3  2  Development  of  the  Chemical  Arts.    { j4mjJa°nur;8 £6harm 
most  recent  developement  of  chemistry,  as  well  as  of  great  technological  importance. 
Unawares,  this  property  has  been  made  use  of  for  ages.  Upon  it  depends  the  trans- 
mutation of  indigo-blue  in  the  vat  into  indigo-white,  and,  consequently,  one  of  the 
oldest  and  most  important  branches  of  the  art  of  dyeing. 
In  1842,  Zinin  succeeded  in  converting  nitrobenzol  into  anilin  by  the  action  of 
nascent  hydrogen,  and  thus  opened  out  an  industrial  region  of  unimagined  extent. 
The  era  of  the  artificial  dyes  followed.  It  was  soon  perceived  that  many  of  these 
substances  shared  with  indigotin  the  property  of  being  decolorised  by  hydrogen,  and 
thus  zinc-powder  was  introduced  into  calico-printing  as  a  discharging  agent,  which, 
developing  hydrogen  in  patterns  where  it  is  printed  on,  remove  artificial  coloring 
matters,  e.g.,  magenta.* 
A  series  of  interesting  observations  showed,  however,  that  the  manner  in  which 
hydrogen  is  evolved  is  not  without  influence  on  hydrogenisation.  Whilst  ammonium 
sulphide,  and  whilst  acids  under  the  influence  of  metals  give  up  so  much  hydrogen 
to  nitrobenzol  as  to  form  anilin  ;  if  other  sources  of  hydrogen  are  employed  the 
reaction  is  arrested  half-way,  and  intermediate  products  are  generated.  Herewith, 
therefore,  nascent  hydrogen  escapes  from  our  general  consideration,  and  its  technical 
application  will  be  described  in  future  parts  of  this  report. 
We  return,  therefore,  to  its  applications  as  a  source  of  heat  and  light.  It  has  been 
briefly  described  in  the  section  on  oxygen  how  the  oxyhydrogen  blast  was  evolved 
from  the  experiments  of  Saron  between  1780  and  1790,  and  how  it  was  introduced 
in  the  manufacture  of  platinum  in  the  middle  of  the  present  century  by  Deville  and 
Debray.  Since  1838!  Desbassains  de  Richemont  found  in  hydrogen  mixed  with  air 
the  means  for  the  autogenous  soldering  of  sheets  of  lead,  and  thus  supplied  the  sul- 
phuric acid  manufacture  with  the  fundamental  condition  of  its  growth,  i.e.,  perma- 
nent lead  chambers  of  any  desired  magnitude.  If,  in  places  where  coal-gas  is  readily 
procurable,  this  combustible  is  substituted  for  hydrogen  in  soldering  lead,  many 
sulphuric  acid  chambers  are  not  near  gas-works,  and  in  them  hydrogen  is  still 
necessary  for  soldering.  The  same  must  be  said  on  the  application  of  hydrogen  for 
the  autogenous  soldering  of  other  metals  and  alloys,  a  process  for  which  Winckler, 
in  his  convincing  essay  already  quoted,  predicts  a  great  future.  More  recently,  lead 
pans  soldered  in  this  manner  have  been  introduced  in  the  manufacture  of  boracic 
acid  in  Italy.  Numerous  conflagrations,  especially  that  of  Canterbury  Cathedral  in 
1 871,  and  that  of  the  Alexandra  Palace  on  Muswell  Hill  in  1873,  demonstrably  due 
to  the  braziers  full  of  fire  used  in  soldering  the  leaden  spouts,  have  led,  in  England, 
to  the  proposal  to  solder  leaden  roofing  and  spouting  with  hydrogen. 
How  far  hydrogen  is  superior  to  other  kinds  of  fuel  appears  from  the  following 
table.  According  to  the  experiments  of  Favre  and  Silbermann,  1  grm.  of  the  follow- 
ing bodies,  when  burnt  in  water,  gave  the  appended  number  of  calorics,  f.  <?.,  it 
raised,  by  i°,  the  temperature  of  the  given  number  of  centigrams  of  water.J 
*  The  transformation  of  the  colored  salts  of  rosanilin  into  the  colorless  salts  of  leucanilin  by  means  of 
zinc  and  hydrochloric  acid,  was  discovered  by  A.  W.  Hofmann,  in  i860, — Proc.  Roy.  See,  vol.  xii.,  p.  2. 
The  above  application  is  due  to  Durand.  See  Schutzenberger,  "  Traite  des  Matieres  Colorantes,"  vol. 
i,  p.  491. 
I  Karmarsch,  "  Geschichte  der  Technologie,"  380. 
J  A.  Witrtz,  "  Dictionnaire  de  Chimie,"  vol.  i,  pp.  825,  826. 
