric  acid  in  a  diminished 
space  start  upon  the  assumption  that  in  the  ordinary  vast  chambers 
the  gases  are  not  sufficiently  well  mixed  ;  some  of  them  also  on  the 
supposition  that  there  is  not  enough  '^  condensing  "  surface  for  the 
sulphuric  acid,  and  that  this  should  be  artificially  increased.  So 
far  as  it  was  assumed  that  the  sulphuric  acid  required  to  be  con- 
densed from  a  vapour  into  a  liquid,  similar  to  the  condensation  in 
distilling  alcohol,  &c.,  this  theory  is,  of  course,  wrong,  inasmuch 
as  the  sulphuric  acid  is  liquid  as  soon  as  formed,  and  does  not 
exist  at  all  in  the  chambers  in  the  state  of  vapour.  But  we  shall 
see  further  on  that  for  other  reasons  it  is  certainlv  true  that  a 
large  amount  of  surface,  for  the  chamber-gases  to  impinge  on,  is 
indeed  a  most  important  factor  in  the  chamber-process,  and  that, 
moreover,  a  certain  amount  of  cooling  is  also  of  great  importance 
in  this  respect.  We  shall  see  that  this  proceeds  from  the  necessity 
of  bringing  about  the  reaction  between  the  nitrososulphuric  acid 
and  the  liquid  water  or  dilute  sulphuric  acid  floating  about  in  the 
chamber.  Whilst,  therefore,  we  must  acknowledge  that  former 
inventors  were  on  the  right  track  when  increasing  the  surfaces  of 
contact,  it  is  a  fact  that  their  efforts  were  unsuccessful;  but  this 
was  caused  by  the  circumstance  that  they  did  not  (and  could  not 
in  the  then  state  of  the  subject)  properly  understand  the  essence 
of  the  process,  and  that  they  consequently  chose  the  wrong  means 
for  their  ends.  Partitions  within  the  chambers,  if  made  of  lead, 
are  most  quickly  corroded ;  if  made  of  glass,  they  soon  collapse 
{vide  p.  474) . 


DIMINISHING  THE  CHAMBER-SPACE.  473 

An  arrangemeDt  of  Ward^s  (E.  P.  1006,  of  1861)  consists  in  a 
kind  of  mixing-chamber,  for  the  combustion  of  7  tons  pyrites  in 
twenty-four  hours,  64  feet  long,  16  feet  high,  and  20  feet  wide, 
followed  by  a  second  lead  chamber,  or  flue,  200  feet  long  by  3  feet 
high  and  3  feet  wide,  almost  filled  up  with  sheets  of  glass  to  a 
length  of  25  feet.  The  sheets  lie  in  a  horizontal  position,  and  are 
kept  a  little  apart  by  strips  of  glass,  to  permit  the  passage  of  the 
gases.  Ward  believed  that  upon  these  sheets  (in  lieu  of  which 
tubes  might  be  used)  nitrous  vitriol  would  condense  and  afPord  a 
large  surface  to  sulphurous  acid.  His  plan  does  not  appear  to 
have  been  carried  out  in  practice,  or  if  it  was  it  must  have  been 
abandoned  again,  probably  because  his  erection  possessed  too 
little  stability  or  was  too  easily  stopped  up.  The  horizontal 
arrangement  is  also  unfavourable  to  a  systematic  action  of  the 
gaseous  and  liquid  agents,  for  which  streams  in  opposite  directions 
(up  and  down)  are  preferable,  as  we  shall  see  below ;  and  the 
total  lack  of  a  cooling  arrangement  would  make  the  whole  principle 
of  reaction  on  the  solid  surfaces  incomplete,  as  will  be  proved 
later  on. 

Mactear  (Jouru.  Soc.  Clvem.  Ind.  1884,  p.  228)  has  carried  out 
some  experiments  showing  the  importance  of  surface  condensation. 
A  tray,  placed  in  a  vitriol-chamber,  one  square  foot  area,  was 
found  to  give  708  grams  H2SO4  in  24  hours.  By  placing  in 
the  tray  12  pieces  of  glass,  12  in.  by  6  in.  each,  in  a  vertical 
position,  the  amount  of  acid  obtained  in  24  hours  rose  to  1644  gr., 
or  2*3  times  as  much,  and  by  placing  the  glass  slips  horizontally, 
the  same  distance  apart  as  before,  the  acid  rose  to  3226  gr.,  or 
4*5  times  more  than  without  the  glass.  Other  experiments  made 
with  "  surface  condensers  '^  within  the  chambers  showed  that  in 
the  case  of  flat  vertically  placed  sheets  the  side  facing  the  gaseous 
current  condensed  more  acid  than  the  opposite  side,  in  the  propor- 
tion of  100  :  78.  When  the  same  plates  were  placed  horizontally, 
with  their  edges  facing  the  current  of  the  gases,  the  amount 
obtained  from  the  double  surface  was  172,  against  178  in  the 
former  case. 

The  principle  of  surface  condensation  is  also  employed  in 
de  Hemptinne's  chamber-system,  which  will  be  mentioned  in  the 
9th  Chapter,  in  connection  with  his  system  of  concentration. 

At  some  places,  e.  g*  at  Uetikon  near  Zurich,  there  existed  for 
a  time  a  peculiar  kind  of  chambers.     Each  set  consisted  of  only 


474 


CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 


one  large  chamber,  330  feet  long ;  ivithin  this,  however,  there 
were  two  partitions,  dividing  it  really  into  three  chambers.     The 
partitions  are  made  as  shown  in 
fig.  181.    A  row  of  perpendicular  ^^S-  ^^^' 

iron  gas-tubes  of  1-inch  bore, 
covered  with  lead,  a,  is  placed 
across  the  chamber^  carried 
through  its  top,  b,  and  hung 
from  one  of  the  joists  c.  At 
vertical  distances  of  2  feet  there 
are  lead  hooks,  dd,  attached  to  the 
tubes^  on  the  opposite  side  other 
hooks^  d^d^,  a  little  lower.  These 
hooks  must  not  be  made  of  sheet- 
lead,  because  they  bend  too  easily, 
but  they  must  be  cast.  On  these 
hooks  sheets  of  glass  2  feet  +  2 
feet  6  in.  are  placed  loosely, 
leaving  chinks  of  about  1  inch 
width  for  the  passage  of  the  gases, 
in  order  to  mix  them  better. 
These  partitions  do  not  seem  to 
offer  any  guarantee  of  durability; 
and  in  fact,  both  at  Uetikou  and 
at  other  works,  formerly  possess- 
ing similar  glass  partitions,  they 
have  been  removed  again  ; 
they  are  said  to  have  sometimes 
suddenly  collapsed  and  cut 
through  the  chamber-bottom. 

The  simplest  kind  of  internal 
partition,  a  lead  one,  is  not  prac- 
ticable, because  the  lead,  exposed 
to  the  heat  and  the  gas  on  both  sides,  is  very  quickly  worn  away. 
This  entirely  disposes  of  the  suggestion  of  Borntrager  (Chem.  Ind. 
1885,  p.  386)  to  make  nearly  horizontal  (rather  slanting)  partitions 
in  the  chambers,  in  order  to  multiply  contact-surfaces.  Both  in 
this  case  and  in  the  Uetikon  plan  the  internal  contact-surface, 
not  being  cooled,  does  very  little  service  (comp.  later  on). 

Walter  and  Boeing  (Germ.  pat.  71,908)  employ  hollow  partitions. 


DIMINISHING  THE  CHAMBER-SPACE.  475 

made  of  acid-proof  material^  arranged  across  the  whole  width  of 
the  chambers.  Double  walls  are  constructed  of  such  a  form  that 
the  principal  gaseous  current  enters  through  large  holes  near  the 
bottom^  rises  upwards  in  the  space  between  the  walls^  and  issues  at 
the  top  ;  at  the  same  time  the  gases  are  allowed  to  penetrate  into 
the  inner  space  by  numerous  small  openings^  and  to  issue  in  the 
same  way  on  the  other  side^  so  as  to  produce  a  good  mixture. 
Buttresses  and  binders  produce  sufficient  stability  without  inter- 
fering with  the  draughty  which  is  also  procured  by  making  the 
sectional  area  of  the  openings  and  joints  much  larger  than  that  of 
ordinary  connecting-pipes.  [This  system  aims  at  attaining  the 
same  object  as  the  previously  introduced  plate-columns  in  a  simpler 
way  and  without^interfering  with  the  draught.  But,  in  consequence 
of  the  many  outlets  offered  to  the  gases^  it  is  doubtful  whether  they 
will  travel  exactly  in  the  desired  path.  The  stability  of  such  inner 
walls^  even  when  made  of  the  best  material^  is  very  doubtful  indeed, 
and  a  collapse  must  produce  most  disastrous  results^  as  has  been 
found  in  practice,  wherefore  the  use  of  these  partitions  has  been 
abandoned.     They  remind  one  of  the  plan  shown,  p.  474.] 

Brulfer  (French  pat.  220,402)  also  employs  hollow  brick  par- 
titions within  the  chambers  ;  he  adds  dividing  apparatus,  made  of 
lead  tubes  with  air-cooling,  fixed  behind  each  partition.  When 
the  gases  have  passed  through  a  cooled  divider,  they  again  pass 
through  a  hollow  brick  divider. 

A  similar  principle,  in  which,  however,  the  idea  of  mixing  the 
gases  was  the  chief  aim  of  the  inventors,  is  involved  in  the 
proposal  made  by  Gossage  and  many  others,  and  frequently 
carried  out  in  practice,  of  filling  the  chambers  partially  or  entirely 
with  coke,  or  of  erecting  special  coke-towers  at  the  end  of  the  set, 
not  as  6ay-Lussac  towers,  but  to  be  merely  moistened  by  water 
or  steam.  In  practice  it  has  been  found  that  even  as  a  matter  of 
construction  this  plan  gave  much  trouble,  because  the  great  weight 
pressing  upon  the  outside  layers  of  the  coke  makes  it  bulge  out  or 
even  cut  through  the  chamber-sides.  But  apart  from  this  it  was 
found  that  th»  yield  of  acid  for  a  given  chamber-space'  was  not 
increased,  that  more  nitre  was  used,  and  that  the  acid  was  rendered 
impure  by  the  coke.  Everywhere,  therefore,  the  coke  has  been 
removed  again  from  the  chambers  themselves,  and  has  been 
relegated  to  its  legitimate  place  in  the  Gay*Lu8sac  tower.  The 
cause  of  this  failure  is  probably  two-fold :  firstly,  the  injurious 


476  CONSTRUCTION    OF  THE  LEAD  CHAMBERS. 

action  of  the  coke  on  the  nitrous  gases,  which  would  thereby 
be  reduced  with  formation  of  carbonic  acid  (comp.  Chap.  \T^-)*i 
secondly,  the  lack  of  any  cooling,  just  as  in  Ward^s  case. 

The  same  objections  hold  good  for  the  apparatus  of  Verstraet 
(Bull.  Soc.  d'encourag.  1865,  p.  531),  which  was  worked  in  Paris 
for  some  time,  but  had  to  be  abandoned  as  impracticable.  It 
consisted  of  a  number  of  stoneware  jars  without  a  bottom,  covered 
430  square  feet  of  ground,  cost  only  £280,  and  was  to  supply 
daily  a  ton  of  sulphuric  acid  of  106°  Tw.  There  were  twelve  per- 
pendicular stacks  of  five  jars  each,  filled  with  coke  and  traversed  by 
the  burner-gas ;  nitric  acid  ran  down  over  one  of  them,  meeting 
the  sulphur  dioxide ;  and  the  resulting  acid  was  run  over  the  other 
stacks  in  regular  rotation. 

The  apparatus  of  Lardani  and  Susini  (Bull.  Soc.  Chim.  viii. 
p.  295)  is  founded  on  the  same  principle.  Its  peculiarity  is  a 
^^  reaction-apparatus,^'  whose  lower  part  is  filled  with  sulphuric 
acid,  on  the  top  of  which  a  thick  layer  of  nitric  acid  is  floating ; 
the  upper  part,  divided  from  the  lower  by  a  perforated  partition, 
is  filled  with  pumice ;  the  nitre-gas  is  regenerated  to  nitric  acid 
by  an  excess  of  air  and  water  in  a  system  of  pipes  filled  with 
pumice  or  coke. 

That  mixing  the  gases  alone  is  not  sufiScient  is  proved  by  the 
small  success  of  Bichter's  apparatus  (G.  P.  15,252),  consisting  of 
a  steain-injector  on  the  top  of  the  chamber,  which  aspirates  the 
gases  from  the  lower  part  of  the  chamber  and  re-introduces  them 
at  the  top.  It  is  true  that  by  this  apparatus  probably  only  a 
small  portion  of  the  gases  would  be  set  into  circulation ;  other- 
wise the  draught  would  have  been  interfered  with  in  an  intolerable 
way.  At  all  events  no  great  advantage  has  been  obtained 
by  using  it  in  all  the  factories  visited  by  me;  but  at  some 
places  a  certain  improvement  is  said  to  have  been  produced  bv 
this  means. 

The  same  proposal  has  been  made  in  a  somewhat  modified  shape 
by  N.  P.  Pratt  (E.  P.  4856,  1895).  He  places  a  fan  or  steam- 
injector  in  front  of  the  chamber,  and  a  tower,  fed  with  weak 
sulphuric  acid,  at  the  end  of  the  chamber,  the  gases  issuing  from 
the  top  of  this  tower  being  re-injected  into  the  chamber  by  means  of 
the  fan.  Baffling  columns  may  also  be  placed  within  the  chamber. 
Modifications  of  this  system  by  the  same  inventor  are  contained 
in  the  U.S.  P.  652,687  to  652,690  and  E.  P.  10,757,  1899. 


MIXING-  AND  COOLING-TOWERS.  477 

The  Meyer's  "  tangential  chambers''  also  belong  to  this  class 
of  apparatus  (comp.  p.  455). 

Dr.  Burgemeister  '(private  communication)  proposed  both  to 
mix  and  to  cool  the  gases  by  arranging  a  number  of  lead  pipes^  15 
to  18  inches  wide,  vertically  between  top  and  bottom  of  the  first 
chamber,  and  cooling  these  by  air  passed  through.  This  plan  is 
hardly  practicable,  as  the  immense  extension  of  joints,  especially 
at  the  bottom,  will  cause  too  many  interruptions  for  repairs,  but 
it  can  be  more  easily  carried  out,  according  to  Hartmann  (Chera. 
Zeit.  1897,  p.  877),  by  constructing  these  inner  pipes  or  shaft*  in' 
the  same  manner  as  an  ordinary  chamber-bottom,  that  is  with  a 
hydraulic  lute,  formed  by  turning  up  the  chamber-bottom  round 
the  bottom  of  the  pipes.  Hartmann  employed  a  number  of  such 
shafts,  5x6  feet  wide,  from  which  he  found  an  increase  in  the 
production  amounting  to  20  per  cent.,  viz.  0*9  to  10  cub.  metre 
chamber-space  per  I'O  kil.  sulphur  burned.  [This  is  not  parti- 
cularly high.] 

F.  Blau  (G.  P.  95,083)  injects  a  spray  of  cooled  sulphuric  acid 
into  the  first  hot  part  of  the  lead  chambers,  in  order  to  keep 
down  the  temperature,  and  a  spray  of  hot  acid  into  the  last 
part  of  the  chambers  where  the  reaction  is  sluggish  and  is  to  be 
revived  in  this  manner.  If  the  exit-gases  thereby  become  too 
hot,  they  are  cooled  by  a  spray  of  cold  acid  before  entering  the 
Gav-Lussac  tower. 

A  fourth  way  for  increasing  the  production  of  acid  is  the 
employment  of  special  mixing  and  cooling  towers  and  columns 
between  the  chambers,  even  to  the  exclusion  of  all  chambei's 
except  a  first  and  perhaps  a  last  small  chamber.  These  ^^  inter- 
mediate "  or  '^  reaction ''  towers  have  had  the  greatest  success  in 
diminishing  the  space  for  the  production  of  sulphuric  acid. 

One  of  the  first  attempts  in  this  direction  was  the  plan  of  Thyss 
(G.  P.  30,211),  of  which  I  have  myself  given  a  detailed  description 
in  Zsch.  f.  angew.  Ch.  1889,  p.  265,  abstracted  in  our  second 
edition,  pp.  378  &  379.  This  system  having  completely  broken 
down  after  a  short  trial,  it  may  suffice  to  say  that  Thyss  employed 
lead  towers,  provided  with  a  number  of  perforated  lead  shelves 
over  which  the  gas  had  to  take  a  zigzag  course.  These  towers 
were  not  fed  with  any  liquid,  and  consequently  they  would  become 
very  hot  and  could  exert  no  cooling  action ;  the  draught  was  very 
much  impeded  and  the  lead  quickly  corroded.     Moreover,  these 


478  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

towers  cost  twice  as  much  as  a  chamber  producing  the  same 
amount  of  acid.  Still,  although  the  Thyss  columns  were  both  an 
economic  and  a  technical  failure,  they  proved  that  even  in  that 
imperfect  form  an  intimate  mixture  of  the  gases  and  their  contact 
with  solid  surfaces  considerably  hasten  the  reaction. 

Much  better  elaborated  was  the  plan  of  Sorel  (French  patent 
of  1886;  comp.  his  ^Fabrication  d'Acide  sulfurique/  p.  398,  and 
Zsch.  angew.  Ch.  1889,  p.  279).     He  proposed  to  start  with  a 
small  chamber ;  from  this  the  gases  were  to  pass  through  cooling- 
pipes  and  then  through  two  or  three  towers^  where  steam  is  also 
injected,  while  acid  of  142°  to  150°  Tw.  is  running  down,  the  out- 
flowing acid  not  to  fall  below  130°  Tw.     Although  he  was  then 
connected  with  one  of  the  largest  chemical  works  in  the  world,  his 
proposal  has  never  been  tried  on  the  large  scale,  probably  owing  to 
constructive  difficulties ;  moreover,  his  idea  of  employing  strong 
acid  for  feeding  the  towers  would  rob  the  process  of  most  of  the 
advantages  of  the  principle. 

It  is  recognized  on  all  sides  that  the  object  in  question  was 
first  accomplished  by  my  ^' plate^towers  *'  (Zeitsch.  f.  angew. 
Cliemie,  1889,  p.  385),  in  which  I  have  endeavoured  to  combine  all 
the  principles  hitherto  recognized  as  paramount  in  the  manufacture 
of  sulphuric  acid.  In  the  7th  Chapter,  when  treating  of  the  Theory 
of  the  Chamber  Process,  we  shall  see  that  I  formulate  this  theory 
as  follows: — ^Nitrous  acid  (or  anhydride),  or  in  the  first  part  of  the 
chambers  nitric  oxide,  acts  as  carrier  of  atmospheric  oxygen  and 
water  upon  sulphur  dioxide,  by  which  action  nitrososulphuric  acid 
is  formed.  This  acid,  which  for  the  most  part  at  once  dissolves 
in  the  sulphuric  acid  already  present,  like  this  floats  about  in  the 
chamber  in  the  shape  of  a  fine  mist.  When  coming  into  contact 
with  water,  or,  which  is  probably  the  usual  case,  with  dilute  sul- 
phuric acid,  a  decomposition  takes  place  by  which  sulphuric  acid  is 
formed,  and  all  the  nitrous  acid  is  returned  into  the  atmosphere 
of  the  chamber  to  recommence  the  above-described  action. 

It  is  evident  that  all  these  reactions  require  in  the  first  instance 
a  most  intimate  and  constantly  renewed  mixture  of  all  the  gases^ 
vapours,  and  misty  particles.  In  the  ordinary  large  chambers  a  long 
course,  a  vast  space,  and  a  correspondingly  long  time  are  needed 
till  the  reactions  are  practically  complete  j  that  is,  till  nearly  aU 
the  SO2  has  been  removed  from  the  gases.  If  it  were  only  the 
question  of  a  mixture  of  gases  and  vapours,  probably  very  much 


THEORY  OF  THE  PLATE-TOWERS.  479 

less  time  and  space  would  be  required ;  but  as  both  the  nitroso- 
sulphuric  acid  and  the  dilute  sulphuric  acid,  which  are  to  act  upou 
each  other,  are  in  the  state  of  mist,  that  is,  of  minute  liquid  drops, 
they  may  travel  for  some  distance  side  by  side  without  coming  into 
actual  contact  and,  reacting  as  thev  are  intended  to  do.  In  manv 
similar  cases  it  has  been  found  that  simply  mixing  up  the  atmo- 
sphere in  question  is  nothing  like  so  efficient  as  presenting  large 
solid  (or  liquid)  surfaces  against  which  the  gaseous  current  must 
strike  in  its  progress.  By  the  shock  against  these  surfaces,  and 
the  loss  of  velocity  thereby  incurred,  and  undoubtedly  also  by 
surface  attraction,  the  misty  particles  which  would  otherwise 
float  about  for  hours  in  the  same  state  are  condensed  on  those 
surfaces  in  larger  drops  or  films,  and  then  the  mutual  reaction 
above  described,  leading  to  the  splitting  up  of  nitrososulphuric 
acid,  will  take  place  at  once.  From  this  we  infer  that  we  ought  to 
arrange  a  number  of  large  solid  surfaces  in  the  path  oi  the  gaseous 
current,  but  so  arrange  them  that  this  current  must  continually 
strike  against  them  and  be  constantly  broken  up  into  small 
parts  and  mixed  up  again.  (In  this  respect  Ward's  glass  sheets, 
p.  473,  running  parallel  with  the  gaseous  current,  were  not 
properly  disposed.) 

There  is,  however,  another  condition  to  be  realized  for  a  proper 
working  of  the  chamber  process.  As  we  shall  see  further  on,  it 
is  indispensable  that  the  temperature  of  the  chamber  is  kept  suffi- 
ciently low  to  condense  the  requisite  quantity  of  aqueous  vapour 
into  liquid  water  or  dilute  acid,  sufficient  for  decomposing  the 
nitrososulphuric  acid.  As  the  reactions  in  progress  within  the 
chambers  produce  a  large  quantity  of  heat,  the  process  cannot  go 
on  without  a  portion  of  that  heat  being  abstracted  again,  which  iu 
the  ordinary  system  is  done  by  radiation  from  the  chamber-sides. 
The  separation  of  the  whole  chamber-space  into  several  smaller 
chambers  acts  favourably  in  this  respect,  as  the  ends  of  the 
chambers  and  the  connecting-pipes  act  as  cooling  surfaces;  and 
Sorel  (comp.  above)  actually  proposed  increasing  this  by  arranging 
a  set  of  cooling-pipes,  which,  however,  would  be  nothing  likfr 
sufficient  for  the  purpose.  My  own  plan  is,  however,  different 
from  anything  hitherto  proposed.  I  eflect  the  necessary  lowering 
of  the  temperature,  not  by  radiation  or  convection  to  the  outer 
air,  but  from  within  by  a  shower  of  water  or  very  dilute  sulphuric 
acid.     Thus  several  objects  are  attained  at  the  same  time.     The 


CONSTRUCTION  OF  THB  LEAD  CHAUIIEBS. 


PLATE -TO  WEB 

Fit'.  18-'- 


482  CONSTRUCTION  OF  THE  LEAD  CHAMBEHS. 

temperature  of  the  chamber  atmosphere  is  reduced  to  a  proper 
level,  parts  of  its  heat  heing  spent  in  heating  and  vaporizing  water ; 
but  this  water  is  just  vliat  is  required  for  carrying  on  the  chamber 
process  itself,  and  thus  s  saving  is  effected  in  the  raising  of  steam 
for  the  purpose  of  supplying  the  vitriol-chambers  j  we  also  supply 
this  water  in  a  finely  divided  form,  and  exactly  where  it  is  needed 
for  meeting  and  decomposing  the  nitrososulphuric  acid  condensing 
on  the  solid  surfaces ;  and  by  this  cooling  we  protect  the  apparatus 
employed  against  rapid  deterioration,  such  as  occurred  iu  the 
Thyssplan  (p.  477). 

The  apparatus  employed  is  the  "  plate-column "  or  "  plate- 
tower,"  invented  by  myself  and  patented  with  Ludwig  Rohrmaiin 
(E.P.  10,355 of  1886  ;  10,037,  1887;  6989,  1889).  It  origin aUy 
coQsiated  of  a  column  of  large  stoneware  cylinders,  filled  with 


the  plates  forming  the  peculiarity  of  the  invention;  and  this  is 
the  construction  still  employed  for  nitric  and  hydrochloric  acid 
(p.  125) ;  but  for  the  purpose  of  sulphuric-acid  manufacture  it  is 
constructed  with  a  leaden  shell  («)  of  either  round  or  angular 


PLATE -TOWERS. 


section,  and  stoneware  plates  {b  b),  as  shown  in  tigs.  182  &  183. 
The  plates  are  supported  by  bearers,  c  c,  in  such  a  way  that  each 
plate  is  independent  of  the  others,  and  presses  ouly  upon  the 
hon^ontal  ledge  of  its  own  bearer,  whilst  the  pressure  of  the 
superposed  plates  and  bearers  is  sustained  by  the  vertical  part  of 
the  bearers.  The  latter  are  easily  arranged  so  as  to  protect  the 
whole  inner  surface  of  the  lead  against  the  attack  of  the  chemicals 
and  the  high  temperature  ruling  within.  We  do  not  here  notice 
sucb  parts  as  the  feeding-arrangemeiitB,  inlet-  and  outlet-pipes, 
and  the  like,  which  require  no  special  explanation ;  the  feeding- 
arrangement  will  be  described  in  the  6th  Chapter,  in  connection 
with  the  Gay-Lussac  tower.  A  special  CKplanation  is  only  necessary 
for  the  plates  b  b.  Fig.  184  shows  a  small  portion  of  their  surface 
as  seen  from  the  top,  fig.  185  the  same  as  seen  from  the  bottom, 
fig.  1 86  a  section  of  pieces  of  two  superposed  plates. 

Each  of  these  is  covered  with  a  network  of  small  ledges,  d  d, 
and  in  each  of  the  squares  thus  formed  there  is  a  perforation,  e  e, 
with  a  somewhat  raised  margin.  The  height  of  this  margin  is 
not  quite  so  great  as  that  of  the  ledges,  hence  there  is  always  a 
layer  of  liquid  about  J  inch  deep  in  each  of  the  squares ;  and  as 

V\g.  186. 


there  is  always  more  liquid  dropping  in,  the  excess  is  forced  out 
through  the  perforations  drop  by  drop.  Tlie  plates  arc  not 
identical  in  shape,  but  differ  as  to  the  position  of  the  holes.  To 
each  perforation  in  any  one  plate  there  corresponds  the  point  of 
union  of  the  ledges  in  the  plates  above  and  below  (see  fig.  186) . 
Hence  the  liquid  cannot  drop  straight  through  the  holes  in  the 
following  plates,  but  strikes  the  solid  portion  of  the  next  plate,  U 

3i2 


484  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

scattered  about^  and  is  divided  among  the  adjoining  squares.  TliU 
action  is  repeated  from  plate  to  plate.  Thus  the  thin  layer  of 
liquid  resting  upon  the  plates  and  clinging  to  the  holes  is  con- 
stantly renewed;  and  by  the  scattering  about  of  the  liquid  another 
absorbing  surface  is  created. 

The  gases  and  vapours  rising  within  the  tower  pass  through 
the  numerous  holes  of  the  lowermost  plate  and  are  thus  divided 
into  a  great  number  of  fine  jets.  Immediately  on  issuing  through 
the  holes  of  this  plate^  they  strike  against  the  solid  places  in  the 
next  plate  above,  which  correspond  to  the  holes,  and  are  thus 
divided  and  again  mixed;  aud  this  process  is  repeated  as  many 
times  as  there  are  plates  provided.  Whilst  the  gases  and  vapours 
thus  travel  upwards  in  continuously  renewed  mixtures  they  come 
into  the  most  intimate  contact  with  the  absorbing-liquid,  which 
they  meet  within  the  narrow  holes  on  the  plates  and  scattered  all 
over  in  fine  drops.  By  the  incessant  changes  in  the  direction  of 
the  current;  aud  the  equally  incessant  renewal  of  the  surface  of 
the  liquid;  the  most  favourable  conditions  are  produced  fur  a 
mutual  action  of  the  gaseous  and  liquid  substances.  Owing  to 
the  principle  of  the  apparatus,  no  false  channels  can  exist  in  which 
the  gases  or  liquids  would  travel  separately  without  coming  into 
proper  contact  with  each  other. 

This  circumstance  partly  accounts  for  the  enormous  difiereucc 
in  condensing-power  between  the  '' plate-tower  ^' and  a  perfectly 
well-constructed  and  packed  coke-tower,  or  any  similar  apparatus^ 
fitted  with  pieces  of  pottery  and  the  like.  The  liquid  within  a 
coke-tower  is  never  quite  evenly  distributed ;  there  are  always 
many  places  where  it  drops  down  a  considerable  height  without 
meeting  a  piece  of  cuke,  aud  where,  on  the  other  hand,  the  gases 
find  channels  in  which  they  can  ascend  without  for  some  time 
getting  mixed  and  coming  into  contact  with  liquid.  Moreover, 
the  individual  gas-channels  are  too  wide,  and  the  inner  portion  of 
the  gaseous  current  does  not  enter  into  reaction  with  the  absorbing- 
liquid.  This  is  unavoidable,  because  the  interstices  between  the 
pieces  of  coke  are  quite  irregular,  and  therefore  the  section  of  the 
tower  must  be  made  wide  enough  and  the  pieces  of  coke  large 
enough  to  secure  a  sufficiency  of  draught  for  the  worst  case.  Nor, 
as  experience  has  demonstrated,  have  any  arrangements  of  cylinder?, 
pipes,  or  other  pieces  of  pottery  hitherto  had  a  better  effect  than 
coke.     Hence  coke-towers  must  be  made  very  wide  and  high,  thus 


PLATE-TOWERS*  485 

offering  a  long  time  and  corresponding  opportunities  for  mixing 
the  gases  and  enabling  them  to  come  into  contact  with  the  liquid ; 
and  in  this  way  the  reaction  is  certainly  very  complete  at  the  end. 
But  this  enormous  enlargement  of  space  can  be  avoided  by  the 
systematic  way  in  which,  in  the  plate-tower,  the  gaseous  current 
is  split  up  into  upwards  of  a  thousand. very  thin  and  exactly  equal 
jets,  which  must  continually  alter  their  direction,  and  must  there- 
fore become  thoroughly  mixed  each  time  they  pass  through  a  new 
plate.  On  their  way  they  come  into  the  most  intimate  contact 
with  constantly  and  systematically  renewed  thin  layers  of  liquid. 
The  network  of  ledges  prevents  any  unequal  downward  passage  of 
the  liquid,  unlike  tbe  action  of  coke-towers  or  of  any  other  hitherto 
known  form  of  similar  apparatus.  Perhaps  a  still  more  important 
difference  is  the  following : — There  is  a  very  thin  and  constantly 
renewed  layer  of  liquid  spread  over  each  plate^  and  the  gases,  in 
passing  through  the  perforations  of  the  plate,  must  frequently 
break  through  the  drops  of  liquid.  This  seems  to  produce  an 
action  somewhat  similar  to  the  Coffey  still  or  other  '^  rectifying  '^ 
apparatus,  and  it  may  to  a  great  extent  explain  why  such  an 
intense  action  takes  place  in  so  small  a  space. 

