394     SOLUTION  OP  PYROPHOSPHATE  OF  SODA  AND  IRON. 
23.  No.  19  yielded  a  clear  brown  solution,  with  an  excess  of 
ammonia ;  nearly  the  whole  of  the  iron  was  deposited  in  the 
course  of  a  few  weeks  as  brown  floccules. 
24.  Pure  pyrophosphate  of  iron,  apparently  dissolves  in  am- 
monia to  a  transparent  brown  liquid,  which  separates  gradually 
the  iron  in  the  form  of  bulky  brown  flocks,  readily  suspended, 
by  agitation  with  syrup,  to  a  nearly  transparent  liquid. 
25.  Tartaric  or  citric  acid  added  to'  No.  24  yields  a  perma- 
nent solution. 
26.  Acetate  of  ammonia  added  to  No.  24  does  not  prevent 
the  separation  of  the  ferric  oxide. 
27.  1  part  officinal  pyroposphate  of  iron  with  5  pyrophosphate 
of  soda,  dissolved  in  120  parts  distilled  water,  yielded  a  faint 
green  yellowish  solution,  in  which,  on  standing,  a  slight  precipi- 
tate occurred. 
28.  Little  alcohol  added  to  No.  27  favors  the  separation  of 
the  deposit  and  increases  it. 
29.  Citric  acid  added  to  No.  27  appears  to  merely  increase  its 
tendency  to  mould. 
30.  Phosphoric  acid  has  little  action  on  No.  27  in  the  cold, 
but  when  heated  will  render  it  turbid. 
31.  An  excess  of  ammonia  added  to  No.  27  yields  a  clear 
liquid  which  slowly  deposits  the  iron,  and  this  may  be  readily 
suspended  again  to  an  almost  transparent  brown  liquid  by 
agitation. 
Summing  up  the  results  of  the  foregoing  experiments  we  find  : 
I.  Pure  pyrophosphate  of  iron,  dissolved  in  pyrophosphate  of 
soda,  will  be  retained  in  permanent  solution  only  in  case  the 
liquid  is  kept  slightly  alkaline  or  strictly  neutral. 
II.  This  solution  will  be  disposed  to  precipitate  gradually  the 
iron  salt  if  alcohol  is  present  or  the  liquid  becomes  acid  from 
j  any  cause  whatever. 
III.  A  boiling  temperature  promotes  the  change  of  the  iron 
salt,  either  to  the  insoluble  modification  of  pyrophosphate  or 
to  the  ordinary  phosphate ;  the  presence  of  acids  and  certain 
salts  hasten  this  change.  j  (jj  Q 
The  difficulty  of  obtaining  a  permanent  liquid  pharmaceutical 
V 
