THE  AMERICAN" 
JOURNAL  OF  PHARMACY 
MAY,  igio 
A  NOTE  ON  A  SUITABLE  ULTIMATE  STANDARD  FOR 
THE  VOLUMETRIC  SOLUTIONS  OF  THE 
U.  S.  PHARMACQPCEIA.' 
The  very  prominent  position  given  to  volumetric  analysis  In  the 
U,  S.  Pharmacopoeia,  and  its  almost  exclusive  use,  wherever  pos- 
sible, in  determining  whether  a  given  substance  comes  up  to  the 
required  standard  of  purity,  render  it  imperative  that  the  most  suit- 
able ultimate  standard  be  adopted  for  the  necessary  volumetric  solu- 
tions. It  is  also  obvious  that  in  considering  what  substance  might 
form  a  suitable  ultimate  standard  for  these  solutions,  we  must  place 
as  of  primary  importance  the  readiness  with  which  such  substance  is 
obtainable  in  a  pure  state,  its  stability  under  ordinary  conditions,  its 
possessing  the  necessary  properties  for  admitting  of  its  use  in  a 
volumetric  process  of  proven  accuracy,  and,  finally,  what  likelihood 
there  is  of  different  operators  obtaining  such  substance  in  different 
degrees  of  purity  although  working  by  the  same  method. 
The  substance  chiefly  relied  on  as  standard  in  the  present 
U.S. P.,  namely,  potassium  bitartrate,  although  meeting  these  re- 
quirements quite  satisfactorily  in  many  ways,  nevertheless  appears 
to  present  the  disadvantage  of  introducing  a  personal  error  in  the 
procedure  for  its  purification.  Thus  Parsons,1  who  investigated 
the  suitability  of  this  substance  as  a  means  for  the  standardization 
of  acid  and  alkaline  solutions,  states  that  he  "  made  up  some  accord- 
ing to  the  directions  given  .  .  .  but  found  it  necessary,  in  order 
to  get  the  pure  salt,  to  crystallize  three  times  in  addition."    He  also 
By  Eli  as  Elvove. 
1Jour.  Anal.  Chew,.,  6,  380-381  (1892). 
(203) 
