126  Soluble  Ferric  Pyrophosphate.  {AmMirch,?9oo.rm' 
orthophosphate  in  pyrophosphate,  using  limited  quantities  of  mag- 
nesium sulphate  and  ammonium  chloride. 
With  the  above  data  before  me,  I  collected  a  number  of  samples 
of  iron  pyrophosphate,  soluble,  taking  only  those  for  examination 
which  could  be  secured  in  the  original  package.  Seven  samples 
were  thus  obtained  and  tested  for  orthophosphate  according  to  the 
method  of  the  U.S.P.,  which  is  as  follows: 
If  I  gramme  of  the  salt  be  boiled  with  10  c.c.  of  potassium  or 
sodium  hydrate,  T.  S.,  a  reddish-brown  precipitate  will  be  produced, 
and  if  the  colorless  filtrate  from  this  precipitate  be  strongly  acidu- 
lated with  hydrochloric  acid,  then  magnesia  mixture  added,  and 
subsequently  a  slight  excess  of  ammonia  water,  no  precipitate  should 
be  produced  (distinction  from  and  absence  of  ferric  phosphate). 
According  to  the  above  test,  all  the  samples  gave  heavy  precipi- 
tates, indicating,  apparently,  the  presence  of  orthophosphate. 
I  here  wish  to  call  attention  to  a  result  of  the  examination, 
which  developed  while  making  the  above  tests.  Samples  Nos.  I,  4, 
5  and  7  evolved  a  very  strong  odor  of  ammonia  when  treated  with 
sodium  or  potassium  hydrate,  T.  S.,  which  indicates  that  the  manu- 
facturers from  whom  these  samples  were  obtained  are  not  making 
"Ferri  Pyrophosphas  Solubilis"  according  to  the  U.S.P.,  1890,  but 
for  some  reason  are  following  a  process  official  in  the  U.S. P.,  i860 
and  1870;  according  to  which  sodium  phosphate  was. converted  into 
the  pyrophosphate,  by  moderately  igniting  it.  This  was  then  dis- 
solved in  water  and  mixed  with  a  diluted  solution  of  tersulphate  of 
iron,  when  ferric  pyrophosphate  was  precipitated.  The  precipi- 
tate was  washed  with  cold  water  and  dissolved  in  a  solution  of 
citrate  of  ammonium. 
A  sample  of  iron  pyrophosphate  was  now  prepared  according  to 
the  directions  of  the  U.S. P.,  1890;  the  sodium  pyrophosphate,  pre- 
pared by  myself,  was  free  from  orthophosphate  by  the  ammonium 
molybdate  test,  as  was  also  the  finished  iron  salt.  However,  this 
product  would  not  stand  the  U.S.P.  test. 
Here,  apparently,  was  some  discrepancy,  and  an  effort  was  made 
to  overcome  the  difficulty.  The  U.S.P.  procedure  was  now  modi- 
fied by  using  varying  proportions  of  magnesia  mixture,  but  the 
results  were  unsatisfactory.  Even  sodium  pyrophosphate,  free  from 
orthophosphate,  by  the  ammonium  molybdate  test,  indicated  the 
presence  of  the  latter  by  the  magnesia  mixture.    This  test  was 
