406 
Solution  of  Potassium  Arsenite. 
f  Atn.  .Tou  r.  Pharm. 
I     August,  1895. 
of  the  filtrate  were  titrated  with  decinormal  rodine  volumetric  solu- 
tion in  the  presence  of  an  excess  of  sodium  bicarbonate.  This  vol- 
ume was  found  to  contain  .699  gramme  of  arsenous  acid.  In  the 
same  proportion  10  grammes  of  arsenous  acid  would  require  71  5 
c.c.  of  liquor  potassae.  The  difference  between  this  amount  and 
that  indicated  above  (100  c.c.)  would  amply  allow  for  any  defect  in 
the  strength  of  the  liquor  potassae,  and  would  insure  the  complete 
solution  of  the  arsenous  acid  under  all  circumstances. 
The  arsenous  acid  used  should,  of  course,  be  pure  and,  as  gen- 
erally recommended,  that  in  mass  should  be  obtained  and  powdered 
as  required,  for  the  best  samples  of  commercial  powdered  arsenous 
acid  were  found  during  the  course  of  these  experiments  to  be  only 
of  about  93  per  cent,  purity. 
In  connection  with  this  subject  eight  commercial  samples  of 
Fowler's  solution  were  examined  by  the  pharmacopceial  method  of 
assay.  Two  of  the  samples  were  from  an  inland  city,  five  from 
retail  druggists  of  Philadelphia,  and  one  from  a  wholesale  drug 
house  of  the  same  place. 
The  results  are  indicated  in  the  amount  of  decinormal  iodine  vol- 
umetric solution  required  by  the  official  method  of  estimation,  and 
also  in  percentage  comparison  with  the  official  requirement  of  arse- 
nous acid. 
Iodine  Percentage 
Number.  Solution.  Comparison. 
I      .    .   48-8  9879 
2   487  98*64 
3  •   48-i  97-42 
4   48  6  98*44 
5   45"o  91 'H 
6   49"o  99*24 
7   498*9  998  28 
8   50*2  ico '40 
These  figures  were  all  verified  by  duplicate  titrations,  and  in  the 
case  of  No.  7  recourse  was  had  to  a  gravimetric  determination  of 
the  arsenous  acid  to  insure  accuracy. 
The  excessive  and  dangerous  strength  of  this  sample  is  significant 
in  showing  that  too  much  care  cannot  be  exercised  in  the  manufac- 
ture of  even  the  galenicals  of  the  Pharmacopoeia. 