Owing  to  these  advantages  a  plate-tower,  in  comparison  with 
a  coke-tower,  does  from  ten  to  twenty  times  as  much  work  in 
the  same  cubic  space.  It  can  therefore  be  made  not  merely  much 
smaller  in  section,  but  also  much  lower  in  height,  and  the  feeding- 
liquid  requires  correspondingly  less  pumping.  A  column  of  40 
plates  would  be  only  18  feet  high.  The  above  is  a  comparison 
between  plate-towers  and  coke-towers ;  the  difference  between  the 
former  and  empty  chamber-space  is  much  greater,  as  we  shall 
see. 

In  our  present  case  it  is  of  special  importance  that  the  injurious 
action  exerted  by  the  reducing  power  of  coke  upon  the  nitrous 
gases  (p.  231)  is  avoided,  the  stoneware  plates  being  absolutely 
stable  in  the  chamber  atmosphere  if  manufactured  of  proper 
quality.  The  plates,  therefore,  last  for  ever;  even  if  cracked 
they  may  still  continue  in  use. 

When  a  plate-column  is  partly  obstructed  by  muddy  deposits, 
it  is  very  easily  cleaned  out  by  a  thorough  flushing  with  water, 
or,  in  bad  cases,  by  removing  the  cover  and  lifting  out  one  plate 
after  another. 

Apart  from  the  great  constructive  difference  between  the  plate- 


486  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

towers  and  all  previously  proposed  apparatus^  there  is  an   equally 
great  difference  in   their  mode   of  application.      If   the    tower 
were  left  to  itself,  like  Ward's  or  Thyss's  apparatus,  the   very 
completeness  of  the  mixture  produced  therein  would  produce  an 
intense  chemical  reaction,  and,  consequently,  a  very  injurious 
development   of  heat.     This  is,   however,   entirely   avoided    by 
feeding  the  towers  with  a  stream  of  water  or  dilute  sulphuric 
acid,  at  such  a  rate  that,  by  the  vaporization  of  water,  the   tem- 
perature does  not  rise  above  70°  or  80°.     The  intimate  contact 
between  gaseous  and  liquid  particles  within  the  plate-tower  must 
bring  out  the  cooling  action  of  the  evaporation  of  water  to   its 
fullest  extent,  and  at  the  same  time  the  water  required  for  the 
chemical  reactions  of  the  acid-making  process  is  supplied    here 
without  any  previous  production  of  steam  or  spray ;  the  superfluous 
steam  passes  over  into  the  next  chamber  and  does  its  work  there. 
The  acid  running  off  at  the  bottom  is  either  used  up  as  it  is,  or  is 
nm  into  one  of  the  chambers,  or  it  is  employed  for  feeding  the 
Gay-Lussac  tower. 

In  plate-towers  there  will  always  be  a  great  excess  of  nitrous 
gas  and  of  oxygen ;  hence  there  is  very  little  fear  that  even  when 
employing  water  for  feeding  them  there  will  be  the  conditions 
present  for  the  formation  of  nitrous  oxide,  which  would  mean 
a  waste  of  nitre.  This  can  be  avoided  in  any  case  by  feeding 
the  columns  with  sulphuric  acid  of  1'3  spec.  grav.  or  upward?, 
since  I  have  already  shown  (Ber.  d.  deutsch.  chem.  Ges.  1881, 
p.  2200 ;  comp.  supra,  p.  218)  that  in  this  case  no  NjO  whatever 
is  formed.  In  practice  such  dilute  acid  or  chamber-acid  is 
employed  for  feeding  the  columns. 

The  principal  advantage  of  this  system  is  that,  like  the  Glover 
tower,  it  brings  about  the  mutual  action  of  the  ingredients  within 
the  smallest  possible  space.  We  shall  see  in  Chapter  VI.  that 
one  cubic  foot  space  in  the  Glover  tower  effects  the  formation 
of  as  much  add  as  at  least  180  cubic  feet  of  ordinary  chamber- 
space  ;  and  a  similar  difference  may  be  looked  for  between  the  latter 
and  the  plate-towers  to  be  interposed  between  the  chambers. 
.  We  will  now  consider  the  question  whether  the  thermal  effects 
produced  in  that  system  are  not  excessively  large  or  small.  The 
heat  of  forming  HjSG^  from  SO2  +  O  +  H2O  is  54,400  calories ; 
to  this  must  be  added  the  heat  produced  in  the  formation  of 
ordinary  chamber-acid,  say,  of  110"  TwaddcU,  or  H2SO4,  3  H5Q 


PLATE-TOWERS.  487 

=  11,100  calories;  altogether  65,500  calories.  This  is  the  heat 
produced  in  the  formation  of  a  quantity  of  chamber-acid  corre- 
sponding to  98  grams  of  H2SO4,  and  it  is  very  little  more  than 
would  be  required  for  converting  98  grams  of  cold  water  into 
steam.  This  quantity  of  water  then  would  have  to  be  evaporated 
within  the  tower  in  order  to  absorb  all  the  heat  produced  in 
the  acid-forming  process,  on  condition  that  the  acid  must  run 
out  cold  at  the  bottom  and  that  the  tower  would  lose  no  heat 
by  radiation.  But  as  the  former  condition  is  unnecessary^  and 
the  latter  even  impossible  to  maintain,  the  quantity  of  water, 
evaporated  will  be  less  than  the  weight  of  monohydrate  produced, 
and  will  probably  be  very  nearly  equal  to  that  required  for  the 
chamber-process,  viz.  three  quarters  of  that  amount.  Any 
deficiency  of  water  could,  of  course,  be  made  up  by  steam, 
probably  best  by  means  of  an  injector  placed  in  the  outlet  tube 
from  the  plate-tower. 

As  a  practical  way  of  applying  the  new  system^  I  proposed 
from  the  first  the  following  plan  : — Considering  that  by  far  the 
greatest  portion  of  the  acid  is  made  in  the  first  part  of  the 
chamber,  we  cut  off  the  back  part  altogether,  and  leave  behind 
the  Glover  tower  a  chamber  of  only  about  50  feet  length.  Behind 
this  we  place  a  plate-tower  of  sufficient  section  for  the  amount 
of  gas  to  pass  through  and  40  plates  high  (say  18  feet).  Then 
comes  a  small  chamber,  say  30  feet  long,  again  a  plate-^tower,  a 
last  chamber  for  drying  the  gases,  and  in  the  end  a  plate-tower 
serving  as  6ay-Lussac  tower. 

The  question  might  be  raised  why  I  did  not  propose  to  carry  on 
the  whole  of  the  sulphuric-acid-making  process  in  plate-towers  or 
similar  apparatus.  But  a  glance  at  the  curves  shown  in  the  7th 
Chapter  will  show  that  the  first  part  of  the  first  chamber  is  really 
very  efficient,  and  whilst  the  gases  are  of  such  concentration 
a  lead  chamber  is  possibly  the  cheapest  apparatus  for  making 
sulphuric  acid.  As  soon  as  the  curves  begin  to  bend  .towards 
the  horizontal,  that  is^  when  the  reactions  become  sluggish,  it  is 
time  to  liven  them  up  by  apparatus  like  the  plate-towers.  But 
if  such  were  attempted  to  be  used  from  the  firsts  the  heat  would 
become  excessive,  which  would  be  very  injurious  both  to  the 
material  of  the  apparatus  and  to  the  process.  For  this  reason 
the  process  proposed  by  Hannay  {E.  P.  12,247,  of  1886,  comp. 
Chap.  XII.)  is  not  likely  to  be  practically  successful. 


488  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

The  first  factory  which  ventured  to  try  my  plate-towers  (which 
have  become  known  as  ^'  Lunge  towers/^  both  in  their  application 
as  intermediate  "  reaction  "  towers  for  the  vitriol-chambers,  and 
as  replacing  coke-towers  for  the  recovery  of  nitrogen  acids,  for 
condensing  hydrochloric  acid,  and  so  forth)  was  the  old-established 
acid-works  at  Lukawetz,  in  Bohemia,  soon  followed  by  a  factor}^ 
at  Valencia,  in  Spain,  both  in  1891,  and  by  othei's  in  various 
countries.  Of  course  here  and  there  diflSculties  were  experienced, 
principally  caused  by  the  obstruction  of  draught.  Thus  in  Zsch.  f. 
angew.  Ch.  1895,  p.  407,  P.  W.  Ilofmann  alluded  to  a  trial  which 
failed  because  the  hole>$  in  the  plates^  8  millm.  bore,  became  filled 
with  liquid  and  thus  stopped  the  draught.  I  myself  (ibid.  p.  409) 
completely  refuted  this  objection,  mentioning  that  already  about 
200  plate-towers  were  then  at  work,  most  of  them  with  even 
smaller  holes,  and  a  large  number  with  8  millim.  holes,  in 
sulphuric-acid  works.  These  works  had  been  very  successful, 
as  was  autfientically  proved  by  the  replies  to  interrogations  put 
to  certain  firms,  which  also  show  that,  if  the  section  of  the  tower 
is  sufficiently  lai*ge,  no  trouble  is  caused  by  draught  of  the  kind 
mentioned  by  Hofmann.  Since  the  principle  of  artificial  draught 
by  means,  of  fan-blasts  is  becoming  more  aud  more  applied  to 
vitriol-chambers,  the  complaint  against  the  plate-towers  on  the 
above  ground  is  practically  meaningless. 

The  greatest  development  of  the  plate-tower  system  took  place 
when  H.  H.  Niedenfiihr,  chemical  engineer  of  Berlin,  took  the 
matter  in  hand.  He  has  designed  and  started  many  chamber- 
plants  on  that  system,  and  studied  all  the  conditions  necessary 
for  success,  so  that  I  shall  refer  principally  to  him  in  the 
following  description. 

The  part  played  by  the  Lunge  towers  in  the  manufacture  of 
sulphuric  acid  has  been  discussed  at  length  by  Niedenfiihr,  iu 
'  Chem.  Zeit.^  1896,  p.  31.  According  to  him,  plate-towers  are 
not  very  well  adapted  for  replacing  the  whole  of  the  ordinary 
vitriol-chambers  ;  the  first  pai't  of  the  process  is  always  best 
carried  out  in  a  single  lead  chamber,  as  here  the  gases  are  still 
sufficiently  concentrated  to  react  upon  each  other.  [In  this 
view,  as  well  as  in  all  other  essential  points  of  Niedenfiihr's 
paper,  I  fully  concur.]  Here  also  the  flue-dust  and  the  excessive 
rise  of  temperature  would  act  injuriously.  Hence  it  is  not  advan- 
tageous to  place  a  Lunge  tower  between  the  Glover  tower  and  the 


APFLICi^TION  OF  PLATE-TOWERS.  489 

first  chamber^  but  it  should  be  placed  in  the  central  or  back  part 
of  the  set  of  chambers.  Even  then  the  results  obtained  with 
these  towers  do  and  must  differ  at  different  works^  according  to 
circumstances^  viz.^  the  available  chamber-space^  the  draughty  the 
size  of  the  burners  and  of  the  connecting-pipes,  of  the  Gay-Lussac 
tower,  and  so  forth.  In  some  cases  the  working  capacity  of  the 
tower  is  partly  taken  up  for  correcting  some  fault  in  the  set  of 
chambers  to  which  it  has  been  applied.  Niedenfiihr  quotes  the 
following  special  instances  of  the  work  done  by  Lunge  towers,  as 
personally  observed  by  him  in  the  cases  stated. 

In  one  case,  a  Lunge  tower  was  placed  between  the  two  chambers 
of  a  set,  which  were  of  equal  size;  the  total  length  of  the  set 
was  193  ft.  6  in.  and  its  contents  =  9^,640  cubic  feet.  The 
quantity  of  Sicilian  sulphur  burnt  previously  did  not  exceed 
30  cwt.  per  24  hours ;  but  after  putting  up  the  tower  it  could  be 
raised  to  46  cwt.,  evidently  because  the  time  and  the  length  of 
the  path  of  the  gases  had  been  thereby  increased  to  such  an  extent 
that  the  set  could  be  worked  with  stronger  draught,  and  more 
sulphur  could  be  burnt  accordingly.  In  another  case  (4  chambers, 
total  capacity  38,150  cubic  feet,  length  78  ft.  6  in.)  the  production 
could  be  increased  from  15  to  18  cwt.  of  Sicilian  sulphur  per  day. 
This  means  that  some  improvement  had  been  effected,  but  prin- 
cipally in  this  respect,  that  the  previously  observed  fault,  viz.  the 
carrying  forward  of  the  process  into  the  Gay-Lussac,  was  now 
avoided.  In  a  similar  case,  the  production  rose  from  16  to  19  cwt. 
of  sulphur ;  in  both  cases  less  nitre  was  consumed  than  previously. 
The  towers  thus  spent  part  of  their  efficiency  in  correcting  the 
faults  of  the  old  plant,  and  this  in  many  cases  would  be  a  very 
desirable  object;  but  the  quantitative  results  thus  obtained  do 
not  represent  the  whole  of  the  working  capacity  of  the  towers, 
which  in  some  more  favourable  cases  has  admitted  of  increasing 
the  production  by  45  per  cent.  Nearly  in  every  case  observed  by 
Niedenfiihr  this  capacity  of  the  towers  had  not  l)een  exhausted, 
for  the  chamber  following  upon  the  towers  had  hardly  any  more 
work  to  do ;  more  work  could  have  been  done  by  increasing  the 
number  of  the  burners,  by  enlarging  the  connecting-pipes,  or  by 
other  suitable  measures.  The  very  low  temperature  of  the  back 
chambers  in  this  case,  however,  is  useful  in  condensing  part  of 
the  nitrous  gases  and  lightening  the  work  of  the  Gay-Lussac 
tower.     Formerly  the  acid  from  the  Lunge  towers  was  sometimes 


490  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

too  nitrous,  but  this  drawback  has  been  avoided  by  feeding  the 
toM'crs  with  acid  of  from  38°  to  42°  Be.  (spec.  grav.  1-357  to 
1-410). 

The  Lunge  tower  cannot  be  simply  substituted  for  a  OloTer 
tower,  as  the  holes  of  the  plates  would  be  too  quickly  stopped  up 
by  flue-dust;  and  in  washing  this  down  they  would  easily  crack. 
Niedenfiihr,  however,  recommends  placing  a  few  tiers  of  plates 
with  ^-inch  holes  in  the  upper  part  of  the  tower.  He  quotes  a 
case  where  a  Lunge  tower  was  found  specially  useful  in  com- 
pletely denitrating  chamber-acid  required  to  be  entirely  free  from 
nitrogen  compounds.  [Comp.  another  case  of  special  utility  in 
the  6th  Chapter.] 

Especially  good  results  have  been  obtained  in  a  number  of 
cases,  personally  observed  by  NiedenfUhr,  where  plate-towers  were 
employed  as  auxiliaries  to  Gay-Lussac  towers.  They  act  uot 
merely  in  promoting  the  absorption  of  the  nitrous  gases,  but  also 
in  rendering  the  chamber-work  much  jnore  regular,  especially  in 
places  where  the  chambers  are  subjected  to  sudden  changes  ot 
weather,  gales,  &c. 

Niedenfiihr  in  the  above-quoted  paper  makes  certain  proposals 
for  the  erection  of  sulphuric-acid  works,  forming  a  combination  of 
chambers  and  plate-towers,  which  we  do  not  quote  here,  because 
they  are  rendered  obsolete  by  recent  experience,  the  result  of 
which  will  be  noticed  in  the  10th  Chapter,  where  a  complete  plan 
for  this  purpose  will  be  given.     [Comp.  also  p.  496.] 

LUty  (Zsch.  angew.  Ch.  1897,  p.  484)  also  discusses  at  length 
the  function  of  '^  Lunge  towers  *'  as  intermediate  reaction-towers. 
He  quotes  the  results  of  ten  different  works  employing  such  towers 
between  the  chambers  as  means  for  reducing  the  chamber-space, 
from  England,  Scotland,  Spain,  Russia,  Denmark,  showing  a  large 
saving  of  space,  without  any  increase  in  the  consumption  of 
nitre.  He  also  gives  detailed  estimates  showing  that,  apart  from 
the  saving  of  ground-space,  a  set  of  chambers  provided  with  such 
reaction-towers  costs  35  per  cent,  less  than  ordinary  chambers  for 
the  same  production. 

More  recently,  Niedenfiihr  (Chem.  Zeit.  1897,  no.  20)  quotes 
practical  results  from  two  English  works.  One  of  them  replaced 
the  last  chamber  of  a  set,  with  a  capacity  of  38,390  cub.  feet,  by 
a  LuDge  tower  of  256  plates  iti  16  layers,  with  the  same  make 
as   before.     Here  each  plate  actually  made  10*6  kils.  H9SO4  in 


ERECTION  UF  PLATE-TOnERS.  491 

Fig.  188.  Fig.  189. 


m 


l^h — 

^^^^i 

p^r-^ — frfii 

&     n 

,pi. 

^': 

<< 

W 

1  ■; 

i. 

...,.    ^1;  fl 

/■: 

•^ 

:y 

492  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

24  hours,  or  216*7  kils.  per  cubic  metre  of  the  space  filled  with 
plates,  e,  g.  about  100  times  as  much  as  ordinary  lead  chambers. 
Another  factory,  with  very  poor  gases,  still  made  88*3  kils,  HoSO^ 
per  cubic  metre  of  plate-space.  [Comp.  also  Zsch.  angew. 
Ch.  1900,  p.  960.] 

Niedenfiihr  (private  communication)  gives  the  following  detailed 
instructions  for  the  erection  of  Lunge  towers,  taking,  for  instance, 
a  tower  of  a  sectional  area  of  20  plates,  2  feet  square  each^  placed 
4x5. 

A  brick  foundation  is  usuallv  made,  but  in  case  of  need  the 
tower  can  be  placed  on  the  flooring  surrounding  the  chambers,  if 
properly  supported.  The  leaden  shell  is  erected,  with  its  outer 
frame  of  wood  and  a  lead  bottom.  On  this  a  dwarf  wall  of 
9-inch  fire-bricks  is  placed  all  round  the  circumference,  and  a 
central  supporting  pillar.  This  wall  supports  an  iron  frame,  con- 
sisting of  one  or  more  (in  this  case  of  six)  pieces.  The  middle 
pillar  supports  the  places  where  four  of  the  six  pieces  meet.  This 
frame  is  covered  with  lead^  the  joints  being  so  arranged  that  the 
upper,  bearing  surface  remains  free  and  smooth.  On  this  frame 
the  stoneware  bearers  (figs.  187-192)  are  placed.  There  are  corner 
pieces,  a,  which  carry  one  of  the  corners  of  the  plates,  the  three 
others  being  supported  by  T-pieces  b  and  cross-pieces  c.  Between 
these  pieces  the  longitudinal  bearers  are  placed  along  the  lead 
sides  of  the  tower.  In  order  to  prevent  any  shifting  of  the  pieces, 
wedges  are  put  in  suitable  places. 

Upon  the  frames  thus  prepared  the  Lunge  plates  are  put,  and 
after  finishing  off  one  layer  the  parts  forming  the  next  frame  are 
placed  upon  the  corresponding  cross-  and  angle-pieces  &c.  The 
parts  a,  d,  c  are  so  chosen  that  there  is  a  distance  of  2^  inches 
between  the  single  layers  of  plates.  If  a  greater  distance  is 
desired,  we  place  below  the  parts  a,  i,  c  other  cross-,  T-.  and 
angle-pieces,  aj,  i^,  Ci,  3*14  inches  high.  According  to  the  number 
of  layers  of  bearing-pieces  we  designate  the  distance  from  plate 
to  plate  as  single,  double,  treble,  &c.  The  tower  in  question  has 
in  its  lower  part  10  layers  at  single  distances  and  6  layers  with 
double  distances. 

The  top  of  the  tower  is  made  of  lead,  and  is  provided  with  a 
proper  feeding-arrangement. 

If  plate-towers  are  to  be  combined  with  existing  systems^  it  is 
of  course  necessary  to  consider  the  place  and  level  where  the 


PLATE-TOWKRS. 


493 


towel's  arc  to  be  erected^  and  their  dimensions^  in  connection  with 
the  existing  circumstances^  so  that  it  is  difficult  to  lay  down 
general  rules.  But  where  new  plant  is  to  be  erected,  long  expe> 
rience  now  admits  of  establishing  certain  rules. 

It  is  possible  (as  Mr.  Niedenfiihr  now  holds)  to  replace  the  lead 
chambers  altogether  by  Lunge  towera,  by  taking  care  to  erect  the 
first  part  with  as  little  loss  of  draught  as  possible,  and  to  remove 
the  heat  of  reaction  to  the  necessary  extent.  This  is  done  by 
making  the  reaction  towers,  immediately  following  the  Glover 
towers,  of  a  wider  section,  and  providing  them  with  a  very 
efficient  feeding  arrangement.  The  last  towers  must  be  made 
narrower  than  corresponds  to  the  volume  of  gases  passing  through 
the  first  towers,  so  as  to  exert  a  certain  pressure  on  the  gases 
which  promotes  the  reaction.  The  plate  distances  in  these  final 
towers  must  be  kept  smaller  than  in  the  first  towers. 

The  horizontal  sections  of  Lunge  towers  may  be  chosen 
according  to  the  following  particulars  : — 


Sulphur  to  be 
burnt  per  24  hours. 


Up  to  1  ton  S   

From  1  to  2^  tons  S. 
From  2i  to  5  tons  S. 


Number  of  plates  to  be  employed  per  ton 
of  sulphur  burnt  in  24  hours  to  replace  the 
chambers  in  dififerent  parts  of  the  system: — 


in  front.        in  the  middle. 


12 
12  to  10 
10  to  6 


10 
10  to  8 
8to5 


in  the  rear. 


6 

6to5 
5to4 


The  number  of  layers  for  a  given  production  is  calculated  as 
follows  : — In  the  first  third  of  a  system,  where  the  plates  are  at  a 
treble  distance  from  each  other,  each  plate  may  be  assumed  to 
produce  in  24  hours  from  10  to  12  kils.  H2SO4 ;  in  the  second 
third,  with  double  distances,  each  plate  =  6  to  8  kils.  H2SO4,  in 
the  last  third,  with  single  distances,  1*25  to  2  kils.  HsSO^. 

Just  as  it  is  irrational  to  make  a  chamber  system  of  one  chamber 
only^  which  favours  the  diffusion  of  the  inactive  residual  gases 
witli  the  active  ones,  it  would  be  wrong  to  try  manufacturing 
with  one  tower  only,  instead  of  dividing  the  work  over  several 
towers. 

Mr.   Niedenfiihr  believes   the   following   arrangement   to   be 


494  CONSTRUCTION  OP  THE  LEAR  CHAMBEaS, 

suitable  for  vorkiiig  with  towers  aloue,  without  chambers 
(figs.  198  and  194).  The  burner-gases  pass  through  a  into  a 
preliminary  tower  b,  and  through  c  into  the  fan.blast  d,  which 
conveys  them  through  e  to  the  denitrator  /.  This  apparatus  is 
fed  with  nitrous  vitriol  and  warm  water  or  dilute  acid  so  as  to 
furnish  acid  of  54"  B.  (  =  119J°Tw.).  It  also  receives  the  nitric 
acid  required  for  making  up  the  losses.  It  is  packed  like  a  Glover 
tower,  preferably  with  dish-like  packing.     Part  of  (he  acid  here 


Fig.  104. 


made  is  employed  for  feeding  tower  d.  This  deoitrating  tower  is 
constmcted  on  the  same  principle  as  Niedenfiihr's  or<linary  Glover 
towers  (comp.  next  Chapter),  viz.  with  an  interruption  of  the 
packing  intended  to  facilitate  the  cleaning  of  the  bottom  part,  and 
with  sufficiently  large  o^ienings  for  the  passage  of  the  gas.  In 
towor  b  the  acid  with  which  it  is  fed  is  concentrated,  the  gases  are 
|)urified  and  partly  cooled  so  that  they  may  pass  through  the  fan- 
Wast  without  any  trouble.  They  effect  the  denitration  in  /  and 
then  pass  through  gi,  g^,  to  the  first  plate-tower  A;  pipes  gi,  g~,  as 
well  as  the  further  pipes  Ji,  ij,  are  provided  with  steam-pi|ies. 
Tower  h  is   filled  with  12  layers  of  24   plates  each   in   treble 


PLATE-TOWKRS. 


495 


distances  ;  tower  k  with  18  layers  of  20  plates  each  in  double 
distances.  In  h  and  k  the  gases  enter  at  the  bottom  and  issue  at 
the  top ;  but  in  the  last  reaction-tower  m  they  enter  at  the  top 
and  leave  it  at  the  bottom  through  n,  which  arrangement  has  been 
found  to  give  the  best  result.  Tower  m  contains  30  layers  of 
12  plates  each  in  single  distances.     The  gases  now  pass  into  the 


Fig.  195. 


«s 


i^^'M:^Mr^;.u!4^.!..|.-.'^ 


Fig.  190. 


^^^^ 

0 


*  ■    •    • 


a 

-il 

^^ 

e 

^ K 

f 

first  6ay-Lussac  tower  o,  containing  16  layers  of  9  plates  each, 
then  into  the  second  Gay-Lussac  p,  packed  with  coke^  and  finally 
through  q  into  the  open  air. 

The  acid  coming  from  the  first  Glover  tower  b  is  freed  from 
most  of  its  impurities  by  means  of  an  air-cooler. 

The  just  described  system  would  serve  to  treat  the  gases  from 


496  CONSTRUCTION  OP  THE  LEAD  CHAMBERS. 

2500  kils.  =  2^  tons  sulphur  per  diem.     The  production  of  acid 
would  be  divided  as  follows : — 

Tower  h,  288  plates  at  10      kils.  HsS04=3168  kils.  HjSO*. 
„     A,  360      „      „     7         „         „      ^2520     „         „ 
„     m,360      „      „     1-75    „         „      =  630     „         „ 
Glover  and  Gay-Lussac  towers 882     „         „ 


Total 7200    „         „ 

If  the  same  production  is  to  be  attained  by  means  of  a  combi- 
nation of  chambers  and  plate-towers^  this  can  be  done  as  shown 
in  figs.  195  &  196. 

From  the  Glover  tower,  a,  the  gases  pass  into  a  lead  chamber^  b, 
containing  1064  cub.  metres  =  about  38,000  cub,  feet,  provided 
with  air-cooling  shafts,  ci,  Cg,  Cz  (comp.  p.  477).  In  this  case  no 
fan-blast  need  be  employed,  but  the  gases  must  have  a  Insufficient 
upward  draught  from  the  burners  to  the  Glover  tower  and  from 
this  to  the  chamber  b.  Now  come  the  two  plate-towers  d  and  e. 
These,  as  well  as  tower  a,  may  be  placed  at  a  lower  level,  which 
is  all  the  better  for  the  work.  The  Lunge  tower  d  receives  20 
layers  of  20  plates  each  in  double  distances,  tower  e  30  layers  of 
12  plates  each  in  single  distances.  At  e  the  gases  are  passed  in 
at  the  bottom  and  out  at  the  top,  and  then  through  /  into  the 
first  Gay-Lussac  tower  (a  plate-tower)  g^  into  the  coke-packed 
Gay-Lussac  h^  and  through  i  into  the  open  air.  The  production 
will  be  approximately  divided  as  follows  : — 

Chamber  A,  1054  cub.  met.  at  2*75  kils.  =  2926  kils.  HjSO^. 

Tower  rf,  400  plates  at  7  kils 2800  „  „ 

„      e,  360  plates  at  1-75  kils 630,,  „ 

Glover  and  Gav-Lussac  towers    844 


}}  9f 


Total  7200 

In  a  similar  way  larger  systems  can  be  constructed  with  one 
chamber  and  a  suitable  number  of  liunge  towers.  Mr.  Nieden- 
fUhr  would  not  even  for  the  largest  systems  propose  more  than 
t\\  o  chambers,  placing  between  them  a  very  wide  plate-tower  with 
great  distances,  and  behind  the  second  chamber  all  the  remaining 
towers.  In  the  10th  Chapter  complete  plans  will  be  given  for 
such  a  combination. 

In  order  to  apply  the  Lunge  towers  to  existing  systems,  for  the 
purpose  of  increasing  the  production,  the  circumstances  of  each 


PLATE-TOWERS.  497 

case  must  be  critically  considered  iu  the  light  of  the  large  ex- 
perience now  gained.  It  will  usually  be  best  to  place  the  towers 
behind  the  last  chamber.  The  horizontal  section  of  the  towers  can 
be  calculated  from  the  last  column  of  the  table  given  on  p.  493 ; 
in  the  case  of  yery  large  systems  from  the  second  and  the  last 
column ;  with  good  draught  the  plates  should  be  kept  at  single  or 
double  distances. 

If,  however,  plate-towers  are  to  be  placed  between  existing 
chambers,  all  the  conditions  of  the  system  must  be  carefully 
considered  according  to  the  experience  gained  therewith.  Above 
all,  the  towers  in  large  systems  should  not  be  arranged  just  after 
the  front  chamber,  but  between  the  back  chambers.  The  hori- 
zontal sections,  the  places  in  the  system,  &c*  must  be  calculated 
according  to  the  general  instructions  given  above.  If  we  were, 
for  instance,  to  place  a  Lunge  tower  between  No.  I.  and  No.  II. 
in  a  system  of  four  chambers,  the  last  three  chambers  would  do 
very  little  work.  It  will  be  much  better  to  place  the  tower 
between  Nos.  III.  and  IV.  or  behind  No.  IV, 

Mr.  Niedenfiihr  thinks  that,  in  view  of  the  considerable  saving 
of  expense  effected  by  these  improvements  of  the  ordinary  chamber 
process,  the  contact  systems  cannot  compete  with  the  former  in 
the  production  of  acid  up  to  142°  Tw.,  and  show  their  superiority 
only  for  acids  above  that  strength. 

