3 1 8  Production  of  Hydrogen.         { AmjlJyUr:;9^arm* 
The  application  of  this  principle  explains  the  high  generating 
capacity  of  this  type  of  generators. 
Owing  to  the  separate  chambers,  the  vertical  cylinder  generators 
may  further  be  heated  directly  by  the  still  combustible  waste  gases 
liberated  during  the  reducing  process.  They  require,  therefore,  no 
expenditure  for  heating  material  or  special  heat  generators  with 
workmen  in  attendance,  as  they  are  self-heating.  This  gives  some 
advantage  of  an  economy  hitherto  unattained.  Losses  of  hydrogen, 
such  as  are  inevitable  by  the  retort  process,  are  avoided  by  the  use 
of  the  vertical  cylinder  type  of  generators,  as  no  glowing  particles 
of  iron  peel  of!  the  exterior  of  the  apparatus,  under  pressure,  owing 
to  the  generator  being  lined  with  fireclay. 
Necessary  repairs  can  be  executed  in  a  few  hours  without  any 
lengthy  interruption  of  work,  as  the  inner  parts  can  be  easily  with- 
drawn and  replaced  by  a  block  and  pulley  arrangement.  Any  kind 
of  reducing  gas  may  be  used  in  the  vertical  cylinder  system  of  gen- 
erators but  it  is  best  to  employ  water  gas  or  half  water  gas. 
A  special  arrangement  further  renders  it  possible  to  heat  the 
contact  mass,  both  directly  and  indirectly  during  the  reducing  proc- 
ess by  means  of  which  uniform  heating  is  secured. 
Many  of  the  defects  incident  to  former  installations  are  avoided 
in  the  vertical  cylinder  system  by  replacing  the  contact  mass  in  com- 
paratively narrow  circular  layers  which  also  secures  uniform  heat- 
ing, reduction  and  oxidation  by  the  corresponding  streams  of  gas. 
Giffard  suggested  ore  as  a  contact  mass.  When  properly  treated, 
specular  iron  ore,  red  hematite  and  iron  oxide  hydrates  have  gen- 
erally been  found  suitable.  The  use  of  purple  ore  was  protected  by 
patent  220,889  and  that  of  sparry  iron  ore  by  patent  241,669  (dated 
1911).  The  former  has  the  disadvantage  of  containing  too  much 
sulphur  and  cakes  easily,  while  the  latter  often  melts  too  easily. 
Their  use,  therefore,  offers  no  advantages.  As  a  rule  briquettes 
act  too  slowly,  owing  to  their  defective  porosity. 
According  to  German  patent  244,732  taken  out  by  the  Inter- 
national Hydrogen  Company,  spongy  iron  free  from  carbon  can  only 
be  produced  by  reduction  and  out  of  it  pure  hydrogen,  when  instead 
of  the  usual  water  gas,  a  gas  consisting  chiefly  of  hydrogen,  but  ab- 
solutely free  from  hydrocarbons,  is  employed. 
In  practice  this  assertion  has  not  been  found  to  be  warranted. 
Besides,  the  fact  is  unimportant,  as  there  exists  no  practical  method 
of  producing  such  a  gas. 
