MANUFACTURE  OF  COMMERCIAL  CARBONATE  OF  AMMONIA.  137 
pipe  was  not  there,  the  pressure  inside  the  balloon  might  cause 
it  to  be  blown  off  the  scaffolding.  Great  attention  has  to  be 
paid  to  the  heating  of  the  retorts.  If  they  were  heated  too 
strongly,  most  disastrous  results  might  occur. 
The  retorts  are  charged  once  every  twenty -four  hours  with  a 
mixture  of  carbonate  of  lime  and  ammoniacal  salt ;  the  chalk 
is  well  dried  on  an  iron  plate  which  is  set  over  the  flue,  so  that 
the  waste  heat  of  the  fires  economically  dessicates  it.  All  the 
retorts  are  not  charged  at  the  same  time,  for  often  there  are  five 
and  six  sets ;  if  they  were,  the  labor  would  be  too  great,  and  a 
greater  number  of  men  would  be  required;  but  to  do  away 
with  that  difficulty  one  retort  in  each  set  is  charged  at  the  same 
hour  every  day ;  the  first  charging  takes  place  at  seven,  the 
second  at  eleven,  and  the  third  at  three,  and  by  that  time  the 
whole  of  the  retorts  have  been  charged.  The  contents  are 
frequently  stirred  up  with  long  iron  rods  (which  are  pushed 
through  holes  made  in  the  door  of  the  retorts)  to  assist  the 
decomposition.  Before  a  new  charge  is  put  in,  the  pipes  lead- 
ing to  the  balloons  are  well  cleaned  out,  as  they  are  very  liable 
to  become  stopped  up.  The  used-up  charge,  which  consists 
principally  of  chloride  of  calcium,  is  drawn  out  into  an  iron 
barrow  and  wheeled  away  to  some  waste  ground;  the  new 
charge  (which  is  generally  two  of  chalk  to  one  of  the  salt) 
and  which  has  been  carefully  weighed  and  well  mixed,  is 
thrown  quickly  into  the  retort,  the  door  is  luted  on,  and  then 
the  retort  is  left  for  twenty -four  hours,  the  contents  receiving  an 
occasional  stir. 
When  the  retorts  have  been  worked  for  about  fourteen  days, 
the  balloons  are  opened,  and  the  impure  carbonate  is  found  as 
a  thick  crust  lining  all  the  sides ;  it  is  deposited  in  different 
colored  layers,  according  to  the  impurity  of  the  carbonate. 
The  chief  impurities  will  be  carbonate  of  lime  and  chloride  of 
calcium,  which  are  carried  over  mechanically  ;  the  salt  is  well 
scraped  down  from  the  sides,  and  the  balloon  prepared  for 
another  fourteen  days'  operation.  These  balloons  have  to  be 
of  considerable  size,  or  there  will  be  much  waste  from  the  salt 
being  carried  off  by  the  steam ;  in  each  balloon  is  a  small  test- 
hole,  closed  with  a  plug  of  wood  ;  this  is  for  telling  how  the  * 