A  very  instructive  plant  was  erected  by  Mr.  Niedenfiihr  at  the 
"  Lazyhiitte  ^'  works.  The  chamber  system  consisted  originally  of 
four  chambers,  with  a  total  capacity  of  7110  cub.  met.  (=250,000 
cub.  feet),  and  three  Glover  towers,  two  of  which  were  always 
working  at  the  same  time.  In  1900,  working  with  zinc-blende 
and  "  forced  style,''  this  set  produced  on  an  average  25,580  kils. 
acid  of  50°  B.  (106°  Tw.)  per  24  hours,  with  303  nitric  acid 
36°  B.  per  cent,  sulphuric  acid.  In  1901  four  Lunge  towers  were 
erected  behind  the  last  chamber,  viz. :  No.  1. 12  layers  at  20  plates, 
double  distances  ;  No.  II.  16  layers  at  20  plates,  partly  single, 
partly  double  distances;  No.  III.  25  layers  at  16  plates,  single 
distances ;  No.  IV.  (acting  as  a  first  Gay-Lussac  tower)  18  layers 
at  25  plates,  single  distances.  The  production  now  rose  to  36,450 
kils.  acid  of  50°  B.,  with  1-90  per  cent,  nitric  acid  36°  B.  per  cent, 
sulphuric  acid.  Evidently  the  plant  was  not  working  up  to  its  full 
capacity,  but  as  there  was  not  enough  draught,  a  fan-blast  was 
placed  behind  tower  No.  IV.      The  production  of  acid  rose  at 

VOL.  I.  2  k 


498 


CONSTRUCTION  OF  THE  LEAO    CHAMBERS. 


once,  but  during  a  few  days  also  the  cousumption  of  nitric  acid 
(to  4-76  acid  36°  B.  per  cent.).  When^  by  a  number  of  tet^, 
the  draught  had  been  properly  regulated  '(which  is  still  not  quite 
perfect,  since  there  is  only  a  temporary  source  of  power  for  the 
fan-blast,  to  be  replaced  by  a  better  engine  at  the  first  opportunity;, 
the  production  rose  permanently  to  44,600  kils.  acid  of  50°  B., 
with  a  consumption  of  only  1-7  per  cent,  nitric  acid  36°  B.  This, 
for  Upper  Silesian  zinc-ores,  is  a  most  excellent  result,  both  as  to 
production  of  acid  and  saving  of  nitre. 

The  following  estimations  of  temperature  and  manometric 
pressure,  made  with  this  system^  after  the  erection  of  the  plate- 
towers,  at  three  specified  times  (viz.,  before  and  after  the  increase 
of  draught  by  means  of  the  fan-blast),  are  quoted  here  for  the 
sake  of  indicating  their  connection  with  the  above-mentioned 
alterations,  but  we  shall  later  on  describe  the  regulation  of  tempe- 
rature and  draught  of  chamber  systems. 


iAit«r  Hpplyin|(  the  fiut-bliMt  (Sortab^ 
and  I>eceinher>. 


\    Before  applying 
the  fan-blaft  (Sept. 
and  Oct). 

Place  where  the  obMrrations  were 
made. 

Freaaure       op 
mm.  water. 

aa8-pip6  between  Cb.  I.  &  II +1-0  90 

„  „      Ch.II.&IIl +11     '  69 

„      Ch.  III.&IV +0-7r)  o4 

„      Ch.IV.  ATowerl.  -f06    ,  ... 

„  „      Tower  I.&II -09    |  ... 

)i  ff  II         11.  &  111....       — I'D 

M      III.  &  Gay-, 

LugsacClV.).'    -3-6    i    38 
It  ,1  „      IV.  &  Coke- 

tower  (Qaj-Lussao) .     —  4r> 
„  „      Coke  Ghiy-Lu9eac& 

chimney  —9*4 


Before  iiroperly        After  tboron^J 

regulating  the  refifnlatiag  the 

draoght.  draught. 


104 
86 


I  Preuare  ; 
mm.  water. 

+  10 
+0-2    i 
-10     ! 
-3-8 
~,rO 

-6-2  :  . 


+7-4 
+4-8 
-1-4 


»C. 


preasnre 
mm.  water. 


+  1-9 
+0i> 
-0  5 
-4-3 

-71 


91 

7.3:1 

61.1 


+7-4 
+40 


-50 


30 


Other  Apparatus  on  the  principle  of  Plaie'towers.-^Atter  the 
success  of  the  principle  embodied  in  the  ''  plate-towers  "  had  been 
thoroughly  established,  it  was  only  natural  that  other  inventors 
should  try,  more  or  less  successfully,  to  attain  the  same  end  bv 
other  means,  not 'coming  under  the  Lunge- Rohrmann  patents. 

[is  was  all  the  more  likely,  as  the  price  of  the  "  plates  ''  and  the 


i 


APPARATUS  SIMILAR  TO  PLAT£-TOWER8.  499 

fittings  belonging  to  them  was  at  first  rather  high^  owing  to  the 
technical  difficulties  of  their  manufacture.  Since  these  difficulties 
have  been  entirely  overcome^  the  price  of  the  plates  &c.  has  been 
so  very  much  reduced  that  most  of  the  imitations  have  lost  even 
any  economical  advantage^  apart  from  their  inferior  efficiency.  I 
shall,  however,  quote  all  the  more  important  of  these  imitations. 

One  of  the  objects  aimed  at  by  some  of  the  inventions  concerned 
is  to  avoid  any  impediment  to  the  draughty  for  which  the  plate- 
towers  are  sometimes  blamed.  As  we  have  seen  (p.  498),  this 
objection  is  of  no  account  in  view  of  the  ease  with  which  the 
chamber-draught  can  be  regulated  by  fan-blasts^  and  it  should  be 
borne  in  mind  that  the  efficiency  of  an  apparatus  of  this  kind 
is  practically  proportionate  precisely  to  its  draught-impeding 
capacity. 

Hacker  and  Gilchrist  (Engl,  patent  15,895,  1893)  employ  the 
same  principle  that  I  have  adopted  in  the  "  plate- towers,^^  to 
which  they  expressly  refer.  Instead  of  my  geometrically  con- 
structed stoneware  plates  for  dividing  the  gases,  the  liquid  acid, 
and  the  acid  vapour,  they  use  a  number  of  horizontal  lead  tubes, 
running  from  one  side  of  the  tower  to  the  other  aud  alternating  in 
position.  These  towers,  which  they  call  ^'  pipe-towers,'^  are  fed 
with  water  or  sulphuric  acid ;  cold  air  is  drawn  or  blown  through 
the  pipes.  A  paper  in  Journ.  Soc.  Chem.  Ind.  1894,  p.  1142, 
contains  a  detailed  account  of  this  system,  in  discussing  which 
several  speakers  threw  great  doubt  upon  its  efficiency.  This  is 
hardly  just,  as  the  introduction  of  these  *' pipe- towers  "  into  many 
American  factories  seems  to  show.  They  cannot  possibly  do  as 
much  work  as  ^^  plate-columns  "  of  the  same  size,  but  undoubtedly 
they  are  of  some  use.  Another  paper  on  these  towers  was  pub- 
lished in  Journ.  Soc.  Chem.  Ind.  1899,  p.  461,  containing  some 
improvements  in  details.  The  success  of  this  system  as  inter- 
mediate towers  between  the  chambers  is  the  best  proof  of  the 
correctness  of  the  principles  which  led  me  to  the  construction  and 
application  of  the  "  plate-columns,"  of  which  the  "  pipe- towers  " 
are  an  imperfect  imitation,  made  of  a  material  liable  to  corrosion 
instead  of  indestructible  stoneware.  A  similar  plan  is  that  of 
Winsloe  &  Hart  (B.  P.  20,142,  of  1901),  who  employ  perpendiculap 
air-cooling  pipes  in  a  shaft  connecting  two  chambers. 

Benker  (French  pat.  238,872)  places  between  the  chambers 
leaden  towers,  5  feet  wide  and  20  or  25  feet  high,  filled  with 

2k2 


500  CONSTKUCTIOX  OF  THE  LEAD  CHAMBERS. 

earthenware  cylinders  4  inches  vide  and  3  to  4  inches  high.  These 
are  fed  with  nitrous  vitriol  from  the  Gay-Lussac  towers  at  the  top, 
and  with  a  steam-jet  at  the  bottom.  The  strength  of  the  out- 
llowing  acid  is  maintained  between  113°  and  ISS'^Tw. ;  it  is  kept  a 
little  nitrons,  to  avoid  the  reduction  going  too  far.  Such  a  tower 
is  placed  behind  the  first  chamber,  which  is  made  lai^  enough  to 
consume  all  the  steam  coming  from  the  Glover  tower;  another 
tower  is  placed  between  the  second  and  third  chambers. — This  is, 
of  course^  a  simple  imitation  of  Lunge  towers  by  cheap,  but  im- 
perfect means. 

Gutlmann  (G. P. 91,815)  recommends  as  a  "packing"  for  re- 
action-towers perforated  globular  bodies  made  of  earthenware, 
glass,  or  metal.  As  shown  in  Hg.  197,  the  perforations  are  con- 
tinued into   short   pipes  turning  into   the   inside  of   the  globe. 

Fi^'.  197. 


These  bodies  may  also  he  undulated  inside  and  outside,  to  increase 
the  acting  surface.  They  can  be  put  into  the  tower  without  any 
special  care  in  packing.  The  liquid  runs  down  both  inside  and 
outside,  and  the  gases  are  well  mixed. 

Niedenfuhr  objects  to  hollow  balls  on  the  system  of  Guttmanu 
and  others,  because,  firstly,  most  of  the  perforations  get  closed  up 
when  filling  the  tower ;  secondly,  the  gases  are  sure  to  take  the 
easier  way  round  the  balls,  instead  of  forcing  their  way  with 
increased  friction  into  the  interior,  and  whatever  does  enter  the 
balls  will  remain  there  for  an  indefinite  time  without  taking  part 
in  the  reactions. 

Another  kind  of  reaction-apparatus  consists  o£  the  "  KegcU 
thiirme "  (cone-towers)  of  the  Bettenhausen  ceramic  works. 
They  are  filled  with  slightly  conical  bodies,  open  at  the  bottom 
and  provided  with  a  shallow  basin  at  the  top.  Niedenf  iihr  (Chem. 
Zeit.  1897,  No.  20)  says  that  they  are  much  less  active  in  dividing 


CHAMBER- FITTINGS.  501 

the  gas  than  Luuge  plates  (only  from  14  to  138  times  per  square 
metre^  against  2400  times  in  the  case  of  Lunge  plates)^  that  they 
contain  less  than  half  the  acid-covered  surface^  and  that  the  hollow 
space  is  altogether  a  mistake^  since  the  gases  will  stagnate  in  them. 
Liity  {eod.  loc.)  also  criticizes  the  Bettenhausen  cones  adversely. 
We  shall  refer  to  them  again  in  the  next  and  also  in  the  12th 
Chapter. 

The  final  result  of  reducing  the  chamber-space  would  be  the 
complete  abolition  of  lead  chambers  in  the  ordinary  sense.  On 
principle^  such  a  step  cannot  be  regarded  as  irrational  or  impos- 
sible, and  it  has  several  times  been  proposed  or  attempted,  both 
in  former  times  (comp.  p.  476)  and  recently  (comp.  p.  493),  since 
the  success  of  the  plate-towers  had  again  shown  that  the  vast 
space  of  ordinary  vitriol-chambers  is  not  indispensable  for  carrying 
on  the  process.  We  shall  discuss  some  of  these  proposals  in 
Chap.  XII. ;  here  I  will  only  refer  to  what  I  have  said  on  p.  487, 
viz.,  that  for  the  commencement  of  the  process  (that  is,  behind 
the  Glover  tower)  I  still  hold  an  ordinary,  comparatively  small, 
lead  chamber  to  be  the  cheapest  kind  of  apparatus  for  the  purpose, 
followed  by  a  number  of  reaction-towers,  perhaps  alternating 
with  one  or  two  small  lead  chambers ;  but  the  last  word  has  not 
yet  been  said  in  that  direction,  aud  it  may  be  that  the  ordinary 
lead  chambers  can  be  entirely  substituted  by  reaction-towers, 
although  hitherto  this  has  not  been  economically  accomplished, 
as  will  be  seen  in  Chap.  XII. 

Chamber^fit  tings. 

Every  set  of  chaml)ers  must  contain  a  number  of  auxiliary  appa- 
ratus, which  in  part  are  absolutely  necessary  for  the  process,  and 
in  part  serve  to  check  it  chemically  and  technically  :  the  former 
are  essentially  those  for  introducing  the  nitre,  the  steam,  and  the 
air ;  the  latter,  smaller  apparatus  will  be  described  first. 

Drawing-off  the  add  is  never  done  by  cocks  attached  to  the 
chambers.  Such  taps  might  be  made  of  hard  lead  (4  to  5  Pb  to 
1  Sb) ;  but  they  would  soon  get  stopped  up  with  sulphate  of  lead, 
and  could  not  very  easily  be  repaired  when  leaking.  It  is  best  to 
place  beside  a  chamber  a  round  or  square  lead^box,  open  at  the  top, 
of  the  same  height  as  the  upstand  of  the  chamber-bottom,  and 
connected  at  or  near  the  bottom  by  a  wide  pipe  with  the  chamber ; 
or  a  suitable  piece  may  be  burnt  on  to  the  chamber,  as  shown  in 


oOJ!  CO.VSTBDCTION  OF  THE  LEAD  CHAUBERS. 

fig.  198,  and   the  connection  made  by  a  slit.     Tbe  )k>x  may  be 
provided  with  a  stopcock  ;  but  more  usually,  asshowain  tbe  Rgure, 


Fig.  199. 


it  carries  in  its  bottom  a  valve-seat  a  of  regulus  metal,  into  which 

fits  a  conical  plug  b  of  the  same  metal  provided  with  an  iron  handle 

covered  with  lead.     The  ruiiuing-off  pipe  d 

is  either  burnt  to  the  valve-seat  or  joined  to 

it  by  an  open  funnel ;  the  latter  permits  the 

running-ofT  to  be  more  easily  observed,  but 

is  apt  to  occasion  running  over,  by  getting 

stopped  up.     Or,  as  shown  in  fig.  199,  a 

lead  siphon  may  be  employed,  with  a  cup 

attached  at  each  end,  a  a,  which  keep  it 

iilways  filled,  so  that  it   begins  to  act  as 

EooQ  as  one  of  its  limbs  has  been  put  into  the  acid.     The  second 

limb  then  enters  into  a  large  funnel  of  the  mnning-off  pipe  b. 

The  simplest  plan,  which  does  not  work  at  all  badly,  is  this :  to 
bum  a  short  piece  of  thick  lead  pipe  to  the  chamber-side,  and  make 
the  joint  very  strong  by  casting  lead  round  it.  'I'hb  pipe  ends 
over  the  funnel  of  the  runuing-off  pipe,  and  is  closed  by  a  good 
india-rubber  cork.     The  men  take  this  out  and  put  it  in  by  hand, 


8IPHUN3.  503 

having  a  bucket  of  water  staadiag  by  to  wash  the  acid  off  their 
hands. 

The  arraDgemeut  shown  in  fig.  200  is  very  good  indeed.  The 
siphon  b  is  firmly  attached  to  tlie  box  c,  or  within  the  npstand  of 
the  chamber.  A  cylinder  d,  surrounding  the  outer  limb  of  the 
siphon,  is  so  suspended  that  it  can  be  drawn  up  or  down  fay  means 
of  the  chain  e  and  the  pulley  /,  and  fixed  in  any  position  by  the 
hook  ff.    The  cylinder  d  forms  a  continuation  of  the  outer  limb  of  b ; 

Fig.  200. 


when  it  is  quite  drawn  up,  so  that  its  overflow  A  is  at  a  higher  level 
than  the  acid  in  c,  it  will  cease  to  run ;  but  when  h  getsjbelow  this 
level,  the  siphon  will  at  once  begin  to  act,  and  the  more  quickly  the 
more  d  is  lowered.  Thus  the  acid  can  be  run  oflF  with  more  or  less 
speed  and  with  the  utmost  cleanliness. 

Fig.  301  represents  a  siphon  suitable  for  hot  acids  in  any  part 
of  the  works.  To  the  top  of  the  siphon  a  a  there  is  joined  by  a  bent 
tube  a  closed  lead  vessel  b,  which  by  an  elastic  tube  is  connected 
with  the  open  vessel  c.  The  latter  is  filled  with  acid  and  lifted 
into  the  dotted  position^  whereupon  b  and  then  the  siphon  a  are 
filled ;  c  is  then  lowered,  upon  which  the  siphon  begins  to  act, 
some  acid  running  back  from  &  to  c  and  thus  producing  a  partiali 


504 


CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 


We  shall  in  this  place  also  mention  the  best  arrangements  for 
inserting  siphons  into  glass  carboys  or  other  vessels  for  carrying 
corrosive  liquids.  The  simplest  and  most  efficient  plan  is  that 
shown  in  fig.  202.  A  glass  or  lead  siphon,  a,  is  inserted  into  a  good 
india-rubber  cork^  made  strongly  conical  so  as  to  fit  bottles  with 
various  sized  necks;  another  short  tube,  b,  passes  through  the 


Fig.  201. 


[ i 


same  cork.  The  siphon,  a,  may  or  may  not  be  provided  with  a 
tap,  c.  It  'will  be  seen  without  explanation  that  the  siphon  can 
be  started  by  blowing  into  b.  The  flow  of  liquid  may  be  stopped 
either  by  closing  the  tap  c,  or,  if  there  is  no  tap^  by  lifting  out  the 
cork,  or  by  opening  a  third  hole  provided  in  the  cork  for  this 
purpose.  In  the  (very  frequent)  case  of  the  mouth  of  the  carboys 
being  too  irregular  in  shape  for  the  cork  to  fit  air-tight,  the  re- 
maining air-channels  are  stopped  up  with  damp  clay  ;  and  in  an 
emergency  a  lump  of  damp  clay  may  replace  the  india-rubber  cork 
entirely. 

Bode  aud  Wimpf  s  siphon  (G.  P.  28,794 ;  Chem.  Zeit.  1885, 
p.  907;  J.  Soc.  Chem.  Ind.  1885,  p.  484;  further  improvements 
in  Zeitsch.  f.  angew.  Ch.  1889,  p.  522)  rests  on  a  very  similar 
principle,  with  addition  of  a  ball-valve  for  stopping  and  starting 
the  siphon.     It  seems  to  be  specially  adapted  for  nitric  acid. 


Fig.  d02. 


506  CONSTRUCTION  OF  THE  LEAD  CBAUBERS. 

Alisch  (G.  p.  9133),  Landel  (G.  P.  9307),  J.  P.  y  More  (G.  P. 
28,721),  Oplander  (G.  P.  30,662),  and  others  hare  constructed 
different  kinds  of  siphons. 

Dc  Hemptinne  has  written  a  pamphlet  in  vhicb  he  traces  a 
great  many  forms  of  siphons  to  their  authors  ;  but  there  is  nothing 
specially  new  in  it. 

Pratt's  carboy -emptier,  sold  by  J.  J.  Griffin  &  Sons,  London,  is 
showu  in  fig.  203. 

J.  Cortin,  of  Newcastle-upon-Tyne,  makes  non-rotative  acid 
valves  of  a  special  mixture  of  regulus  metal,  the  plug  rising  or 
falling  into  its  seat  out  of  a  mixed  setting  without  turning  round, 
so  that  it  is  free  from  friction  in  working,  and  the  wear  and  tear 
are  reduced  to  a  minimum. 

Acid-dishes  (drips,  tell-tales)  are  placed  inside  the  chambers,  in 
oitler  to  examine  the  process  by  ascertaining  the  quantity,  strength, 
and  nitrosity  of  the  condensing  acid.  They  are  made  in  very 
different  ways— for  instance,  that  shown  in  fig.  204.     A  is  a  lead 

Fig.  204. 


ACID-DRIPS.  -  507 

vessel^  burnt  inside  against  the  chamber-side  about  3  feet  above 
the  bottom.  The  acid  caught  here  runs  by  the  tube  a  through  the 
chamber-side  into  the  lead  cylinder  B,  containing  a  hydrometer. 
B  is  provided  near  its  bottom  with  a  side-branchy  b,  reaching  above 
its  top^  and  ending  in  a  funnel  for  receiving  the  acid,  which  thus 
constantly  runs  in  at  the  bottom  and  out  at  the  top  of  B  into  a 
vessel  C^  from  which  it  is  carried  back  by  a  small  pipe  into  the 
chamber.  The  greater  the  length  of  A,  the  quicker  the  acid  will 
be  renewed  in  B,  and  the  more  reliable  are  the  indications. 

Many  manufacturers  place  S-shaped  drip-tubes  in  the  connection 
between  ihe  chambers,  for  a  similar  purpose.  Others  do  not  trust 
to  the  collectors  burnt  to  the  chamber-sides,  but  place  leaden 
or  stoneware  dishes  at  some  distance  from  the  side  within  the 
chamber.  These  rest  on  feet  made  of  lead  tubes^  or  upon  a  stand 
of  stoneware,  so  as  to  be  elevated  above  the  level  of  the  acid ;  and 
they  have  an  outlet  leading  outside  the  chamber.  In  some  works,, 
both  kinds  of  drips  are  fixed  side  by  side ;  and  it  is  noticed  that 
those  fixed  to  the  sides  always  yield  acid  of  6°  to  10°  Twaddell 
less  than  the  inner  drips,  evidently  because  more  aqueous  vapour 
is  condensed  on  the  sides  along  with  the  sulphuric  acid. 

Generally  the  cylinders  of  acid-drips  are  made  far  too  large,  so 
that  they  show  the  changes  in  the  process  much  too  slowly.  It 
is  therefore  preferable  in  all  respects  to  make  the  cylinders  very 
small,  say  holding  about  20  cubic  centimetres,  with  a  side  tube 
and  funnel,  into  which  the  fresh  drips  fall,  as  shown  in  fig.  204, 
whilst  the  cylinder  itself  keeps  overflowing,  and  thus  its  contents 
are  renewed  about  once  in  every  ten  minutes.  Special  small  hydro- 
meters, having  only  a  range  of,  say,  about  20  degrees  Twaddell,  are 
made  for  the  purpose  of  showing  the  strength  of  acid  in  these  small 
drips. 

For  taking  samples  of  the  bottom  acid  itself  a  recess  is  usually 
made  in  some  part  of  the  chamber  by  dressing  back  the  lower  part 
of  the  side.  Some,  in  order  to  be  quite  sure,  always  take  the 
sample  out  of  the  chamber  itself  through  a  special  small  man-hole 
luted  with  moist  clay ;  in  this  case  there  is  a  slight  loss  of  gas,  but 
no  danger  of  getting  stagnant  acid.  Such  a  man-hole  is  shown  in 
fig.  205  in  section.  The  large  man-holes  may  be  made  in  exactly 
the  same  way ;  or  else  their  lids  may  fit  into  a  groove  luted  with 
damp  clay,  as  shown  in  fig.  206.  Large  chambers  are  fitted  with 
several  acid-drips,  man-holes,  &c. 


508  CONSTRUCTION  OF  THE  LEAD  CHAUBBRS. 

For  taking  the  samples  themselves  a  dipper  of  leatl  or  glai 
emplovedj  which  is  lowered  slowly,  so  as  to 
get  all  layers  of  the  acid  into  it."   There  is     ^'?-  ^^-      ^f-  ^***- 
often  a  great  difference  between  the  top  and 
bottom  acid. 

In  German  works  tkermomelers  are  fixed 
at  re^Iar  intervals  of  30  to  50  feet  in  the 
length  of  a  chamber,  whose  mercury- vessel 
is  inside,  and  whose  scale  is  outside  the 
chamber.  This  means  of  observing  the  tem- 
perature is  undoubtedly  infinitely  better  than 
the  rough  one  formerly  in  general  use  in  England,  by  touching 
with  the  hand. 

For  chambers  not  exceeding  100  feet  in  length,  one  set  of  drips, 
thermometers,  &c.  is  generally  thought  sufficient.  For  longer 
chambers  this  is  not  the  case ;  at  the  German  works  there  is 
generally  a  special  set  of  these  fittings  for  about  every  60  feet 
length  of  chamber. 

The  pressure  inside  the  chambers  might  be  indicated  by  any  of 
the  anemometers  to  be  described  further  on;  but  usually  simpler 
means  are  employed,  such  as  ordinary  glass  pressure-gauges. 

Sometimes  stoneware  plugs  are  put  into  holes   made    in    the 
chamber-sides,  in  order  to  indicate  the  pressure  inside  the  chamber. 
The  tension  of  the  gas  is  also  seen  by  lifting  the  lids  of  the  small 
man-holes  {fig,  207),  which  are  al- 
waj's   made    on    the    top   of    the  I'ig-  207. 

chambers  with  hydraulic  lutes,  and 
which  generally  cousistof  glass  jars, 
so  as  to  give  light  for  observation 
through  the  side-windows  (see 
p.  510). 

A  very  sensitive  pressure-gauge 
has  been  described  by  Vogt  (Joum. 
f.  prakt.  Chem.  xiv.  p.  284).     The 

pressure  is  observed  by  the  movement  of  a  small  air-bubble 
playing  in  a  horizontal  glass  tube  of  4  or  5  millimetres  diameter. 
The  glass  tube,  besides  this  bubble,  is  filled  with  water  or  another 
liquid,  and  is  connected  on  each  side  with  a  bottle  tubulated  near 
the  bottom.  One  of  these  bottles  is  15  to  16  centims.,  the  other 
6  to  8  centims.  wide ;  the  liquid  stands  at  the  same  level  in  each. 


FBESSUHE-OAUaES.  509 

The  pressure  within  the  lead  chamber  \»  made  to  act  upoD  the 
surface  of  the  liquid  iu  ooe  of  the  bottles,  and  its  amount  measured 
by  tiie  position  of  the  air-bubble.  The  apparatus  is  all  the  more 
sensitive  the  greater  the  difference  between  the  diameter  of  the 
tube  and  that  of  the  bottles.  There  is  a  contrivance  for  admitting 
a  bubble  of  air  previous  to  using  the  apparatus,  and  for  again 
equalizing  the  levels  after  use. 

A  lery  simple  pressure-gauge,  sufficiently  sensitive  for  ordinary 
purposes,  is  shown  in  fig.  208  (from  Sorel, '  Industries  Chimiques,' 
p.  142).  The  tube  a  has  an  inchnation  from  the  level  in  the  pro- 
portion of  1  :  10 ;  it  is  connected  with  a  reservoir  i,  1  ^  or  2  inches 
wide,  upon  which  the  pressure  is  brought  to  act  by  the  clastic 

Fi;-.  208. 


tube  c  (if  there  is  suction,  the  vessel  to  be  tested  must  be  con- 
nected with  the  bulb  d) ,  The  gauge  is  filled  with  a  mixture  of 
water  and  spirit  of  wine  coloured  with  magenta  or  otherwise. 
As  the  movement  of  the  liquid  in  the  bulb  b  can  be  neglected, 
any  movement  of  the  liquid  in  the  tube  a,  as  measured  on  the 
scale  e,  corresponds  to  one-tenth  of  its  extent  in  real  height.  If,. 
for  instance,  each  degree  on  the  scale  is  =  jL  inch,  it  indicates  a 
real  pressure  of  -^^  inch.  It  is  best  to  cause  the  liquid  to  move 
before  each  observation,  in  order  to  counteract  the  effect  of  friction 
within  the  tube. 

For  gavffinff  the  height  of  the  odd  there  are  cither  stationary  lead 


510 


CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 


Fig/ 209. 


gauges  (which,  however,  are  difficult  to  read-off  exactly),  or  ac- 
curately divided  copper  rods,  which  are 
dipped  in  every  time,  but  always  in 
the  same  place,  since  the  chambers  arc 
never  absolutely  level,  or  glass  floats  like 
that  shown  in  fig.  209,  the  stem,  a,  of 
which  slides  in  a  small  lead  frame,  i, 
whose  upper  edge  serves  as  an  index 
for  reading-off.  The  float  will  sink 
more  or  less  in  the  acid  according 
to  any  alterations  in  its  specific 
gravity.  To  make  this  cause  of  inac- 
curacy less  sensible,  the  ball  of  the  float 
is  made  pretty  large.  These  floats  are 
the  most  convenient  for  reading-off. 

A  very  great  assistance  in  judging 
of  the  chamber-process  is  afforded  by 
glass  ivindows  or  sights^  which  permit 
the  colour  inside  the  chambers  to  be 
Whoever  has  once  got  used  to 


seen. 


these  windows  will  never  do  without  them.     They  are  8  or  9  inches 
square,  and  are  placed,  at  a  convenient  height  for  looking  through, 
in  those  places  in  the  chamber-side  which  lie  in  a  line  with  the 
glass  man-hole  lids  in  the  chamber-tops ;  thus  they  are  sufficiently 
lighted.    Where  the  chambers  are  roofed  in,  light  must  be  procured 
in  some  other  way  (for  instance,  by  two  opposite  windows  corre- 
:sponding  with  a  window  in  the  chamber-shed,  &c.) .    The  chamber- 
glasses  are  put  into  small  lead  rabbets,  and  luted  with  white  lead 
:and  boiled  oil.    The  assertion  is  occasionally  made  that  the  colour 
of  the  gaseous  mixture,  looked  at  across  the  width  of  the  chamber, 
-or  in  the  diagonal  line  from  the  side  to  the  man-hole  lid  in  the  top, 
is  too  deep,  and  that  "  sights  '^  in  the  connecting-tubes  are  pre- 
ferable; but  just  the  opposite  is  the  case,  since  the  observations 
are  evidently  far  more  accurate,  and  any  alterations  of  colour 
much  more  easily  perceived,  in  the  former  than  in  the  latter  case. 
-Only  in  the  first  part  is  the  gaseous  mixture,  through  copious 
condensation  of  acid,  too  opaque  for  observing  its  colour;   but 
just  there  it  is  quite  unnecessary,  for  only  in  the  back  parts  of 
the  set  is  it  important  to  have  always  an  excess  of  red  vapours. 
At  some  works  they  prefer  to  the  ordinary  side-windows,  which 


APPARATUS  POR  INTRODUCING  NITRIC  ACID.  511 

are  rather  difficult  to  keep  clean^  glass  jars^  similar  to  those  shown 
in  fig.  207,  p.  508,  but  placed  on  special  short,  wide  branch-tubes, 
burnt  in  the  sides  of  the  chambers  at  convenient  places.  These  jars 
when  dirty  can  be  exchanged  in  a  moment  for  clean  ones,  and  they 
are  supposed  to  show  all  the  changes  in  the  chamber-atmosphere 
quite  as  well  as  the  glass  panes  fixed  in  the  lead  walls  themselves ; 
but  my  experience  is  decidedly  to  the  contrary,  as  sometimes  the 
side  jars  are  quite  yellow  while  the  chambers  are  already  pale, 
and  vice  versd. 

Apparatus  for  introducing/  Nitric  Acid  into  the  Chambers. 

