*j5K8$"m'}     Development  of  the  Chemical  Arts. 
Hydrogen,        .              .              .              .             .              .  34*462 
Carbonic  oxide,       .                         .  ,              .              .  2-403 
Oil  of  turpentine,            .....  10*852 
Stearic  acid,             .              .              .              .              .  9*7 1 6 
Alcohol,          ......  7*814 
Marsh-gas,              .....  13*063 
Wood  charcoal  (burnt  to  carbonic  acid),       .              .              .  8*080 
Ethylen,    .              .              .              .              .              .  11-858 
Ether,             .             .             .              .             .             .  9*028 
The  temperature  of  the  flame  does  not,  however,  depend  exclusively  on  the  heat 
of  combustion.  The  density  of  the  burning  body  and  the  specific  heat  of  the  prod- 
ucts of  combustion  must  also  be  taken  into  account.  Hence  it  comes  that  the  tem- 
perature of  the  hydrogen  flame  in  pure  oxygen  is  about  68000,  in  air  about  26000; 
the  temperature  of  the  flame  of  carbonic  oxide  in  oxygen  amounts  to  70000,  in  air 
about  30000  ;*  further  according  to  calculation  1  vol.  of  hydrogen  =  1  grin,  is 
capable  of  fusing  205  grms.  of  platinum,  whilst  the  same  volume  of  carbonic  oxide 
can  fuse  238  grms,  of  platinum  (melting-point,  20000).  In  practice,  however,  even 
under  the  most  favorable  conditions,  as  Deville  and  Debray  determined  in  their 
researches  on  platinum,  about  half  the  heat  is  lost  by  conduction  to  the  furnace  and 
other  surrounding  matter,  and  the  above  authorities  with  120  litres  of  hydrogen  and 
60  of  oxygen  succeeded  in  fusing  only  1  kilo,  of  platinum  instead  of  double  the 
amount  as  calculated.  Platinum  can  also  be  smelted  and  refined  under  similar  cir- 
cumstances with  coal-gas.  But  for  the  more  infusible  metals  of  the  platinum  group, 
iridium,  ruthenium,  and  their  alloys,  the  hydrogen  flame  must  be  retained,  which,  if 
costlier  than  coal-gas,  is  cheaper  than  carbonic  oxide. 
In  the  use  of  gases  as  fuel,  the  metal  itself  can  be  brought  in  contact  with  the 
flame,  which  is  impracticable  in  case  of  carbon,  and  thus  the  great  loss  of  heat  is 
avoided  which  ensues  when  the  crucible  is  heated  from  without.  Their  application 
renders  it  also  possible  to  inspect  the  condition  of  the  metal  at  any  moment.  In  the 
metallurgy  of  the  common  metals  these  two  advantages  do  not  come  into  consider- 
ation. Carbon,  moreover,  is  not  only  the  cheapest  but  the  most  productive  fuel,f 
and  the  application  of  hydrogen  as  a  source  of  heat  seems  therefore  limited  to  auto- 
genous soldering  and  to  the  fusion  of  the  most  refractory  platinum  metals. 
The  property  of  platinum-black  to  ignite  hydrogen,  of  which  Dobereiner  made 
a  well-known  and  widely  utilized  application  in  his  hydrogen  lamp  in  1823,  has  lost 
its  practical  importance  owing  to  the  discovery  of  friction  matches. 
The  more  intense  and  permanent  was  the  interest  which  hydrogen  created  as  a 
source  of  light. 
As  the  luminous  power  depends  on  the  temperature  at  which  a  solid  ignited  body 
is  maintained,  the  suggestion  was  near  at  hand  to  produce  an  intense  light  by  means 
of  this  gas,  in  which  an  incombustible  body  was  heated  to  whiteness.  To  this  end 
the  Scotch  military  engineer  Drummond  used  in  1826  cylinders  of  caustic  lime 
heated  in  the  oxyhydrogen  flame.  The  Drummond  light  has  been  widely  employed, 
*  Debray  "  Sur  la  Production  des  Temperatures  Elevees  et  sur  la  Fusion  de  la  Platine."  Lecons  de 
Chimie  en  1861,  65  ;  Paris,  1861. 
f  The  calculated  temperature  of  the  flame  of  carbon  in  oxygen  is  io,ooo°,  from  which  has  to  be  deducted 
the  unknown  amount  of  heat  which  at  this  temperature  is  lost  by  dissociation.    See  Debray,  opus  citat, 
3 
