64 
The  Assay  of  Drugs. 
f  Am.  Jour.  Pharni. 
\   February,  1909. 
in  a  certain  volume  of  tenth-normal  sulphuric  acid  which  is  more 
than  that  necessary  to  combine  with  and  bring  them  into  solution, 
the  excess  being  then  titrated  back  with  fiftieth-normal  potassium 
hydroxide  to  the  neutral  point  as  indicated  by  cochineal  or  iodeosin 
solution.  Owing  to  the  relatively  high  molecular  weight  of  alkaloids 
and  the  small  amount  usually  present,  small  differences  in  measuring 
the  few  cubic  centimetres  of  tenth-normal  sulphuric  acid  required 
have  a  relatively  large  effect  upon  the  result.  It  seems  desirable 
to  substitute,  for  tenth-normal,  twentieth-  or  fiftieth-normal  acid  in 
corresponding  amount,  even  though  it  should  prove  necessary  to 
hasten  solution  by  the  use  of  neutral  alcohol.  In  any  case  a  blank 
titration  is  advisable  for  comparison. 
These  volumetric  solutions  are  standardized  upon  purified  potas- 
sium bitartrate  as  a  basis.  The  standard  is  somewhat  unfamiliar 
to  analysts  and  a  comparison  with  the  usual  standards  has  been 
instituted,  but  no  conclusion  has  yet  been  reached.  Experiments  on 
checking  the  purity  of  the  bitartrate  by  incinerating  and  cautiously 
igniting  one  of  two  equal  portions  and  neutralizing  the  resulting 
carbonate  with  the  reserved  bitartrate  resulted  in  a  mixture  of  acid 
reaction.    This  may  be  attributable  to  loss  in  ignition. 
The  principle  of  the  standardization  is  faulty  in  adjusting  the 
normal  potassium  hydroxide  (from  which  the  fiftieth-normal  is 
prepared  by  dilution)  from  the  potassium  bitartrate  by  the  use  of 
phenolphthalein  indicator,  and  then  adjusting  the  normal  sulphuric 
acid  from  the  normal  alkali  with  the  use  of  methyl-orange.  In  the 
absence  of  carbonates  the  end  points  of  phenolphthalein  and  methyl- 
orange  do  not  differ  so  materially  with  normal  as  with  weaker 
solutions.  The  methyl-orange,  however,  is  used  backward,  so  to 
speak,  titrations  with  it  being  more  commonly  made  to  a  pink  than 
to  a  yellow  color.  The  Pharmacopoeia  takes  cognizance  of  the  fact 
that  in  alkaloidal  titrations  neither  of  these  indicators,  but  a  third, 
cochineal  or  iodeosin,  is  employed,  and  directs  a  special  experiment 
and  adjustment  of  the  solutions  for  use  with  this  indicator.  The 
intention  is  apparently  to  have  the  tenth-normal  acid  adjusted  to  the 
fiftieth-normal  alkali,  whereas  the  acid,  owing  to  its  permanence  and 
stability,  is  much  better  suited  for  a  secondary  standard.  Cochineal 
as  an  indicator  seems  to  give  satisfaction  to  most  analysts.  As  with 
other  indicators  experience  teaches,  and  a  dummy  in  proximity  aids 
in  determining  the  exact  end  point. 
Lack  of  time  precludes  any  discussion  of  special  methods  such  as 
