^^Aprrissr""' }  Feri'iG  Citro-Phosphate  and  Citro-Pyrophosphate.  169 
When  272  grains  of  ferric  citrate  is  combined  with  358  grains  of 
disodic  phosphate  the  resulting  product  weighs  405  grains.  The  for- 
mula of  this  salt  is  therefore, 
Fe  =  PO4 
I  .  Aq. 
Ci  =  Na^H 
and  molecular  weight  405. 
A  mixture  of  272  grains  of  ferric  citrate,  358  grains  of  disodic 
phosphate,  and  84  grains  of  hydrosodic  carbonate,  yields  a  product 
weighing  445  grains.    The  formula  of  this  salt  is  therefore 
Fe  =  PO, 
I         I     .  2Aq. 
Ci  =  Nag 
and  the  molecular  weight%45.    It  has  an  alkaline,  unpleasant  taste. 
When  272  grains  of  ferric  citrate,  179  grains  of  disodic  phosphate, 
and  42  grains  of  hydrosodic  carbonate  are  united,  the  result  weighs 
354  grains.    The  formula  of  the  salt  is  consequently 
Fe  =  PO, 
i  I 
Ci  —  Nag.    3  Aq. 
Fe  =  Ci 
and  its  molecular  weight  708.  This  is  an  exceedingly  elegant  yellow- 
ish-green salt,  having  a  sweetish,  agreeable  taste.  It  may  be  looked 
upon  as  a  derivative  of  the  salt  formed  by  dissolving  two  ms.  of  ferric 
phosphate  in  one  m.  of  trisodic  citrate,  whose  formula  is 
Fe  =  PO, 
Ci  —  Nag. 
Fe  =-  PO4 
In  that  case  one  phosphoric  radicle  is  replaced  by  one  citric  radicle. 
It  may  also  be  viewed  as  derived  from  one  m.  of  ferric  citro-phosphate 
("American  Journal  of  Pharmacy,'^  April,  1876), 
Fe  =  PO, 
I  I 
Ci  =  Fe 
by  coalescence  with  one  m.  of  trisodic  citrate. 
The  formulas  of  these  citro-phosphates,  like  those  of  the  citro-pyro- 
phosphates,  are  capable  of  taking  a  variety  of  different  forms,  indicat- 
ing that  the  respective  salts,  under  the  proper  conditions,  may  assume 
changed  molecular  characters.  For  instance,  the  ferric  citro-phosphate 
above  noted  is  largely  decomposed  into  th6  two  primary  salts  when 
dissolving  the  dried  scales  in  water.  The  old  official  pyrophosphate 
is  prone  to  a  similar  decomposition  at  the  outset  of  dissolving  it.  All 
