MANUFACTURE  OF  AMMONIA,  ETC. 
227 
all  these  cases,  the  salts  employed  are  mixed  with  sawdust  or 
some  other  porous  substance,  and  the  material  so  compounded  is 
placed  in  the  purifying  vessels  of  the  gas-works.  The  gas  in  its 
passage  through  the  purifiers  gives  up  its  ammonia,  which  is 
afterwards  obtained  as  sulphate  or  muriate  of  ammonia,  by  wash- 
ing the  material  when  it  has  become  fully  saturated  with  am- 
monia. 
Messrs.  Crane  and  Jullien,  in  their  patent  of  January  18, 1848, 
describe  a  method  of  manufacturing  ammonia  in  the  state  of  car- 
bonate, hydrocyanate,  or  free  ammonia,  by  passing  any  of  the 
oxygen  compounds  of  nitrogen,  together  with  any  compound  of 
carbon  or  even  free  hydrogen,  through  a  tube  or  pipe  containing 
any  catalytic  or  contact  substance,  as  follows  : — Oxides  of  nitro- 
gen (such  for  instance  as  the  gases  liberated  in  the  manufacture 
of  oxalic  acid),  however  procured,  are  to  be  mixed  in  such  pro- 
portion with  any  compound  of  carbon  and  hydrogen,  or  such 
mixture  of  hydrogen  and  carbonic  oxide  or  acid  as  results  from 
the  contact  of  the  vapor  of  water  with  ignited  carbonaceous 
matters,  and  the  hydrogen  compound  or  mixture  containing 
hydrogen,  may  be  in  slight  excess,  so  as  to  ensure  the  conversion 
of  the  whole  of  the  nitrogen  contained  in  the  oxide  so  employed, 
into  either  ammonia  or  hydrocyanic  acid,  which  may  be  known 
by  the  absence  of  the  characteristic  red  fumes  on  allowing  some 
of  the  gaseous  matter  to  come  in  contact  with  atmospheric  air. 
The  catalytic  or  contact  substance  which  Messrs.  Crane  and 
Jullien  prefer,  is  platinum,  which  may  be  either  in  the  state  of 
sponge,  or  asbestos  coated  or  covered  with  platinum.  This 
catalytic  substance  is  to  be  placed  in  a  tube,  and  heated  to  about 
600°  Fahr.,  so  as  to  reduce  the  temperature  of  the  product,  and 
at  the  same  time  prevent  the  deposition  of  carbonate  of  ammonia, 
which  passes  onwards  into  a  vessel  of  the  description  well  known 
and  employed  for  the  purpose  of  condensing  carbonate  of  am- 
monia. The  condenser,  for  this  purpose,  must  be  furnished  with 
a  safety-pipe  to  allow  of  the  escape  of  uncondensed  matter,  and 
made  to  dip  into  a  solution  of  any  substance  capable  of  combining 
with  hydrocyanic  acid  or  ammonia  where  they  would  be  con- 
densed.   A  solution  of  salt  of  iron  is  preferable  for  this  purpose. 
Mr.  Hills  took  out  a  patent,  October  19,  1848,  for  improve- 
ments in  treating  certain  salts  and  gases  or  vapors,  in  which  he 
