AmDec!iSarm"}  A  Sfudy  °fthe  Use  of  Mayer's  Reagent. 
585 
equivalent  of  the  alkaloid  is  remarkably  high.  Results  of  titration 
in  solutions  1:200  to  1:400  are  reasonably  constant,  but  the  alkaloid 
is  nearly  always  associated  in  the  plants  in  which  it  occurs  with  others 
having  a  very  different  behavior  towards  Mayer's  reagent.  The  esti- 
mation of  this  alkaloid  is  moreover  easily  made  by  a  colorimetric 
method.  It  is  noticeable  that  very  little  excess  of  reagent  is  required 
for  the  complete  precipitation  of  berberine,  and  the  alkaloid  might, 
therefore,  possibly  be  used  to  estimate  excess  of  reagent,  but  for  this 
purpose  strychnine  is  to  be  preferred. 
Brucine. — Results  of  titrations  vary  widely,  and  apparently  capri- 
ciously under  varying  conditions. 
In  solutions  exactly  neutral,  a  larger  quantity  of  alkaloid  is  re- 
quired than  in  those  containing  a  little  acid,  the  end  of  the  reaction 
being  ill  defined.  On  the  other  hand  addition  of  more  acid,  a  small 
proportion  after  all,  gives  a  high  result  in  the  titration.  The  alkaloid 
is  so  easily  determined  by  other  methods  that  the  use  of  Mayer's  re- 
agent cannot  be  recommended  where  this  alkaloid  is  in  question,  a& 
e.  g.y  in  the  examination  of  preparations  of  nux  vomica  and  ignatia. 
Cinchonine  and  cinchona  alkaloids  generally  do  not  give  satisfac- 
tory titrations,  as  has  been  long  since  observed.  In  roughly  estimat- 
ing the  total  alkaloids  in  a  preparation  of  bark,  the  titration  method 
may  be  adopted  for  rapidity,  an  arbitrary  equivalent  being  assumed 
for  the  value  of  Mayer's  reagent.  Observation  shows  that  this  must 
be  a  very  low  one,  viz. :  not  far  from  5  mg.,  for  reagent  N  1-20. 
Cocaine. — [This  subject  has  been  recently  pretty  fully  discussed  by 
the  writer  in  the  columns  of  the  Journal,  and  the  conclusions  then 
reached  need  not  be  here  restated.] 
Colchieine  can  be  satisfactorily  estimated  by  Mayer's  reagent,  pro- 
vided there  is  present  in  the  solution  a  somewhat  large  proportion 
of  free  acid.  It  requires  that  about  10  per  cent,  of  the  volume  of  the 
solution  shall  be  dilute  sulphuric  acid  (1  vol.  acid  in  5).  Under  this 
condition,  the  results  of  the  titration  are  to  be  interpreted  by  the  fol- 
lowing rule :  Correct  the  result  obtained  by  subtracting  for  each  cc. 
of  fluid  present  at  the  end  of  the  titration  0*08  cc,  and  multiply  the 
remainder  by  29  to  obtain  the  quantity  of  colchicine  in  milligrams. 
Emetine  may  be  estimated  by  Mayer's  reagent  with  a  fair  degree 
of  precision.  Correct  the  result  by  subtracting  for  each  cc.  of  fluid 
present  at  the  end  of  the  titration  0*038,  and  multiply  the  remainder 
by  12  to  obtain  the  quantity  of  emetine  in  milligrams. 
