522  New  Color  Reaction  for  Vanillin.  {Am^oZ'^vm' 
rapidly  drop  by  drop,  until  the  yellow  coloration  results,  and  the 
test  set  aside  for  a  few  minutes,  the  original  bluish-green  color 
reappears  with  full  intensity. 
If  too  much  bromine  water  be  added  at  once,  or  if  it  be  added 
slowly  until  the  yellow  color  results,  the  bluish-green  color  will  not 
reappear. 
The  test  succeeds  in  solutions  of  vanillin  I  :  100,000  and  then  is 
more  easily  recognized  than  is  the  ferric  chloride  test  with  vanillin 
solutions  1  :  2,000. 
It  is  also  interesting  to  note  that  if  to  the  vanillin  solution  be 
added  a  little  of  a  dilute  ferric  chloride  solution  and  then  a  drop  of 
bromine  water,  a  much  more  intense  color  is  produced,  but  in  this 
case  a  yellowish  green  ;  this  color  is  discernible  in  vanillin  solutions 
I  :  50,000. 
The  presence  of  free  acid  does  not  interfere  much  with  the  intensity 
of  these  colors,  and  hence,  the  test  would  seem  to  depend  upon  the 
action  of  bromine  upon  vanillin  and  then  the  further  action  of  this 
compound  upon  the  salts  of  iron,  especially  ferrous  salts. 
That  this  is  the  case  can  be  proven  by  carrying  cut  the  test  in  a 
manner  which  will  enable  one  to  detect  one  part  vanillin  in  200,000 
parts  of  solution  : 
To  the  vanillin  solution  is  added  a  drop  of  bromine  water  or 
sufficient  to  impart  the  odor  of  bromine,  and  then  a  freshly  prepared 
solution  of  ferrous  sulphate  is  carefully  added  in  slight  excess,  that 
is,  a  drop  or  two  are  added  after  the  bromine  odor  has  disappeared. 
Coumarin  not  giving  this  color  reaction,  it  can  be  used  to  estimate 
approximately  the  vanillin  in  mixtures  of  vanillin  and  coumarin  as 
they  are  used  in  the  vanilla  substitutes ;  to  do  this  the  same  weights 
of  vanillin  and  the  substitute  (about  50  milligrams)  are  dissolved 
each  in  100  cc.  of  water;  of  this  solution  5  cc.  are  taken,  diluted 
with  about  10  cc.  of  water,  and  bromine  water  added  drop  by  drop 
until,  after  agitation,  the  bromine  odor  is  permanent,  then  add  of  a 
freshly  prepared  I  per  cent,  ferrous  sulphate  solution  until  the 
bluish-green  color  no  longer  intensifies ;  lastly,  dilute  with  water 
the  two  tests  until  they  are  of  the  same  tint. 
A  comparison  of  the  two  volumes  will  give  the  percentage  of 
vanillin  in  the  substitute,  if,  for  instance,  the  vanillin  solution  meas- 
ures 75  cc.  and  the  substitute  solution  55  cc,  then 
75  :  50  :  :  100  :  x  =  66  66  per  cent. 
