^ecembeV^S)™'  \    Preparing  Pharmaceutic  Chemicals.  583 
small  quantity  of  hypophosphorous  acid  (the  solution  should  contain 
about  0.5  per  cent,  of  the  absolute  acid).  In  this  condition  it  will 
keep  unchanged  for  more  than  a  year. 
The  yield  is  quantitative  provided  that  the  precipitates  are  washed 
completely. 
ACIDUM  HYPOPHOSPHOROSUM. 
The  U.  S.  Pharmacopoeia  does  not  give  any  process  for  preparing 
this  acid.  An  imperfect  preparation  may  be  made  by  using  potassium 
hypophosphite  and  tartaric  acid  in  the  same  manner  as  the  potassium 
iodide  was  used  in  the  manufacture  of  hydriodic  acid.  The 
National  Dispensatory  also  suggests  to  make  the  acid  from  calcium 
hypophosphite  by  exact  precipitation  with  oxalic  acid.  The  result- 
ing calcium  oxalate,  although  insoluble  in  water,  is,  however,  to  a 
considerable  extent,  soluble  in  hypophosphorous  acid.  The  acid 
prepared  that  way  will  consequently  not  stand  the  U.  S.  P.  require- 
ment of  giving  a  clear  solution  after  neutralizing  with  ammonia. 
Calcium  oxalate  as  an  impurity  is  really  very  objectionable,  owing 
to  its  marked  poisonous  character. 
It  is  evident  that  the  best  way  to  prepare  hypophosphorous  acid 
would  be  to  decompose  barium  hypophosphite  with  the  exact  quan- 
tity of  sulphuric  acid.  This  salt  is,  however,  about  six  times  as 
expensive  as  the  official  potassium  and  calcium  salts,  and  therefore 
the  buying  of  the  same  for  making  hypophosphorous  acid  would 
not  be  economical. 
The  author  uses  the  following  method  for  preparing  a  solution 
of  pure  barium  hypophosphite : 
Calcium  hypophosphite  in  solution  is  precipitated  with  somewhat 
more  than  the  equivalent  quantity  of  ammonium  oxalate  (prepared 
by  neutralizing  a  solution  of  oxalic  acid  with  ammonia  water). 
The  reaction  is  thus : 
Ca(H2P02)2  +  (NHJ2C204  =  2NH4H2P02  +  CaC204 
The  calcium  is  completely  precipitated,  the  oxalate  being  perfectly 
insoluble  in  the  neutral  solution  of  ammonium  hypophosphite  (with 
the  small  excess  of  ammonium  oxalate).  The  solution  is  filtered 
and  the  nitrate  boiled  with  barium  carbonate  in  excess,  preferably 
under  a  hod,  until  the  odor  of  ammonia  has  disappeared.  The 
reaction  is  thus: 
2NH4H2P02  +  BaCOs  =  Ba(H2P02)2  +  2NH3  +  C02  +  H20 
