MANUFACTURE  OF  CARBONATES  OF  SODA. 
47 
water  in  a  suitable  vessel,  to  remove  ashes,  smoke,  or  other  dirt ; 
a  little  lime,  carbonate  of  lime,  or  alkaline  matter  being  mixed 
with  the  water  in  the  said  vessel,  to  absorb  and  remove  any  sul- 
phurous acid,  the  presence  of  which  would  injure  both  apparatus 
and  materials.  It  is  found  in  practice  that  1  lb.  of  lime  is  suffi- 
cient for  10,000  cubic  feet  of  gas. 
The  carbonic  acid  is  transmitted  through  the  liquid  in  the  vats 
until  the  decomposition  of  sulphuret  of  sodium  into  carbonate  of 
soda  is  found  in  the  lower  vat  to  be  complete,  which  is  easily 
known  by  suitable  chemical  tests,  when  it  may  be  drawn  off  to  be 
filtered  and  evaporated  in  the  usual  manner.  The  liquor  in  the 
upper  vat  is  then  to  be  brought  into  the  lower  one,  and  fresh 
liquor  into  the  upper  one,  and  the  process  repeated  as  before. 
The  patentee  remarks,  that  any  arrangement  of  apparatus  may 
be  used  that  will  bring  carbonic  acid  into  intimate  contact  with 
sulphuret  of  sodium. 
During  the  whole  process  a  constant  stream  of  gases  is  escaping 
from  a  pipe  in  the  upper  vat,  consisting  of  sulphuretted  hydrogen, 
nitrogen,  and  other  gases.  The  whole  of  the  sulphur  originally 
in  the  sulphate  of  soda  is  contained  in  the  sulphuretted  hydrogen, 
which  may  be  recovered,  or  made  into  compounds  of  sulphur  by 
means  well  known  to  chemists. 
If  bicarbonate  of  soda,  or  "soda-salaratus"  as  it  is  called  when 
impure,  is  to  be  made,  the  solution  of  carbonate  of  soda,  obtained 
from  the  vats  wherein  the  sulphuret  of  sodium  is  converted  into 
carbonate  by  means  of  carbonic  acid,  as  previously  described,  is 
filtered  and  boiled  down  until  the  carbonate  of  soda  separates 
from  the  liquor  as  a  crystalline  powder,  consisting  of  1  equiv.  of 
real  carbonate  of  soda  united  with  1  equiv.  of  water ;  or,  if 
thought  desirable,  commercial  soda-ash  or  sal-soda  may  be  dis- 
solved in  water,  and  substituted  for  the  solution  spoken  of 
above.  The  powder  of  carbonate  of  soda,  above  mentioned,  is 
ladled  out  of  the  liquor,  drained,  and  allowed  to  cool.  This  is 
coarsely  powdered  and  spread  upon  frames,  which  are  piled  one 
upon  another  in  air-tight  chambers.  When  the  chambers  are 
full,  the  openings  are  closed,  except  a  vent  at  the  top  ;  and  car- 
bonic acid,  by  preference,  obtained  and  purified,  as  mentioned  in 
the  preparation  of  soda-ash,  is  forced  into  them  until  the  satura- 
tion is  complete ;  when  the  soda  will  be  found  to  have  absorbed 
