80  Development  of  the  Chemical  Arts.  {Am-FJe0bur;8P76arm- 
water  by  means  of  coal  yields  a  luminous  gas  for  half  the  cost  of  coal-gas.  Here, 
however,  as  we  shall  presently  see,  the  depreciation  of  the  plant  has  not  been  taken 
into  account. 
If  we  now  inquire  in  what  manner  the  hydrogen,  however  obtained,  is  rendered 
luminous,  we  find  two  essentially  different  methods.  The  one  depends  on  mixing 
the  water-gas  with  hydrocarbons.  As  early  as  18  34*  Selligue  employed,  at  Prais, 
the  oils  obtained  by  distilling  the  marl-shales  of  Autun  in  order  to  saturate  the 
water-gas  with  gaseous  hydrocarbons.  White  subsequently  passed  the  water-gas 
through  retorts  in  which  rosin  or  coal  was  converted  into  luminous  gas,  and  his  pro- 
cess was  carefully  examined  in  1851  by  Frankland,f  who  concludes  a  laudatory 
report  with  certain  propositions,  of  which  the  following  are  the  most  important: 
1.  The  production  of  gas  from  given  weights  of  common  coal  or  of  cannel  is 
increased  by  46  to  290  per  cent.,  according  to  the  quality  of  the  material  employed. 
2.  The  luminous  power  is  increased  by  12  to  108  per  cent.,  the  more  when  coals 
are  employed  which  produce  gas  of  a  highly  luminous  power. 
3.  The  quality  of  the  residual  tar  is  lowered,  a  part  of  it  being  converted  into 
gas  of  a  strong  luminous  power. 
It  must  be  remarked  that  tar  had  not  at  that  time  the  value  which  it  has  subse- 
quently reached. 
White's  process  recurs,  with  trifling  modifications,  under  a  variety  of  names. 
As  the  "  systeme  Leprince/'  or  "gas  mixte  Leprince,"  it  was  introduced  into  in- 
dustrial concerns  at  Liege,  adopted  by  the  town  of  Mastricht,  and  by  some  depart- 
ments of  the  Vieille  Montagne  at  Verviers,  and  was  critically  described  by  Verver 
in  1848  in  his  work  above  quoted.  Four  years  afterwards  a  similar  procedure  was 
elaborated  by  Baldanus  and  Griine,J  for  which  Schaffer  and  Walcker  obtained  a 
patent  in  Prussia.  Their  process  consisted  in  passing  steam  through  retorts  in  which 
coal-shales,  turf,  and  other  combustibles  were  heated  to  redness.  It  differs,  there- 
fore, from  White's  process  herein  that  the  production  of  hydrogen  and  its  carbura- 
tion  are  effected  in  the  same  retort.  An  ordinary  gas  retort  8 \  feet  in  length,  is 
said  to  yield,  in  twenty-four  hours  8,000  to  9,000  cubic  feet  of  this  gas  j  and  in 
*  Wagemann's  manufactory  at  Benel,  near  Bonn,  where  this  process  has  been  intro- 
duced, 1  cwt.  of  coal-shale  was  consumed  per  1,000  cubic  feet  of  gas. 
Essentially  different  is  the  second  method  of  employing  hydrogen  for  lighting,  as 
carried  out  in  1846  by  Gillard,  at  Passy,  near  Paris.  He  fixed  on  the  burners,^ 
from  which  the  water-gas  issued,  baskets  of  platinum  wire,  which,  on  the  ignition 
of  the  gas,  were  heated  to  brilliant  whiteness.  Hence  it  was  called  platinum  gas 
(gaz  platine).  The  immobility  of  the  light,  even  in  a  strong  wind,  the  dispensing 
with  lamp-glasses,  which,  according  to  Verver,  absorb  22  per  cent  of  the  light,  and 
the  brilliance  obtained  on  this  principle,  must  be  considered  as  advantages,  although 
the  intensity  is  not  free  from  objections.  Its  use  was  not  continued  at  Passy,  but  it 
was  introduced  by  the  celebrated  firm  of  Christofle  &  Co.,  into  their  electro-plating 
works  at  Paris, ||  and  was  employed  to  light  the  streets  of  Narbonne.    The  hourly 
*  Dumas,  "  Handbuch  der  Chemie,"  vii. 
f  Frankland,  "  Ann.  Chem.  Pharm.,"  lxxxii.,  48. 
%  "Journal  fur  Gasbeleuchtung,"  1862,  p.  63. 
g  Report  by  O.  Henry,  "  Journ.  Pharmacie "  [3],  xvii.,  105;  Dingler's  Journal,  cxvi.,  222;  and  the 
Reports  of  Bromeis  and  Ververs. 
U  Wagner,  "  Handbuch  der  Technologie,"  1873,  ii.,  371. 
