FERRI  PYROPHOSPHAS. 
39 
perature,  the  precipitate  is  far  less  soluble,  and  when  from  warm 
solutions  scarcely  at  all  soluble,  in  the  given  proportion  of 
citrate.  When  the  solutions  are  at  50°,  the  writer  has  never  had 
the  slightest  trouble,  even  with  a  somewhat  smaller  proportion 
of  citrate. 
The  clear  solution  should  be  evaporated  or  boiled  down, — for 
boiling  does  not  injure  it  at  all,  until  reduced  to  twenty-four 
parts,  and  then  filtered  through  paper.  This  filtration  is  brisk 
enough  at  first,  but  the  last  portions  pass  very  slowly,  and  it  is 
best  to  take  a  new  filter  for  the  last  two  or  three  parts  of  solu- 
tion. It  should  be  poured  out  in  thin  layers  upon  the  plates, 
and  if  ounces  be  taken  for  the  parts  of  the  formula,  eight  large 
dinner  plates  will  be  required  for  the  drying.  The  dry  salt  is 
slightly  deliquescent,  and  hence  the  direction  to  keep  it  in  well 
closed  bottles.  The  formula  yields,  by  calculation,  verified  by 
assay,  three  and  sixty-eight  hundredth  parts  of  anhydrous 
pyrophosphate,  or  if  avoirdupois  ounces  be  taken  for  the  parts, 
the  yield  of  the  iron  salt  is  1610  grains. 
The  compound  salt  amounting  to  a  little  more  than  seven  and 
a  half  parts,  is  in  the  form  of  beautiful  yellowish  green,  or  apple 
green  granular  fragments  or  scales  looking  like  crystals.  These 
are  a  little  tough  in  consistence,  but  still  break  between  the 
teeth.  It  is  odorless,  but  has  a  pleasant  acidulous,  slightly 
saline  taste, — almost  tasteless.  It  is  thoroughly  andreadiy  solu- 
ble in  water  in  all  proportions,  reproducing  the  bright  yellowish 
green  solution,  in  which  solution  ferrocyanide  of  potassium  pro- 
duces only  a  sky  blue  coloration,  without  precipitate. 
In  composition  it  is  very  nearly  as  follows  : — 
2Fe203  =    80  X 2      =160   =20-86  p.  c.  )  _48-8  per  cent. 
3bP05  =71-4X3      =214-2=27-94    "    /  ~2Fe203,3bP05 
2NHiO  =   26X2       =  52  =  7*97    "    {  _34-66  per  cent. 
Gi2HtOi2  =  174  =26-69    "  j"-2NHiO,Ci 
13-22  HO,  =      9x13  22=119   =16.54    "      =16-54  per  cent.  Water. 
2Fe203, 3bP05 +2NHiO,  Ci+ HO= 719  -2=  100  100 
Or,  expressed  approximatively  and  near  enough  for  memory, 
the  salt  consists  of  one-half  pyrophosphate  of  iron,  and  one-third 
citrate  of  ammonia,  thus  making  the  mean  dose  two  or  three 
grains. 
Hitherto  the  syrup  of  this  salt  has  been  almost  exclusively 
used.    This  is  a  very  elegant,  convenient,  and,  as  far  as  obser- 
