130 
The  Assay  of  Coca. 
J  Am.  Jour.  Pharm. 
I      March,  1901. 
contents  of  the  separator  an  additional  10  c.c.  of  ether,  making  in 
all  30  c.c.  for  the  second  extraction. 
Shake  the  separator  with  its  contents  actively  for  a  few  moments, 
then  allow  the  liquids  to  separate,  drawing  off  the  aqueous  portion 
into  the  separator  previously  emptied,  the  ethereal  layer  being 
added  to  that  already  in  the  beaker. 
This  operation  is  repeated  a  third  time. 
The  beaker  containing  the  ethereal  solution  of  the  alkaloids  is 
set  in  a  warm  place  (30°-35°  C),  and  as  soon  as  the  ether  has 
evaporated,  it  is  dried  at  a  temperature  of  6o°  C.  until  of  a  constant 
weight,  this  usually  requiring  about  three  hours. 
The  weight  obtained  multiplied  by  four  expresses  the  percentage 
of  alkaloids  in  the  leaf. 
The  alkaloids  so  obtained  are  almost  colorless,  possessing  only  a 
faint  cream  tint,  and  are  beautifully  crystalline  in  appearance. 
If  it  is  desired,  as  a  check  upon  the  ^weight,  they  may  be  titrated, 
N 
using  an  excess  of  _  sulphuric  acid  V.S.  (about  25  c.c.)  and  a  few 
cubic  centimetres  of  ether  to  facilitate  the  solution,  and  after  the 
ether  has  been  entirely  dissipated,  the  excess  of  acid  is  determined 
N 
by  means  of         potassium  hydrate  V.S.,  using  (2)  two  drops  of  a 
cochineal  tincture  (1  gramme  in  25  c.c.  of  25  per  cent,  alcohol). 
The  factor  for  the  pure  alkaloids  as  determined  by  numerous  as- 
N 
says  is  0*01514  gramme  as  the  equivalent  of  I  c.c.  of  —  HoS04V.S.t 
20 
the  extremes  being  0-01493-0  0155  gramme. 
However,  if  the  assay  has  been  carefully  conducted,  this  is  entirely 
unnecessary,  for  the  gravimetric  result  is  in  reality  the  more  accurate, 
this  being  due  not  only  to  the  difference  in  the  molecular  weights  of 
the  alkaloids,  but  also  to  the  variable  composition  of  this  mixture. 
The  claim  has  been  made  by  A.  R.  L.  Dohme1  that  the  so-called 
Keller  method  is  far  superior  to  all  other  methods  for  assaying  coca, 
but  as  none  of  the  methods  employed  in  his  comparison  was  similar 
to  the  one  just  described,  it  was  thought  advisable  to  institute  such 
a  comparison. 
The  following  results  speak  for  themselves : 
Proceedings  Amer.  Pharm.  Assoc.,  1895,  268. 
