^""'Srim^'^'"*}         Precipitated  Ferrous  Sulphate.  485 
COMPOSITION   OF   PEECIPITATED    FERROUS  SUL- 
PHATE.i 
By  Henry  Trimble. 
Query  No.  7. — Is  the  precipitated  sulphate  of  iron  of  constant  composi- 
tion? Does  it  contain  the  same  proportion  of  water  of  crystallization  as 
the  large  crystals  ? 
As  inquiry  at  several  stores  in  Philadelphia  revealed  the  fact  that 
this  officinal  preparation  is  not  usually  kept  in  stock,  I  made  the  ex- 
periments on  four  samples  prepared  by  myself.  No.  1  was  made 
according  to  the  U.  S.  P.  No.  2  according  to  the  Br.  P.,  with  the 
quantity  of  water  reduced  to  twenty  per  cent.,  and  without  boiling 
the  solution.  No.  3  according  to  the  proportions  of  the  Br.  P., 
omitting  the  boiling ;  as  this  solution  was  quite  dilute,  the  yield  was 
small.  No.  4  was  made  exactly  according  to  the  directions  of  the 
Br.  P.  This  authority  directs  that  the  solution  be  boiled  for  ten 
minutes  in  an  open  dish,  but  leaves  one  in  doubt  whether  to  take  into 
account  the  loss  by  evaporation  or  not ;  therefore  if  the  strength  of  the 
solution  and  consequently  the  proportion  of  alcohol  affect  the  compo- 
sition, it  will  be  shown  by  samples  3  and  4.  The  directions  for  get- 
ting rid  of  adhering  moisture  and  acid  are  not  so  exact  as  our  own, 
consequently  a  slight  excess  of  acid  will  be  found  in  the  Br.  P.  sam- 
ples. In  the  following  results,  the  amount  of  iron  was  determined 
by  both  gravimetric  and  volumetric  methods,  the  latter  being  by  titra- 
tion with  potassium  permanganate.  The  results  by  the  two  methods 
were  not  materially  different.  The  sulphuric  acid  was  determined  by 
barium  chloride. 
No.  1. 
u.  s.  p. 
No.  2. 
Br.  P.  less  20  p.  c 
Water,  not  boiled. 
No.  3. 
Br.  P. 
Not  boiled. 
No.  4. 
Br.  P. 
No.  5. 
Larger 
Crystals. 
Theoreti- 
cal. 
re ,  ,  ,, 
20-48  p.  c. 
35-40  " 
44-12  " 
20-86  per  cent. 
35-84 
43-30 
20-35  p.c, 
35-40  " 
44-25  " 
20-37  p.c. 
35-44  " 
44-19  " 
20-53  p.c. 
36-40  " 
43  07  " 
20-12  p.  c. 
34  54  " 
45-34  " 
S04.. 
H20  
Total  
100-00 
100-00 
100-00 
100-00 
100-00 
100-00 
^  Eead  at  the  Detroit  meeting  of  the  American  Pharmaceutical  Associa- 
tion ;  communicated  by  the  author. 
