Am.  Jour.  Pharm.  \ 
October,  1899.  / 
Alkaloidal  Assays. 
465 
Volumetric  Test  Solution  of  Thiosulphate  of  the  U.S.P.  may  be 
used. 
(3)  The  Starch  Test  Solution  of  the  Pharmacopoeia. 
(4)  The  burettes  and  centesimal  measuring  vessels  for  any  volu- 
metric work  in  analysis. 
THE  VOLUMETRIC  OPERATION. 
The  final  alkaloidal  solution  obtained  by  whatever  mode  of 
extraction,1  but  always  representing  a  definite  quantity  of  the  drug 
to  be  assayed,  is  poured  slowly  and  with  constant  stirring  into  a 
flask  holding'  ioo  c.c,  in  which  has  been  previously  drawn  20  or 
30  c.c.  of  the  standardized  solution  of  iodine,  and  I  or  2  c.c.  of 
dilute  hydrochloric  acid 2  (U.S.P.).  The  flask  is  then  filled  up  to  100 
c.c,  stoppered,  and  well  shaken  till  the  periodide  has  separated  out. 
The  supernatant  liquid  is  to  be  perfectly  transparent,  but  of  a  red 
iodine  color.  Fifty  c.c.  are  then  filtered  off,  and  in  this  portion  the 
excess  of  iodine  determined  by  means  of  standard  sodium  thio- 
sulphate. The  amount  of  iodine  consumed,  multiplied  by  the 
proper  factor,  gives  the  amount  of  alkaloid  present  in  the  quantity 
of  drug  taken.3 
In  case  more  than  one  alkaloid  be  present  in  the  drug,  a  mean 
iodometric  factor  can  be  drawn,  as  shown  for  strychnine  and  brucine 
in  the  list  of  factors.  In  alkalimetric  estimations  a  mean  factor  is 
often  used  in  assay  for  total  alkaloids,  and  the  same  is  equally  justi- 
fiable in  iodometric  work,  when  the  data  are  known. 
Should  there  be  no  precipitate  with  iodine,  but  only  a  slight  tur- 
bidity, then  the  drug  is  extremely  poor,  and  for  the  assay  a  much 
larger  quantity  than  has  been  used  should  be  taken.  On  the  other 
hand,  should  the  supernatant  liquid,  after  adding  the  alkaloidal  solu- 
1  Directions  for  extraction  are  given  further  on.  Other  procedure  for  extrac- 
tion is  given  in  L/yons'  "Handbook  of  Assaying,"  i899,*Detroit,  Nelson,  Baker 
&  Co.,  pages  26  to  30. 
2  It  is  always  to  be  remembered  that  this  estimation,  by  formation  of  higher 
periodides,  requires  the  alkaloid  to  be  added  slowly  to  the  iodine,  with  excess 
of  the  latter.  Except  in  the  case  of  morphine,  an  excess  of  acid  is  not  hurtful, 
and  even  promotes  the  separation  of  the  periodide.  Hydrochloric  is  to  be  pre- 
ferred to  sulphuric  acid. 
3  For  example  :  If  operating  upon  2  grammes  of  powdered  ipecac  root,  the 
iodine  consumed  be  0*957764,  then  the  percentage  of  emetine  in  the  drug  equals 
o*957764  X  0-55  X  100/2  =  2  63. 
