466  Purity  of  Commercial  Aspirin:      { Am'J{Syr-I^9arm' 
nearly  so  in  the  case  of  sample  3  (27.67  and  27.61),  as  required  by 
theory,  whilst  sample  2  is  placed  in  the  other  group.  But  in  the  re- 
maining samples,  for  a  constant  value  in  the  ester,  the  acid  varies  in 
the  ratio  of  from  100:  100.7  to  100 :  I02-7>  and  the  presumed  disso- 
ciation does  not  account  for  this  difference  in  any  degree.  It,  there- 
fore, appears  that  there  is  a  certain  acidity  either  in  the  preparation 
or  developed  in  solution  of  many  samples,  which  is  neither  due  to 
free  salicylic  acid  alone  nor  to  dissociated  acetylsalicylic  acid. 
Bromine  Value. — In  considering  the  bromine  value  in  its  rela- 
tion to  the  acid  and  ester,  in  the  case  of  the  first  group,  it  is  seen  to 
approximate  the  acid  value  rather  than  the  ester.  This  is  what  one 
would  expect,  since  it  is  the  salicylic  group  in  the  molecule  that  is 
responsible  for  both  figures.  It  might  further  be  supposed  that  any 
dissociation  would  be  reflected  in  the  acid  value  exceeding  the  bro- 
mine, the  difference  being  due  to  dissociated  acetic  acid  and  equal 
to'  the  free  salicylic  found  by  the  iron  test  in  terms  of  iV/5  soda  per 
1  gram.  If  the  salicylic  acid  found  occurred  as  such,  and  not  as  a 
product  of  dissociation,  both  acid  and  bromine  value  should  agree, 
but  on  looking  into  the  figures  this  is  seen  not  to  be  the  case.  In 
eleven  out  of  the  fifteen  examples  the  bromine  is  in  excess  of  the 
acid,  in  Group  I  slightly,  in  Group  II  very  markedly,  and  at  the 
same  time  noticeably  agreeing  with  the  ester  value. 
With  regard  to  these  two  points,  after  reviewing  the  figures  and 
making  allowances  for  the  probable  dissociation,  it  would  appear 
that  the  excess  of  bromine  in  the  first  set  of  examples  can  best  be 
explained  by  assuming  salicyl-salicylic  acid  being  present  in  minute 
quantities.  In  the  second  series  one  might  expect  acetyl-salicyl- 
salicylic  acid  to  be  in  the  main  the  contaminating  substance,  as  with 
this  substance  there  are  two  salicylic  groups  in  the  molecule  and  the 
ester  value  is  also  double  the  acid  value,  hence  to  the  extent  of  its 
presence  in  aspirin  both  ester  and  bromine  value  would  rise  in  agree- 
ment. Sample  15  is  suggestive  of  both  salicyl-salicylic  acid  and 
acetyl-salicyl-salicylie  acid  being  present. 
In  this  connection  it  has  been  observed  that  on  taking  about  a 
gram  of  the  aspirin,  fifteen  to  twenty  drops  of  methyl  alcohol,  about 
8  Cc.  of  water  and  adding  some  crystals  of  sodium  carbonate, 
warming  to  effect  solution  and  then  boiling  for  about  half  a  minute, 
both  during  the  operation  and  on  allowing  to  cool  a  strong  odor  of 
methyl  salicylate  is  developed  in  samples  of  the  second  group.  In 
those  represented  by  2,  6  and  10  there  is  no  trace  of  the  wintergreen 
