BISMUTHI  ET  AMMONIA  CITRAS.  8 
Filter  the  liquid  through  paper,  returning  the  first  portions 
that  pass,  should  they  be  turbid. 
Spread  the  clear  solution  on  glass,  that  the  salt  may  dry  in 
scales. 
Liquor  Bismuihi  et  Ammonice  Citratis. 
Take  of 
Citrate  of  Bismuth  and  Ammonia  260  grains ; 
Alcohol  two  fluidounces ; 
Distilled  water  fourteen  fluidounces; 
Water  of  Ammonia,  a  sufficient  quantity. 
Dissolve  the  citrate  of  bismuth  and  ammonia  in  the  distilled 
water,  neutralize  the  liquid  with  water  of  ammonia,  and  mix  it 
with  the  alcohol. 
Or,  take  of 
Citrate  of  Bismuth,  recently  precipitated,  and  still  moist, 
a  convenient  quantity  ; 
Water  of  Ammonia, 
Alcohol, 
Distilled  water,  each,  a  sufficient  quantity. 
Add  gradually  to  the  citrate  of  bismuth  water  of  ammonia,  until 
the  precipitate  is  dissolved,  and  a  neutral  solution  is  obtained. 
Dilute  this  with  its  volume  of  distilled  water,  and  filter  through 
paper,  returning  the  first  portions  of  the  filtrate,  if  necessary, 
until  the  liquid  passes  clear. 
To  half  a  fluidounce  of  this  solution  add  hydrosulphate  of 
ammonia  in  slight  excess.  Pour  the  mixture  on  a  tared  paper  fil- 
ter, wash  the  precipitate  thoroughly  with  distilled  water,  and  dry 
it  at  a  temperature  of  212°.  Weigh  the  filter  and  its  contents, 
deducting  the  weight  of  the  former  to  obtain  that  of  the  tersul- 
phide  of  bismuth,  which,  in  grains,  is  to  form  the  third  term  in 
a  rule-of-three  proportion,  thus  : 
(Bi  S8)  (Bi  08) 
261  :  "  237  :  : 
the  weight  of  tersulphide  of  bismuth  to  that  of  teroxide  of  bismuth 
in  half  a  fluidounce  of  the  solution. 
Apply  the  same  ratio  to  the  remainder  of  the  liquid,  and 
dilute  it  to  such  an  extent  that  a  grain  of  teroxide  of  bismuth 
will  be  contained  in  each  fluidrachm  of  the  finished  solution ; 
