Am  Jour  Pharm.)        Detection  of  Chlorine,  Bromine  and  Iodine.  321 
June.  1884.  J  ' 
DETECTION  OF  CHLORINE,  BROMINE,  AND  IODINE.1 
By  C.  Thompson. 
In  the  "  Chemical  News "  (vol.  xlviii,  p.  296)  there  appeared  a 
process  by  Mr.  Jones,  for  detecting  chlorine,  bromine  and  iodine  in 
the  presence  of  each  other.  The  process  was  as  follows:  " Place  a 
small  quantity  of  the  mixture  to  be  tested  in  a  good  sized  test-tube, 
add  a  few  pieces  of  manganese  dioxide  and  then  a  little  water.  Add 
now  1  drop  of  dilute  sulphuric  acid  (1  part  acid  to  10  parts  of  water), 
a  brown  tinge  indicates  the  presence  of  iodine.  Boil  the  mixture  and 
confirm  the  presence  of  iodine  by  the  violet  vapors  in  the  upper  part 
of  the  tube.  Continue  the  boiling  till  these  vapors  cease  to  appear, 
then  add  another  drop  of  sulphuric  acid  and  boil  again  until  they 
cease.  If  necessary,  repeat  this  addition  of  acid  and  boiling  until 
violet  vapors  have  entirely  ceased.  Now  add  about  2  cubic  centime- 
ters of  the  dilute  acid  and  boil  again ;  brown  vapors  indicate  bromine. 
Continue  the  boiling  until  the  vapors  no  longer  smell  of  bromine,  then 
add  another  cubic  centimeter  of  dilute  acid  and  boil  again.  When  the 
vapors  no  longer  smell  of  bromine,  allow  the  tube  to  cool  thoroughly, 
add  an  equal  bulk  of  strong  sulphuric  acid  and  warm;  a  green  gas 
bleaching  a  piece  of  moist  red  blotting-paper  at  the  mouth  of  the  tube 
indicates  chlorine.  Occasionally  some  more  bromine  comes  off  on  the 
addition  of  the  strong  sulphuric  acid,  but  if  so,  it  is  soon  got  rid  of 
and  is  succeeded  by  the  chlorine,  which  is  chiefly  evolved  on  heating 
the  mixture.  As,  moreover,  red  blotting-paper  is  far  more  quickly 
acted  on  by  chlorine  than  by  bromine  there  can  be  no  difficulty  in 
distinguishing  between  the  two."  Mr.  Jones  also  adds  that  he  has 
found  this  process  to  compare  very  favorably  with  others.  This  pro- 
cess is  somewhat  similar  to  that  recommended  by  Vortmann,  except 
that  sulphuric  acid  is  the  active  agent  instead  of  acetic  acid.  Mr. 
Barnes  has  shown  that  unless  very  great  care  is  exercised,  Vortmann's 
process  is  not  trustworthy ;  so  that  it  would  not  at  first  sight  seem 
likely  that  Mr.  Jones's  process  in  which  sulphuric  acid  is  to  be  used 
would  answer  much  better. 
Experiments  tend  to  confirm  this  statement.    If  there  be  a  large 
1  Report  on  Analytical  Chemistry  read  before  the  School  of  Pharmacy 
Students'  Association. 
21 
