152 
LIQUOR  BISMUTHI. 
freely  soluble  in  potassa,  and  thus  involves  a  loss  of  bismuth  if 
any  excess  happens  to  be  used ;  caustic  potassa  is  a  very 
troublesome  chemical  to  keep  in  good  condition,  being  very 
prone  to  attract  both  moisture  and  carbonic  acid  from  the  atmos- 
phere, by  which  means  it  becomes  in  a  great  degree  unfitted  for 
use.  It  is  a  difficult  matter  to  get  caustic  potassa  free  from  car- 
bonate, and  still  more  difficult  to  keep  it  so,  even  if  free  from  this 
impurity  when  the  bottle  is  first  opened.  Another  objection  is 
that  caustic  potassa  is  expensive. 
The  following  modified  process  ofi'ers  a  substitute  for  the 
caustic  potassa  that  gives  excellent  results.  This  substitute 
is  well  crystallized  carbonate  of  soda,  a  salt  that  can  at  all  times 
be  obtained  of  good  quality  at  a  very  low  price.  Citrate  of 
bismuth  is  less  soluble  in  carbonate  of  soda  than  in  caustic 
potassa,  hence  a  gain  is  made  by  using  the  former. 
The  process  is  the  following  : 
Take  of  subcarbonate  of  bismuth,  one  troyounce. 
Citric  acid  (in  powder),  420  grains. 
Nitric  acid  (sp.  gr.  1-42),  one  and  a  half  troyounces. 
Crystallized  carbonate  of  soda,  1150  grs. 
Distilled  water. 
Alcohol,  each  a  sufficient  quantity. 
Dissolve  by  gradual  addition  the  subcarbonate  of  bismuth  in 
the  nitric  acid,  and  when  the  solution  is  completed  dilute  it  with 
a  fluidounce  of  distilled  water,  add  the  citric  acid,  stir  until  it 
is  dissolved.  Dissolve  the  carbonate  of  soda  in  ten  fluidounces 
of  distilled  water  and  gradually  add  the  soda  solution  to  the 
bismuth  solution,  constantly  stirring  the  mixture.  After  stand- 
ing for  six  or  eight  hours,  transfer  the  mixture  to  a  moistened 
paper  filter,  and  wash  to  remove  nitrate  of  soda.  Transfer  the 
magma  to  a  mortar  or  evaporating  dish  and  carefully  add  water 
of  ammonia  until  the  citrate  of  bismuth  is  dissolved.  Dilute 
the  solution  with  an  equal  volume  of  distilled  water  and  treat 
half  a  fluidounce  (14*7  cubic  centimetres)  with  an  excess  of 
sulphide  of  ammonium,  or,  better  still,  "  sulphide  of  sodium,''  (as 
suggested  by  the  writer  in  a  paper  presented  to  this  Associa- 
tion, and  publisked  in  the  Proceedings  for  1866,  252) ;  collect 
and  wash  the  sulphide  of  bismuth  on  a  tared  filter,  (which  has 
