78 
IMPURITY  OF  BROMIDE  OF  POTASSIUM. 
possesses  therapeutic  powers  differing  from  those  of  iodide  of 
potassium ;  at  the  same  time  it  does  not  cause  certain  very  un- 
pleasant symptoms  which  so  commonly  occur  during  the  admin- 
istration of  the  iodide,  and  which  not  unfrequently  prohibits  its 
exhibition.  I  refer  more  especially  to  the  affection  of  the  mu- 
cous membranes  of  the  nose,  throat,  &c.  Bromide  of  potassium 
is  usually  given  in  much  larger  doses  than  the  corresponding 
iodide,  and  it  is  therefore  of  considerable  importance  that  it 
should  be  dispensed  in  a  pure  state,  and  especially  that  it  should 
be  free  from  admixture  with  other  salts  liable  to  produce  power- 
ful effects  upon  the  animal  economy. 
Is  it  usually  found  in  a  pure  state  ? 
From  my  own  experience,  I  fear  not.  During  the  present 
summer,  when  about  to  lecture  on  the  bromide  to  the  class  at 
University  College,  I  procured  some  of  the  urine  from  one  of  my 
patients  in  the  hospital,  who  at  that  time  was  taking  the  drug  in 
rather  large  doses,  and  proceeded  to  examine  the  fluid  by  means 
of  starch  and  chlorine  water :  to  my  surprise,  however,  a  very 
copious  precipitate  of  the  dark  blue  iodide  of  amidin  took  place, 
and  no  evidence  of  the  presence  of  bromine  was  afforded.  I  was 
forced,  therefore,  to  conclude  either  that  iodide  of  potassium  had 
been  dispensed  in  lieu  of  the  bromide,  or  that  the  bromine  had 
been  converted  into  iodine  in  its  passage  through  the  animal 
economy,  a  not  very  probable  occurrence,  or  lastly  that  the 
bromide  of  potassium  made  use  of  contained  a  considerable 
amount  of  iodide.  The  last  supposition  was  found  to  be  the  true 
one,  for,  on  making  an  examination  of  the  salt  with  the  starch 
test,  such  was  the  intensity  of  the  blue  produced  by  the  contained 
iodine  that  none  of  the  orange-colored  bromide  of  amidin  could 
be  seen. 
Since  the  time  I  first  found  iodine  in  bromide  of  potassium,  I 
have  made  several  qualitative  examinations  of  different  specimens 
of  the  salt  procured  from  different  sources.  One  sample  in  my 
possession  since  1845  was  found  quite  free  from  iodine.  Another, 
obtained  in  1850  from  one  of  the  largest  drug  establishments  in 
town,  was  rich  in  that  element ;  and  I  have  specimens,  probably 
recently  prepared,  some  strongly  contaminated,  others  without  a 
trace  of  iodine.  I  believe,  however,  from  what  I  have  observed, 
that  the  presence  of  iodine  in  the  bromide  of  potassium  of  com- 
