3H 
Production  of  Hydrogen. 
Am.  Jour.  Pharm. 
July,  1917. 
action  generally  takes  place,  while  the  reaction  generally  decreases 
in  intensity  in  the  direction  of  the  outlet  of  the  gas. 
Compact  iron,  such  as  waste  or  filings,  is  little  suited  as  contact 
substance  for  the  process,  but  iron  oxide,  either  artificial  or  natural,  1 
e.  g.,  iron  oxide  clay  briquettes  or  iron  ore,  are  eminently  suitable. 
All  these  substances  become  more  or  less  porous  during  the  reducing 
process. 
Theoretically  speaking,  the  contact  mass  could  be  used  over  and 
over  again  indefinitely  in  accordance  with  the  before  mentioned 
formulae,  so  that  an  unlimited  quantity  of  hydrogen  could  be  pro- 
duced by  means  of  a  limited  quantity  of  contact  mass. 
In  practice,  however,  a  limit  is  placed  to  the  life  of  the  contact 
mass  by  the  fact  that  as  it  is  only  the  surface  of  the  latter  that  is 
being  acted  on,  the  substance  gradually  becomes  impregnated  by  the 
dust,  silicic  acid  and  sulphides  liberated  by  the  gases.  These  im- 
purities form  a  layer  on  the  surface,  diminishing  the  reacting 
capacity,  so  that  the  yield  of  hydrogen  is  gardually  lowered  and 
other  disadvantageous  combinations  take  place. 
It  is  necessary,  therefore,  to  renew  the  contact  mass  periodically, 
say  after  the  plant  has  been  in  operation  for  from  8  to  30  days. 
The  principal  difficulty  with  the  iron  contact  method  arises  from 
the  fact  that  a  considerable  amount  of  heat  is  absorbed  during  the 
various  stages  of  the  process  by  the  chemical  reaction.  It  is  there- 
fore not  easy  to  keep  the  contact  mass  at  a  correct  temperature  with- 
out overheating. 
If  overheated,  the  contact  mass  loses  its  porosity,  cakes  and  even 
melts.  This  renders  the  replacing  of  the  contact  mass  difficult  or 
even  impossible.  The  action  of  the  gases  becomes  defective  and  the 
yield  of  hydrogen  falls  considerably,  as  channels  and  cavities  are 
formed  which  can  no  longer  be  acted  upon  regularly  by  the  gas  and 
steam. 
As  the  iron  contact  method  is  very  old,  all  kinds  of  suggestions 
have  been  made  in  the  course  of  time  in  connection  with  the  prac- 
tical method  of  dealing  with  this  process. 
A  voluminous  mass  of  patent  literature  on  this  subject  is  in  ex- 
istence. Only  the  most  important  of  these  patents,  most  of  which 
have  long  ago  expired,  are  here  passed  under  review. 
Giffard,  who  made  the  method  public  in  1878,  may  be  considered 
the  discoverer  of  the  method.  He  employed  a  shaft  filled  with  ore 
which  he  heated  and  reduced  by  means  of  gases  coming  from  a 
