n8 
U.  S.  P.  Assay  Methods. 
(  Am.  Jour.  Pbarn'i. 
|     March,  1909. 
On  pages  578  and  579,  Chapter  IV  of  the  Appendix,  the  Phar- 
macopoeia gives  instructions  concerning  alkaloidal  assay  by  immis- 
cible solvents,  but  it  is  not  complete,  as  some  of  the  most  essential 
points  in  alkaloidal  assay  have  been  omitted.  This  chapter  explains 
the  process  and  what  takes  place  at  certain  stages  of  the  assay ;  for 
instance,  it  states  what  is  formed  upon  shaking  out  with  a  dilute 
acid  solution,  describes  a  separator,  tells  how  to  break  up  emulsions, 
and  states  that  the  ethereal  layer  is  above  the  aqueous  layer  in  the 
separator.  This  is  necessary,  as  no  effort  should  be  spared  that 
would  be  of  value  to  those  who  must,  of  necessity,  use  the  U.  S.  P. 
methods  for  the  determination  of  alkaloidal  strength.  In  the  treat- 
ment of  this  subject  probably  the  most  important  part  of  an  alka- 
loidal assay,  and  one  which  may  cause  an  error  in  the  result,  has 
not  been  touched  upon,  and  that  is  the  necessity  of  washing  the  tip 
of  the  separator  stem  with  some  of  the  solvent.  This  must  be  done 
because  when  the  ether  or  chloroform  containing  the  alkaloid  is 
drawn  off,  some  is  drawn  up  around  the  outside  of  the  stem,  from 
which  it  is  evaporated,  leaving  the  alkaloid,  and  if  this  is  not  washed 
off  it  will  be  a  cause  of  error  in  the  result.  It  is  more  likely  to  occur 
with  ethereal  than  with  chloroformic  solutions. 
Another  factor  in  alkaloidal  assay,  and  one  which  is  of  sufficient 
importance  to  'deserve  mention  in  the  chapter  under  discussion,  is 
the  absolute  necessity  of  excluding  any  acid  or  ammonia  fumes  from 
the  room.  It  is  not  necessary  to  do  this  during  the  whole  of  the 
operation,  but  only  after  the  time  the  ethereal  or  chloroformic  solu- 
tion is  drawn  off  into  the  vessel  in  which  the  alkaloid  is  to  be  titrated. 
There  are  no  reasons  why  these  suggestions  should  not  be  incor- 
porated in  this  chapter.  It  would  be  establishing  no  precedent,  and 
they  are  of  vastly  more  importance  to  the  operator  and  are  more 
conducive  to  accurate  work  than  the  knowledge  that  a  salt  is  formed 
when  the  alkaloid  is  shaken  out  with  dilute  acids,  or  even  how  to 
break  up  an  emulsion. 
For  the  titration  of  alkaloids  the  Pharmacopoeia  instructs  (with 
the  exception  where  iodo-eosin  is  used  as  an  indicator)  that  the 
solution  be  drawn  into  and  the  evaporation  be  performed  in  a 
beaker,  but  we  have  found  that  white,  glazed  porcelain  dishes  are 
superior  for  this  purpose.  In  these  dishes  the  evaporation  of  the 
solvent  is  more  readily  accomplished  on  account  of  the  larger  surface 
exposed.  The  end  reaction  is  also  more  easily  detected  because  of 
the  white  background.  This  is  particularly  true  when  cochineal  is 
used  as  an  indicator. 
