MANUFACTURE  OF   AMMONIA,  ETC. 
135 
chambers  used  in  the  process.  The  liquid,  undergoing  distillation 
in  this  apparatus,  necessarily  covers  the  upper  surface  of  each  di- 
aphragm to  the  depth  of  about  an  inch,  being  prevented  from  pas- 
sing downward  through  the  small  perforations  by  the  upward  pres- 
sure of  the  rising  steam  and  other  elastic  vapors  ;  and  on  the  other 
hand,  the  steam  being  prevented,  by  the  traps,  from  passing  up- 
wards, by  the  pipes,  is  forced  to  ascend  by  the  perforations  in  the 
diaphragms ;  so  that  the  liquid,  lying  on  them,  becomes  heated, 
and  in  consequence  gives  off  its  volatile  matters.  When  the  am- 
moniacal  liquid  accumulates  on  one  of  the  diaphragms,  to  the  depth 
of  an  inch,  it  flows  over  one  of  the  short  pipes  into  the  trap  below, 
from  whence  it  overflows  into  the  next  diaphragm,  and  so  on. 
The  management  of  the  apparatus  varies  in  some  measure  with 
the  form  in  which  it  is  desirable  to  obtain  the  ammonia.  When 
the  ammonia  is  required  to  leave  the  upper  chamber,  in  the  form 
of  gas,  either  pure  or  impure,  it  is  necessary  that  the  steam  which 
ascends,  and  the  current  of  ammoniacal  liquid  which  descends,  be 
in  such  relative  proportions  that  the  latter  remain  at  or  near  the 
atmospheric  temperature,  during  its  passage  through  some  of  the 
upper  chambers,  becoming  progressively  hotter  as  it  descends,  un- 
til it  reaches  the  boiling  temperature  ;  in  which  state  it  passes 
through  the  lower  chambers,  either  to  make  its  escape,  or  to  enter 
a  cistern  provided  to  receive  it,  and  in  which  it  may  for  some  time 
be  maintained  at  a  boiling  heat.  On  the  contrary,  if  the  ammonia, 
either  pure  or  impure,  be  required  to  leave  the  upper  chamber,  in 
combination  with  the  vapor  of  water,  the  supply  of  steam  entering 
below  must  bear  such  proportion  to  that  of  the  ammoniacal  liquid 
supplied  above,  that  the  latter  may  be  at  a  boiling  temperature  in 
the  upper  part  of  the  apparatus. 
Solutions  of  ammoniacal  salts,  which  have  had  their  respective 
acids  abstracted  by  any  of  the  usual  means,  afford,  by  being  thus 
treated,  ammoniacal  gas,  either  alone  or  in  combination  with  wa- 
ter, of  considerable  purity ;  but  the  apparatus  is  equally  service- 
able in  obtaining  similar  results',  more  or  less  impure,  from  the 
ammoniacal  waters  obtained  by  the  distillation  of  coals,  or  of  bones, 
or  other  animal  matters,  as  well  as  from  stale  urine.  Acids  and 
certain  other  matters,  contained  in  these  impure  liquids,  may  first 
be  partly  removed  by  lime  and  other  well-known  means  ;  and  some 
of  them  will  be  further  removed  during  the  passage  of  the  ammo- 
