584  A  Study  of  the  Use  of  Mayer's  Reagent.  {Am^cu.%£a rm 
tinctures,  estimations  of  alkaloid  can  be  very  satisfactorily  made  by 
the  titration  method.  Since  the  character  of  the  alkaloid  is  easily 
changed  by  heat  and  the  action  of  chemicals,  the  method  cannot  be 
trusted  in  the  examination  of  solid  extracts  and  still  less  for  commer- 
cial aconitine.  In  all  cases  the  physiological  test  should  supplement 
the  estimation  by  titration  of  this  alkaloid. 
Atropine. — Results  of  titrations  vary  greatly  with  different  sam- 
ples of  the  alkaloid,  and  are  much  influenced  by  variations  of  con- 
ditions. The  end  of  the  reaction  is  never  very  sharply  defined.  After 
reaching  a  certain  point  it  will  be  found  that  a  drop  of  the  reagent 
will  produce  a  precipitate  which  immediately  re-dissolves,  while  addi- 
tion of  several  drops  will  produce  a  distinct  precipitate.  If  collected 
at  once  and  weighed,  the  precipitate  will  be  found  to  fall  much 
short  of  the  theoretical  weight,  whereas  if  allowed  to  stand  a  few 
hours,  it  becomes  firmly  adherent  to  the  sides  and  bottom  of  the 
containing  vessel,  but  has  a  resinous  appearance:  its  weight  is  then 
near  what  theory  requires.  I  have  not  observed  in  this  precipitate 
any  tendency  to  crystallize.  Most  of  my  experiments  were  made  with 
commercial  atropine,  containing  no  doubt  a  considerable  admixture 
of  hyoscyamine.  A  sample  of  Merck's  pure  atropine  showed,  how- 
ever, the  same  peculiarities,  somewhat  exaggerated,  perhaps. 
From  my  experiments,  the  following  practical  rule  may  be  de- 
duced for  interpreting  the  results  of  a  titration  of  atropine,  Mayer's 
reagent  N  1-20  being  used,  and  the  end  of  the  reaction  being  fixed 
at  the  point  where  two  drops  of  reagent,  added  to  the  filtered  solu- 
tion, produce  only  an  evanescent  cloud. 
Rule. — For  each  cc.  of  fluid  present  at  the  end  of  the  titration  de- 
duct from  the  quantity  of  reagent  consumed  0*05  cc,  and  multiply 
the  remainder  by  7*5.  The  product  will  be  the  quantity  of  alkaloid 
present,  expressed  in  milligrams. 
If  the  modified  reagent  No.  1  is  used,  its  equivalent  may  be  taken 
as  about  8*7  mg.,  the  dilution  of  the  alkaloidal  solution  being  be- 
tween 1:200  and  1:400.  The  ordinary  reagent  is  probably,  on  the 
whole,  to  be  preferred.  If  the  excess  of  reagent  is  estimated  and  de- 
ducted from  the  amount  consumed  in  the  titration,  the  equivalent  be- 
comes, where  the  ordinary  reagent  is  used,  about  9'5  to  10  mg. ;  with 
the  modified  reagent,  No.  1,  about  12.  mg. 
JBerberine. — Mayer's  reagent  produces  in  solutions  of  berberine,  as 
in  those  of  morphine,  a  bulky  crystalline  precipitate.    The  titration 
