394       CRITICAL  NOTE  ON  PERMANGANATE  OF  POTASSA. 
article  on  the  ready  distinction  of  chlorine,  bromine  and  iodine, 
by  means  of  permanganate  of  potassa. 
As  so  ready  a  method  of  distinguishing  between  these  sub- 
stances would,  if  accurate,  be  of  much  practical  value,  I  was  in- 
duced to  make  a  trial  of  the  method  for  my  own  satisfaction. 
The  substances  used  in  my  experiments  were  chloride  of  sodium, 
iodide  of  potassium,  and  bromide  of  potassium.  Of  each  of  these 
I  made  two  neutral  solutions,  one  of  the  strength  of  one  part  of 
the  respective  salts  to  thirty  parts  of  water,  and  the  other  one 
part  to  two  hundred  and  forty  parts  of  water.  I  also  made  two 
solutions  of  permanganate  of  potassa, — one  a  saturated  solution 
(1  in  16),  and  the  other  quite  dilute.  The  results  obtained  I 
give  below,  under  the  respective  heads  of  the  salt  experimented 
with. 
Chloride  of  sodium, — When  a  few  drops  of  the  saturated  so- 
lution of  permang.  potass,  is  added  to  the  strong  neutral  solu- 
tion, no  immediate  change  is  produced.  After  a  short  time, 
however,  the  pink  color  of  the  solution  changes  to  a  reddish 
color,  and  after  the  lapse  of  a  day  or  two  to  a  brownish  color, 
and  if  allowed  to  stand  long  enough  a  brownish  'precipitate  is 
thrown  down,  and  the  supernatant  liquid  becomes  clear.  These 
changes  are  accelerated  by  the  action  of  heat,  or  by  the  addition 
of  a  few  drops  of  nitric  acid.  When  the  dilute  solutions  are 
used  no  change  is  apparent,  even  after  the  lapse  of  a  day  or 
two,  beyond  the  characteristic  pink  coloration  produced  by  the 
permanganate. 
Iodide  of  potassium. — When  the  saturated  solution  of  potass, 
permang.  is  added  to  the  strong  solution,  a  brownish  precipitate 
is  produced,  and  the  supernatant  liquid  has  a  brownish  color, 
with  odor  of  free  iodine  ;  but  on  standing  becomes  colorless. 
The  addition  of  nitric  acid  to  the  original  solution  causes  an 
immediate  liberation  of  iodine. 
With  the  dilute  solutions  the  effects  produced  are  the  same, 
except  that  no  precipitate  Mh  until  the  lapse  of  a  few  hours 
after  the  addition  of  the  permanganate. 
Bromide  of  potassium. — With  the  strong  solution  (of  this  salt) 
the  saturated  solution  of  permanganate  gives  a  brownish  precipi- 
