THE  AMERICAN 
JOURNAL  OF  PHARMACY. 
JUNE,  1886. 
NOTE  ON  THE  ESTIMATION  OF  COCAINE  BY  MAYER'S 
REAGENT. 
By  A.  B.  Lyons,  M.  D. 
In  an  article  published  last  October  in  the  Journal,  the  writer 
made  some  statements  with  regard  to  the  use  of  Mayer's  reagent  in 
estimating  cocaine,  which,  to  be  of  any  value,  require  expansion  and 
qualification.  The  experiments,  although  few  in  number,  on  which 
those  statements  were  based,  were  carefully  made,  and  the  conclusions 
as  nearly  correct  as  they  could  be  made  in  so  bald  a  presentation  of 
the  subject.  Recurring  some  time  afterwards  to  the  subject,  and  ap- 
proaching it  from  a  different  quarter,  I  was  led  to  believe  that  in  re- 
porting my  earlier  experiments  I  had  made  a  blunder  which  ought  to 
be  at  once  corrected.  A  note  was  accordingly  published  in  the 
Journal  explaining  the  nature  of  the  supposed  mistake.  My  later 
conclusion,  however,  I  find  was  too  hastily  drawn,  and  I  owe  it  to  the 
readers  of  the  Journal  to  make  a  new  and  more  complete  statement 
of  the  facts. 
It  has  been  generally  assumed  that  the  precipitates  produced  by 
Mayer's  reagent  are  double  iodides  of  mercury  with  the  alkaloidal 
base,  having  the  general  formula  RI,  HgI2,  R  standing  for  the  alka-  * 
loidal  basic  radical.  This  theory,  however,  I  do  not  find  borne  out  by 
fact  in  the  case  of  most  alkaloids,  and  certainly  is  not  true  of  cocaine. 
The  precipitates  produced,  indeed,  appear  generally  to  vary  in  compo- 
sition under  varying  conditions,  and  it  is  only  by  accident  that  the 
equivalent  numbers  originally  given  by  Mayer  and  quoted  in  all  the 
text  books,  agree  with  those  found  by  observation. 
On  the  above  hypothesis  each  c.c.  of  Mayer's  reagent  ought  to  precip- 
itate '01515  gm.  of  cocaine,  and  the  precipitate  from  O'l  gm.  of  the 
alkaloid  should  weigh  0*292  gm.  The  weight  of  the  precipitate  ob- 
tained falls  considerable  below  this,  and  is  not  constant.    It  averages 
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