These  are  divided  into  two  classes.  In  the  first  class  the  nitric 
acid  enters  the  chambers  in  a  state  of  vapour,  mixed  with  the 
burner-gas,  whose  heat  evolves  it  from  a  mixture  of  sodium  nitrate 
and  sulphuric  acid  contained  in  an  iron  pot.  This  is  styled 
^^  potting.^^  In  the  second  class  the  nitric  acid  is  made  in  a 
liquid  form  in  special  apparatus,  and  introduced  as  such  into  the 
chambers.  Opinions  still  differ  as  to  which  of  the  two  plans  is 
best.  The  plan  of  introducing  acid  in  the  state  of  vapour^  which 
is  quite  general  in  England  but  only  rarely  used  on  the  Continent 
(in  America  both  processes  are  found,  but  the  English  plan  more 
frequently  than  the  other),  has  the  advantage  of  greater  simplicity 
and  of  saving  labour  and  fuel.  The  advantage  sometimes  claimed 
for  it^  that  there  is  less  loss  than  by  making  and  employing  liquid 
nitric  acid,  is  hardly  a  real  one ;  for  in  the  first  plan  some  nitric 
acid  is  easily  condensed  during  the  conveyance  of  the  gas  to  the 
chambers^  and  may  corrode  brickwork,  iron,  &c.,  whilst  liquid 
nitric  acid  is  always  introduced  exactly  in  the  place  where  it  is 
needed.  It  is  necessary  to  employ  much  more  sulphuric  acid  for 
the  decomposition  of  the  nitrate  of  soda  in  'Spotting''  than  in 
the  regular  manufacture  of  nitric  acid.  The  presence  of  nitric 
acid  in  the  burner-gas  will  also  induce  a  premature  formation  of 
sulphuric  acid,  especially  if  it  be  'much  cooled ;  but  the  Glover 
tower  obviates  any  inconvenience  arising  from  this.  On  the  other 
hand,  some  are  afriEtid  that  in  "  potting  "  the  nitre-ovens  may  get 
so  hot  that  a  portion  of  the  nitric  acid  will  be  decomposed  down 
to  NO  or  even  to  N ;  but  the  men  generally  employ  so  much 
sulphuric  acid  for  decomposing  the  nitre,  that  this  cannot  easily 
happen,  nor  are  NO  and  N  formed  so  very  readily  as  was  formerly 
supposed  (see  later  on). 


512  CONSTRUCTION  OF  THE  LEAD  CHAHBEES. 

The  advantages  of  introducing  nitric  acid  in  the  liquid  form  are 
the  following : — avoiding  the  entrance  of  false  air  into  the  chambers 
and  the  escape  of  burner-gas  into  the  atmosphere^  both  of  which 
occur  in  many  (not  all)  systems  of  employment  of  gaseous  acid; 
the  possibility  of  employing  as  much  nitric  acid  and  as  quickly 
as  desired,  whilst  in  the  other  case  this  depends  on  the  heat 
of  the  burner-gas,  which  during  a  bad  process,  just  when  most 
nitric  acid  is  needed,  proves  insufficient ;  lastly,  and  most  of  all, 
the  exact  regulation  possible  with  liquid  nitric  acid  and  its  con- 
tinuous supply,  whilst  gaseous  acid  is  always  given  off  from  the 
nitre-mixture  very  unequally.  These  advantages  have  induced 
the  great  majority  of  continental  manufacturers  to  adopt  liquid 
nitric  acid.  Muspratt  ('  Dictionary  of  Chemistry,^  ii.  p.  1029) 
reports  that  a  continental  manufacturer,  who  previously  worked 
with  liquid  nitric  acid,  after  having  seen  the  use  of  solid  nitre  in 
England,  had  saved  one  third  of  his  nitre  by  introducing  the 
English  plan.  This  simply  proves  that  that  manufacturer  had 
not  been  very  careful  before,  and  is  no  guide  whatever.  The 
opposite  experience  has  been  much  more  frequent.  Liquid  nitric 
acid^  however,  will  do  harm  if  the  apparatus  for  introducing  it 
is  not  constructed  in  such  a  way  as  to  completely  volatilize  it  or 
convert  it  into  gaseous  products  before  it  reaches  the  chamber- 
bottom,  since  it  will  act  upon  this.  Accordingly,  sulphur  dioxide 
and  aqueous  vapour,  which  decompose  the  nitric  acid,  must  be 
brought  into  as  complete  contact  with  it  as  possible. 

It  is  claimed  as  an  advantage  for  introducing  the  nitre  by 
^^  potting,^'  that  the  chambers  are  not  exposed  to  the  damage  possible 
with  incautious  handling  of  nitric  acid,  whilst,  on  the  other  hand, 
the  irregular  evolution  of  gas  from  the  nitre-mixture  is  equalized 
by  employing  several  decomposing  apparatus^  and  charging  them 
in  turns,  say,  once  every  hour,  just  after  a  fresh  pyrites-burner  has 
been  charged;  thus  the  stronger  evolution  of  nitre-gas  runs  parallel 
with  that  of  sulphur  dioxide.  Some  prefer  a  contrivance  for 
supplying  gradually,  and  not  all  at  once,  the  sulphuric  acid  serving 
for  decomposing  the  niti*e.  It  is  contended  that  the  best  English 
works,  all  of  which  employ  soUd  nitre,  work  with  as  small  a  con- 
sumption of  it  and  as  good  a  yield  of  vitriol  as  the  best  of  the 
continental  works  employing  liquid  nitric  acid ;  also  on  the  Con- 
tinent some  manufacturers  work  quite  as  well  with  solid  nitre  as 
their  neighbours  with  nitric  acid ;  but  it  is  extremely  difficult  ta 


INTRODUCTION  OF  NITRIC  ACID.  513 

check  such  statements^  as  few  manufacturers  divulge  their  real 
working  results  to  outsiders,  and,  moreover,  very  many  of  them  do 
not  even  know  these  results  themselves  with  that  degree  of 
accuracy  which  is  required  to  decide  this  question. 

There  is  no  doubt  whatever  that  the  chamber-process  can  be 
worked  more  regularly  by  the  continuous  supply  of  nitric  acid  in 
the  liquid  form  (comp.  Eschellmann^s  experiments  at  Widne3, 
infra)  \  and  the  just  objection  to  this,  formerly  existing,  that 
there  was  a  risk  of  damaging  the  first  chamber  in  case  of  a  collapse 
of  the  ''cascades^'  (see  p.  521)  has  been  entirely  removed,  in  the 
first  place  by  the  almost  general  plan  of  introducing  the  nitric  acid 
into  the  Glover  tower,  and  in  the  second  instance  by  spray-pro- 
ducers &c.  The  labour  of,  making  nitric  acid  in  large  apparatus 
and  condensing  it  in  receivers  is  not  much  greater  than  that  of 
frequent  '^  potting  ^'  on  the  English  plan ;  the  waste  of  sulphuric 
acid  for  decomposing  the  nitrate  of  soda  is  much  less  in  the  former 
than  in  the  latter  case,  in  spite  of  utilizing  the  i\itre-cake,  which 
pays  for  the  coal  consumed  in  manufacturing  nitric  acid.  The 
nitric-acid  retorts  are  even  sometimes  heated  by  pyrites-burner 
gases.  These  reasons  explain  why  the  majority  of  continental 
manufacturers  prefer  the  employment  of  liquid  nitric  acid  for 
the  chamber-process,  in  spite  of  the  somewhat  greater  *'  trouble '' 
involved,  which,  however,  is  more  apparent  than  real.  If  all  the 
trouble  caused  by  the  English  potting-process,  in  producing  a 
nuisance,  running  over  of  the  mixture  into  the  kilns,  occasional 
bad  decomposition  of  the  nitre,  frequent  introduction  oE  an 
excess  of  air  into  the  chambers,  &c.,  were  summed  up,  it  would 
greatly  exceed  that  involved  in  making  and  supplying  liquid  nitric 
acid.  There  remains  hardly  anything  in  favour  of  the  English 
plan  except  the  force  of  habit  and  the  fear  of  having  some 
trouble  in  the  transition  from  one  mode  of  working  to  another. 
That  the  imperfection  of  the  present  plan  is  felt  even  in  England 
is  proved  by  the  various  attempts  at  feeding  the  chambers  with 
a  solution  of  sodium  nitrate,  which  are  irrational  in  principle 
and  have  necessarily  failed  (see  later  on). 

We  shall  now  describe  both  ways  of  introducing  nitric  acid,  and 
begin  with  the 

Introduction  of  Nitric  Acid  as  Vapour  (''  Potting ''), 

The  apparatus  serving  for  this  has  been  partially  described  in  a 
VOL.  I.  2l 


514  CUXSTRVCTIOX  OP  THK  LEAD  CIIAMUEK3. 

former  chapter  (pp.  270,  279,  AU),  along  with  the  BulphuT'  aud 
pyrites-burnerB.  The  drawbacks  huve  heeo  pointed  out  which 
attend  placing  the  iiitre-pota  within  tiie  burners,  or,  generally, 
in  such  a  way  that  the  acid  emlphate  boiling  over  can  run  iutu 
the  burners.     Recently,  however,  there  has  always  been  a  special 

I'ifT  -JIO. 


nitre-oven  constructed  by  enlarging  a  suitable  place  in  the  gas-flue. 
It  is  situated  either  above  or,  preferably,  just  behind  the  .burner-, 
and  provided  with  the  necessary  working-doors  and  a  cast-iron 
saucer  for  collecting  what  boils  over.  The  nitre-pots  ibemselvcN 
have  various  shapes — for  instance,  that  shown  in  tig.[210,;   at  «'« 


ledges  are  cast  ou  the  bottom,  which  facilitate  pushing  tbe  pots 
backwards  and  forwards.     Thev  hold  from  8  to  12  lb.  of  nitre. 


FOTTIXO  THE  NITKE.  515 

TLe  "pottiug"  with  these  pots,  which,  strauge  to  say,  are  atill 
(or  have  been  uutil  quite  recently)  met  with  in  some  English 
works  otherwiBe  abreast  of  the  times,  is  very  troublesome  and 
imperfect.  During  the  emptying  and  refilling  of  the  pots  the 
doors  of  the  nitre-oven  are  wide  open,  which  does  even  more 
harm  than  in  the  case  of  the  burners.  The  heavy,  pots,  along 
with  their  melted  contents,  have  to  be  taken  up  with  long  fork- 


Fig.  212. 


shaped  touls  and  emptied,  wliicli  requires  great  strength  and  skill. 
The  pots,  freshly  charged  with  nitre,  are  placed  just  within 
the  door  of  the  oren ;  ilie  necessary  acid  is  poured  in  from  a  jug 
by  superficial  estimation,  and  the  pot  pushed  into  its  place;  not 
till  then  eau  the  door  be  closed.  If  the  draught  is  good,  a  great 
deal  of  air  must  enter,  meeting  not  even  the  same  resistance  as  in 
the  burners;  if  it  is  not  very  strong,  which  will  more  frequently 
be  the  case,  so  much  gas  escapes  that  it  can  be  smelt  for  some 

2l2 


516  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

distance.  Special  clampers  would  partly  obviate  this,  but  are 
rarely  met  with.  (Such  dampers  are  mentioned  in  the  official 
Belgian  Report  of  1855,  p.  23.)  The  pots  are  quickly  worn  out, 
and  must  be  replaced,  especially  if  chamber-acid  is  employed  in 
them.     They  last  much  longer  if  acid  of  140°  Tw.  is  used. 

A  much  more  perfect  plan  is  that  of  decomposing  the  nitre  in  a 
fixed  apparatus,  and  running  off  the  acid  sulphate  (nitre-cake)  in 
a  liquid  form.     This  consists  of  a  seraicylinder  of  cast-iron^  a 
(figs.  211  &  212),  with  a  cast-on  tube  i,  bored  somewhat  conicallr. 
The  latter  projects  out  of  the  nitre-oven,  and  during  the  working  is 
closed  by  a  ground-in  iron  plug  with  a  long  handle.    Outside  there 
is  a  cast-iron  saucer  for  holding  the  nitre-cake,  which  at  once  soli- 
difies.   The  internal  saucer,  c,  catches  the  boilings-over.    The  nitre 
is  introduced  by  the  hopper,  rf,  which  is  provided  with  a  damper: 
and  after  putting  in  the  damper  again,  it  is  made  gas-tight  by  filling 
up  with  the  next  charge  of  nitre.     An  S-shaped  tube  (not  shown 
in  the  diagram)  serves  for  running  in  the  sulphuric  acid,  for  which 
it  is  best  to  provide  a  small  tank  with  a  siphon  or  stopcock.     The 
acid  should  be  run  out  of  this  tank  by  a  pipe  with  a  very  fine 
point  into  the  S-shaped  tube,  so  that  the  running  shall  take  a  long 
time,  and  the  nitre  be  only  gradually  decomposed.     Sometimes  au 
iron  scraper  with  a  long  handle  (passing  through  one  of  the  ends 
of  the  oven)  serves  for  stirring  up  the  mixture  in  the  pan.     The 
hole  for  this  must  be  kept  air-tight  with  clay.     An  apparatus  of 
the  size  drawn  here  holds  56  lb.  of  nitre,  which  can  be  easilr 
decomposed  in  two  hours.     In  any  case  there  should  be  two  or 
more  of  these  apparatus,  so  as  to  make  the  current  of  nitre-gas 
more  regular  by  charging  them  in  turns. 

Even  preferable  to  the  arrangement  here  shown  is  that  of  placing 
the  nitre-trough  in  such  a  way  that  the  burner-gas  can  play  round 
the  bottom  as  well.  The  saucer  for  the  boiling-over  stuff,  which 
forms  the  bottom  of  the  nitre-oven,  must  then  be  placed  some- 
what lower. 

At  Oker  the  potting  is  effected  in  cast-iron  retorts  set  in  the 
liigh  kilns  used  there  (p.  295) ;  the  gas-delivery  pipe  opens  into 
the  gas-flue  belonging  to  the  kilns. 

Rice  (Engl.  pat.  16,757,  1892)  patents  a  contrivance  which  has 
been  in  operation  in  several  places  for  many  years  past,  viz. 
putting  the  nitre-oven  between  the  burnei-s  and  the  Glover 
tower  in  such  a  way  that,  l)y  means  of  valves,  the  burner-gas  can 


INTRODUCTION  OF  LIQUID  NITRIC  ACID.  517 

be  made  to  travel  either  through  the  oven  or  directly  into  the 
chambers. 

A.  P.  O'Brien  (U.S.  P.  694,024)  describes  a  very  complicated 
nitre-oven,  the  practical  results  of  which  are  unknown  to  me. 

An  intermediate  process  between  the  ''  potting ''  system  and  the 
application  of  liquid  nitric  acid  is  the  generation  of  nitric  acid  in  the 
ordinary  retorts,  fired  with  coals  (p.  103  et  seq.),  but  without  con- 
densing the  vapours  to  liquid  nitric  acid  by  passing  them  straight 
into  the  chambers.      This  system,  which  was  followed  in  several 
English  works  about  1880  (Jurisch,  '  Schwefelsaurefabrikation,' 
p.   130),  seems  to  have  neither   the  simplicity  and   (apparent) 
cheapness  of  potting  in  the  nitre-oven,  nor  the  exact  regularity  of 
supply  by  liquid  nitric  acid.     It  costs  as  much  coal  and  very  nearly 
as  much  labour  as  the  latter;  and  the  passage  of  the  vapours  from 
the  nitric-acid  retorts  to  the  chambers  presents  great  difficulties 
on  account  of  the  unavoidable  comdensation  of  liquid  acid,  which 
is  not  entirely  overcome  or  rendered  harmless  by  lining  the  cast- 
iron  pipes  with  stoneware  pipes,  with  an  asphalt  or  asbestos  cement 
between  them.     If  an  acid-maker  once  emancipates  himself  (as  he 
ought !)  from  the  old  system  of  **  potting,"  he  should  proceed  to 
the  thorough  reform  of  making  and  using  liquid  nitric  acid. 

Introduction  of  Liquid  Nitric  Acid 

Any  of  the  apparatus  described  (p.  103  et  seq.)  may  be  employed 
for  the  manufacture  of  nitric  acid  intended  for  use  in  vitriol- 
chambers,  but  no  special  precautions  are  needed  for  obtaining 
the  acid  in  a  concentrated  state  or  free  from  lower  nitrogen 
oxides.  On  the  contrary,  any  low-strength  and  impure  acid  ob- 
tained in  the  manufacture  of  commercial  nitric  acid  may  be 
turned  to  use  in  the  vitriol- chambers. 

It  is,  however,  of  the  greatest  importance  for  the  process  to 
supply  the  acid  in  an  even,  continuous  way,  and  to  regulate  the 
supply  to  a  nicety.  This  can  be  most  simply  done  by  a  Mariotte's 
vessel,  as  shown  in  fig.  213  on  a  scale  of  'f^y  The  stoneware 
vessel.  A,  containing  the  nitric  acid,  is  closed  by  a  caoutchouc  cork, 
a,  holding  a  glass  tube,  b.  The  latter  is  the  only  channel  for  the  air 
which  must  take  the  place  of  any  acid  running  out  through  the 
cock,  c.  As  the  liquid  above  the  level  h  h\  down  to  which  the 
tube  h  reaches,  is  supjiorted  by  atmospheric  pressure,  only  the 


'I 


CONSTRUCTION  OP  THE  LKAD  CtlAMRKKS. 


IMTBODUtTlON  OF  LIQUID  NITRIC  ACIU.  519 

Iieight  of  acid  below  this  can  iaflueuce  the  speed  of  outflow  ;  and 
this  i-emains  coustant  till  the  level  of  the  acid  has  suok  below 
this  point.  The  glas-4  watcr-gau^,  d,  and  the  lead  scale,  e,  admit 
of  observing  the  height  of  liquid  within  the  vessel.  The  latter  is 
tilled  up  through  the  tube  b,  which  ends  in  a  funnel  at  the  top. 
During  this  either  the  cork  must  be  raised,  or  it  must  be  provided 
with  a  separate  open  glass  tube  which  at  other  times  is  kept 
closed.  The  funnel  /  carries  the  acid  into  the  glass  or  stone- 
ware pipes  conveying  it  into  the  chambers. 

At  some  works  there  are  two  tanks  which  are  filled  up  in  turn, 
one  of  them  every  \i  liours,  or  both  every  24  hours.  The  acid 
is  coDtinually  running  out  of  each  tank.  When  one  of  them 
is  half  empty,  the  other  is  just  full ;  and  thus  the  vanatiou  of 
pressure  is  compensated  to  a  certain  extent ;  but  this  plan  cannot 
at  all  vie  in  regularity  with  a  Mariotte's  bottle. 

The  Mariottc  bottles  sometimes  become  stopped  up  by  grains  of 
saud  &c.  getting  inio  the  >ligbtly  opeiicd  stopcock.     Bode  (Diugl. 
Jovrn.  vol.  220.  p.  538)  avoids  this 
by  opening  the   cock   full   bore,  i-jp.  ^14, 

stopping  the  neck  of  the  bottle 
tightly  by  a  caoutchouc  cork  {as 
shown  in  fig,  214),  through  which 
a  tube,  a,  goes  down  to  the  desired 
depth,  and  is  connected  by  an 
clustic  tube  b  with  a  metal  or 
glass  cock,  c,  of  5  inch  bore, 
which  serves  for  regtilaiing  the 
supply.  further  improvements 
in  this  apparatus  have  been  made 
hy  Liebig  (Post's  Z<-it8chr.  f,  d. 
chem.  Grossgew.  1878,  part  2). 

Formerly  the  nitric  acid  used 
to  be  introduced  in  one  or  two 
"tambours"  (that  is,  small  lead 
chambers)  about  a2x  lOx  12  feet, 
or  cylinders   of    10    to    13    feet 

diameter  and  12  feet  height,  placed  between  the  burners  and  the 
main  chamber.  The  second  of  these  contained  the  "cascades" 
or  other  sprcading-apparatus;  it  stood  at  a  higher  level  than  the 
first   tambour,  into  which  it  emptied  its  acid,  and  which   only 


520 


C  OXSTKUCTlOiV  OF  THE  LEAD  CHAMBERS. 


Fig.  215. 


served  for  furthler  exposing  it  to  sulphur  dioxide  and  completely 
driving  oflP  •  the  nitrogen  oxides.  This  first  chamber  received 
enough  steam  to  prevent  the  formation  of  chamber-crystals,  or  to 
decompose  them  if  they  arrived  in  solution  from  the  second 
chamber ;  the  acid  collecting  in  the  first  small  chamber  ran  away 
into  the  main  chamber.  The  first  tambour  is  unnecessary  ;  with 
proper  regulation  the  nitric  acid  can  be  completely  decomposed  in 
the  first  apparatus  by  means  of  SO2  and  steam  ;  but  the  latter 
ought  to  be  supplied  to  such  an  extent  that  the  sulphuric  acid 
formed  contains  rather  more  than  four  molecules  of  water  to  each 
molecule  of  acid.  At  some  French  works  the  above-described 
faulty  arrangement  of  the  cascades  caused  the  acid  in  the  second 
tambour  to  contain  a  good  deal  of  iiilric  acid. 

The  tamboui*s  have  been  mostly  abolished^  and  the  process  is 
carried  on  in  the  main  chamber;  where  the  nitric  acid,  as  is  now 
usual,  is  introduced  through  the  Glover  tower,  the  tambours  are 

entirely  unnecessary. 

Some  manufacturers  do  not  prefer  to  run  the  acid  continuously 

in  a  very  small  jet,  but  intermit- 
tently in  larger  quantities.    For  this 

a   siphon    arrangement    is    mostly 

employed   (fig.   215).      a   conveys 

nitric  acid  into  the  stoneware  vessel 

b ;  through  its  bottom  passes  a  tube      ? 

reaching   about    three-fourths    up 

its  height,  and  open  at  both  ends. 

This  is  covered  by  the  wider  tube  d, 

which  is  closed  at  the  top  and  open 

at  the  bottom,  so  that  the  acid  fills 

up  the  space  between  the  inner  tube      ;  \ 

and  d.     As  soon  as  it  has  got  to     [ 

the  top  of  the  former,  this,  along 

with  fl?,  forms  a  siphon  which  almost  directly  empties  the  contents 

of  d,  whereupon  this  is  slowly  filled  till  the  acid  has  again  risen 

to  the  top  of  til e  inner  tube,  and  so  forth. 

If  the  nitric  acid  were  simply  run  into  the  chambers  it  would 

cause  very  great  mischief.     It  would  dissolve  in  the  chamber-acid 

and  quickly  destroy  the  chamber-bottom ;  moreover,  much  of  it 

would  find  its  way  outside  with  the  chamber-acid  without  doing 

its  duty  within  the  chambers.     It  is  therefore  necessary  that  no 


CASCARES  run  NITKIU  ACIU.  521 

nitric  acid  should  arrive  as  such  at  the  bottom  of  the  chambers, 
but  tliat,  before  reachiDg  there,  it  should  be  decomposed  into 
gaseous  osides  of  nitrt^en.  This  is  doue  by  exposing  it  to  the 
action  of  sulphur  dioxide,  that  is  by  the  chamber-gases  them- 
selves. Before  the  introduction  of  the  Glover  tower,  and  even 
long  after,  no  other  means  were  known  for  this  purpose  than 


ri-. : 


spreading  the  nitric  acid  out  over  a  large  surface  so  that  it  w&i 
thoroughly  exposed  to  the  chamber-gases,  and  nothing  could  reach 
the  bottom  in  an  undecomposed  state.  This  was  done  by  means 
of  stoneware  or  glass  "cascades,"  of  which  there  existed  many 
descriptions,  which  are  fully  explaineil  and  illustrated  in  the  first 
edition  of  this  work,  pp.  308  to  318.  Since  these  cascades  have 
been  almost  entirely  superseded  by  the  Glover  towers,  we  will  here 


522  CONSTRUCTION  OF  THE  LEAD  CllAMBER-S. 

show  only  one  of  the  best  descriptions  of  cascades,  that  made  by 
Fikentscher,  of  Zwickau,  and  shown  in  fig.  216.  The  acid  ran  into 
its  top  is  spread  over  a  large  surface  before  reaching  the  bottom. 

A  fault  inherent  to  all  such  systems  is  this :  that  there  is  no 
really  practical  way  of  knowing  whether  the  nitric  acid  has  been 
entirely  decomposed  before  the  chamber-bottom  is  reached.  The 
means  adopted  for  this  end  at  some  works  leave  much  to  be 
desired. 

By  far  the  simplest  method  of  feeding,  which  dispenses  with  all 
cascades,  tambours,  &c.,  is  that  otrunninff  the  nitric  acid  along  with 
the  nitrous  vitriol  through  the  Glover  tower »  Few  manufacturers 
ventured  to  do  this  at  first,  because  a  loss  of  nitre  was  apprehended 
with  this  plan ;  but  at  most  of  the  best-manacred  works  it  has  now 
been  done  for  many  years  without  involving  any  extra  consumption 
of  nitre,  and  it  may  be  safely  asserted  that  wherever  a  Glover 
tower  in  proper  working  order  exists,  no  other  apparatus  is  re- 
quired for  feeding  the  chambers  with  nitric  acid. 

This  is  a  principle  universally  accepted,  and  borne  out  not 
merely  by  the  practice  of  nearly  all  sulphuric-acid  works  where 
liquid  nitric  acid  is  used,  and  where  a  Glover  tower  forms  part  of 
the  plant,  but  also  by  the  practice  of  all  the  works  following  the 
universal  English  plan  of  " potting^'  nitre  between  the  burners  and 
the  Glover  tower.  It  is  all  the  stranger  that  in  a  modern  treatise 
on  the  manufacture  of  sulphuric  acid  (Jurisch,  ^  Schwefelsaure- 
fabrikation,'  pp.  135  &  153)  the  old  story  is  repeated  of  a  great  L)ss 
of  nitre  in  the  Glover  tower  by  reduction  to  NjO  or  elementary  N, 
on  the  strength  of  some  absolutely  inconclusive  experiments  made 
by  Vorster,  and  refuted  25  years  ago  by  me  (comp.  Chap.  VI.), 
and  of  some  alleged  '^experiences'^  made  in  the  North  of  Prance, 
without  any  proof  by  positive  data.  Wherever  figures  are  given, 
e,g,  Hurter's  experiments  of  1877,  Jurisch  is  compelled  to  concede 
that  with  careful  work  no  more  nitre  was  used  after  introducing 
the  Glover  tower  than  before. 

But  the  reduclio  ad  absurdum  becomes  even  more  complete  by 
the  fact  that  Jurisch,  when  speaking  of  the  deuitration  of  nitrous 
vitriol,  states  that  he  decidedly  prefers  the  Glover  tower  to  all 
other  descriptions  of  apparatus  !  Seeing  that  far  more  nitre  passes 
through  the  Glover  tower  in  the  shape  of  nitrous  vitriol  than  in 
that  of  nitric  acid,  and  that  the  alleged  destructive  action  of  the 
tower  must  be  precisely  the  same  in  both  cases,  the  above  is  a 


INTRODUCTION  OF  LIQUID  NITRIC  ACID.  523 

case  of  straining  at  a  gnat  and  swallowing  a  camel.  And  this  is 
further  illustrated  by  his  remark  (p.  156)  that  the  amoiint  of 
nitre  might  be  to  some  extent  reduced  by  employing  the  Glover 
tower  only  for  treating  the  chamber-acid  and  itetiitrating  the  Oay- 
Lu»!>ac  acid  in  cascades,  but  that  the  slight  gain  in  nitre  would  not 
pay  for  the  expenie  of  working  l/ie  cascades  [which  is  almost  nil,  so 
that  the  "gain  in  nitre"  would  amount  to  the  same  thing]  ! 

The  strangesc  oversight  committed  by  that  obstinate  adherence 
to  the  exploded  idea  of  the  destruction  of  nitre  in  the  Glover 
tower  is  this:  whenever  the  "  potting"  process  is  employed,  t.  e. 
everywhere  in  England,  in  the  majority  of  American  and  in  many 
continental  works,  the  whole  of  the  nitric  acid  is  evolved  in  the 
presence  of  the  greatest  possible  excess  of  sulphur  dioxide 
and  at  the  highest  possible  temperature ;  hence  Voster,  Hurter, 
Kuhlmann,  Jurisch,  and  all  those  who  believe  in  the  destructive 
action  of  the  Glover  tower  on  nitrous  vapours,  ought  to  wonder 
why  the  greater  part  of  the  nitric  acid  is  not  reduced  to  N^O  or 
N  in  the  ordinary  nitre-oven  t 

Sorel  ('  Fabrication  de  I'Acide  sulfurique,'  1887,  p.  SOi)  states, 
as  the  positive  ri-sult  of  the  experience  of  the  St.  Qobaiu  works, 
that  there  is  no  destruction  of  nitric  acid  in  the  Glover  tower. 

Since  in  exceptional  cases  a  Glover  tower  is  not  available  for 


the  introduction  of  nitric  acid,  we  shall  describe  a  very  efficient 
spray-apparatus,    constructed    for    this  purpose   by   M.     Liebig 


Mi  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

(Xeitsch.  des  Vereiiis  deiitscher  Ingenieure,  ]879,  p.  111).       Ii 
consists  of  a  lead  steam-pipe  li  (fig.  217)  with  a  platinum   noule. 


parallel  to  which  ruos  a  glass  pipe  m,  for  coDvejing  the  nitric  acid, 
bent  up  in  front  and  drawn  out  into  a  fine  point,  Tlie  steam  mafa- 
ing  past  this  causes  a  vacuum  in  the  glass  tube,  and  sucks  acid 


INJECTORS  FOR  NITRIC  ACID.  525 

through  the  latter  from  a  stock-bottle^  a  glass  cock  h  regulating 
the  supply.  The  acid  is  divided  into  a  fine  mist,  and  none  of  it 
arrives  at  the  bottom  undecomposed. 

An  apparatus  for  the  same  purpose,  constructed  by  Mr.  Stroof, 
of  the  Griesheim  Avorks,  has  been  made  known  to  me  by  that 
gentleman,  and  is  illustrated  by  figs.  218  &  219. 

