34  Development  of  the  Chemical  Arts.  {Am' j^^m' 
not  merely  in  geodetic  measurements  and  in  lighthouses,  which  the  inventor  had 
principally  in  view,  but  also  for  projections  of  microscopic  objects  and  photographic 
images  on  glass,  or  drawings  upon  gelatin  for  demonstration  in  lecture-halls,*  for 
dissolving  views,  and  chromatropes.  In  the  American  civil  war  it  was  used  in  sieges 
to  light  up  forts. f  The  English  war  department  has  tried  it  in  barracks,  in  large 
halls  and  courts,  in  whichj  it  is  said  to  have  proved  cheaper  than  coal-gas,  whilst  the 
smallest  characters  could  be  read  at  a  distance  of  90  metres  from  the  source  of 
light. 
Since  lime  partially  loses  its  luminous  power  by  continued  use,  platinum-wire, 
magnesia,  and  latterly  zirconia,  have  been  employed  in  its  stead. g 
The  above-mentioned  application  of  the  hydrogen  lamps  are,  however,  of  a  very 
limited  nature.  To  utilize  it  on  the  large  scale  for  street  lighting,  the  simultaneous 
use  of  oxygen  has  been  laid  aside,  and  cheaper  methods  of  preparation  have  been 
sought  for.  For  this  purpose  advantage  was  taken  of  Felice  Fontana's  method  of 
decomposing  water  by  means  of  ignited  iron  and  ignited  carbon,  as  proposed  in 
1780.ll  On  the  latter  scheme  Donovan  founded  his  industrial  preparation  of 
hydrogen  gas  in  Dublin,  in  1830.  His  process  has  been  repeatedly  described  with 
modifications,  referring  in  part  to  the  needful  apparatus,  and  in  part  to  the 
diminution  of  the  proportion  of  carbonic  oxide.  The  presence  of  this  poisonous 
gas  was  at  first  justly  urged  as  an  argument  against  the  use  of  the  "  water  gas." 
Langlois  found  that  the  mixture  obtained — on  allowing  steam  to  pass  over  iron 
retorts  filled  with  red  hot  coke  in  Kirkham's  apparatus — had  the  tolerably  constant 
composition  of  58  to  60  per  cent,  of  hydrogen,  19  to  26  carbonic  oxide,  and  15  to  20 
carbonic  acid. 
It  was  subsequently,  however,  discovered^  that  at  higher  temperatures  carbonic 
oxide  is  oxidized  by  watery  vapor  to  carbonic  acid,  so  that  if  the  steam  is  in  excess 
a  gas  may  be  obtained  relatively  free  from  carbonic  oxide,  as  shown  in  the  reaction 
—  C-j-2H20=4.H-|-C02.  In  the  water-gas  prepared  at  Narbonne,  where  the  gas  on 
issuing  from  the  retorts  is  conducted  through  ignited  tubes  along  with  fresh 
quantities  of  superheated  steam,  Verver**  found  in  1858,  3*54  per  cent,  of  carbonic 
oxide.  According  to  other,  observers  the  amount  ranged  from  2*5  to  5  per  cent. 
In  the  water-gas  at  Passy,  Payen  found  6  per  cent,  of  carbonic  oxide,  whilst  in 
ordinary  coal-gas  he  found  an  average  of  no  less  than  14  per  cent.  The  above- 
mentioned  objection,  therefore,  no  longer  holds  good. 
The  carbonic  acid  is  removed  by  milk  of  lime,  or,  perhaps,  more  economically, 
according  to  the  suggestion  of  Heurtebiseff  by  soda,  which  is  thereby  converted 
into  bicarbonate,  a  readily  saleable  substance. 
FayesJ|  constructed  for  lighting  the  town  of  Narbonne  an  apparatus  which  he 
:i;  This  Report,  Nov.,  1875,  p.  509  ;  also  H.  Vogel,  "  Ber.  d.  Chem.  Gesell.,"  iii,  901. 
f  Wagner,  "  Lehrbuch  der  Technologic"    9th  edit ,  ii,  p.  377. 
j"  Journal  of  Gas-lighting,"  1869. 
§  See  the  work  of  Phillips,  quoted  above. 
j|  Mem.  Soc.  Hal.,  xv. 
«j[Bromeis,  Zeitsch.  d.  Ver.  deutsch.  Ing.,  iii.  82,  and  Dingier  Polyt.  J.,  clxiv.  33,  1859. 
**  B.  Verver.    "  L'eclairage  au  gaz  a"  l'eau  a  Narbonne  et  l'eclairage  au  gaz  Leprince."  Leiden  1858. 
See  Bromeis,  opus  citat. 
ft  Heurtebise,  Dingl.  Pol.  J ,  cxxcvi.  (?),  393,  1867. 
tX  Fayes,  Genie  industries  1868,  329.    Dingl.  Pol.  J,,  clix.  47. 
