FEKRI  PYROPHOSPHAS. 
37 
Ferri  Pyrophosphas. 
Take  of  Pyrophosphate  of  Soda,  four  parts. 
Solution  of  Tersulphate  of  Iron,  eight  parts. 
Citric  Acid,  two  and  three-fourth  parts. 
Solution  of  Ammonia,  six  and  three-fourth  parts. 
Water,  a  sufficient  quantity. 
Dissolve  the  Pyrophosphate  of  Soda  in  sixty  parts  of  water 
by  means  of  heat,  cool  the  solution  to  50°,  and  filter  it  into  a 
bottle  of  the  capacity  of  two  hundred  and  fifty  parts.  Then 
add  the  solution  of  Tersulphate  of  Iron,  shake  the  mixture  well, 
fill  the  bottle  up  with  water,  again  agitate  it,  and  set  it  aside  for 
twenty-four  hours  to  settle.  Decant  the  clear  liquid  from  the 
precipitate  by  means  of  a  syphon,  and  repeat  the  washing  and 
decantation  twice.  Then  pour  the  precipitate  upon  a  strainer, 
drain  it  for  twenty-four  hours,  and  transfer  the  magma  to  a 
tared  porcelain  basin.  Upon  the  Citric  Acid,  contained  in  a 
suitable  vessel,  pour  the  solution  of  Ammonia,  a  little  at  a  time, 
with  constant  stirring  till  the  crystals  are  dissolved,  and  the 
acid  accurately  saturated.  Then  add  this  solution  to  the  magma 
in  the  basin,  and  apply  heat.  Stir  the  mixture  constantly  till 
the  magma  is  perfectly  dissolved,  and  evaporate  the  solution  to 
twenty-four  parts  and  filter  it  through  paper.  Finally  pour  the 
solution  upon  plates,  dry  the  salt  by  a  moderate  heat,  and  keep 
it  in  well  closed  bottles.  The  vield  is  a  little  more  than  seven 
and  a  half  parts. 
The  anhydrous  pyrophosphate  of  soda  is  so  difficult  of  solution 
that  even  though  in  powder  it  saves  time  to  apply  heat  for  dis- 
solving it.  When  dissolved  in  boiling  water  it  readily  crystal- 
lizes with  ten  equivalents  of  water  of  crystallization,  and  there- 
fore if  the  crystallized  salt  be  used  in  this  formula  six  and 
three.fourth  parts  is  required,  because  the  crystals  contain  40-21 
per  cent,  of  water.  The  solution  of  the  anhydrous  salt  is  always 
opaque  in  consequence  of  phosphates  and  impurities  that  are 
rendered  insoluble  by  the  heating,  and  it  therefore  requires  fil- 
tering before  precipitation.  The  proportion  of  the  iron  solution 
is  accurately  adjusted  by  calculation  and  assay,  and  in  practice 
yields  accurate  results,  without  the  trouble  of  filtering  and  test- 
ing to  get  the  point  of  saturation.  If  it  be  deficient  in  quan- 
tity or  strength,  however,  there  will  be  a  corresponding  loss. 