Fig.  218  shows  the  general  disposition,  fig.  219  the  details  of 
the  injector  b.  The  nitric  acid  runs  from  a  Mariotte^s  bottle  A 
into  a  Woulfe's  bottle  B,  standing  in  a  glass  dish,  provided  with  an 
overflow-pipe  c,  which  conveys  the  acid,  in  case  of  the  injector 
breaking  down,  on  to  the  cascade  C.  From  the  bottle  B  the  acid 
is  sucked  away  by  the  glass  injector  b,  whose  steam-jet  is  connected 
with  the  steam-pipe  a  by  a  stuffing-box.  Such  injectors  are  best 
made  of  well-annealed  water-gauge  pipes,  drawn  out  to  a  point. 
The  point  projects  but  loosely  into  the  suction-pipe,  so  that  a  little 
air  is  sucked  in  as  well,  and  no  breakage  can  take  place  by  expan- 
sion. At  a  pressure  of  1^  atm.  the  injector  can  carry  away  16  cwt. 
of  nitric  acid  in  24  hours  in  the  form  of  spray,  along  with  a  little 
air.  The  mouth-piece  of  the  injector  must  be  contracted  and 
widened  out  again,  like  that  of  a  fire-engine,  to  prevent  any  larger 
drops  forming  at  that  place.  The  acid  is  thus  completely  converted 
into  a  mist,  and  a  sensible  saving  effected  in  compai*isou  with 
cascades. 

Another  glass  injector  for  nitric  acid  has  been  described  by 
Burgemeister  (Fischer^s  Jahresb.  1880,  p.  228).  He  employs  a 
platinum  nozzle  {not  soldered  with  gold !)  and  a  steam-jet  placed 
just  below,  the  latter  consisting  of  a  platinum  nozzle,  about  ^  inch 
wide,  inside  the  chamber,  continued  outside  into  a  copper  tube. 
Both  tubes  pass  through  a  lead  pipe  burnt  into  the  chamber-side, 
and  are  fastened  in  this  with  glycerine-lead  cement. 

At  the  Freiberg  works,  where,  in  consequence  of  the  complete 
cooling  of  the  roasting-gases,  they  do  not  employ  a  Glover  tower, 
formerly  the  nitric  acid  was  introduced  by  cascades.  These  have 
been  replaced  by  glass  injectors,  constructed  by  Wolf,  as  shown  in 
fig.  220  &  221.  A  glass  tube,  a^,  28  mm.  wide,  is  sealed  to  a 
narrower  central  tube,  a*,  at  the  place  a.  At  b  there  are  three 
glass  knobs  for  steadying  the  inner  tube  a^,  and  at  c  four  small 
glass  knobs  for  steadying  the  platinum  capillary  d.  Tube  a^  is 
provided  with  a  funnel  e  for  running  in  the  nitric  acid.  The 
tube  d,  made  of  platinum-iridium,  is  connected  with  a  steam-pipe 


526 


CONSTRUCTION  OP  THE  LEAD  CHAMBERS. 


and  is  held  in  the  centre  of  pipe  a*  by  an  india-rubber  cork  / 
and  the  knobs  c,  c.  The  outlet  of  a'  is  6  or  7  mm.  wide.  The 
nitric  acid  flows  through  e  into  the  aimular  space  between  a'  and 
a"  and  is  sprayed  into  the  chamber  by  the  steam  issuing  througli 
the  platinum  capillary.  The  whole  is  inserted  into  the  chanaber- 
side  by  means  of  an  india-rubber  joint  at  g^  so  that  it  is  easily 
taken  out  and  cleaned. 


•-7 


Potut  (G.  P.  122,920)  introduces  the  nitric  acid  (or  nitrate  of 
soda  solution,  com  p.  later  on)  by  a  steam  injector  into  the  pipe 
leading  from  the  Glover  tower  to  the  first  chamber,  with  the 
ridiculous  assertion  that  thus  two-thirds  of  the  nitre  are  saved  in 
comparison  with  running  the  nitric  acid  down  the  Glover  tower  or 
straight  into  the  first  chamber. 

Other  manufacturers  inject  nitric  acid  into  the  last  chamber 
(com p.  next  Chapter). 

The  simplest  way  of  introducing  the  nitric  acid  through  tlit 
Glover  tower  is  to  run  a  suitable  quantity  of  it  into  the  uitfois- 
vitriol  tank  at  the  bottom  of  the  tower,  and  pump  up  the  mixture 
in  the  usual  manner.    It  is  sometimes  preferred  to  carry  the  nitiic 


I.NTROIICCIKO  SOLUTION  OF  NITRATE  OF  SOKA.  53? 

acid  to  tlie  top  of  the  chambers  or  the  tower,  and  so  run  it  into 
one  of  the  lutes  of  the  toirer  as  required. 

The  slorivg  of  nitric  acid  on  the  top  of  the  chambers  or  of  the 
(ilover  tower  is  geuerally  effected  iu  large  stonewure  receivers,  or 
else  iu  a  number  of  smaller  stoneware  jars  or  ordinary  glass 
carboys,  ail  of  which  are  connected  by  glass  siphons,  so  that  the 
niDiiing  olf  by  means  of  a  tap-sipliOD  need  take  place  only  from 
the  last  vessel  of  the  set  (Hg.  222),      Vessels  proof  against  nitric 

rij;.  23S.  Fig.  223. 


acid  may  also  be  composed  of  single  pieces  of  stone  joined  togetlicr 
by  a  cement  made  of  finely-ground  asbestos  and  a  dilute  solution 
of  silicate  of  soda,  kneaded  into  a  putty  and  preferably  mixed  with 
ground  sulphate  of  baryta. 

E.  Pohl  (0.  P.  30,188)  employs  irou  vessels  lined  inside  with 
asbestos  cloth  soaked  in  paraffin.  The  riveting  of  the  iron 
shell  is  effected  in  the  manner  shown  iu  fig.  223,  so  that  the  acid 
nowhere  comes  into  contact  with  the  iron. 

Introducing  Nilre  as  an  Aqueous  Solution  of  Nitrate  of  Soda. 

There  is  yet  a  third  way  of  introducing  the  nitre.  Many  yeara 
ugo  several  w oiks  ran  their  nitre  as  a  solution  in  water  into  the 
chambers.  This  has  long  since  been  discontinued,  both  because 
sodium  sulphate  gets  into  the  acid,  which  is  not  allowable  for 
nian\  purposes,  and  because  the  lead  always  wears  away  very 
quickly  at  the  point  where  the  solution  enters.  The  same  method 
was  patented  by  Burnard  {14th  Aug.,  1S75).  The  solution  of 
nitre  was  to  be  injected  into  the  chamber  in  a  thin  jet,  or,  better 
still,  at  once  mixed  with  sulphuric  acid  by  means  of  a  steam, 
jet,  exactly  similar  to  Sprengel's  water-spray  (videinfr&).     The 


528  CONSTRUCTION  OF  THB  LKAD  CHAMBERS. 

chief  object  sought  to  be  attaiucd  in  this  process  was  an  imaginary 
saving  of  nitric  acid,  which  in  the  decomposition  of  nitre  by  the 
burner-gas  was  supposed  to  be  I'educed  to  NjO  and  N.     It  h&^ 
been  shown  on  p.  522,  and  will  again  be  referred  to  in  Chapter  VI., 
that  no  sensible  decomposition  of  this  kind  takes  place  at  all ; 
and  any  advantage  accruing  therefrom  would  be  far  more  than 
-counterbalanced  by  the  difficulty  of  keeping  the  nitre  solution 
long  enough  in  suspension  to   completely  decompose  it  and  to 
prevent  liquid  nitric  acid  from  getting  at  the  chamber-bottom* 
The  process  also  takes  so  much  steam  that  the  acid  in  the  first 
chamber  gets  too  weak.     This  is  certainly  contradicted  by   tlie 
patentees    (Chem.  News,    xxxvii.  p.  203)  ;   but  no  independent 
favourable  testimony  has  yet  been  published^  and  a  saving  of  nitre 
appears  out  of  the  question.     It  would,  however,  seem  feasible  to 
tun  a  solution  of   nitre   through   the  Glover  tower  along  with 
chamber-acid  and  nitrous  vitriol,  so  that  the  nitre  would  he  decom- 
posed  in  the  tower  itself,  sodium  sulphate  and  nitrous  vapours 
being  formed.     Of  course  this  plan,  as  well  as  that  mentioned 
before,  is  restricted  to  the  case  of  all  the  sulphuric  acid   heins: 
intended  for  decomposing  salt,  or  for  the  manufacture  of  super- 
phosphates, &c. 

The  last-mentioned  plan  is  undoubtedly  the  simplest  imagin- 
able for  introducing  the  nitre,  uniting  the  advantages  of  both 
solid  nitre  and  nitric  acid — easy  regulation,  introduction  of  anv 
quantity  at  a  time,  dispensing  with  all  apparatus  for  introducing 
the  nitre  or  manufacturing  nitric  acid,  saving  of  labour  and  coals 
(in  the  case  of  nitric  acid),  avoiding  the  handling  of  nitric- 
acid  carboys  or  of  fluxed  nitre-cake,  the  latter  being  an  article 
difficult  to  utilize  to  any  extent.  Unfortunately  these  advantages 
are  counterbalanced  by  a  drawback,  which  has  induced  most  manu- 
facturers who  have  tried  this  process  to  give  it  up  :  it  is  found  that 
sodium  sulphate  crystallizes  in  the  towers,  tanks^  and  connecting- 
pipes  and  causes  obstructions.  It  would  be  necessary  to  have  two 
Glover  towers  for  each  set,  and  to  run  the  nitre  solution  down  oulv 
one  of  these,  whose  acid  would  not  be  used  for  the  G  ay-Lussac  tower, 
but  for  the  salt-cake  pans  or  for  superphosphate  only.  This  would 
be  verv  inconvenient,  and  for  smaller  works  not  at  all  feasible. 

Blinkhorn  (E.  P.  1084,  1878)  runs  a  solution  of  sodium  nitrate, 
of  spec.  grav.  1*35,  in  a  regular  jet  upon  sulphuric  acid  contained 
in  a  pot  heated  by  the  burner-gas,  and  draws  off  the  solution  of 
sodium  sulphate  from  time  to  time.  This  will  hardly  decompose 
all  the  nitrate ! 


NITROUS  OASES  OBTAINED  AS  BY-PRODUCTS.  529 

Potut  (B.  P.  7710,  1900)  injects  a  solution  of  sodium  nitrate 
between  the  Glover  tower  and  the  first  chamber  (comp,  p.  526). 

Feeding  the  Chambers  with  Nitrous  Gases  obtained  as 

By-products, 

Several  proposals  partly  carried  out  in  practice  have  had  no 
lasting  success.  Thus,  for  instance,  the  attempt  has  been  made 
in  France  to  obtain  oxalic  acid  as  a  by-product  in  evolving  the 
nitre  gas  by  heating  molasses  with  nitric  acid  and  conducting  the 
vapours  into  the  chambers.  The  yield  of  oxalic  acid,  however,  was 
not  large  enough  to  compete  with  its  manufacture  from  sawdust 
by  fusing  caustic  potash.  Not  more  successful  was  a  proposal  of 
Laing  and  Cossins,  to  heat  sodium  nitrate  with  arsenious  acid  or 
chromium  oxide,  in  order  to  obtain  arseniates  or  chromates  along 
with  nitrous  acid  for  the  chamber-process  (Wagner's  Jahresb. 
186 "i,  p.  207).  It  is  also  quite  feasible  to  convey  any  nitrous  gas 
generated  in  making  arsenic,  antimonic,  phthalic  acid,  &c.  by 
means  of  nitric  acid,  which  formerly  used  to  be  lost,  into  the  lead 
chambers;  but  this  process,  which  (like  all  similar  ones)  can 
hardly  be  so  conducted  as  to  give  a  sufficiently  regular  supply  of 
nitre  to  the  chambers,  is  no  longer  called  for,  since  the  respective 
works  now  regularly  regenerate  nearly  the  whole  of  the  nitric  acid 
by  mere  contact  of  the  vapours  with  an  excess  of  air  and  water  in 
^'plate-towers^'  or  similar  apparatus  (comp.  p.  125  et  seq.). 

An  ingenious  process,  invented  by  Dunlop,  was  for  many  years 
carried  out  at  St.  RoUox,  but  it  has  not  been  used  at  the  new  works 
at  Hebburn  belonging  to  the  same  firm.  A  mixture  of  common 
salt,  nitrate  of  soda,  and  sulphuric  acid  is  heated  in  large  iron 
cylinders ;  the  principal  reaction  setting  in  is  as  follows : — 

3SO4H8  +  2NaN03  +  4NaCl = SNajSO^  +  N2O3 + 4C1  +  SU^O ; 

but  the  further  deoxidation  of  nitric  acid  will  only  be  prevented 
by  keeping  within  certain  limits  of  temperature.  Thus  there  re- 
mains a  soluble  residue  of  sodium  sulphate,  whilst  chlorine  and 
nitrous  acid  are  given  off  in  a  gaseous  state.  The  two  gases  are 
separated  by  passing  them  through  a  series  of  leaden  Woulfe's 
bottles  filled  with  sulphuric  acid  of  1*75  spec,  grav.,  which  retains 
the  nitre-gas,  being  converted  into  "  nitrous  vitriol  ^'  and  used  as 
such  {vide  infi'a) ;  the  chlorine  passes  through  without  absorption 
and  is  utilized  for  bleaching-powder.  The  advantage  of  this 
VOL.  I.  2  m 


530  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

process  is^  that  chlorine  is  obtained  direct  from  salt  without 
making  any  hydrochloric  acid  and  without  wasting  manganese. 
The  drawbacks  are : — that  the  nitre-gas  has  to  be  evolvcsd  again 
from  the  nitrous  vitriol^  which  at  that  time  could  only  be  done  by 
diluting  with  hot  water^  necessitating  a  reconcentration  of  the 
vitriol ;  that  there  is  a  danger  of  losing  nitrogen  compounds ;  and 
that  the  apparatus  is  very  complicated.  This  process  consequently 
did  not  obtain  permanent  success. 

At  the  Uetikon  works^  near  Zurich^  nearly  all  the  nitre  re- 
quired for  the  chambers  is  obtained  in  the  manufacture  of  iron 
mordant  for  dyeing  purposes.  This  is  made  by  treating  ferrous 
sulphate  with  nitric  acid^  and  thus  oxidizing  the  ferrous  to  ferric 
sulphate.  The  nitric  acid  is  thereby  reduced  mostly  to  lower 
oxides  of  nitrogen;  these  gases  are  conveyed  into  the  vitriol- 
chambers^  and  there  do  exactly  the  same  duty  as  if  the  nitric  acid 
had  been  directly  supplied  to  the  chambers.  Recently  the  manu- 
facture ofcupric  sulphate  from  metallic  copper^  sulphuric  and  nitric 
acid  has  been  introduced  at  the  same  works^  equally  carrying  all 
the  nitrous  vapours  into  the  vitriol-chambers. 

Supply  of  Water  as  Steam  or  Spray. 

The  water  required  to  produce  UsS04  and  to  dilute  this  to  the 
point  required  for  the  practical  working  of  the  chambers  must  be 
presented  to  the  gases  in  as  fine  a  state  of  division  as  possible. 
This  was  formerly  in  all  cases  and  is  still  generally  effected  by 
injecting  into  the  chamber  a  certain  quantity  of  steam,  which 
rushes  forward  and  on  its  way  is  condensed  to  a  mist  of  very  fine 
particles  of  liquid  water.  At  many  works^  however,  water  is  now 
injected  in  the  shape  of  a  mechanically  produced  spray* 

The  Steam 

is  always  generated  in  an  ordinary  steam-boiler,  since  boilers 
placed  above  the  sulphur-burners  have  been  given  up  everywhere. 
The  boilers  are  constructed  in  the  usual  manner,  but  are  mostly 
made  for  low  pressure,  rarely  working  above  two  atmospheres^ 
more  frequently  only  at  one  or  one  and  a  half  atmosphere;  in  the 
south  of  France  they  work  at  three  or  three  and  a  half  atmo^ 
spheres.  A  high  pressure  has  no  object  so  long  as  the  liquid  is 
spread  over  the  whole  chamber-space ;  for  even  low-pressure  steam 
fulfils  this  requirement  and  sufficiently  assists  the  draught.     Low^ 


SUPPLY  OF  STEAM.  531 

pressure  steam  is  more  easily  kept  at  a  uniform  tension  tlian  high- 
pressure :  without  this  no  regulation  of  the  supply  of  steam  to  the 
chambers  by  the  attendant  is  of  any  avail.  High-pressure  steam 
certainly  condenses  less  readily  than  low-pressure  steam ;  but  this 
is  a  doubtful  advantage^  so  long  as  the  steam  possesses  enough 
'^  carrying-power"  to  convey  the  minute  globules  of  water  right  to 
the  other  end  of  the  chamber.  Experience  has  shown  that  this  is 
the  case  even  with  low-pressure  steam;  at  most  English  works  they 
employ  only  a  single  jet  at  one  end  of  each  chamber^  and  consider 
this  quite  sufficient  to  supply  the  whole  chamber  with  moisture^ 
but  I  do  not  like  this  practice  (see  p.  534). 

Of  course  low-pressure  steam  may  be  obtained  from  a  boiler 
working  at  high  pressure  by  means  of  a  reducing-valve.  Thus  at 
the  Oker  works  the  steam-pressure  in  the  boilers  is  8  to  3*5 
atmospheres^  and  is  reduced  to  1  to  1*5  atmosphere  for  feeding 
the  chambers.  At  small  works  the  same  boiler  may  be  utilized 
for  supplying  the  chambers  and  for  driving  the  machinery  of 
stone-breakers^  air-pumps,  and  so  forth. 

It  is  also  almost  a  matter  of  course  that  the  chambers  may  be  fed 
with  the  exhaust-steam  of  engines^  if  these  are  worked  in  such  a 
way  as  to  leave  some  pressure  in  the  exhaust.  The  utilization  of 
the  waste  steam  of  the  Gay-Lussac  air-pump  for  this  purpose  had 
been  practised  by  myself  for  many  years,  as  described  in  the  first 
edition  of  this  work  (1879),  vol.  i.  pp.  393  &  565.  A  proposal 
not  essentially  differing  from  this  was  patented  much  later  by 
Sprengel  (No.  10,798, 1886). 

At  some  large  works,  in  order  to  control  the  uniform  tension 
of  the  steam,  so  important  for  the  regularity  of  the  chamber 
process,  registering  steam-gauges  are  employed,  which  show  the 
tension  during  the  whole  day  on  a  sheet  of  paper  wrapped  round 
a  drum  making  one  revolution  in  twenty-four  hours.  Such  a 
gauge,  made  by  Schaeffer  and  Budenberg,  of  Magdeburg,  is  de- 
scribed in  'Dingler's  Journal,'  ccxxvii.  p.  519. 

The  conveyance  of  the  steam  to  the  chambers  usually  takes  place 
in  cast-iron  pipes,  with  one  or  more  branches  for  each  chamber^ 
The  main-pipes  in  any  case,  and,  if  possible,  also  the  branch-pipes^ 
considering  their  great  length,  should  be  surrounded  by  bad  con* 
ductors  of  heat  to  restrict  radiation  as  much  as  possible,  and  avoid 
a  considerable  loss  by  condensation  of  water. 

The  pipes  must  always  be  laid  with  a  slight  fall  towards  the 

2m2 


532 


CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 


boiler^  so  that  the  condensed  water  may  run  back.  Where^  from 
local  circumstances^  this  cannot  be  done^  automatic  apparatus  for 
removing  the  water  should  be  fixed  at  the  lowest  points. 

Of  course  the  size  of  the  main-pipes  must  correspond  to  the 
number  and  size  of  the  chambers.  When  more  than  one  steam* 
boiler  is  required^  they  are  placed  together  and  their  main-pipes 
connected  so  as  to  equalize  the  pressure.  The  branches  for  each 
chamber  need  not  be  above  1  inch  wide^  even  for  large  chambers 
(up  to  70,000  cubic  feet)  supplied  by  one  jet.  They  are  made  of 
wrought-iron  tubes,  a  (fig.  224),  sometimes  of  copper,  up  to  a  short 

Fig.  224. 


distance  from  the  chamber,  where  they  end  in  a  cock  or  valve,  b, 
to  which  a  lead  pipe,  c,  equal  in  width  to  a,  is  attached  and  pro- 
jects into  the  chamber  itself.  It  is  not,  however,  burnt  to  the 
chamber-side,  c;  but  a  short  wider  tube,  rf,  is  burnt  to  this, 
and  c  is  loosely  put  into  it,  the  joint  being  made  tight  with  tar, 
cement,  &c.  Sometimes  in  lieu  of  this  an  india-rubber  cork  is 
employed,  but  this  does  not  last  long.  In  the  latter  case,  if  the 
outlet  is  stopped  up  by  lead  sulphate,  the  pipe  c  can  easily  be  drawn 
out  and  cleaned  and  no  platinum  nozzles  are  required  (as  had 
been  proposed  by  Scheurer-Kestner). 


SUPPLY  OF  STEAM.  533 

The  same  figure  shows  another  commendable  contrivance^  viz.  a 
simple  mercurial  pressure-gauge y  consisting  of  a  bent  glass  tube,  f, 
with  a  scale^  g,  connected  by  means  of  a  caoutchouc  bung  with  a 
branchy  h,  of  the  lead  pipe  c.  Thus  the  pressure  behind  the  regu- 
lating.cock  can  be  observed  at  any  time ;  and  the  chamber«manager 
has  thus  a  means  of  very  accurately  regulating  the  supply  of  steam. 
Any  water  condensed  in  the  gauge  can  be  easily  allow^  for. 

A  good  steam-cock  is  preferable  to  a  wheel-valve,  because  the 
wheel  does  not  show  how  far  the  valve  is  opened,  whilst  the  handle 
of  the  cock  can  be  fitted  with  a  graduated  arc  so  that  its  position 
can  be  fixed  with  precision. 

Automatic  steam-regulators,  if  reliable^  save  a  great  deal  of 
trouble^  but  do  not  dispense  with  constant  supervision  on  the  part 
of  the  attendant,  as  they  are  somewhat  liable  to  get  out  of  order. 

In  England  the  usual  way  is,  or  formerly  was,  this :  to  employ 
only  one  jet  of  steam  for  each  chamber^  mostly  beside,  above, 
below,  or  even  within  the  pipe  conveying  the  gas  from  the  burners, 
the  Glover  tower,  or  the  preceding  chamber.  Some  introduce  the 
steam  quite  near  the  top,  others  in  the  centre  of  the  chamber^end. 
A  single  steam-jet  sufiices,  if  the  length  of  the  chamber  does  not 
exceed  about  130  feet ;  in  longer  chambers  it  would  not  carry 
right  through. 

It  is  maintained  by  English  practical  men  that  a  single  steam, 
jet  from  a  1-inch  pipe  is  quite  snfiicient  for  feeding  chambers  up  to 
130  feet  length,  and  also  that*  the  distribution  of  moisture  through 
the  chambers  is  thus  properly  efibcted.  By  arranging  a  single 
8team-jet,  the  cost  of  cocks,  branches,  &c.  is  saved,  and  the 
regulation  of  the  supply  of  steam  is  much  simpler  and  easier  than 
if,  for  instance,  four  cocks  were  to  be  opened  a  quarter  as  much 
as  the  cock  of  a  single  jet.  It  is  also  true  that  in  this  way  the 
front  part  of  each  chamber,  which  makes  most  acid  and  evidently 
requires  the  greatest  supply  of  moisture,  actually  receives  it ;  but 
this  does  not  hold  good  of  the  first  chamber,  which  obtains  a 
considerable  portion  of  its  steam  from  the  Glover  tower,  so  that 
a  steam-jet  placed  in  the  just  described  way  is  certainly  not  in  the 
right  position.  The  steam-jet  should  enter  the  chamber  near  the 
top,  or  at  least  in  the  upper  part  of  the  side.  Experience  has 
shown  that  it  is  not  advisable  to  send  the  steam  into  the  lower 
portion  of  the  chamber. 

Most  experienced  managers,  however,  now  agree  that  the  single 


534  CONSTRUCTION  OP  THE  LEAD  CHAMBERS. 

steam-jet  for  each  chamber  is  a  faulty  appliance.  The  chamber 
should  not  be  left  to  haphazard  supply  of  its  different  parts  witli 
the  necessary  amount  of  moisture^  but  each  part  should  receive 
just  what  it  needs. 

On  the  Continent^  indeed^  most  manufacturers  have   alwa^^s 
preferred  employing  a  number  of  steam-jets  for  each  chamber,  so 
as  to  make  themselves  independent  of  any  casualties  in  the  proper 
distribution  of  steam  by  a  single  jet.    These  branch  jets  are  intro- 
duced at  right  angles  to  the  direction  of  the  gaseous  current  either 
in  the  long  chamber-sides^  not  far  from  the  top,  or,  which  is 
most  usual,  through  the  roof  of  the  chamber,  so  that  the  single 
jets  can  be  regulated  by  a  man  walking  over  the  top.     Thu9^  for 
instance,  at  the  Oker  works  there  is  a  steam-pipe  extending  above 
the  chambers,  from  which,  at  intervals  of  17  feet,  branches  of 
I -inch  bore  enter  the  latter;  from  these  the  steam  issues,  by 
several  small   openings  immediately  below  the   top^  in   several 
directions  (BiiLuning,  Preuss.  Zeitsch.  1877,  p.  137).     A  similar 
arrangement  exists  at  Aussig  and  elsewhere.     In  all  these  cases 
each  branch-cock  must  be  regulated  separately. 

Where  a  Glover  tower  is  in  use,  the  first  steam-jet  should  not  be 
in  front  of  the  first  or  ^Meading '^  chamber,  as  this  part  receives 
enough  steam  from  the  Glover  tower ;  the  first  steam-jet  should 
be  20  or  80  feet,  or  even  farther,  from  the  front  side. 

An  apparatus  by  which  steam  can  be  introduced  at  many  places 
and  yet  regulated  at  a  single  point  has  been  described  by  Scheurer- 
Kestner  (Wurtz,  Diet,  de  Chimie,  iii.  p.  149) ;  it  is  shown  in 
fig.  225  :  a  is  the  copper  main-pipe  running  in  the  centre  of  the 
chamber-top,  and  held  fast  by  the  joist  £  6j,  as  well  as  the 
branches  c.  The  latter  are  arranged  alternately  on  the  left  and 
right  hand  at  distances  of  16^  feet ;  they  are  made  of  lead,  pa^ 
through  the  chamber-top,  and  are  burnt  into  it.  The  arm  rf, 
covered  with  straw  rope,  serves  for  making  the  communication 
between  a  and  c.  Both  pipes  have  hydraulic  lutes,  so  that  only  a 
very  low  pressure  can  be  employed.  The  main-pipe,  a,  is  provided 
with  a  cock,  and  the  supply  of  steam  regulated  by  this.  The 
steam,  entering  the  pipe  at  the  front  end  of  the  chamber,  will 
principally  escape  through  the  first  branches,  where  it  is  most 
needed,  because  in  the  beginning  a  large  quantity  of  unchanged 
sulphur  dioxide  is  present.  The  pipe  a  has  suflScient  fall  for 
emptying  the  condensed  water.     (This  arrangement  seems  to  offer 


SUPPLY  OF  STEAM. 


535 


no  advantage  over  simple  branches  on  a  main-pipe^  and  has  the 
great  drawback  that  only  a  very  low  pressure  can  be  employed, 
as  the  water  is  easily  thrown  out  of  the  hydraulic  joints  a  and  c. 
Moreover,  it  disregards  the  necessity  of  supplying  the  various 
parts  of  the  chamber  with  different  amounts  of  steam.) 


Perfectly  absurd  is  the  arrangement  given  in  every  edition  of 
Payen's  '  Precis/  even  up  to  the  last  one  (1877),  and  copied  from 
it  into  many  other  treatises.  Here  the  steam-jets  are  shown  partly 
in  the  chamber-bottom,  coming  through  the  chamber-acid.  No 
practical  man  can  imagine  that  this  plan,  if  it  has  been  actually 
carried  out  anywhere,  has  not  been  discontinued  at  the  first  oppor* 
tunity;  for  the  shaking  by  the  steam  must  gradually  cause  a 
leakage  at  the  joint,  which  cannot  be  got  at,  owing  to  the  chamber- 
floor,  nor  can  it  be  repaired  till  the  chamber  has  been  entirely 
emptied. 

The  total  quantity  of  steam  required  for  a  set  of  chambers,  which 
should  be  known  approximately  in  order  to  fix  upon  the  boiler- 
space  and  the  size  of  the  main-pipes,  of  course  depends,  first, 
upon  the  quantity  of  sulphur  to  be  burnt,  secondly  upon  the 
existence  of  a  Glover  tower,  and  thirdly  upon  the  strength  to 
which  the  acid  is  brought  in  the  chambers.  A  general  rule, 
therefore,  cannot  be  laid  down.     The  two  latter  conditions  are 


536  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

partly  reciprocal ;  the  stronger  the  acid  is  made  in  the  chambers, 
the  less  water  is  evaporated  in  the  Glover  tower,  and  vice  versd.  If 
we  assumCj  adopting  a  proportion  very  usual  in  England,  that  all 
the  chamber-acid  is  brought  up  to  124°  Tw.,  and  that  it  is  con- 
centrated in  the  Glover  tower  up  to  148°  Tw.^the  amount  of  steam 
required  will  be  as  follows: — 

Each  pound  of  sulphur  burnt  requires, 

Ist,  for  forming  -   SO4H2,  -^  water  =0-5623  lb. 

2nd,  for  diluting  it  down   to  124^  Tw. 

(  =  70percent.  SO,H2),^2^|| =  1-3125    ,. 


1-8750    „ 


Of  this  nothing  is  lost  with  the  escaping  gas, 
as  this  passes  in  the  Gay-Lussac  tower  through 
strong  vitriol ;  on  the  contrary,  the  Glover 
tower  saves  the  steam  corresponding  to  a  con- 
centration from 

124°  (=70 percent.)  to  l48°Tw.  (=80 per 

cent.),  viz.^^^  -^ =0-43/0  lb. 


Leaving 1*4375  lb. 

which  must  be  supplied  to  the  chambers.  To  this  must  be  added 
a  certain  quantity  for  water  condensing  in  the  steam-pipes  ;  but 
this  cannot  be  estimated  generally^  since  here  everything  depends 
upon  the  length  of  the  pipes,  their  thickness,  surroundings,  &c. 
On  the  Continent  the  chamber-acid  is  kept  more  dilute  and  cor- 
respondingly more  steam  is  used.  It  is  safe  to  say  that  the  steam 
to  be  generated  in  the  boiler,  without  a  Glover  tower,  amounts  to 
about  2^  times — with  it,  to  about  twice  the  weight  of  sulphur 
burnt. 

Employment  of  Water  in  the  form  of  Spray, 

Instead  of  feeding  the  chambers  with  steam,  Sprengel  (patent 
of  October  1st,  1873)  proposed  liquid  water  in  the  form  of  a 


INJECTION  OF  WATER  AS  SPRAY. 


