^'"jin"^883^'^°''}         Ferrous  Citrate  and  Double  Salts.  43 
iron,  is  a  dingy  white  and  sparingly  soluble  salt.  Prepared,  however, 
by  acting  on  ferrous  hydrate  or  carbonate  with  citric  acid  it  dissolves 
rapidly  in  the  generated  ferric  citrate  formed  by  atmospheric  oxidation 
and  produces  one  of  the  numerous  ferroic  citrates.  Owing  to  this 
peculiarity  ferrous  citrate  was  credited  with  such  solubility  as  to  be 
even  deliquescent. 
One  equivalent  of  ferrous  citrate  treated  with  one  equivalent  of 
hydrosodic  carbonate  yields  a  very  soluble  apple-green  amorphous 
double  salt,  the  sodio-ferrous  citrate  FeNaCi,  which  is  readily  obtained 
in  elegant  scales.  But  when  one  equivalent  of  ferrons  citrate  is  acted 
on  by  two  equivalents  of  the  carbonate  a  very  soluble  grass-green 
amorphous  secondary  double  salt  is  formed,  the  sodio-ferrous  hydro- 
citrate. 
Fe— (OH) 
FeNa2Ci(OH)  or 
Ferrous  citrate  heated  with  even  four  equivalents  of  sodic  phosphate 
is  not  entirely  dissolved,  but  the  solution  is  deeply  green,  and  on  cool- 
ing yields  a  large  crop  of  spiny  crystals  of  sodic  phosphate.  Addi- 
tion of  citric  acid  to  the  heated  mixture  immediately  separates  a  copi- 
ous transparent  green  gelatinous  precipitate,  which  requires  a  very 
large  proportion  of  sodium  citrate  for  solution.  It  is  therefore  evident 
that  ferrous  citrate  cannot  be  successfully  treated  with  sodic  phosphate 
alone. 
If  two  equivalents  of  sodio-ferrous  hydrocitrate  are  mixed  with  two 
equivalents  of  sodic  phosphate  an  abundant  precipitate  of  ferrous 
phosphate,  together  with  a  deep  green  solution,  results.  An  equiva- 
lent of  citric  acid  now-  added  dissolves  the  precipitate  completely,  or, 
if  incorporated  previous  to  the  sodic  phosphate,  prevents  the  precipi- 
tation. 
The  admixture  of  one  equivalent  of  sodic  phosphate  to  two  equiva- 
lents of  sodio-ferrous  citrate  also  occasions  a  precipitate  of  ferrous 
phosphate,  redissolved  by  an  equivalent  of  citric  acid,  or  prevented 
when  this  is  previously  added. 
Both  of  the  above  cases,  therefore,  show  that  half  as  much  more 
citric  acid  as  these  double  salts  already  contain  counteracts  the  forma- 
tion of  precipitates  insoluble  in  the  presence  of  sodic  phosphate.  The 
resulting  splendidly  emerald-green  solution  contains  two  very  remark- 
