302 
Alkaloidal  Assay. 
Am.  Jour.  Pharm 
July.  1907. 
oughly  shaken  together  they  become  minutely  divided  and,  pre- 
senting the  maximum  of  surface  to  each  other,  are  thus  in  a  favorable 
condition  to  exert  their  respective  selective  properties.  The 
presence  of  resin,  fat,  gum  or  other  colloidal  bodies  scarcely  affects 
the  solubilities  of  the  alkaloids  and  their  salts,  but  the  increased 
viscosity  of  the  fluids  tends  to  prevent  the  intimate  contact  necessary 
for  their  transference  from  one  solvent  to  the  other  unless  by  pro- 
longed and  vigorous  agitation.  But  such  treatment  often  results  in 
the  formation  of  an  inseparable  emulsion  and  the  assay  process 
cannot  be  completed. 
Emulsification  then  is  one  of  the  objectionable  features  of  the 
shaking  out  process  as  usually  applied.  In  order  to  prevent  the 
formation  of  emulsions  the  U.  S.  P.  modifies  the  proportions  of  the 
solvents  to  suit  the  extractive  matter  characteristic  of  different 
drugs.  Inasmuch,  however,  as  the  amounts  of  these  inert  substances 
differ  in  the  products  of  similar  drugs,  it  is  often  necessary  to  further 
modify  the  quantities  of  solvent  to  suit  the  particular  preparation  in 
hand.  Alcohol  is  often  present  in  a  preparation  or  it  may  be  added  ; 
it  increases  the  mobility  of  the  aqueous  layer  and  tends  to  prevent 
emulsification.  Its  drawback  is  likewise  two-fold  ;  it  decreases  the 
ratio  of  solubility  and  sometimes  permits  of  sufficient  coloring 
matter  being  carried  through  to  seriously  impair  the  delicacy  of  the 
color  changes  in  any  final  titration. 
In  the  last  stage  of  this  assay  process  the  purified  "  ethereal  " 
solution  of  free  alkaloid  is  warmed  to  dissipate  the  solvent  together 
with  any  adherent  ammonia,  leaving  the  alkaloid  in  a  suitable  con- 
dition for  weighing  or  titrating.  The  application  of  heat  to  free 
alkaloids  under  these  conditions  is  liable  to  occasion  loss  from  various 
causes:  reactions  with  chloroform,  hydrolysis  of  cocain,  evaporation 
of  coniine,  spurting  of  strychnine,  and  more  or  less  resinification  of 
alkaloids  in  general.  It  would  be  preferable  to  simply  shake  the 
final  "ethereal"  extract  with  standard  acid  and  so  estimate  its 
alkaloidal  content.  Such  procedure  has  often  been  mooted  and  its 
advisability  has  recently  been  emphasized  by  Gordin.1 
The  chief  difficulty  is  the  elimination  of  traces  of  ammonia  which 
is  ever  present,  as  salts,  in  drugs  and  their  preparations,  and,  being 
liberated  by  a  fixed  alkali,  is  transferred  in  part  to  the  ethereal 
extract. 
1  Amer.  Journ.  Phar.,  Vol.  78,  p.  458 