537 


fine  spray.  His  reasons  are  these : — that  the  steam  increases  the 
volume  of  the  gases  by  its  heat,  and  consequently  more  chamber- 
space  and  nitre  are  required,  which  can  be  avoided  by  introducing 
the  water  in  a  liquid  form,  suflSciently  divided  ;  and  that  the 
cost  of  evaporation  can  be  saved  in  this  way.  The  water  is 
made  into  a  spray  by  the  employment  of  steam,  a  steam-jet  of 
301b.  tension  escaping  through  a  platinum  nozzle  in  the  centre 
of  a  water-jet,  as  shown  in  fig.  226  (where  a  is  the  steam-pipe, 
b  the  water-pipe) ;  20  lb.  of  steam  is  sufficient  for  converting 
80  lb.  of  water  into  a  mist.  Such  jets  are  arranged  in  the  chamber- 
sides,  at  distances  of  40  feet  apart,  and  supplied  with  water  from 
a  tank  fixed   at   some   height   above.      Sprengel   assumed   that 

FiK.  226. 


two-thirds  of  the  coal  can  be  saved  in  this  way,  instancing  the 
M'orks  at  Barking  Creek,  where  at  the  same  time  a  saving  of 
6|  per  cent,  pyrites  and  of  14|  per  cent,  nitre  is  said  to  have  been 
effected.  At  those  works  there  was  no  Gay-Lussac  or  Glover 
tower.  In  the  case  of  factories  working  with  a  Glover  tower, 
Sprengel  estimated  the  saving  in  coal  at  a  third  less  (Chem.  News, 
xxxii.  p.  150).  Of  course  the  water-  and  steam-cocks  must  be 
exactly  regulated,  and  the  two  nozzles  must  have  a  particular 
shape,  so  that  only  a  fine  mist  and  no  lai^er  drops  shall  be 
formed,  which  would  at  once  fall  to  the  bottom  and  only  dilute  the 
chamber-acid. 

A  different  way  of  producing  a  spray  or  mist  of  water  instead 
of  a  steam-jet  for  feeding  vitriol-chambers  is  employed  at  the 
Griesheim   works,  and  has  thence   been  introduced  with  great 


538  CONSTBUCTION  OF  THE  LEAD  CHAMBERS. 

success  into  several  other  factories.    The  spray  is  here  not  produced 
by  the  injection  of  steam^  but  by  allowing  the  water,  at  a  pressure  of 
two  atmospheres,  to  issue  from  a  small  platinum  jet  against  a  small 
platinum  disc.  Two  rows  of  such  water- jets  are  introduced  through 
tubes  in  the  chamber-top,  each  tube  about  20  feet  away  from  the 
other.    Thus  the  whole  chamber  is  uniformly  filled  with  a  fine 
mist,  which,  together  with  the  steam  comiug  from  the  Glover 
tower,  supplies  all  the  water  required  for  the  chamber-prcicess. 
The  water  must  be  carefully  filtered,  as  otherwise  the  jets  would 
soon  be  stopped  up ;  but  this  trouble  is  far  more  than  compensated 
by  the  considerable  saving  in  fuel  caused  by  doing  away  with  the 
chamber  boilers.    The  fear  formerly  entertained,  that  the  intro- 
duction of  the  moisture  in  the  shape  of  liquid  water  would  reduce 
the  temperature  of  the  chambers  below  that  most  favourable  for 
the  acid-making  process,  is  entirely  groundless.     At  Griesheim  it 
was  noticed  that  the  temperature  of  the  gases,  arriving  from  the 
Glover  tower  sometimes  at  only  35^  C,  quickly  rose  within  the 
chambers  to  50°  C.     Similar  observations  have  been  firequently 
made,  most  extensively  by  Lunge  and  Naef  (comp.  Chap.  VII.) . 
This  is  explained  by  the  fact  that  the  evolution  of  heat,  con- 
sequent upon  the  chemical  reactions  going  on  within  the  chamber, 
is  far  more  important  than  the  heat  brought  in  by  the  steam, 
and   that,   in   fact,   the    local  cooling    produced    by   the   water 
being  supplied  in  the  liquid  form  is  actually  beneficial  in  most 
cases. 

It  might  be  objected  to  the  introduction  of  the  water  in  the 
shape  of  a  spray,  that  steam  is  preferable  on  account  of  being  only 
gradually  condensed  in  its  onward  course  within  the  chamber,  and 
that  the  moisture  would  thus  be  more  uniformly  distributed 
through  the  chamber.  But  this  objection  is  not  at  all  valid,  and 
would  not  be  so  even  if  no  sulphuric  acid  were  present  in  the 
chamber.  Calculation  shows  that  the  gas  introduced  for  each 
kilogram  of  sulphur,  whose  volume  at  50°  C.  and  760  millim. 
pressure  amounts  to  83  4*5  litres,  can  contain  only  0*6868  kilogram 
of  aqueous  vapour,  whilst  the  total  amount  of  water  is  nearly  four 
times  as  much,  and  three-fourths  of  the  steam  entering  into  the 
chamber  must  therefore  be  at  once  condensed  into  water.  This 
calculation,  given  in  our  1st  edition,  pp.  348  &  349,  is  not  repeated 
here,  since  it  docs  not  take  into  account  the  fact  that  the  tension 
of  aqueous  vapour  within  the  chamber  is  very  much  reduced  by 


INJECTION  OF  VTATEVL  AS  SPRAY.  539 

the  presence  of  sulphuric  acid^  and  it  is  hence  useless  for  our 
purpose.  Hurter  (J.  Soc.  Chem.  Ind.  1882,  p.  51)  somewhat 
more  correctly  applies  to  our  case  Regnault's  table  for  the 
tension  of  aqueous  vapour  in  sulphuric  acid  of  various  strengths, 
and  he  there  gives  a  diagram  which  allows  of  finding  this  tension 
for  any  intermediate  concentration  of  acid.  But  this  is  in- 
correct for  the  principal  working  part  of  the  vitriol-chamber ;  for 
Regnault's  determinations  only  go  as  far  as  35^  C,  that  is  much 
below  the  ordinary  chamber-temperature,  and  it  is  not  admissible 
to  calculate  tensions  at  60°,  80°,  or  even  higher  temperatures  by 
simply  applying  Regnault's  table  or  Hurter's  diagram  to  them. 
This  gap  has  been  filled  by  a  set  of  elaborate  observations  made  by 
Sorel,  and  first  rendered  accessible  to  the  public  by  me  (Zeitsch. 
f.  angew.  Ch.  1889,  p.  272).  Sorel's  table  extends  to  acids 
from  44  to  82  per  cent.  H2SO4,  and  to  temperatures  from  10° 
to  95°.  We  have  given  it  in  the  third  Chapter,  p.  196,  where 
the  specific  gravities  corresponding  to  the  acid  percentages  have 
been  added  for  the  reader's  convenience.  At  the  close  of  this 
Chapter  we  shall  give  a  table  for  reducing  volumes  of  gases  to 
the  conditions  of  the  vitriol-chamber  atmosphere,  which  equally 
takes  into  account  the  aqueous-vapour  tensions  of  sulphuric  acids 
of  various  strengths. 

The  importance  of  this  table  will  be  indicated  at  present  by  only 
one  example.  In  a  special  instance  the  temperature  close  to  the 
chamber-side  was  80° ;  the  acid  running  down  the  side  stood  at 
114°  Tw.=66  per  cent.  H2SO4,  and  the  aqueous-vapour  tension  at 
this  place  was,  therefore,  =39  millim.  Only  6  centim.  (say  2^ 
inches)  within  the  chamber  the  temperature  was  already  95° ;  but 
at  this  temperature  an  acid,  whose  aqueous-vapour  tension  is=39 
millim.,  must  have  a  strength  of  128 J°  Tw.  =  72*33  per  cent. 
H2SO4,  and  this  was  found  to  be  really  the  case.  We  shall  see 
the  importance  of  this  in  Chapter  VII. 

Looking  at  the  great  reduction  of  the  tension  of  aqueous  vapour 
by  the  presence  of  sulphuric  acid,  we  must  conclude  that  the 
steam  introduced  into  the  chamber  must  be  condensed  almost 
immediately  into  a  liquid  mist,  and  this  must  reduce  the  alleged 
superiority  of  steam  in  "  carrying  power "  to  a  properly  com- 
minuted spray  of  water,  introduced  at  high  pressure,  to  almost  nil. 

Of  course  the  water  mtist  be  properly  comminuted  ;  otherwise, 
that  is  when  it  drops  from  the  jets  in  the  shape  of  rain,  it  dilates 


540  COSSTROCTION  OF  THE  LEAD  CMAMBEBS. 

the  chamber-acid  to  aa  intolerable  degree,  and  this  is  all  the 
more  injurious  as  this  dilute  acid  floats  on  the  top  of  the  stronger 
chamber-acid,  and  is  not  noticed  for  a  long  time  at  the  places 
where  the  acid  is  drawn  off,  till  it  becomes  too  late  to  meet  the 
evil  at  once.     This  accident  will  happen  whenever  the  jets  are  out 


Fig.  229. 


of  order,  and  this  has,  very  unnecessarily,  caused  several  works  to 
abandon  the  plan  of  introducing  the  water  in  the  shape  of  a  liquid 
spray. 

A  special  platinum  jet  for  converting  water  or  acid  liquids  into 
ft  thin  spray  has  been  constructed  by  P.  Benker,  of  Paris,  aad  is 
shown  in  fig.  227.  In  this  jet  the  distance  between  the  noszle  a 
and  the  disc  b  is  adjustable,  the  disc  being  moved  backwards  or 
forwards  by  means  of  a  rod,  at  the  end  of  which  is  cut  a  6ne 
thread,  which  works  in  a  similar  nut  c,  placed  on  the  top  of  the 


IXJECTION  OP  WATEIt  AS  SFKAY.  Oil 

cylinder.    The  screw  and  nut  are  made  _, 

of  en  alloy  of  platinum  and  iridium,  so 

that  there  is  no  fear  of  their  wearing 

out.     In  this  manner  the  best  distance 

betireeii  a  and  b  can  be  easily  attained, 

and    by    removing    b  altogether    the 

nozzle    a    is    easily    cleaned.      More 

I'ecently  Benker  has  employed  spray- 

producera    of    the    shape    shovn    in 

fig.  228,  with  the  platinum-iridium  jet 

cased   in  antimony ^lead,  and  without 

an  adjusting-screw. 

Korting  Brothers'  spray-producer 
(fig.  229)  (Zeitscb.  f.  angw.  Chem. 
1888,  p.  401)  contains  within  the  con- 
tiacted  part  a  metal  spiral,  which  by 
the  pressure  of  the  liquid  is  kept 
tightly  ill  its  place,  whilst  the  liquid  on 
passing  through  the  helicoidal  channel 
takes  a  rotating  movement,  so  that, 
on  issuing,  it  is  projected  equally  OD 
all  sides  as  a  conical  spray.  Tlie 
nozzle  and  spiral  spring  can  be  ar- 
ranged for  spray  of  any  degree  of 
fineness.  This  apparatus  was  origin- 
ally intended  for  damping  the  air  in 
cotton-mills  &c.  for  precipitating  dust, 
for  absorbing  acid  vapours,  and  so  forth. 
It  has  also  been  made  of  platinum,  and 
is  in  several  places  used  for  producing  a 
fine  spray  of  water  in  vitriol-chambers. 

These  K  or  ting's  spray-producers 
("  Streudiisen ")  were  also  made  of 
antimony-lead  with  a  platinum  lining, 
but  this  did  not  stand  the  corrosion  in 
acid- chambers,  and  had  to  be  replaced 
by  solid  platinum  nozzles.  Even  these 
do  not  last  eo  long  as  nozzles  made  of 

glass,  as  shown  in  fig,  230.     The  glass  tube  a  is  drawn  out  to  a 
capillary  point  at  a',  where  it  is  cut  oSf  quite  straight  so  that  the 


542  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

jet  of  water  comes  out  centrallj^  not  sideways ;  in  24  hours  9UL) 
or  1000  litres  of  water  should  be  delivered  from  this.  This  glass 
nozzle  is  fixed  in  the  antimony-lead  part  d  by  means  of  a  iIud 
india-rubber  washer  b,  the  joint  being  made  tight  by  the  vater 
pressure^  and  both  orifices  being  at  the  same  level.  Within  a 
the  Korting  spiral  e,  made  of  gun-metal  (this  metal  can  be  employed, 
as  no  acid  penetrates  here) ,  is  fixed  by  the  thick  india-rubber  tube  c. 
This  apparatus  is  set  in  the  chamljer-top  in  such  a  way  thit 
the  jet  comes  out  horizontally^  and  that  the  whole  can  be  re- 
moved at  will  for  the  purpose  of  cleaning  or  inserting  a  nev 
glass  nozzle. 

In  practice  the  orifice  of  the  glass  tube  a  is  about  0*75  mm.  bore, 
that  of  the  hard-lead  nozzle  d  is  4  mm.  wide.  In  order  to  fix  a  iu 
the  hard-lead  part  d,  the  small  india-rubber  washer  d  is  put  od 
and  placed  with  its  orifice  at  the  top,  and  d  is  put  on  with  a  twisting 
motion^  but  without  exercising  much  pressure  or  trying  to  centn* 
a  exactly  in  d,  the  water  pressure  afterwards  accomplishing  this 
much  better.  With  a  pressure  of  3  to  5  atmospheres  and  a 
properly  adjusted  nozzle  no  droplets  whatever  are  formed,  but  a 
uniform  mist  travelling  over  a  great  distance.  The  Korting  spray 
is  bought  in  the  ordinary  ^ay,  and  is  fitted  at  the  works  with  a 
glass  jet^  as  shown  here  with  every  detail. 

[Glass-nozzled  spray-producers,  precisely  as  here  shown,  have 
been  employed  for  many  years  at  one  of  the  best  conducted 
continental  factories,  and  are  still  preferred  there  to  every  other 
form  of  apparatus  of  this  kind.  Since  their  introduction  all 
previous  trouble  in  feeding  the  chambers  with  liquid  water  has 
disappeared.  The  orifice  of  the  glass  jet  has  |  millim.  bore,  that 
of  the  hard-lead  nozzle  4  millim.  bore.] 

A  special  advantage  of  the  introduction  of  liquid  water  in  the 
form  of  spray  is  that  the  temperature  of  the  chambers  is  kept 
lower  than  when  employing  steam,  since  the  latent  heat  of  the 
latter,  becoming  free  in  its  condensation,  decB  not  come  into  play. 
How  useful  such  a  cooling  effect  is,  will  be  seen  in  Chapter  VII. 
The  only  drawback  to  the  spray  system  is  the  liability  of  the 
orifice  of  the  spray-producer  to  get  choked  up  by  dirt,  or  else  to 
be  widened  by  corrosion.  The  former  is  avoided  by  careful 
filtration  of  the  water,  the  latter  by  a  suitable  construction.  Glass 
nozzles,  as  shown  above,  are  much  better  even  than  platinum.  I 
have  found  this  system  applied  for  many  years  with  full  succes: 


=3h 


I 


CHAMBERS  SUPPLIED  WITH  WATEll-SPRAYS. 


543 


in  a  number  of  the  best  managed  works^  e.g.  Griesheim  and  Aussig. 

AVherever  it  has  proved  unsuitable^  this  has  been  due  to  want  of 

attention. 

During  the  warmer  portion  of  the  year  the  whole  of  the  chambers 

can  be  supplied  with  water  as  a  spray  ;  but  in  the  winter  season 

the  back  part  of  the  system  must  sometimes  get  a  little  steam. 

For  all  descriptions  of  spray-producers  the  water  must  be  care- 
fully filtered^  preferably  by  means  of  sponge-filters.  Benker  more- 
over places  wire-gauze  in  front  of  every  spray-producer.  He  works 
these  at  a  pressure  of  from  2\  to  5  atmospheres,  by  means  of  a 
small  intermediate  cylinder^  about  3  feet  wide  and  6  or  9  feet  high. 
For  the  first  start  a  little  high-pressure  air  is  employed ;  after- 
wards the  feed-pump  gives  sufficient  pressure^  which  can  be  reduced 
by  means  of  a  tap  if  too  much  water  is  discharged. 

This  plan  is  very  well  illustrated  by  figs.  231  &  232  (folding 
plate)  ^  which  at  the  same  time  show  a  chamber  as  erected  by 
Mr.  Benker  for  the  French  ''high-pressure  style."     A  is  a  small 

Fig.  2.33. 


air-pump^  B  the  water-pressure  vessel,  made  ot  an  old  steam- 
boiler,  with  two  safety-valves,  a  and  b.  One  of  these,  destined 
for  the  air,  is  very  small ;  but  the  other,  for  the  water,  must 
be  lai^e  enough  to  discharge  the  whole  of  the  water  supplied  by 
pump  D ;  otherwise  B  might  burst.  The  second  valve  is  weighted 
i  atmosphere  more  than  the  air- valve.  The  level  of  the  water  in  B 
must  be  kept  12  inches  below  the  top.     Pump  D  is  an  ordinarv 


541'  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

feed-pump,  kept  continuously  going;  between  B  and  D  is  interposed 
the  sponge- filter  C.  The  water  rises  in  the  high-pressure  pipeEE 
to  the  top  of  the  chamber,  where  there  are  taps  c  c  at  distances  of 
about  16^  feet.  Behind  each  tap  is  placed  a  leaden  filter  (shown 
on  a  larger  scale  in  fig.  233),  with  a  very  fine  wire-gauze  sieve; 
then  comes  a  swan-neck  pipe,  which  passes  through  the  chamber 
top^  and  this  ends  in  a  spray-producer,  fig.  228  [or  else  230]. 
From  time  to  time  the  air-tap  on  B  is  opened  in  order  to  replace 
the  air  dissolved  by  the  water  under  the  high  pressure. 

ArrangemefiU  for  producing  the  Draught  in  Vitriol-Chambers. 

The  draught  necessary  for  driving  acid-chambers  is  produced  bv 
various  agencies,  the  most  important  being  the  high  temperature 
with  which  the  gases  leave  the  burners  and  enter  the  chambers, 
which  counterbalances  the  greater  density  of  the  burner-gases 
when  compared  with  that  of  air  in  the  cold  state.  We  shall  cal- 
culate these  factors  for  the  various  cases  in  question,  employing 
the  following  values  for  the  density  of  gases  and  vapours  at  CP  C. 
.and  760  mm.  mercurial  pressure: — 

grams. 
1  litre  of  dry  atmospheric  air  weighs . . .     1-2932 

1     „  „   oxygen    1-4298 

1     „  ,,   nitrogen 1-2562 

1     „  „   sulphur  dioxide 3-8721 

1     „        aqueous  vapour 0*804343 

We  shall  begin  with  burner^gases  from  brimstone,  the  normal 
•composition  of  which  has  been  calculated  (p.  397  et  seq,)  =0*1123 
SO3  +  OO977  0  +  0-7900  N  =  1  litre  of  gas.  This  must  weigh  at 
O^  and  760  mm.  pressure  : 

01 123  X  2-8731 +00977  X 1-4298 +07900  x  12562 

=  1"4547  grams. 

Taking  the  temperature  in  the  outlet-pipe  from  the  brimstone- 
burner  to  average  100°  C,  (which  is  much  below  the  actual 
temperature),  the  above  1*4547  grams  would  occupy  a  space  of 

?Z^t^  =  1-3663  litres,  or  1  litre  of  the  burner-gas  at  100°  C 

1-4547 
and  760  mm.  =  ttqc^q  =  1*0647  grams. 


PRODUCTION  OF  DRAUGHT.  545 

Atmospheric  air  at  0^  and  760  mm.  pressure  weighs  per  litre 
1*2932  grams;  at  20^  this  quantity  occupies  the  space  of  1*0733 
litres,  at  35°=1'1282  litres,  so  that  even  at  the  highest  summer 

temperature,  say  35°  C,  1  litre  of  air  weighs  as  much  as  rrrooo 

=  1*1463  grams;  it  is  therefore  in  any  case  heavier  than  the  burner- 
gas  at  100°  C. 

The  aqueous  vapour  always  present  in  the  air  need  not  be  taken 
into  account,  since  by  its  expansion  in  the  heat  of  the  burner  it 
can  only*increase  the  difference  between  the  weight  of  the  gas  and 
that  of  the  air. 

Owing  to  the  fact  that  the  gaseous  mixture  in  the  vertical  pipe 
of  the  sulphur-burner  is  lighter  than  air,  it  must  issue  out  of  the 
top  of  the  pipe  into  the  chamber  with  a  speed  corresponding  to 
the  excess  pressure  of  the  atmosphere  acting  upon  it  from  bdow. 
It  must  therefore  by  itself  exercise  a  pressure  upon  the  gas  in  the 
lead  chamber.  Its  speed  or  the  draught  increases  with  the  height 
of  the  vertical  pipe ;  and  the  latter  therefore  ought  to  enter  the 
chamber-side  as  high  up  as  possible.  By  thus  providing  more 
than  sufficient  drawing-power  the  supply  of  air  is  assured  in  any 
case ;  and  its  excess  can  always  be  moderated  by  narrowing  the 
area  of  the  inlets. 

A  second  cause  of  draught  is  the  formation  of  sulphuric  acid 
itself,  as  the  space  occupied  by  the  consumed  gas  cannot  remain 
empty,  and  must  at  once  be  filled  again.  The  condensation  of 
the  gas  to  sulphuric  acid  thus  acts  as  an  aspirator. 

A  third  cause  of  draught  is  the  vertical  pipe  taking  the  gas  away 
from  the  last  lead  chamber  or  the  chimney  with  which  it  is  con- 
nected. As  the  gas  in  these  contains  all  the  nitrogen  introduced 
into  the  chambers  with  only  5  per  cent,  of  oxygen  (a  mixture  of 
95  vols.  N-f  5  vols.  O  has  the  litre  weight  grav.  1*263;  ordinary 
atmospheric  air  1"293),  as  it  is  saturated  with  aqueous  vapour, 
and  as  it  is  usually  warmer  and  never  can  be  colder  than  the 
atmospheric  air,  it  must  necessarily  be  lighter  than  the  latter ; 
this  is  evident  without  any  calculation. 

If  the  nitrogen-acids  are  not  recovered  by  a  special  process,  to- 
be  explained  later  on,  the  gas  certainly  contains  a  little  of  those 
acids  and  of  sulphur-dioxide,  by  which  its  specific  gravity  is 
somewhat  increased.  We  shall,  however,  see  that  their  eflFect 
is  very  slight,  and  does  not  materially  interfere  with  the  causes 
producing  the  draught. 

VOL.  I.  2  N 


546  COXSTHUCTION  OF  THE  LEAD  CHAMBERS. 

The  draught  produced  by  all  the  above-mentioned  causes  regu- 
lates the  quantity  of  air  which  can  enter  the  apparatus  by  openings 
of  a  certain  size.  We  have  already  seen^  on  p.  '697,  that  we  mu&t 
not  introduce  the  exact  quantity  of  air  required  for  transforming 
the  burnt  sulphur  into  SOs,  but  a  certain  excess,  which  we  have 
calculated  =  5*18  vols,  of  oxygen  upon  each  14  vols,  of  SO^. 
With  this,  for  each  14  vols,  of  SO^, 

14  +  7  +  518=21+   5-18=26-18  vols,  oxygen, 

and  79 +  19-50= 98-50    „     nitrogen,. 


together   124'68    „     atmospheric  air, 

must  be  introduced  into  the  chambers.    From  this  it  follows  that  for 

121*68 
each  vol.  SOg     iX"  =8*906  vols,  of  air  are  required.     Now  1  litre 

of  SO2  at  0°  and  760  millims.  pressure  weighs  2*8731  grams,  and 
SO3  consists  of  equal  parts  by  weight  of  sulphur  and  oxygen. 
Accordingly  1  litre  of  SOj  at  0°  and  760  millims.  contains 

'- —  =  1*43655  gram  sulphur, 
and  1*43655     „       oxygen. 

Thus  for  each  1-43655  gram  of  sulphur  burnt  8*906  litres  air  at 
0°  and  760  millims.  are  required.     Since 

1*43655  :  1000  :  :  8-906  :  jc, 

QQTift 

each  1000  grams  or  1  kilogram  sulphur  requires  ,  .o^^.,==6199 

litres  air  at  0°  and  760  millims.  pressure  to  be  introduced  into  the 
sulphur-burner,  weighing  6199x1-2932=8017  grams  or  8017 
kilograms. 

At  20^  C.  this   weight   would   occupy  ^^U,-^-x  6199  =  ^565:5 

litres. 

All  these  calculations  refer  to  dri/  air.  If  the  air  is  saturated 
with  moisture,  its  volume  is  increased  by  the  vapour-tension  e  for 
the  temperature  in  question,  according  to  the  formula : 

^n     V  X  760 
V  =-  ,     -   > 
o—e 


IMPORTANCE  OF  KEOULATINO  THE  DRAUGHT.  54?7 

where  b  is  the  actual  barometric  pressure.  At  20^  C,  c  is  =  17*4min., 
and  for  b  =  760  the  above  6653  litres  will  be  =  6809  litres,  if 
saturated  with  moisture. 

The  last  increase  of  156  litres  is  only  fully  realized  in  the  ex. 
ceptional  case  of  air  completely  saturated  wit^  moisture.  As  this 
increase  is  only  2*34  per  cent,  of  the  volume  of  the  necessary  dry 
air,  whilst,  according  to  the  calculation  on  p.  398,  nearly  25  per 
cent,  of  the  theoretical  quantity  of  air  (that  is,  more  than  ten  times 
as  much)  is  introduced  in  excess,  the  changes  in  the  moisture  of 
the  air  and  the  differences  of  volume  resulting  therefrom  are  of  no 
practical  consequence.  We  shall  therefore  not  enter  into  a  calcu- 
lation of  the  differences  caused  by  the  real  percentage  of  moisture 
in  the  air. 

In  the  case  of  pyrites-kiln  gases,  it  follows  from  the  data  given 
on  p.  399,  that  for  each  100  pts.  of  sulphur  employed  as  FeSo, 

375  pts.  oxygen  must  be  supplied  for  oxidizing  the  Fe, 
1000  ,,  „  „  forming  SOg, 

500  „  ,,  ,,  oxidizing  this  to  SO;,. 

Since  1  litre  of  air  at  QP  and  760  miilims.  pressure  weighs  1*42S8 
gram^  at  this  temperature  and  pressure 

375  grs.  O  give  262-3  lit.  mixed  in  the  air  with    9867  lit.  X. 
1000     .,         „      699-A  „  „  „    26311     ,, 

500     „         „      349-7  ,,  ,,  .,    1315-5     ,, 


1875     „         „    1311-4  „  .,  ,.    4933-3 

Theoretically,  then,  for  each  kilogram  of  sulphur  consumed 
as  FeSg,  131 1*4 +  4933-3  =  6244-7  litres  air  at  0°  and  760  miilims. 
pressure  must  be  supplied. 

The  normal  pyrites-burner  gases,  as  calculated  p.  400,  contain 
8-59  per  cent,  by  vol.  SOo,  9*87  O,  and  81-54  N  (not  reckoning  any 
SOa  present). 

1  litre  of  this  gas  at  0^  and  760  miilims.  weighs 

0-0859  X  2-8731  +0-0987  x  1-4298  +  0-8154  x  1-2562=1-4122  grm. 

whilst  the  1  litre  of  the  gas  resulting  from  the  combustion  of 
brimstone,  according  to  our  former  calculation,  weighs   1-4547. 

o  V  *> 

¥W     •'I     /W 


548  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

I 

The  former  being,  under  equal  conditions,  lighter  than  the  latter,    I 
consequently  gives  stronger  draught. 

Of  course  the  volume  of  air  necessary  for  a  certain  consumptiou 
of  sulphur  is  also  dependent  upon  the  elevation  of  the  site  above 
the  level  of  the  sea,  which  regulates  the  mean  barometrical  pressure. 
Thus  at  Munich  a  quantity  of  air  will  occupy  a  space  larger  by  5*3 
])er  cent,  than  the  same  quantity  at  Widnes  or  New  York. 

It  is  easy  to  introduce  the  minimum  of  air  required  for  proper 
work.     But  this  is  not  all ;  an  excess  of  air  is  just  as  hurtful  a< 
a  deficiency,  although  not  to  the  same  extent.     Air  in  excess  cools 
the  gas,  and  thus  may  sometimes  interfere   with  the   process; 
it  fills  a  portion  of  the  chamber-space  and  renders  it  inoperative ; 
it  dilutes  the  gas  and  weakens  the  energy  of  the  chemical  action. 
The  regulation  of  the  supply  of  air  must  therefore  be  accurate, 
and  must  be  adapted  to  the  frequent  variations  in  the  state  of  the 
atmosphere.     This  must  be  done  by  great  attention  in  enlarging 
or  diminishing  the  openings  serving  for  introducing  the  air  and  for 
taking  away  the  gas.     By  either  means  the  supply  of  air  can  l)e 
diminished  ;  but  it  is  not  indifferent  which  of  them  is  selected.     Br 
the  latter  the  draught  acting  upon  the  contents  of  the  chambers  at 
the  end  of  the  apparatus,  by  the  former  the  pressure  upon  the 
contents  of  the  chambers  at  the  beginning  of  the  apparatus,  is 
lessened.   With  the  latter  method  the  pressure  inside  the  chamber 
is  increased ;  with  the  former  it  is  diminished.    Accordingly,  if  the 
chimney-draught  is  too  much  cut  off,  the  gas  issues  forcibly  from 
any  openings  in  the  chambers,  &c.,  whilst  the  air  may  enter  properly 
by  the  holes  in  the  front  of  the  sulphur-burners.     If,  however, 
these  latter  are  stopped  up  too  far,  the  chambers  suck  in  air  in  any 
places  not  completely  closed  against. the  atmosphere. 

The  draught  may  also  be  increased  in  two  different  ways,  viz.,  by 
enlarging  the  opening  in  the  exit-tube,  or  by  increasing  the  inlet- 
holes  in  the  door  of  the  burner.  Then  the  chambers,  if  the  exit- 
tube  is  not  suflBciently  closed,  suck  in  air;  if,  on  the  other  hand, 
the  inlet-openings  are  too  wide,  gas  is  forced  out  from  any  leaks  in 
the  chambers  by  the  excess  pressure.  This  is  especiallv  noticed 
when  the  doors  are  opened  for  charging.  Both  can  be  avoided  bv 
arranging  a  certain  proportion  between  the  inlet  and  the  outlet 
openings.  Usually  the  area  of  the  latter  is  two-thirds  that  of 
the  former.  For  the  changes  of  draught  made  necessary  by  the 
variations  in  the  state  of  the  atmosphere  no  certain  rules  can  be 


PRODUCTION  OP  DRAUGHT.  549 

given ;  observation  and  practice  must  come  into  play  here.  In 
well-arranged  works,  however,  this  is  not  left  to  chance,  but  the 
supply  of  air  is  checked  by  regularly  estimating  the  oxygen  in  the 
escaping  gas,  as  we  shall  see  later  on. 

