SOLUTION  OF  PYROPHOSPHATE  OF  SODA  AND  IRON.  391 
known,  except  in  acids.  It  seems  that  in  England  this  solution 
of  the  phosphate  in  citrate  of  ammonia  is,  or  rather  was  used 
under  the  name  of  pyrophosphate,*  with  which  it  closely  agrees 
in  color,  solubility,  stability  and  taste ;  and  it  is  remarkable, 
therefore,  that  our  pharmacopoeia  adopted  this  last  preparation, 
which  possesses  probably  no  advantage  except  that  of  a  higher 
price. 
Beydenreichf  examined  more  closely  the  behaviour  of  phos- 
phate of  iron  in  contact  with  its  various  solvents,  and  again  re- 
commended it  for  medicinal  use. 
•»  The  latest  investigation  is  by  J.  H.  Gladstone,!  who  confirms 
the  analysis  of  the  hydrated  pyrophosphate  of  iron  (2Fe203, 
3bP05,  9HO),  and  observed  the  existence  of  an  allotropic  ferric 
pyrophosphate,  which  is  insoluble  in  alkaline  pyrophosphates, 
and  which  is  obtained  by  heating  a  solution  of  the  pyrophosphate 
with  a  large  excess  of  sulphuric  acid. 
Before  I  had  seen  Dr.  Gladstone's  paper,  and  while  experi- 
menting with  the  view  of  obtaining  a  permanent  solution  of 
pyrophosphate  of  iron  and  soda  ("  Subscriber's  "  note  was  re- 
ceived in  the  beginning  of  June),  I  had  noticed  that  the  precipi- 
tate from  a  mildly  acid  solution  of  the  double  pyrophosphate, 
which  had  formed  in  the  course  of  a  few  weeks,  was  so  different 
in  its  behaviour  to  the  usual  solvents  of  ferric  pyrophosphate, 
that  I  inferred  a  change  to  ferric  phosphate  had  taken  place 
under  the  influence  of  the  acid.  Since  meeting  with  the  above 
paper,  however,  I  have  convinced  myself  that  it  consists  still  of 
pyrophosphate,  though  Stromeyer  may  be  correct  in  regard  to 
the  conversion  of  pyrophosphates  into  phosphates  by  continued 
boiling  with  acids. 
I  have  endeavored  to  prevent  this  change,  and  from  a  large 
number  of  experiments  which  have  been  made  I  select  the  follow- 
ing, as  capable  of  throwing  some  light  on  the  subject.  To  avoid 
frequent  oxidation  of  the  protosulphate  of  iron,  I  made  use  of 
the  carefully  prepared  officinal  solutions  of  persulphate  of  iron, 
— namely,  of  the  liquor  ferri  subsulphatis  and  liquor  ferri  ter- 
*  Araer.  Jour.  Pharm.  Sept.  1859,  412. 
f  Chem.  News,  iv.  158. 
%  Chem.  News,  xv.  327. 
