EXAMINATION  OF  IODIDE  OF  POTASSIUM. 
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EXAMINATION  OF  IODIDE  OF  POTASSIUM. 
By  J.  M.  Maisch. 
Having  lately  had  opportunity  of  testing  the  purity  of  vari- 
ous parcels  of  iodide  of  potassium,  I  deem  it  proper  to  state  the 
result  of  these  investigations,  and  at  the  same  time  to  call  atten- 
tion to  a  very  easy  way  of  determining  very  nearly  the  purity 
and  value  of  this  salt ;  not  only  the  present  high  price  of  it 
may  justify  the  publication  of  this  paper,  but  still  more  so  its 
high  value  and  extensive  use  by  practitioners,  and  its  liability  to 
adulteration,  against  which  to  put  the  apothecaries  on  their  guard 
is  the  object  of  these  lines. 
Several  years  ago  Marozeau  proposed  to  ascertain  the  purity 
of  iodide  of  potassium  by  dissolving  5  grs.  *of  it  and  two  grs.  of 
corrosive  sublimate — that  is  two  equivalents  of  the  former  and 
one  of  the  latter — separately  in  about  3  oz.  of  distilled  water, 
and  dropping  the  last  into  the  first  solution  until  a  red  tinge  is 
produced  which  does  not  disappear  after  stirring  well  with  a 
glass  rod ;  comparing  the  quantity  of  the  solution  left  with  its 
original  quantity  indicates  the  purity  of  the  iodide.  In  this  pro- 
cess the  iodide,  as  will  be  seen  by  reference  to  some  table  of 
weights  of  the  equivalents,  just  suffices  to  dissolve  the  formed 
biniodide  of  mercury  (2  KI  +  Hg  CI  ==  KI,  Hgl  +  KC1,)  and 
consequently  no  precipitation  can  take  place,  if  the  first  ar- 
ticle is  chemically  pure,  the  commercial  corrosive  sublimate  in 
general  being  pure.  As  soon  as  on  the  addition  of  the  last,  that 
iodide  necessary  for  keeping  in  solution  the  binodide  of  mercury, 
is  decomposed,  a  red  tinge  appears,  owing  to  the  separation  of 
the  mercurial  iodide. 
Thinking  that  thus  easily  within  a  fraction  the  per  centage  of 
impurities  might  be  found,  I  have  altered  a  little  the  above  quan- 
tities. In  the  following  examinations  I  have  dissolved  10  grs.  of 
iodide  of  potassium  in  about  2  oz.  of  water,  and  4  grs.  of  the  cor- 
rosive sublimate  in  exactly  2  oz.  2  scr.  (1000  grs.  troy)  of  water. 
The  weight  in  grs.  of  the  solution  of  corrosive  sublimate  left  after 
the  reddish  tinge  appears  expresses  very  nearly  the  amount  of 
impurities  present  in  1000  parts  of  the  examined  sample.  The 
annexed  table  shows  the  purity  of  several  different  articles  of 
odide  of  potassium  ascertained  in  the  above  way : 