We  have  thus  seen  that  the  hot  gaseous  mixture  in  itself  con- 
tains the  conditions  for  causing  a  draught,  since  it  is  much  lighter 
than  the  air,  and  will  always  have  a  tendency  to  rise  from  the 
burners  to  the  chambers.  We  must  also  point  to  the  second  source 
of  draught,  viz.  the  formation  of  liquid  sulphuric  acid  within  the 
chambers  from  the  mLxture  of  the  gases,  which  must  necessarily 
have  an  aspirating  action,  although  not  only  from  the  burners,  but 
from  all  sides. 

Along  with  these  two  sources  of  draught  furnished  by  the  peculiar 
nature  of  the  acid-making  process  itself,  there  must  always  be 
another  arrangement  for  causing  further  draught,  especially  because 
otherwise  the  current  of  gas  could  not  be  turned  into  the  required 
direction.  In  the  simplest  case  a  plain  outlel-pipe  behind  or  above 
the  last  chamber  will  suffice.  The  Belgian  Commission  of  1854  even 
preferred  this  arrangement  to  a  chimney,  because  the  latter  might 
produce  an  excessive  draught;  and  many  factories  work  quite 
well  in  this  way.  But  it  cannot  be  said  that  the  excessive  draught 
of  a  chimney  must  lead  to  a  loss  of  uncondensed  gas  and  too  quick 
a  passage  through  the  chambers ;  for  it  is  always  very  easy  to  cut 
off  an  excess  of  draught  by  a  damper  &c.  in  the  outlet  ;  but  it  is 
nothing  like  so  easy  to  increase  the  draught  in  the  outlet-pipe  or 
chimney  if  insufficient.  For  the  latter  object  a  steam-injector 
placed  in  the  outlet-pipe  was  formerly  considered  the  most  con- 
venient apparatus.  Sometimes,  in  lieu  of  a  proper  injector,  a 
simple  steam- jet,  turned  in  the  direction  of  the  draught,  is  used; 
hut  this  is  a  very  wasteful  proceeding,  and  a  proper  Korting's 
injector,  made  of  regulus  metal  (lead  and  antimony),  should  always 
be  employed.  Such  injectors  can  be  applied  in  various  places. 
Scheurer-Kestner  (Bull.  Soc.  Chem.  xliv.  p.  98)  describes  his 
experience  in  this  direction.  He  employed  a  Korting^s  injector 
which  produced  a  gaseous  mixture  of  7*9  per  cent,  steam  and 
92' 1  per  cent.  air.  Thus  a  quantity  of  1814  kilog.  of  water  in  the 
shape  of  steam  sufficed  for  aspirating  the  air  required  for  burning 
7000  kilog.  of  45  per  cent,  pyrites.  At  first  the  injector  was  placed 
in  the  pipe  entering  into  the  first  chamber.  This  is  the  best  place, 
where  there  is  no  Glover  tower,  as  the  steam  is  then  very  service- 


I 


550  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

able  for  workiug  the  chambers^  and  thus  costs  nothing ;  but  iu 
case  of  a  Glover  tower  this  produces  an  excess  of  steam  in  the  first 
chamber.     The  regulus  metal  of  the  injector  wore  out   pretty 
quickly ;  nor  could  it  be  replaced  by  porcelain,  which  cracked  very 
soon ;  a  thin  casing  of  platinum^  howeyer^  was  found  sufficient  for 
protecting  a  regulus  injector.     It  was  tried  to  place  the  injector 
between  the  first  and  second  chambers^  but  here  also  too  much 
steam  was   introduced   into  the   chamber.     This   is   avoided   by 
applying  the  injector  at  the  exit  from  the  Gay-Lussac  tower  ;  but 
then  all  the  steam  is  lost  and  the  process  is  thus  made  expensive. 
In  the  case  of  seleniferous  pyrites  the  injector  between  the  burners 
and  the  chambers  is  stopped  up  so  quickly   with  a  deposit  of 
selenium^  that  two  injectors  must  be  employed  side  by  side^  one  of 
which  can  be  cleaned  out  while  the  other  one  is  going. 

Steam-injectors  between  the  Glover  tower  and  the  chambers 
are^  as  we  see^  impracticable.  This  holds  good  of  any  place  in  the 
system,  except  in  the  exit-pipe  or  chimney  itself.  But  in  the 
chimney  where  the  steam  cannot  be  utilized  for  the  chamber 
process,  they  cause  considerable  expense. 

It  must  not  be  overlooked  that  with  steam-injectors  a  regulation 
is  all  the  more  called  for,  lest  the  draught  should  be  too  strong; 
and  in  the  end  a  cheap  source  of  draught,  viz.  the  chimney,  has 
been  replaced  by  a  dear  one,  without  any  gain  as  to  constant 
supervision  and  regulation.  We  should  accordingly  in  ordinary 
cases  prefer  a  chimney  to  a  steam-jet,  all  the  more  as  the  former 
will  always  be  necessary  in  any  case  for  the  steam-boilers.  Of 
course  the  chimney,  to  do  its  work,  must  be  higher  than  the 
chambers. 

Where  a  chimney  cannot  be  employed  for  one  reason  or  another, 
nothing  remaius  buc  to  have  recourse  to  a  mechanical  contrivance 
(fan-blast),  as  will  be  described  below. 

It  answers  much  the  same  purpose  as  a  chimney  if  the  outlet-pipe 
fixed  to  the  last  chamber  has  a  considerable  height — for  instance, 
50  feet  (in  the  south  of  France).  Where  several  sets  of  chambers 
exist  in  the  same  works,  it  is  preferable  to  carry  them  all  into  a 
common  chimney,  providing  the  connecting-pipe  of  each  set  with  a 
contrivance  for  regulating  the  draught.  It  is  not  a  good  plan  to 
utilize  for  the  chambers  a  chimney  with  which  ordinary  furnaces 
are  connected,  as  the  draught  will  be  of  a  very  variable  character  in 
this  case,  and  the  working  of  the  chambers  will  not  be  easily  kept 


PRODUCTION  OF  DRAUGHT  BY  CHIMNEYS.  551 

entirely  regular.  Stilly  at  some  works  this  plan  cannot  be  avoided^ 
and  must  be  provided  for  by  more  careful  regulation  of  the 
draught.  In  such  works  more  than  anywhere  else  the  auto- 
matically acting  dampers^  described  below,  are  recommended  to 
be  used. 

The  employment  of  a  chimney  is  even  more  advisable  if,  as  is 

now  the  case  in  all  well-appointed  works,  a  Gay-Lussac  tower  is 

fixed  at  the  end  of  the  set.     In  this  case  the  draught  must  be 

regulated  with  even  greater  care  than  otherwise ;  but  there  must 

he  an  excess  of  draught  at  disposal  to  begin  with.     It  is  also  a  great 

improvement  if  the  "  sight  ^'  necessary  for  checking  the  work  of 

the  tower  (comp.  Chap.  VI.)  can  be  arranged  in  the  down-draught 

near  the  ground-level,  or  at  least  the  gangway  round  the  chambers. 

If  there  is  no  down-draught,  but  a  direct  top-draught  out  of  the 

tower,  it  is  always  necessary  to  mount  to  the  top  to  observe  the 

'^  sight/'     It  is  certainly  quite  possible  to  employ  the  tower  itself 

as  a  chimney,  if  it  is  built  with  its  top  a  good  deal  higher  than  the 

chambers ;  and  this  is  actually  done  at  a  good  many  works,  but 

probably  in  some  cases  only  because  there  is  no  chimney  available. 

The  drawbacks  of  this  plan  are  well  illustrated  by  the  following 

passage  from  the  oflBcial  Alkali  Reports,  No.  21  (for  1884),  p.  74; — - 

"No. 2256.  The  vitriol-exit  from  the  plant  in  which  the  pyrites 

smalls  are  burnt  used  to  be  at  the  top  of  the  Gay-Lussac  tower.    I 

found  an  exceedingly  high  escape  from  here  on  my  first  three  visits. 

The  manager  has  since  connected  this  exit  to  the  main  chimnev, 

and  now  finds  he  can  better  regulate  the  draught  in  his  chambers. 

Since  this  has  been  done  the  tests  have  been  invariably  good.'^ 

The  more  recent  sets  of  chambers  at  Oker,  utilizing  the  configura- 
tion of  the  ground,  are  arranged  in  such  a  way  that  the  burners, 
Glover  towers,  chambers,  and  Gay-Lussac  towers  rise  one  above 
the  other,  terrace-wise.  The  outlet  of  the  whole  is  at  a  height 
of  62  feet  above  the  level  of  the  burner-grates.  Drawings  of  this 
arrangement  are  given  by  Brauning  (Preuss.  Zeitschr.  f.  Berg-, 
Hiitten-  u.  Salinenwesen,  1877,  table  ii.).  It  is  stated  there  that 
formerly  the  draught  could  not  be  made  suflScient,  even  by  con- 
necting the  Gay-Lussac  towers  with  the  boiler-chimneys. 

I  have  received  the  following  notes  concerning  the  Oker  system 
during  1902:— A  set  of  chambers,  started  in  October  1883,  was 
formerly  connected  by  a  2-foot  pipe  from  the  Gay-Lussac  towers 
with  the  steam-boiler  chimney.     The  draught  was  good,  but  the 


552  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

chimney,  made  of  common  bricks,  suffered  very  much.  Since  1896, 
when  the  chimuey  became  superfluous  through  the  centralization 
of  the  boiler  plant,  the  gases  have  been  passed  straight  out  of  the 
Gay-Lussac  tower  in  all  five  sets  of  chambers.  The  draught  is 
quite  sufficient,  without  any  artificial  help;  but  this  is  easy  to  i 
understand  from  the  conditions  described  above.  There  is  also 
the  convenience  of  running  both  the  chamber-acid  and  the  Gay- 
Liissac  acid  into  the  Glover  tower  bv  natural  fall. 

It  has  been  noticed  at  Oker  that  a  very  long  draught-pipe, 
connecting  the  last  chamber  with  the  tower,  has  the  advantage  of 
neutralizing  to  some  extent  the  oscillations  of  the  outer  atmo- 
spheric pressure,  and  thus  facilitating  the  regulation.  Se  this  as 
it  may,  such  a  long  pipe,  although  it  causes  some  loss  of  draught 
by  friction,  will  always  be  very  useful,  by  cooling  the  gas  previously 
to  entering  the  absorbing-tower.  The  same  has  been  found  at  the 
Stolberg  works  (1902). 

Very  frequently  one  chimney  has  to  serve  two  or  more  sets  of 
chambers.     It  is   perfectly  well  understood,  from  innumerable 
analogous  cases  in  ordinary  firing  operations^  that,  where  several 
apparatus  are  served  by  the  same  chimney,  special  care  must  be 
taken  that  they  receive  the  same  amount  of  draught.     Wherever 
possible,  the  main  flues  are  taken  separately  to  the  chimuey  and 
are  introduced  into  the  latter  in  such  a  way  as  not  to  interfere 
one  with  another,  which  can  be  attained  by  erecting  mid-feathers 
within  the  chimney.     Where  it  is  necessary  to  connect  several 
sets  of  chambers  with  the  same  main  flue,  it  must  not  be  over- 
looked that  the  draught  is  stronger  in  the  part  nearer  than  in  the 
part  further  removed  from  the  chimney  i  by  suitable  arrangement 
of  the  dimensions,  by  avoiding  sharp  angles  in  the  places  where 
the  branches  form  the  main  flue,  by  midrfeathers,  and  by  regu- 
lation by  means  of  dampers,  a  proper  equalisation  can  generally 
be  attained. 

Sometimes  none  of  the  ordinary  measures  secure  an  equal 
draught  for  two  sets  of  chambers,  even  when  the  flues  from  these 
meet  about  the  same  distance  from  the  chimney.  In  such  cases 
it  is  best  to  make  the  individual  flues  end  in  a  large  chamber, 
from  which  starts  the  main  leading  to  the  chimney,  and  to  fill 
this  chamber  loosely  with  bricks,  ot  course,  not  to  such  an  extent 
that  the  draught  is  too  much  restricted.  This  produces  numerous 
small  and  constantly  changing  currents,  which  prevent  any  odc 


PJIODUCTION  OF  DRAUGHT  BY  CHIMNEYS.  553 

of  the  large  currents  getting  the  advantage  of  the  others,  and  thus 
equalizes  the  draughts. 

C.  L.  Vogt  has  patented  (July  29th,  1875)  a  peculiar  contri- 
vance for  producing  draught  in  acid-chambers,  which  introduces 
the  air  along  with  the  necessary  steam  through  a  pipe  with  an 
opening  of  ^  inch.  The  steam  is  under  a  pressure  of  3  to  4  atmo- 
spheres. Sorel  ('Fabrication*  &c.  p.  291)  states  that  this  had 
been  practiced  in  France  20  years  earlier.  Such  a  contrivance 
is  only  exceptionally  called  for ;  but  there  are  cases  in  which  a 
supply  of  air  behind  the  burners  seems  desirable  (7th  Chapter). 

At  some  factories  they  work  in  this  way :  the  Glover  tower 
is  packed  very  loosely,  and  itself  acts  as  a  chimney,  so  that  the 
burners  have  always  very  good  draught  and  never  blow  out, 
whilst  it  is  quite  possible  at  the  same  time  to  keep  the  exit  draught 
so  low  that  there  is  some  little  outward  pressure  even  in  the  last 
chamber.  In  the  next  Chapter  we  shall  describe  an  arrangement 
by  which  this  aim  can  be  attained  even  more  perfectly. 

We  have  already  said  something  about  the  principles  according 
to  which  the  supply  of  air  must  be  regulated ;  and  we  shall  have  to 
return  to  this  in  the  next  Chapter.  Here  we  can  only  remark 
that  there  must  be  in  any  case  enough  total  draught  behind  the 
chambers,  but  not  too  much  j  otherwise,  even  if  the  burners  them- 
selves are  protected  against  excess  of  draught  by  diminishing  the 
air-holes  below  the  grates,  there  is  all  the  more  tendency  for  air 
to  enter  the  chambers  from  all  other  sides  through  the  finest 
chinks  and  thus  disturb  the  process.  If  the  draught  is  excessive, 
the  incubus  of  the  vitriol-maker,  pale  chambers,  at  once  makes  its 
appearance. 

Whether,  therefore,  the  draught  is  produced  by  a  chimney  or  by 
ail  open  pipe,  there  must  always  be  some  contrivance /or  regulating 
it.  At  many  works  this  is  done  by  a  simple  damper,  introduced 
into  the  respective  lead  pipe  by  a  slit,  luted  with  clay  or  not  at  all. 
The  arrangement  shown  in  fig.  234,  partly  in  elevation,  partly  in 
section,  and  in  fig.  235,  in  cross  section,  is  far  more  perfect.  The 
draught-pipe,  a  a,  is  widened  out  into  a  rectangular  vessel  sur- 
rounded by  a  jacket,  bb,  forming  a  hydraulic  joint;  and  the 
damper,  c,  is  surrounded  on  all  sides  by  the  jacket  dd,  dipping 
into  the  water-lute  at  6.  The  damper  is  raised  and  lowered  by 
the  help  of  the  chain^  pulley,  and  balance- weight,  e,f,g. 

In  continental  works  the  arrangement  shown  in  fig.  236  is 


aoi  CON'STKUCTION  OP  THE  LEAD  CHAMBERS. 

frequently  met  with.  The  draught-pipe,  a  a,  is  interrupted  b;  a 
vider  drum,  b,  divided  iuto  two  parts  by  a  horizontal  diaphragm,  c. 
The  latter  is  perforated  by  a  number  of  holes  whose  total  area  is 


somenhat  larger  than  that  of  the  pipe,  a  a.  When,  therefore,  all 
the  holes  are  open,  there  is  no  obstacle  whatever  to  the  draught ; 
but  this  can  be  produced  at  will  by  closing  a  certain  number  of  the 
holes  with  clay  or  lead  plugs.     For  this  purpose  the  space  above 


HEOULATION  OP  THE  DRAUGHT.  555 

the  diaphragm  is  accessible  by  a  small  door,  vhich  may  consist  of 
a  pane  of  glass,  d  (fig.  236),  to  which  another  on  the  other  side 
corresponds,  so  that  the  whole  at  the  same  time  serves  as  a 
"  sight." 

Automatic  regulation  of  the  draught  in  the  chambers. — Especially 
in  the  case  of  cliambera  not  connected  with  a  high  chimney,  where 
changes  of  wind  &c.  produce  great  variations  of  draught,  it  is 
advisable  to  adopt  some  automatic  regulation  along  with  the  ordi- 

Fig.  237. 


nary  dampers,  &c.  Such  an  automatic  apparatus  can  be  made  by 
putting  on  to  the  horizontal  part  of  the  exit-pipe  a  perpendicular 
12-inch  pipe,  closed  by  a  bell  standing  in  an  annular  water-lute. 
The  bell  hangs  on  one  arm  of  a  lever,  the  other  arm  of  which  is  so 
weighted  that  the  bell  can  travel  freely.  When  the  draught  is 
just  right,  this  second  arm  has  a  certain  position,  in  which  a  throttle- 
valve  within  the  exit-pipe  connected  with  it  is  half  open.  When 
the  draught  increases,  the  bell  descends,  owing  to  the  iucrease  of 


556  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

atmospheric  pressure^  and  partly  shuts  the  throttle-valve;  in  the 
opposite  case  of  the  draught  decreasing,  the  throttle-valve  is  opened 
wider.  This  apparatus^  as  constructed  by  M.  Delplace^  is  shown 
in  fig.  237,  where  a  is  the  entrance-pipe  from  the  Gay-Lussac 
tower,  c  the  exit-pipe,  b  a  conical  valve,  d  the  regulating  bell, 
ee  the  water-line  of  the  hydraulic  joint,/  the  lever,  g  the  balance- 
weight. 

Somewhat  different  in  detail,  and  apparently  very  accurately 
working,  is  the  apparatus  of  Mr.  W.  G.  Strype,  of  Wicklow,  of 
which  the  following  is  a  description  (patent  No.  705,  Feb.  21st, 
1879)  :— 

The  drawings  illustrate  two  forms  of  the  apparatus,  fig.  238 
being  the  most  desirable,  although  somewhat  more  expensive  in 
construction  than  the  arrangement  shown  in  fig.  239.  Refer- 
ring to  fig.  238,  an  inverted  vessel  or  receiver  A,  open  at  its 
lower  end,  dips  into  a  tank  A',  containing  water  or  other  suitable 
liquid  acting  as  a  hydraulic  joint.  The  interior  of  A  is  placed  in 
communication,  by  means  of  the  pipe  or  passage  a  b  c,  with  a 
receptacle  R  connected  with  the  main  flue  from  the  Gay-Lussac 
towers  and  chambers.  This  receptacle  is  also  in  communication 
with  a  flue  leading  to  the  chimney,  or  other  device  for  supporting 
the  draught,  and  is  divided  by  a  partition  having  apertures  fitted 
with  valves  or  dampers  D  D,  made  of  an  alloy  of  lead  and  anti- 
mony. The  operation  of  opening  and  closing  D  D  to  ensure 
uniformity  of  draught  is  regulated  automatically  by  the  action  of 
the  suction  itself  in  the  following  manner: — The  dampers  are  con- 
nected to  a  lever  B,  mounted  and  turning  on  a  centre  or  fulcrum  e. 
Suspended  from  one  end  of  the  lever  is  the  vessel  A,  whilst  the 
opposite  end  is  loaded  with  a  weight  C,  sufficient  to  preponderate 
to  the  required  extent  over  the  load  of  A.  Assuming  that  the 
draught  has  an  excess  of ''  pull  '^  over  that  which  is  adjusted  and 
necessary  for  the  proper  working  of  the  chambers,  the  dampers 
being  open,  the  suction  within  the  vessel  A,  when  accelerated, 
will  draw  down  that  end  of  the  lever  and  elevate  the  opposite  or 
weighted  end,  and  so  partially  close  the  dampers.  C  is  so  calculated 
that  the  weighted  end  of  the  lever  can  only  be  elevated  when  the 
required  draught  is  exceeded,  and  it  will  fall  by  gravitation  as 
soon  as  the  draught  is  unduly  diminished.  It  follows  that  thus 
the  desired  uniform  action  is  obtained. 

The  connection  between  the  dampers  and  the  lever  B  is  by 


HEGULATIQN  OF  THE  DBAUOHT.  557 

means  of  rods  or  links  passing  through  vater-sealed  stuffing-boxes, 
0  G';  and  to  avoid  friction  these  rods  are  suspended  from  knife- 
edge  centres  d  d'.  The  other  centres  are  constructed  with  knife- 
edges  in  like  manner. 

The  vessel  A  becomes  sensibly  lighter  when  deeply  immersed  in 

the  liquid,  owing  to  the  thickness  of  the  sides,  and  would  thereby 

constitute  a  source  of  disturbance  to  the  proper  action  of  the 

Fig.  238. 


apparatus.  To  counteract  this,  the  lever  B  is  provided  with 
a  projecting  arm  E,  carrying  an  adjustable  weight  F,  arranged  in 
such  a  position  that,  as  the  arm  partakes  of  the  motion  of  the 
lever,  the  centre  of  gravity  of  the  system  will  be  moved  in  the 
direction  and  to  the  extent  necessary  to  effect  the  required 
correction. 

Fig.  239  is  a  simpler,  and  in  some  applications  a  more  convenient 
form  of  the  apparatus,  the  action  being  of  course  identical  with 
that  described  for  the  arrangement  in   fig.    238.      Should   the 


558  CONSTRUCTION  OF  THE  LEAD  CHAMBERS, 

draught  fluctuate  very  much,  the  diaphragm  shown  dotted  at  H 
{with  an  opening  in  its  centre  to  conimuaicate  with  the  vessel  A) 
can  be  interposed  to  prevent  the  movements  of  the  regulator 
being  too  sudden  and  rapid. 

This  apparatus  has  no  wearing  surfaces,  is  practically  frictiouiess 
in  its  working,  and  is  balanced  in  all  positions.  By  means  of  it 
any  disturbance  to  the  steady  and  uniform  flow  of  gases  through 

Fig.  L'39. 


the  chambers  caused  by  irregular  chiniuey-draugbt  is  prevented, 
the  admiGHion  of  air  to  the  burners  is  more  uniformj  the  regulation 
of  the  proper  quantity  and  relation  o£  the  gases  to  each  other 
throughout  the  chambers  is  facilitated,  and  better  working  and 
more  economical  results  are  obtained  in  the  process  with  less 
supervision  and  attention  than  hitherto  required  to  carry  on 
successfully  the  manufacture  of  sulphuric  acid. 


MECHANICikL  PRODUCTION  OF  DRAUGHT.  559 

Mechanical  Production  of  Draught  in  the  Chamber  System, 

We  have  spoken  above  (p.  549)  of  the  various  drawbacks 
connected  with  the  application  o£  injectors  for  this  object :  I  have 
indeed  not  found  such  apparatus  at  any  of  the  works  I  have 
recently  visited.  But  several  works  have  adopted  the  plan, 
originally  followed  at  Freiberg*,  of  promoting  the  draught  by 
fans  made  of  lead  alloyed  with  antimony,  or  wood  or  iron  covered 
with  lead,  fixed  on  iron  axles,  running  in  somewhat  tightly  fitting 
lead  journals  without  stuflSng-boxes.  Such  fans  are  arranged 
either  between  the  Glover  tower  and  the  first  chamber,  or  between 
the  last  chamber  and  the  Gay-Lussac  tower,  or  in  both  places. 
These  fans  are  worked  at  a  trifling. expense,  most  conveniently  by 
electromotors,  which  avoid  the  necessity  of  shafting  and  gearing ; 
and  this  process  should  be  more  frequently  employed,  not  merely 
in  such  extreme  cases  as  at  the  Freiberg  works,  where  the  gases 
must  travel  through  flues  of  330  feet  length,  but  in  ordinary 
chambers,  which  are  thus  made  independent  of  accidental  variations 
of  pressure,  of  low  chimneys,  &c. 

At  the  works  of  Messrs.  Matthiesen  and  Hegcler  at  La  Salle 
(111.),  where  zinc-blende  is  roasted  in  a  mechanical  shelf-burner, 
and  the  necessary  draught  for  the  chambers  could  not  be  obtained 
by  a  chimney,  an  iron  fan-blast,  covered  with  an  alloy  of  lead  and 
antimony,  is  placed  between  the  Glover  tower  and  the  first 
chamber,  and  another  such  apparatus  between  the  Gay-Lussac 
tower  and  the  chimney.  This  arrangement  had  been  working  foe 
several  years  when  I  visited  the  works  in  1890. 

The  systematic  production  of  draught  by  placing  one  fan 
behind  the  Glover  tower  and  another  in  front  of  the  Guy-Lussac 
has  been  especially  worked  out  by  F.  J,  Falding :  comp.  Min. 
lud.  vii.  p.  672.  In  this  way  the  draught  of  the  burners  is 
rendered  independent  of  the  pressure  in  the  chambers,  where  quite 
different  conditions  prevail. 

Falding's  fans  have  a  cast-iron  casing  lined  with  lead,  and 
a  spindle  and  arms  made  of  antimony-lead.  They  are  very 
carefully  and  substantially  mounted,  and  work  up  to  700  revolu- 
tions per  minute. 

Niedenfiihr  (1902)  considers  that  a  fan-blast  would  be  best 
placed  between  the  burners  and  the  Glover  tower,  but  he  believes 

♦  According  to  Miihlhauser  (Zsch.  angew.  Ch,  1902,  p.  072),  this  invention 
is  due  to  a  mining  engineer  of  the  name  of  Ilageu,  at  the  Ilalsbriicke  works. 


I 
I 


560  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

this  to  be  impossible  with  ordinary  fans  on  account  of  the  high 
temperature  and  the  flue-dust.  Directly  behind  the  Glover  tower 
a  fan  would  also  act  very  weil^  but  here  antimony-lead  is  too 
quickly  corroded,  and  it  is  therefore  generally  preferred  to  put 
the  fan  between  the  last  chamber  and  the  Gay-Lussac  tower. 
Recently  the  firm  of  March  Sohne,  at  Charlottenburg  (nov 
"Vereinigte  Thonwaarenfabriken''),  have  constructed  very  good 
fans  of  stoneware,  which  probably  will  do  perfectly  well  at 
temperatures  below  70°  C,  for  instance,  between  the  Glover  tower 
and  the  first  chamber  (comp.  Chem.  Zg.  1902,  p.  1057).  But 
even  in  that  case  it  is  best  to  place  another  fan  between  the  last 
chamber  and  the  Gay-Lussac  tower.  In  very  long  sets  with 
small  sections,  such  as  are  found  when  a  small  original  plant  is 
gradually  enlarged  by  adding  more  chambers,  there  is  frequently 
irregular  work  with  large  consumption  of  nitre,  which  is  very 
easily  remedied  by  a  rational  use  of  fan-blasts. 

Usually   the   faus   are   made   of  iron   covered   with    lead,  or 
altogether  of  "  hard  lead  "  or  "  regulus  '^  (antimonial  lead),  but  of 
course  the  axle  or  spiudle  should  be  made  of  iron,  and  the  jouma/s 
must  also  consist  of  this  metal.     This  is  a  weak  pointy  at  least 
where  there  is  heat  to  contend  with  as  well  as  the  acids.     In  very 
hot  places,  however,  where  lead  is  out  of  the  question,  cast-iron 
may  be  employed,  which  is  not  acted  upon  so  long  as  no  acid 
is  condensed  upon  it.     Here  also  the  journals  are  the  weak  point, 
but  this  has  been  overcome  by  A.  P.  O'Brien,  at  Richmond,  Va. ; 
in  the   following  manner  (Falding,  *  Min.  Ind.*  ix.  p.  621) : — A 
cast-iron  fan  is  placed  immediately  behind  the  burners,  before  the 
nitre-oven  and  Glover  tower.     It  serves  five  Herreshoff  furnaces, 
consuming  30,000  lbs.  49  per  cent.  Rio  Tinto  fines  per  24  hours. 
The  fan  has   27   in.   suction    and   discharge,   and   is  cast-iron 
throughout,  including  the  spindle:   it  is  covered  with  a  1-inch 
coat  of  asbestos  cement.    The  temperature  inside  the  fan  is  about 
540*^  C.     The  journals  are  not  oiled  at  all,  but  flooded  with  water 
from  several  g-iuch  pipes.     Water  also  surrounds  the  jacket  of 
each  journal,  and  is  admitted  to  the  oil-ehamber  in  lieu  of  oil  as  a 
lubricant.    After  9  months'  work  it  had  not  required  a  cent's  worth 
of  repair  or  oil.     No  wrought-iron  or  steel  is  in  contact  with  the 
gas,  only  cast-iron ;    otherwise  there  is   nothing  special  in  its 
construction. 

Figs.  240  to  242  show  the  construction  of  a  hard-lead  fan,  as 


HECHANICAi.  PRODUCTION  OF  DBADOHT.  561 

coBstructed  by  H.  Lentpold,  at  the  Dora-Lys  works  at  Pont 
Saint-Martin  (commnnicated  by  him  to  the  author).  Fig.  240  is 
a  sectional  elevation,  fig,  241  a  sectional  plan,  fig.  242  a  per- 
specfive  view  of  the  iron  casing.  It  is  clearly  seen  bow  the  iron 
spindle  is  protected  by  a  hard-lead  casing. 


Fig.  240, 


Henker  (1902)  always  employs  fan-blasts  (and  water-sprays) 
for  the  " high- pressure  work"  (oomp.  pp.  468,  543,  and  Chap. 
VII.),  where  8  kil.  acid  of  116°  Tw.  is  made  per  cubic  metre  in 
24  hours.  He  places  the  fans  preferably  between  two  Oay-Lussac 
towers  ;  if  there  is  only  one  Gay-Lussac,  the  fan  is  placed  behind 
this,  but  is  followed  by  a  small  tower  fed  with  water  in  order  to 

VOL.  I.  2  o 


562  CONSTRUCTION  OF  THE  LEAD  CHAHBEHS. 

condeaae  the  acid  miat.  For  this  purpose  Beaker  prefers  plate- 
towers  to  any  other  kind  of  apparatus ;  he  places  one  of  these 
towers  at  such  a  height  that  the  weak  acid  contained  therein 
can  be  mu  into  the  Glover  tower.  The  object  of  the  fan-blast 
is  to  avoid  the  inequalities  and  temporary  losses  of  draught 
caused  in  the  case  of  chimneys  by  wind,  sunshine,  &c.,  and  to 

Tig.  242. 


produce  a  regular  composition  of  the  exit-^ases,  4'5  to  5  per  cent, 
oxygen  for  ordinary  pyrites,  up  to  6"5  per  cent,  for  cupreous 
pyrites.  As  there  is  a  difiereuce  of  temperature  between  day  aud 
night,  the  speed  of  the  fan  must  be  regulated  at  least  twice  a  day. 
Attempts  at  placing  a  fan  between  the  Glover  tower  and  the  first 
chamber  were  not  successful,  principally  on  account  of  the  necessity 
of  frequent  repairs,  although  even  shells  made  of  Volvic  lava  were 
tried. 

