ADe'ceZerPi9aor8m" }    Preparing  Pharmaceutic  Chemicals.  585 
be  prepared  through  the  hydrolytic  dissociation  of  the  neutral  salt 
just  as  the  subnitrate  precipitates  out,  by  diluting  a  solution  of 
bismuth-trinitrate. 
The  hydrolysis  takes  place  according  to  the  equation : 
[C6H4(OH)COO]3Bi  +  H20  =  C6H,OH  COO  BiO 
+  2C6H4OH  COOH 
The  actual  course  for  preparing  bismuth  trisalicylate  and  effecting 
its  subsequent  hydrolysis  is  briefly  as  follows : 
Metallic  bismuth,  or  the  subnitrate,  is  dissolved  in  nitric  acid,  care 
being  taken  to  obtain  a  concentrated  solution  with  a  minimum 
amount  of  free  acid.  Into  this  an  ammonium  salicylate  solution 
containing  somewhat  more  than  3  molecules  of  salicylic  acid  to  1 
atom  of  bismuth,  is  slowly  poured,  under  constant  stirring  (both 
solutions  have  to  be  cold  in  order  to  avoid  a  pink  coloration  due  to 
the  oxidation  of  salicylic  acid  through  the  ammonium  nitrate 
formed).  At  first  salicylic  acid  precipitates  out  in  quantity  equiva- 
lent to  the  free  nitric  acid  in  the  bismuth  solution.  After  that  the 
salicylic  acid  loosely  combines  with  the  bismuth,  forming  the  un- 
stable trisalicylate.  Ammonium  salicylate  is  added  until  no  further 
precipitate  is  produced  in  the  filtered  solution. 
In  order  to  remove  the  bulk  of  the  ammonium  nitrate,  the  precipi- 
tate is  poured  upon  a  strainer  and  washed  twice  or  thrice  with  cold 
water,  after  which  it  is  transferred  to  a  kettle,  boiled  with  water, 
again  strained  and  the  operation  repeated  until  the  filtrate  does  not 
redden  blue  litmus  paper. 
The  salt  when  dried  at  a  low  temperature  is  perfectly  white,  bulky, 
and  conforms  to  all  requirements  of  the  U.  S.  Pharmacopoeia.  The 
salicylic  acid  is  recovered  from  the  wash  water  by  concentration. 
As  the  alkali  salts  of  salicylic  acid  readily  dissolve  in  water,  it 
seems  as  if  advantage  could  be  taken  of  that  property  by  using  an 
alkaline  solution  for  washing  out  the  loosely  combined  salicylic  aci  1 
This  is,  however,  not  advisable  as  even  a  very  diluted  alkali-solution 
readily  decomposes  the  subsalicylate,  while  pure  boiling  water  has 
no  effect  upon  the  same.  By  using  for  the  first  washing  a  sodium 
carbonate  solution,  in  a  quantity  not  sufficient  to  combine  with 
all  the  salicylic  acid  present  in  excess  of  the  subsalicylate,  and  wash- 
ing until  neutral  with  hot  water,  the  product  left  by  ignition  67.6% 
Bi203  showing  that  the  carbonate  already  had  acted  upon  some  sub- 
salicylate with  formation  of  the  hydroxide. 
