PROCESS  FOR  REDUCING  OXIDE  OF  IRON. 
119 
the  employment  of  sulphuric  acid  and  zinc,  which  are  more 
costly  than  those  used  for  preparing  carbonic  oxide. 
The  apparatus  that  I  have  employed  in  my  experiments  is 
composed  of  a  metallic  [iron]  tube  placed  horizontally  in  a  fur- 
nace in  such  a  manner  as  to  be  easily  surrounded  by  burning 
charcoal.  Two-thirds  of  this  tube  is  filled  with  oxide  of  iron  in 
troches,  the  other  third  with  charcoal  of  poplar  or  willow  in 
small  fragments  which  are  prevented  from  mixing  with  the  oxide 
by  a  piece  of  iron  wire  gauze.  The  end  of  the  tube  containing 
the  carbon  is  connected  witha  generator  of  carbonic  acid,  obtained 
by  means  of  marble  and  muriatic  acid,  the  gas  before  entering 
the  reduction  tube  is  washed  in  a  bottle  containing  sulphuric 
acid,  which  serves  to  regulate  the  evolution  of  the  gas.  The 
other  end  of  the  tube  is  furnished  with  a  tube  dipping  into  a 
vessel  of  mercury  through  which  the  resulting  gas  escapes. 
The  apparatus  being  mounted,  the  whole  of  the  reduction  tube 
is  carried  to  a  red  heat;  when  the  carbonic  acid  in  passing  the 
red  hot  carbon  is  deoxidized  and  converted  into  carbonic  oxide, 
which  by  its  contact  with  the  oxide  of  iron  becomes  again  carbonic 
acid.  By  this  process  the  iron  is  reduced  much  more  certainly 
and  a  great  deal  more  promptly  than  by  hydrogen,  because  the 
affinity  of  carbonic  oxide  for  oxygen  is  much  stronger  than  that 
of  hydrogen  for  oxygen,  a  fact  demonstrated  by  M.  Henry  in  a 
conclusive  manner,  in  mixing  hydrogen,  oxygen  and  carbonic 
acid  in  an  eudiometer  and  passing  an  electric  spark  through  the 
mixture  when  the  carbonic  oxide  had  become  carbonic  acid. 
Besides  the  economy  of  time,  this  process  gives  also  a  great 
advantage  in  reference  to  the  cheapness  of  the  materials  used. 
Marble  is  of  no  value,  muriatic  not  much  dearer  than  sulphuric 
acid,  whilst  the  carbonic  acid  which  flows  from  the  apparatus,  if 
it  is  not  used  to  saturate  the  carbonated  alkalies,  can  be  conducted 
by  means  of  a  caoutchouc  tube  to  the  generating  apparatus. 
Instead  of  the  subcarbonate  of  iron,  which,  notwithstanding  the 
washing,  retains  always  sulphate  of  soda,  I  prefer  to  employ  the 
oxide  of  iron  obtained  by  precipitating  the  chloride  by  ammonia, 
because  by  calcination  it  can  be  totally  deprived  of  the  ammoniacal 
salt  admixed  with  the  oxide. — Repertoire  de  Pharm.  from 
Journal  des  Connaissances  Med, 
