486 
Precipitated  Ferrous  Sulphate. 
Am.  Jour.  Pharm. 
Oct.,  1888. 
No.  5  settled  out  from  the  filtrate  of  No.  3,  which  was  more  dilute 
than  the  others  and  therefore  contained  a  larger  quantity  of  the  salt. 
The  deposit  took  place  during  three  weeks,  in  granular  crystals  much 
larger  than  in  the  other  samples. 
None  of  the  specimens  when  first  made  gave  more  than  slight 
indications  of  ferric  iron  and  the  determinations  by  potassium  per- 
manganate failed  to  indicate  any  appreciable  quantity.  The  above 
results  are  sufficient  to  show  that  the  salt  precipitated  under  different 
conditions  is  of  constant  composition. 
This  is  contrary  to  the  results  gotten  by  Barkhausen  (Archiv  der 
Pharmacie,  Band  148,  1871),  who  found  it  to  contain  less  than  7H2O, 
and  to  lose  moisture  rapidly  on  exposure  to  air.  His  results  may  be 
attributed  to  the  method  used  in  analysis  (with  calcium  hypochlorite), 
or  to  over-drying  the  salt  in  its  preparation. 
L.  Caro  (Liebig's  Annalen,  165,  29)  contradicted  these  statements 
and  found  the  salt  to  contain  7H2O,  and  to  remain  of  the  same  com- 
position after  a  month's  exposure  to  the  atmosphere.  While  I  can 
agree  with  the  first  part  of  Caro's  statement,  which  has  also  been 
verified  by  Tilden  {Phar.  Jour,  and  Trans.,  3,  11,  p.  1026),  it  is 
difficult  to  believe  that  this  salt  will  remain  unchanged  for  a  month 
when  exposed  to  the  atmosphere. 
To  investigate  this,  portions  of  samples  1,  2,  3  and  4  were  placed 
on  filter  paper  loosely  covered  with  the  same,  and  exposed  to  the 
air  in  a  room  without  artificial  heat,  well  ventilated,  with  a  tem- 
perature varying  between  55°  and  90°  F.  (13°  and  32°  C.)  for  a 
month. 
As  the  change  appeared  to  be  on  the  surface  the  samples  were 
well  mixed  and  bottled.  The  ferrous  and  total  iron  were  estimated 
by  titration  with  potassium  permanganate,  with  the  following  re- 
sults : 
1. 
2^ 
3. 
4. 
20-92 
21-86 
21-74 
21-72 
Total  Fe  
21-12 
21-86 
21-74 
21-92 
By  calculation  we  get  the  following  percentages  of  water  :  No.  1, 
42-45  ;  N0.2,  40-67  ;  No.  3,  40-94 ;  No.  4,  40-28. 
It  will  be  seen  that  oxidation  took  place  in  two  of  the  samples  only, 
