242 
PKEPARATION  OF  LIQUOR  POTASS^. 
for  the  production  of  the  compound  of  carbonate  and  hydrate 
of  lime  already  alluded  to,  after  allowing  for  some  impurity 
"which  will  be  retained  even  in  the  hydrate  of  lime,  and  also  for 
uncombined  water  which  may  be  present.  Lastly,  by  reducing 
the  total  quantity  ordered  in  the  formula,  such  a  quantity  is  in- 
dicated for  an  operation  as  can  be  easily  subjected  to  the  active 
and  continued  agitation  required  to  effect  the  complete  decom- 
position of  the  carbonate  of  potash  within  a  moderately  short 
time.  When  good  hydrate  of  lime  is  used,  the  decomposition 
may  be  effected  in  about  half  an  hour  by  continued  and  very 
active  agitation. 
The  ingredients  being  confined  in  a  stoppered  bottle,  which 
is  itself  a  measure  of  the  quantity,  there  are  but  few  probable 
sources  of  error  in  the  process  or  of  defect  in  the  product,  pro- 
vided the  solid  ingredients  be  in  a  sufficient  state  of  purity  and 
accurately  weighed.  If  from  any  cause  the  process  when  com- 
menced cannot  receive  continued  attention  up  to  its  completion, 
no  evil  will  arise  from  the  ingredients  being  left  at  rest  until 
another  opportunity  for  shaking  the  bottle  presents  itself.  It 
must  not  be  supposed,  however,  that  such  periods  of  rest  con- 
tribute much,  if  anything,  to  the  decomposition  of  the  carbonate 
of  potash  by  the  lime,  as  the  latter  quickly  subsides  to  the  bot- 
tom of  the  vessel,  and  then,  of  course,  ceases  to  produce  any 
effect  upon  the  carbonate  of  potash  contained  in  the  solution 
above  it.  I  have  found  the  agitation  of  the  mixture  to  be  most 
easily  effected  by  placing  the  bottle  on  its  side,  with  a  folded 
cloth  under  it,  on  a  table,  and  rolling  it  to  and  fro  with  a  short 
quick  motion,  one  hand  of  the  operator  being  placed  over  the 
stopper  of  the  bottle.  In  operating  thus  without  heat  there  is 
not  much  probability  of  the  stopper  becoming  fixed  in  the  mouth 
of  the  bottle,  unless  the  process  be  protracted ;  if,  however,  the 
solution  has  to  be  kept  for  any  length  of  time  in  a  well-stoppered 
bottle,  it  will  be  found  advantageous  to  put  a  piece  of  thin  gutta 
percha  tissue  between  the  stopper  and  the  mouth  of  the  bottle, 
which  will  effectually  prevent  the  adhesion  of  the  stopper,  which 
otherwise  often  occurs.  A  small  quantity  of  the  solution  must 
be  filtered  from  time  to  time  to  test  it  for  carbonic  acid,  and 
when  it  has  become  nearly  caustic  the  filtration  of  even  a  drachm 
or  two  cannot  be  well  effected  through  paper  without  causing  the 