Anemomelera. 
Although  we  have  in  a  previous  Chapter  {p.  322)  excluded  the 
use  of  a  Combes'  anemometer  for  regulating  the  access  of  air  to 
the  burners,  because  it  is  too  delicate  an  inBtrument,  and  because 
it  OD^  shows  the  draught  in  the  place  which  it  occupies,  vre  have 
here  to  speak  of  an  anemometer  adapted  for  controlling  the  draught. 
This  is  P^clet's  differential  anemometer  as  modified  by  Fletcher 
and    Swau.      Fletcher's    modification  is  described  in  the  Third 


ANEMOUETBKS.  563 

Annual  Report  on  the  Alkali  Act,  1863,  by  the  Inspector,  for  1866, 
p.  54  el  aeq.  ;  Swan'a  in  the  '  Transactions  of  the  Newcastle 
Chemical  Society/  Jan.  26,  1871.  Peclet's  anemometer  is  founded 
upon  the  physical  principle  that  a  eurrent  of  air  passing  the  open 
CQcl  of  a  tube  causes  a  partial  vacuum  in  the  tube.  If,  therefore,  a 
straight  tube  is  introduced  through  a  hole  iuto  a  chimney,  or  into 
the  draught-pipe  taking  away  the  chamber-gas,  so  that  the  gaseous 
current  passes  the  open  end  of  the  tube  at  a  right  angle,  a  partial 
vacuum  will  be  formed  in  the  latter,  proportionally  to  the  velocity  of 
the  current ;  but  the  aspirating  action  of  the  chimney  will  be  equally 
communicated  to  this  tube.     We  must  here  distinguish  between 

Fiv'.  i>43. 


these  two  actions.  To  do  this,  we  must  introduce  two  tubes  into  the 
chimney,  one  of  which  euds  straight,  whilst  the  other  is  bent  to 
a  right  angle,  so  that  the  current  of  air  blows  into  it.  Both  tubes 
will  now  be  affected  by  the  aspirating  action  of  the  chimney;  but  in 
the  straight  tube  this  is  increased  by  the  aspirating  action  of  the  cur- 
rent crossing  its  open  end,  whilst  in  the  bent  tube  it  is  dminished 
by  the  air  blowing  into  it.  The  drEerence  between  the  aspirating 
action  of  the  two  tubes  is  thus  reducible  to  the  action  of  the  current 
of  air ;  and  by  measuring  it  the  speed  of  that  current  can  be 
ascertained.  For  this  purpose  the  two  tubes  are  connected  with  a 
U-shaped  glass  tube  containing  water  or  another  liquid  ;  this  will 
rise  in  one  of  the  limbs  to  an  extent  corresponding  to  the  difference 

2o3 


564  CONSTBUCTIO\  OF  THE  LEAD  CHAUBEKS. 

of  suction.  Since  the  sucking-action  of  the  chimney  acts  upon  botb 
limbs,  it  is  eliminated,  iind  the  difference  of  level  corresponds 
merely  to  the  different  action  exerted  hy  the  current  of  air  upon 
the  straight  tube,  which  it  crosses,  and  the  bent  one,  into  which  it 
bloH'S.  This  action  rises  and  falls  with  the  speed  of  the  curreut; 
and  the  latter  accordingly  can  be  de<Iuced  from  it.  Water  (used 
by  Peclet),  on  account  of  the  friction  exercised  in  the  U-tobe,  is 
only  adapted  for  currents  of  a  greater  speed  than  5  feet  per  second. 
Fletcher  overcame  this  difficulty  thus : — In  order  to  lessen  the 
friction,  he  employed  two  cylinders,  a  a'  (fig,  2i3),  of  4  iuches 


diameter,  connected  at  the  bottom  by  a  narrow  tube,  i.  This 
arrangement  is  ten  times  as  sensitive  as  a  U-tube  of  0'4  inch 
width  would  be,  since  the  area  upon  which  the  pressure  acts  is 
increased  100-fold,  but  tiie  circurafereuce  upon  which  friction  acts 
only  10-fold.  The  rising  and  falliug  of  tlic  liquid  is  observed  by 
means  of  metal  floats,  c  c,  upon  which  a  very  fine  horizontal  line  is 
marked  by  a  lathe  ;  and  the  scale,  d,  provided  with  a  vernier  and  a 
very  fine  adjusting-screw,  permits  the  difference  of  level,  down  to 
one- thousandth  part  of  an  inch,  to  he  read  off.  This  is  possible, 
not  with  water,  whose  mobilitVj^owiug  to  its  adhesion  to  the  glass. 


ANEMOMETERS.  565 

is  too  slight,  but  with  ether,  whose  adhesion  is  only  one  two- 
«thousandth  of  that  of  water.  The  two  glass  tubes,  e  and  /,  are 
inserted  into  the  draught-pipe,  k,  by  means  of  a  cork,  ^,  at  right 
angles  to  the  current  of  gas  (so  that  it  blows  into  the  bent  tube,  /), 
and  are  connected  by  elastic  tubes,  h  i,  with  a  a' . 

The  form  of  anemometer  shown  in  fig.  243  has  now  been 
replaced  by  the  simpler  one  represented  in  fig.  244.  Lenses  have 
also  been  added  to  make  the  readings  more  accurate;  but  these, 
in  my  experience,  give  more  trouble  in  making  the  observations 
than  is  gained  by  the  greater  accuracy  of  reading  the  scales. 

In  the  original  communication  by  Mr.  Fletcher,  as  well  as  in 
the  6rst  edition  of  this  w^ork  (pp.  333-335),  we  find  the  mathe- 
matical evolution  of  the  laws  for  ascertaining  the  relation  of  the 
readings  to  the  speed  of  the  currents.  We  abstain  from  repeating 
this  reasoning  here,  and  merely  give  the  final  formula  found  for 
ascertaining  the  velocity  of  the  gaseous  current  v  from  the  height 
of  the  column  of  ether  (of  0*740  spec,  gravity)  =jo,  for  any  tem- 
perature t  (in  degrees  Fahrenheit)  and  barometric  pressure  A  (in 
inches)  : — 


/• 


/' 29-92       519        „-.. 


The  Table  given  on  p.  567  et  seq,,  for  the  speeds  corresponding  to 
different  readings  of  the  anemometer,  is  computed  from  the  formula 

t;=  Vj»x28'55  j 

and  another  Table  is  added  for  correcting  the  variations  in  the 
temperature  of  the  current  of  gas.  Tlie  corrections  for  small 
variations  in  the  barometrical  pressure  are  usually  not  consider- 
able ;  but  they  can  be  made  by  means  of  the  above  formulae — 

,,_      /    29-92 


t'''=Y/yrYx  28-55, 

or 

X  28-55. 


^=\/^29^92 


If  the  pressure  is  read  off  in  millimetres  the  number  760  is 
everywhere  substituted  for  2992  ;  or  if  the  readings  are  in  milli- 
metres and  the  speed  in  metres  per  second  is  required  to  be  known. 


566  CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 

the  constant  28'55    is  converted  into  another,  accoi'ding  ta  the 

formula 

0-8048     ^^_     ,  .^ 
-7-=  X  28-55  =  1-727; 
V25-4 

so  that  the  formula  for  t/  and  j/  in  metrical  measures  will  read 

r'=  1-727  x/j?. 

A  correction  for  the  expansion  and  contraction  of  the  ether  in 
the  instrument  itself  is  mostly  unnecessary,  since  it  is  only  ex- 
posed to  the  ordinary  temperature ;  it  amounts  to  about  1  per 
cent,  of  the  speeds  shown  in  the  Table  for  each  10°  F.  (  =  5°-55  C.) 
deviation  from  60°  P., — more  for  temperatures  below,  less  for 
temperatures  above  60°  F. 

In  order  to  make  the  readings  more  exact^  first  the  height  of 
ether  in  one  of  the  limbs  is  noticed,  then  the  current  is  reversed 
by  connecting  the  tube  e  with  a  and  /  witli  a!  (fig.  243) ;  another 
reading  is  made  ;  and  thus  twice  the  difference  of  pressure  caused 
by  the  suction  at  /  is  found.  The  number  thus  found  is  read  off  in 
Table  I.  and  corrected  for  temperature  by  Table  II.  To  take  an 
instance^  let  the  first  reading  be  ]'039^  and  the  second  readings 
after  reversing  the  current,  0-861,  the  difference  will  be  0*178. 
On  referring  to  Table  I.,  the  speed  12*05  feet  per  second  will  be 
found.  This,  however,  is  only  true  if  the  temperature  of  the  air 
is  60°  F.  Should  it  in  the  case  in  question  be  520°  F.,  Table  II. 
gives  the  correcting  multiplier,  0*7280.  This,  multiplied  by  12*05, 
is  8*772,  the  true  speed  of  the  current  if  measured  at  the  tempera- 
ture of  60°  F. 

This  instrument  is  not  influenced  by  soot,  heat,  or  corrosive 
vapours ;  it  can  be  placed  at  some  distance  from  the  flue  to  be 
tested,  if  longer  elastic  tubing  be  used  ;  and  it  can,  of  course,  be 
employed  both  for  aspirating  and  for  pressure  currents  (fan-blasts 
&c.),  and  as  a  measure  for  the  speed  of  atmospheric  currents. 

Of  course,  like  every  other  anemometer,  Fletcher's  only  indi- 
cates the  pressure  at  the  place  occupied  by  its  receiving  portion ; 
and  accordingly  the  tubes  e  and  /  must  be  introduced  so  far  as  to 
reach  into  the  air-current  to  the  extent  of  about  one  sixth  of  the 
diameter  of  the  flue.  The  velocity  at  this  place  is  assumed  to  be 
nearly  equal  to  the  average ;  but  this  is  very  doubtful,  and  there 
are  no  means  at  present  known  of  measuring  the  absolute  quan- 
tities of  air  passing  through  a  flue  of  any  considerable  sectional 
area  with  any  degree  of  certainty. 


ANEMOMETERS. 


567 


Table  I. — Showing  the  Speed  of  Currents  of  Air  as  indicated  by  the 

Ether  Anemometer, 

t;=2i/jox  28-55. 
Temperature  60^  Fahr.     Barometer  29*29  inches. 


Manometer 
readiDg. 

Speed  of  air. 

ft.  per  see. 
0-903 

Manometer 
reading. 

in. 

Speed  of  air. 

Manometer 
reading. 

1 

Speed  of  air. 

in. 

ft.  per  sec. 

in. 

ft.  per  sec.   \ 

0001 

0047 

6-189 

0-093 

8-707 

0-002 

1-277 

0048 

6-255 

0-094 

8-754 

0003 

1-564 

0049 

6-320 

O095 

8-800        i 

0-004 

1-806 

0-050 

6-384 

0-096 

8-846 

0005 

2019 

0-051 

6-448 

0-097 

8-892        , 

OOOG 

2-212 

o-a52 

6-510 

0O98 

8-938 

0007 

2-389 

o-a53 

6572 

0-099 

8-988        : 

0-008 

2-554 

0-054 

6634 

OlOO 

9-028 

0000 

2-709 

0-a55 

6-695 

0-102 

9118 

0010 

2-855 

0056 

6-756 

0104 

9-207 

O-Oll 

2-994 

0-057 

6-816 

0106 

9-295 

0012 

3127 

0-058 

6876 

0-108 

9-383 

0013 

3-255 

0059 

6035 

0-110 

9-469 

0014 

3-378 

0-060 

6993 

0-112 

9-554 

0-015 

3-497 

0-061 

7051 

0114 

9-639 

'      0016 

3-612 

0062 

7-109 

0-116 

9-724 

0017 

3-723 

0063 

7-166 

0118 

9-808 

0-018 

3-830 

0064 

7-223 

0-120 

9-891 

,     ooio 

3-935 

0065 

7-279 

0-122 

9972 

0-020 

4-038 

O066 

7-336 

0-124 

10O63 

0-021 

4-137 

0067 

7-390 

O120 

10-13 

0022 

4-235 

0-068 

7-445 

0128 

10-21 

,      0023 

4-330        ' 

0069 

7-500 

O130 

10-29 

0024 

4-423 

0-070 

7-554        ' 

0132 

10-87 

I      0-025 

4-514 

1      0-071 

7-608 

0-134 

10-45 

0026 

4-604 

0-072 

7-661 

0-136 

10-53 

1      0027 

4-691        ! 

0^3 

7-713 

0-188 

10-60 

1      0028 

4-777 

;      0074 

7-766 

O140 

10-68 

.      0-029 

4-862 

1      0-075 

7-819 

0-142 

1076 

0-030 

4-1^5 

'      0-076 

7-871 

0*144 

10-88 

:      0031 

5-027 

0-077 

7-922 

0-146 

10-91 

^      0032 

5-107 

1      0078 

7-974 

0148 

10-98 

0-033 

5187 

0079 

8-0-25        I 

O150 

11-06 

0034 

5-265 

0080 

8075        ' 

0-152 

11-18 

0-035 

5-342 

0-081 

8125 

0-154 

11-20 

a036 

5-418 

0-082 

8175 

0166 

11-27 

0-037 

'       5-492        ; 

0-083 

8225 

0-158 

11-34 

0038 

5-565        1 

0-084 

8-275 

0-160 

11-42 

0039 

5-638 

0-085 

8324        1 

0162 

11-49 

0-(M0 

5-710 

1      0-06*5 

8-373        1 

0164 

11-56 

0-04J 

5-781 

O087 

8-421 

0-166 

1103 

00i2 

5-851 

0K)88 

8-469 

0168 

11-70 

aoi3 

5-921 

'      0069 

8-517 

O170 

11-77 

0044 

5-989 

0-090 

8-565 

0-172 

11-84 

0045 

6-056 

O091 

8-618 

0174 

11-91 

0046 

6-123 

0-092 

8-660 

1 

0176 

1108 

568 


CONSTRUCTION  OP  THE  LEAD  CHAMBERS. 


Table  I.  (continued). 


'  Manometer    g ^    -   .     i  Manometer    «      j    *    • 

reading.       ^P*^  ^^  *»'•  '     reading.       ^P^  *^^  ^*'"- 


Manometer 
reading. 


Speed  of  air. 


■ 

in. 

ft.  per  sec. 

in. 

] 

0178 

1205 

0-284 

0180 

i       12-11 

0-286 

0182 

12-18 

0-288 

0184 

12-25 

0-290       1 

0186 

12-31 

0-292       ! 

0-188 

12-38 

0-294 

0190 

12-45 

0-296 

0-192 

12-61 

0-298       1 

0-194 

1257 

0300 

0-196 

1264 

0-302 

0-198 

'       12-71 

0-304 

0-200 

12-77 

0-306 

0-202 

1283 

0-308 

0-204 

12-90 

0-310 

0-206 

1296 

0-312 

0-208 

1302 

0-314 

0-210 

13-08 

.      0-316       1 

0-212 

1315 

0-318 

I      0-214 

13-21 

0-820 

0-216 

1327 

0-322 

0-218 

13-33 

0-324       ! 

0-220 

13-39 

0-326 

0-222 

13-45 

0-328 

0-224 

13-51 

0330 

0-226 

13-57 

0-332 

0-228 

13-63 

0-334 

1      0-230 

13-70 

0-336 

1      0-202 

13-76 

0-838 

;      0-234 

13-82 

0-3-10       1 

0-236 

13  88 

0-342 

0-238 

1394 

0-344 

0-240 

13-99 

0346 

0-242 

1405 

0-348 

0-^44 

14-11 

oaoo 

0-246 

14-17 

0352 

0-248 

14-23 

0-354 

0-260 

14-28 

0-356 

0-252 

1 

14-34 

0-358 

0-254 

14-40 

0360 

0-266 

14-45 

0-362 

;      0-258 

14-50 

0-364 

0-260 

14-56 

0-366 

0-262 

14-62 

0-368 

0-264 

14-68 

0-370    ; 

0-266 

14-74 

0372 

1      0-268 

14-79 

0-374 

0-270 

14-84 

0-376 

0-272 

14-90 

0-378 

0-274 

14-96 

0-380 

0-276 

15-01 

0-382       ; 

;      0-278       I 

1506 

0-384       ! 

.      0-280       i 

15-11 

0-386 

0-282 

15-17 

1 

0-388 

ft.  per  sec. 

in.       : 

ft.  |3er  aec.    , 

15-23 

0-390       . 

17-83 

15-28 

0392       * 

17-88         ; 

15-33 

0394       ' 

l7-4» 

15-38 

0396 

17»8 

15-44 

0-398 

18H)2- 

15-49 

0-400 

18-06 

15-54 

0-402 

18-11 

15-59 

0-404 

1816 

15-64 

0-406 

18-20 

15-70 

0-408 

'        18-34 

15-75 

0410 

18-28 

15-80 

0-412 

18-33 

15-85 

0-414 

183S 

15-90 

0-416 

18-42 

15-95 

0-418 

1846 

16-00 

0420 

18o0 

1605 

0-422 

18-5r> 

1610 

0424 

18-60 

1615 

0-426 

18-64 

16-20 

0-428 

18-68 

16-25 

0430 

18-72 

16-30 

0432 

18-77 

16-35 

0-434 

18-82 

16-40 

0-436 

18-86 

16-45 

0438 

18-90 

16-50 

0-440 

18-94 

16-55 

0-442 

18-99 

16-60 

0444 

19-03 

16-65 

0-446 

19-or 

16-70 

0-448 

1911 

1675 

0-450 

1915 

1680 

0-452 

19-20 

1685 

0454 

19-24 

16-89 

0-456 

10-28     ; 

1694 

0-458 

19-32 

1699 

0460 

1936 

1704 

0-462 

19-41 

17-09 

0464 

19-45 

17-13 

0466 

19-49 

17-18 

0468 

19-53 

17-23 

0-470 

19-57 

17-28 

0472 

1962 

17-33 

0-474 

19-66 

17-37 

0-476 

19-70 

17-42 

,      0-478 

1974     ; 

17-47 

0-480 

1978        I 

17-52 

0-482 

1982        1 

i7-r>6 

0-484 

1986       ' 

17-(50 

0-486 

19-90 

17-65 

0-488 

19-94        ' 

1770 

0-490 

1998       1 

17-75 

0-492 

2002       1 

17-79 

0-494 

20-06 

ANEMOMETERS. 


569 


■Table  I.  (continued). 


Manometer 
reading. 

1 
1  Speed  of  air. 

Manometer 
reading. 

Speed  of  air. 

Manometer 
1     reading. 

in. 

1 
Speed  of  air. 

in. 

ft.  per  sec. 

in. 

ft.  per  sec. 

ft.  per  sec. 

0-49C> 

20-10 

0-590 

21-94 

0-700 

23-89 

0-498 

2014 

0-600 

•.>*^12 

0-750 

•24-73 

0-500 

2018 

0-610 

22-30 

'     0-800 

25-^ 

0-510 

2o-;« 

0-620 

22-48 

0850 

26-32 

0-520 

20-58 

0-630 

22  66 

0-900 

27-08 

0-530 

20-78 

0-640 

22-84 

0-950 

'       27-83 

0-540 

20-98 

0650 

23-02 

1-000 

28-55        1 

0-550 

2117 

0-660 

23-20 

1-250 

31-93 

0-560 

21-37 

0-670 

23-38 

1-500 

34-97 

'     0-570 

21-56 

0680        ; 

23-55 

1-750 

37-77 

,      0-580        1 

1 
( 

21-75 

0-690 

23-72 

2000 

40-37 

/    519 

Table  II. — Showing  the  Values  ^/\/Tro  •  //^^ 

Values  of 

if' 

om  0  /O  ICK 
\/  459+^ 

}0;  or  Cor 

rectionsfo) 

■  Temperat 

degrees 
Fahrenheit. 

ure. 

'     degrees 

1  Fahrenheit.  ' 

1                      ' 

degrees 
Fahrenheit.  | 

1 

/~5i9~ 
\/  459+ j5. 

/   519 

\/  459+ J'. 

0 

10634 

130        ' 

0-9388 

260 

08497 

5 

l-a>77 

135        : 

0-9348 

265 

0-8467 

10 

10520 

140 

0  9309 

270 

0-8438 

15 

10464 

145 

0-9270- 

275 

08409 

1>0 

10409 

150 

0  92;^2 

280 

08380 

25 

1-0355 

155 

0-9194 

285 

0-8352 

;jo 

10302 

160 

0-9156 

290        i 

0-8324 

a-> 

1-0250 

165 

0-9119 

295 

0-8296 

40 

10198 

170 

0-9083 

300 

0-8269 

45 

1-0148 

175 

0-9047 

305 

08242 

50 

1-0098 

180 

0-9012 

310        1 

0-8215 

55 

10049 

185        , 

0-8977 

315        ' 

0-8189 

HO 

1-0000 

190 

0-8943 

320 

0-8163 

«J5 

0-9952 

195        ; 

0-8909 

325        1 

0-8137 

70 

0-9905 

200        1 

0-8875    ' 

330 

0-8111 

75 

0-9858 

205 

0-8841 

335        1 

0-8086 

1          80 

09812 

210 

0-8808 

340        : 

0-8060 

'^ 

09767 

215 

0-8775 

345 

0-8035 

90        ' 

0-9723 

220 

0-8743 

350 

0-8010 

!          95 

0-9679 

225 

0-8711 

.355 

0-7985 

i        100 

0-9636 

230 

0-8680 

360 

0-7960 

105 

0-9593 

235        i 

0-8649 

3(>5 

0-7936 

110 

0-9551 

240        1 

0-8618 

370        1 

0-7912 

115 

0-9509 

245        ! 

0-8687 

375 

0-7888 

120 

0-9468 

250        1 

0-8557 

380        ' 

0-7865 

125 

1 

0-9428 

255 

0-8527 

:J85        1 

0-7842 

570 


CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 


Table  II.  (continued). 


degrees 

/  519   ' 

,   degrees 

/  519 

degrees 

Fahrenheit. 

1 

^  /  -^'^ 

Fahrenheit. 

\/  469 -f^  . 

'  Fahrenheit. 

1 

\/  459+/. 

• 

390 

1 

0-7819   1 

595 

0-7017 

800 

0-6420 

395 

0-7786 

6U0 

0-7000 

805 

0-6407 

400 

0-7763 

605 

0-6983 

810 

0-6395   1 

405 

0-7741   , 

610 

0-6967 

815 

0-6382 

410 

07729 

615 

0-6951 

820 

0-6369 

415 

0-7707 

620 

0(>9a5 

825 

0-6357 

420 

0-7685   , 

625 

0-6919 

'    830 

0-6345 

425 

07(M>3 

630 

0-6903   1 

835 

0-6333 

430 

0-7G41 

635 

0-6887 

840 

0-6321 

435 

07619 

640 

0-6871 

845 

0-6309 

440 

0-7598 

645 

0-(>85(i 

850 

0-6297 

445 

0-7577 

650 

0-(>841 

855 

0-6285 

450 

0-7556 

655 

0-6826 

860 

0-6273 

455 

0-7535 

660 

0-6811 

865 

0-6-261 

4(30 

0-7514 

665 

0-6796 

870 

0-6249 

465 

0-7494 

670 

0-6781 

875 

0-6237 

470 

0-7474 

675 

0(5766 

880 

0-6225 

475 

0-7464 

($80 

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. 

Fletcher^s  anemometer  has  been  improved  by  Swan  in  the 
following  way,  practically  returning  to  Peclet's  original  construction 
(a  similar  plan  has  been  independently  proposed  by  P.  Hart,  Chem. 
News,  vol.  xxi.  p.  200).  In  lieu  of  the  4-inch  cylinders  he  takes 
a  U-tube  of  \  inch  diameter,  narrowed  in  the  bend  to  diminish 
the  oscillations.      The  tube  is  10  inches  long,  and  placed  with  an 


ANEMOUETEKS.  571 

inclination  of  1  ia  10 ;  each  limb  has  a  scale  and  vernier,  the  latter 
partly  made  of  glass  and  coverinx  at  the  same  time  the  scale  and 
the  tube,  so  that  it  is  easy  to  read  off  to  ^^^  inch.  The  ends  of 
the  tube  are  connected  with  a  two-way  cock,  so  that  the  current 
can  he  reversed  without  opening  any  joint.  Fig.  345  shows  the 
instrument  as  seen  from  above,  so  that  its   inclination  to  the 


vertical  line  does  not  appear.  It  is  fixed  on  a  stand  provided  with 
a  spirit-level  and  adjusting-screws.  It  is  employed  just  like 
Fletcher's  anemometer;  hut,  owing  to  the  inclination  of  1  in  10, 
the  column  of  ether  in  the  tube  occupies  ten  times  the  space 
corresponding  to  its  height,  and  the  reading  of  j},^  inch  gives  thus 
the  same  result  as  the  very  difficult  one  to  iQti(i  i^"^^  ''^  Fletcher's 
instrument.  The  narrowness  of  the  tubes  does  not  matter  in  the 
case  of  ether,  as  the  friction  may  he  entirely  neglected  with  this 
substance  (the  later  form  of  Fletcher's  anemometer,  shown  in 
fig.  244,  hears  this  out  as  well).  Swan's  anemometer  must 
always  be  placed  exactly  level  in  the  direction  of  its  length; 
hut  it  need  not  he  levelled  across,  if  a  reading  be  made  in  one 
limb,  the  two-way  cock  turned,  and  the  new  reading  in  the  same 
limb  subtracted  from  the  first  j  thus  it  is  unnecessary  to  read  ofi 
at  both  limbs,  which  would  involve  levelling  across  as  well.  The 
speeds  are  found  from  Fletcher's  table,  dividing  the  readings 
by  10.  Quite  similar  to  the  above  is  the  presaure-guage  designed 
by  Sorel  (comp.  supra,  p.  509). 

Other  instruments  for  measuring  the  draught  are,  for  instance, 
those  of  Kretz  (Dingl.  Journ.  cxc.  p.  16),  of  Ramshottom  (ib. 
c^xxx.  p.  SSi),  of  Scheurer-Kestner  (ib.  ccvi.  p.  448  and  ccxxi. 
p.  427),  none  of  which  can  vie  with  Fletcher's  in  sensitiveness. 


^72  Construction  op  the  lead  cbajibers. 

The  very  iagenious  anemometer  of  Hurler  (Dingl.  Journ.  ccxxis. 
p.  160)  is  only  adapted  for  laboratory  use.  Compare  also  Bour- 
don's multiplying  anemometer  (Compt.  Kend.  vol.  xcir.  p.  5 ; 
Joura.  Soc.  Chem.  Ind.  1882,  p.  60). 

One  of  the  most  delicate  anemometers  is  Fryer's,  described  in 
the  Inspector's  Report  on  the  Alkali  Acts  for  1877-78,  p.  08.     Its 

Fig.  2«. 


principle  is  to  measure  the  difference  of  pressure  on  each  side  of 
a  watch-glass  shaped  copper  plate  connected  vith  a  spiral  spriug. 
It  will  measure  a  pressure  of  ^j/^g  of  au  inch. 

Recently  difi'erential  anemometers  on  another  principle  have 
come  into  use  very  largely,  and  seem  to  be  preferable  to  nil  others. 
There  are  already  a  good  many  forms  of  this  apparatus,  one  of  the 
best  known  being  that  of  Professor  Seger  (ti.  F.  19,426),  slioivii 


VOLUMES  OF  CHAMBER-GASES.  573 

in  fig.  246.  The  calibrated  U-tube  A  is  surmounted  by  two 
cylindrical  cups^  B  and  C,  of  equal  width.  The  board  on  which  it 
is  fastened  also  carries  the  sliding-scale  D^  adjustable  by  slits  a  a 
and  screw-pins  bb.  The  tube  is  filled  with  two  not  miscible 
liquids^  for  instance  heavy  paraffin  oil  and  dilute^  coloured  spirits 
of  wine,  of  nearly  equal'specific  gravity,  to  such  an  extent  that  the 
zero-point  of  the  scale  D  can  be  put  exactly  at  the  lin'e  of  contact 
of  both  liquids  at  X.  If  an  aspirating  force  is  acting  on  the 
surface  of  the  liquid  in  C,  which  raises  the  level  in  that  part  of  the 
tube,  the  point  X  will  be  lowered  at  a  multiplied  ratio,  corre- 
sponding to  the  difference  in  the  sectional  area  of  the  narrow  part 
of  A  and  the  enlargement  in  C.  If,  for  instance,  the  ratio  of  the 
sections  is  as  I  to  20,  a  difference  of  pressure  of  1  millimetre  will 
be  indicated  on  the  scale  by  a  sinking  of  X  to  the  amount  of  20 
millimetres.  The  scale  is  graduated  in  such  a  way  that  it 
indicates  the  pressure,  expressed  in  millimetres  of  water.  This 
instrument  is  much  cheaper  and  easier  to  handle  than  those 
constructed  on  Peclet's  principle  and  quite  as  accurate. 

Calculation  of  the  Volume  of  Chamber-gases  according  to 

Temperature  and  Moisture. 

In  all  calculations  concerning  chamber-gases  it  is  not  sufficient 
to  take  into  account  the  difference  of  temperature  and  barometric 
pressure  from  the  normal  state  of  0^  and  760  millim.,  but  the 
amount  of  moisture  present  in  the  chamber-atmosphere  must  be 
equally  brought  into  the  calculations.  It  is  evidently  impossible 
to  do  this  on  the  assumption  that  the  tension  of  aqueous  vapour 
within  the  chambers  is  that  ordinarily  existing  for  any  given 
temperature  ;  the  presence  of  sulphuric  acid,  not  merely  at  the 
bottom  but  all  over  in  the  shape  of  mist,  greatly  changes  the 
aqueous-vapour  tension  according  to  the  varying  strength  of  the 
acid.  The  tables  of  Regnault  and  Sorel,  given  on  pp.  195  and  196^. 
would  admit  of  making  the  calculation  in  the  proper  manner;  but 
it  will  be  more  convenient  to  consult  the  following  Table,  p.  574 
(calculated  by  Sorel),  which  immediately  gives  the  volume  occt^ied 
by  a  cubic  metre  (or  cubic  foot)  of  air,  originally  at  0°  C.  and  760 
miUtmetres  pressure,  after  being  brought  into  equilibrium  of  tempe- 
rature and  vapour-te^ision  with  dilute  sulphuric  acid  of  varying 
strength  and  temperature,  but  without  any  change  of  pressure. 


574 


CONSTRUCTION  OF  THE  LEAD  CHAMBERS. 


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