328 
ON  PYROPHOSPHATE  OF  IRON. 
however,  is  now  nearly  insoluble  in  water,  evidently  from  some 
change  that  has  taken  place  during  desiccation. 
Citrates  of  soda,  potash,  and  ammonia  dissolve  freely  pyro- 
phosphate of  iron,  yielding  salts  readily  dissolved  by  water  ; 
but  the  soda  citrate  I  find  to  give  the  most  satisfactory  result. 
With  it  an  elegant  preparation  may  be  made,  easily  scaled, 
readily  dissolved  by  water,  and  which,  when  exposed  to  the  air, 
retains  its  brilliancy  for  a  much  longer  time  than  when  pre- 
pared with  citrate  of  potash  or  ammonia. 
To  prepare  the  citro-pyrophosphate  of  iron  (perhaps  the  best 
name  we  can  give  it),  take  citrate  of  soda  in  solution,  or  dissolve 
citric  acid  and  neutralize  it  with  carbonate  of  soda,  and,  with 
the  assistance  of  heat,  dissolve  in  it  as  much  recently  precipi- 
tated pyrophosphate  of  iron  as  it  will  take  up.  Filter  and 
evaporate  to  the  consistence  of  a  syrup.  Lastly,  spread  on 
glass  plates  to  dry,  when  beautiful  scales  of  a  greenish-yellow 
color  will  be  obtained. 
One  part  of  dry  citrate  of  soda  is  required  to  dissolve  the 
pyrophosphate  precipitated  from  one  part  of  pyrophosphate  of 
soda,  free  from  water  of  crystallization. 
As  it  may  be  considered  desirable  to  introduce  as  much 
bibasic  phosphoric  acid  into  this  preparation  as  possible,  the 
following  formula  may  be  preferred : — 
Take  of  Pyrophosphate  of  soda  1  part 
Syrupy  citrate  of  ammonia  1  part 
Citrate  of  soda  2  parts. 
Dissolve  in  it  as  much  recently  precipitated  pyrophosphate  of 
iron  as  possible,  and  proceed  as  before. 
The  salt  formed  by  this  process  is  also  a  very  elegant  one, 
having  a  greenish  hue,  and  is  perfectly  soluble.  If  a  reddish 
tint  be  desired,  that  can  be  easily  attained  by  the  smallest 
addition  of  ammonio-citrate  of  iron,  after  being  reduced  to  a 
syrupy  consistence. 
One  of  the  chief  points  of  success  in  scaling  the  above  prepara- 
tions is  to  take  care  that  the  glass  plates  be  not  subjected  to  a 
heat  much  above  summer  temperature. — London  Pharm.  Journ. 
April,  1860. 
