SYRUP  OF  PYROPHOSPHATE   OF  IRON. 
215 
The  pyrophosphate  of  iron,  corresponds  to  the  soda  salt,  and 
has  the  formula,  2Fe*  08+3POs.  It  is  obtained  by  double  de- 
composition between  ter-sulphate  of  iron  and  pyrophosphate  of 
soda.  It  is  insoluble  in  water,  but  is  soluble  in  a  solution  of 
pyrophosphate  of  soda. 
I  will  now  speak  of  the  syrup  of  pyrophosphate  of  iron. 
Take  of  Ter-sulphate  of  iron,  in  powder,      -     55  grains. 
Water,  1  fl.  oz. 
Dissolve  the  salt  in  the  water,  cold,  by  occasional  agitation  for 
several  days,  or  it  may  be  more  quickly  effected  by  digestion  at 
a  moderate  heat  in  a  flask  placed  in  a  water  bath. 
On  the  other  hand, 
Take  of  Pyrophosphate  of  soda,  crystallized,         462  grs. 
Pure  water,        -       -        -       -  7  s  fl.  oz. 
Distilled  mint  water,   -        -  31  fl.  oz. 
Dissolve  without  heat,  and  add  to  the  solution  the  solution  of 
sulphate  of  iron  previously  made  and  agitate.  The  precipitate 
which  first  forms  quickly,  redissolves  when  the  liquid  is  filtered 
and  poured  on  19  ounces  troy  of  white  sugar,  contained  in  a  bottle. 
Dissolve  without  heat.  It  is  necessary  to  make  the  solution 
without  heat,  or,  at  least,  below  the  temperature  of  120°  F., 
otherwise  the  syrup  will  assume  the  color  of  wine  dregs,  and  at 
160°  to  180°  F.  it  becomes  very  deep:  A  tablespoonful  of  this 
syrup  (about  five  drachms  troy,)  contains  2  centigrammes  (about 
J  of  a  grain)  of  iron  in  the  state  of  double  phosphate. 
If  the  ter-sulphate  of  iron  is  not  at  hand,  it  may  be  prepared 
for  the  occasion  quickly  as  follows.    For.  the  quantity  necessary 
for  the  preceding  formula. 
Take  Crystallized  proto-sulphate  of  iron,  77  J  grains 
Sulphuric  acid,       -  25  grains 
Nitric  acid,      -     -        •       -  -        Q.  S. 
Put  the  sulphate  in  a  capsule  with  a  little* water  and  the  sulphuric 
acid,  heat  and  add  nitric  acid  in  drops,  until  the  mixture  ceases 
to  disengage  nitrous  fumes  ;  then  evaporate  to  dryness  at  a 
moderate  heat.  The  product  is  the  ferric  salt  free  from  excess 
of  acid  Jour,  de  Pharm.  Jan.  1853. 
