THE  AMERICAN 
JOURNAL  OF  PHARMACY. 
JANUARY,  1887. 
ON  THE  USE  OF  MAYER'S  REAGENT  IN  THE  ESTI- 
MATION OF  ALKALOIDS. 
By  A.  B.  Lyons,  M.  D. 
Experimental  researches,  the  details  of  which  were  published  in 
the  December  number  of  the  Journal,  justified  the  following  general 
conclusions : 
1.  Results  of  titrations  with  Mayer's  reagent  are  influenced  by 
various  conditions  to  such  an  extent  that  their  indications  have  at  best 
only  an  approximate  value. 
2.  In  dilute  solutions  the  results  of  titration  are  always  high,  not 
low.  Either  a  stated  correction  must  be  made,  or  a  second  experi- 
ment carried  out  in  which  the  solution  is  brought  to  a  standard 
strength,  say  of  1 : 200  or  1 : 300. 
3.  The  influence  of  alcohol  and  of  iodides  (the  same  is  true  to  a 
certain  extent  also  of  bromides  and  chlorides)  is  to  interfere  with  the 
precipitation,  and  yet  the  effect  of  their  presence  may  be  beneficial 
rather  than  otherwise,  the  end  of  the  reaction  being  more  sharply  de- 
fined with  them  than  without.  This  is  especially  true  where  a  modi- 
fied reagent  is  employed,  containing  an  excess  of  potassium  iodide. 
Such  a  reagent  gives  more  uniform  results  with  certain  alkaloids  than 
the  usual  solution,  but  with  many  alkaloids  is  not  to  be  preferred,  and 
is  not  to  be  recommended  for  general  use. 
The  object  of  the  present  paper  is  to  record  some  further  observa- 
tions bearing  on  the  question,  how  Mayer's  solution  may  be  most  ad- 
vantageously employed.  That  it  is  capable  of  yielding  useful  prac- 
tical results  is  conceded  even  by  those  who  criticise  it  most  unspar- 
ingly. 
