AmjtJ?uli9?7arm'5'  Production  of  Hydrogen.  315 
producer  connected  with  the  shaft  and  which  passed  through  a  dust 
chamber,  in  order  to  remove  the  particles  of  dust  introduced  during 
the  operation.  The  defect  of  this  system  was  that  the  ore  was  easily 
contaminated  by  the  impurities  contained  in  the  gases  and  that  a 
sufficiently  high  temperature  could  not  be  maintained. 
In  1889  Clans  (English  Patent  No.  50)  published  a  method  for 
the  production  of  hydrogen  in  a  shaft  furnace.  He  too  employed 
"  porous  though  solid  blocks  of  iron  oxide  "  which  he  alternately 
reduced  with  water  gas  and  oxidized  by  means  of  superheated 
steam.  i 
Walker's  English  patent  8373,  dated  1890,  describes  the  operation 
of  the  contact  method  in  iron  retorts,  which  were  heated  in  a  retort 
furnace  from  the  outside.   He  employed  water  gas  for  the  reduction. 
In  1892,  the  firm  of  Krupp  published  various  improvements  of 
the  process  (D.  R.  P.  No.  73,978)  which,  however,  did  not  produce 
satisfactory  results  and  were  ultimately  rejected. 
Iron  ores  were  employed  in  heated  shafts  or  retorts  and  atten- 
tion was  drawn  to  the  importance  of  employing  reducing  gases  as 
rich  as  possible  in  hydrogen  with  a  minimum  of  hydrocarbon. 
Stracke  returned  in  1893  to  the  Giffard  shaft  furnaces  (German 
Patent  No.  77,350)  and  filled  a  shaft  furnace  with  layers  of  "  iron, 
iron  oxide  and  ore  in  any  form,"  heating  and  reducing  the  whole  by 
heated  generator  gas  or  water  gas  which  he  introduced  through  the 
ore  from  the  generator.  He  used  charcoal  in  the  generator  in  order 
to  avoid  the  formation  of  sulphur  compounds  while  producing  ex- 
ceptionally pure  gas.  The  waste  gases  formed  during  the  process 
of  reduction  were  completely  consumed  in  a  superheater  with  fire- 
proof cage-work  which  served  to  raise  to  a  high  temperature  the 
steam  used  in  producing  the  hydrogen.  Here  too  the  heating  was 
insufficient. 
Schimming  took  out  a  German  patent  No.  95,071  for  the  pre- 
liminary heating  of  the  reducing  gases  which  he  achieved  by  blow- 
ing air  into  the  reducing  shaft  in  order  to  cause  combustion  of  a 
portion  of  the  reducing  gas.  This  method  had  the  grave  defect  of 
overheating  and  melting  the  ore  at  the  entrance,  while  the  ore 
further  away  was  not  sufficiently  heated.  He  tried  to  remedy  this 
defect  by  mixing  pieces  of  fire  brick  with  the  contact  mass  in  order 
that  the  former  might  retain  a  portion  of  the  heat,  but  the  system 
involved  serious  drawbacks. 
Caro  in  German  patent  249,269  tried  to  overcome  the  want  of 
