584  Preparing  Pharmaceutic  Chemicals.  {ADeCembeVPi908m' 
The  surplus  of  ammonium  oxalate  is  also  eliminated  by  the  pro- 
cess, the  reaction  products  being  ammonia,  carbonic  acid  and  in- 
soluble barium  oxalate.  To  accelerate  the  reaction  it  is  advisable  to 
keep  the  mixture  very  concentrated,  avoiding,  however,  an  evapora- 
tion to  dryness,  which  would  cause  a  decomposition  of  the  barium 
hypophosphite  with  evolution  of  the  exceedingly  poisonous  phosphine- 
gas.  When  the  reaction  is  complete  the  product  is  treated  for  a 
considerable  time  with  a  large  amount  of  water,  and  filtered  away 
from  the  surplus  of  insoluble  barium  carbonate  and  the  small  amount 
of  barium  oxalate.  The  strength  of  the  barium  hypophosphite  solu- 
tion is,  after  concentration,  exactly  determined  and  the  decomposi- 
tion with  the  calculated  quantity  of  dilute  sulphuric  acid  is 
conducted,  preferably  in  boiling  hot  solution.  The  filtrate  should  be 
absolutely  free  from  barium  and  give  only  a  slight  test  for  sulphuric 
acid. 
BISMUTH  SUBSALICYLATE. 
As  other  metals  with  a  weak  positive  nature,  bismuth  is  char- 
acterized by  the  easy  hydrolysis  of  its  neutral  salts,  with  forma- 
tion of  insoluble  basic  salts.  Theoretically  the  bismuth  hydroxide 
Bi(OH),  gives  with  the  monobasic  salicylic  acid  C6H4OH  COOH 
the  following  salts: 
Neutral  bismuth  trisalicylate  (C6H4OH  COO)3Bi  with  an  igni- 
tion residue  of  37.9%Bi203. 
Monobasic  bismuth  salicylate  (C6H4OH  COO)4Bi20  with  an 
ignition  residue  of  47.8%Bi203. 
Dibasic — or  bismuth  subsalicylate  C6H4OH  COO  BiO  with  an 
ignition  residue  of  64.5%Bi203. 
The  National  Dispensatory  states  that  bismuth  subsalicylate  can 
be  prepared  by  Duyk's  process  by  shaking  freshly  precipitated 
bismuth  hydroxide  with  salicylic  acid  in  the  presence  of  water. 
The  author  has  tried  the  process,  but  even  by  using  a  large  excess 
of  salicylic  acid,  in  order  to  get  the  benefit  of  the  mass  action,  and 
shaking  continuously  for  several  days,  the  product  when  washed 
with  hot  water  until  free  from  salicylic  acid,  consisted  mainly  of 
the  hydroxide  with  only  a  small  amount  of  subsalicylate,  showing 
that  the  action  of  the  weak  salicylic  acid  upon  the  insoluble  bismuth 
hydroxide  is  very  slight  indeed.    The  dibasic  salt  must  consequently 
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