536 
Assay  of  Ipecae. 
{km.  Jour.  Pharm. 
Nov.,  1885. 
iodide.  Add  of  this  reagent  two  or  three  cc.  at  first,  and  filter.  As 
soon  as  a  sufficient  quantity  of  clear  filtrate  has  run  through  (5  to  10 
cc.)  add  to  this  a  few  drops  of  the  reagent,  and  if  a  copious  precipitate 
is  produced,  add  about  1  cc.  and  immediately  return  the  mixture  to 
the  filter.  The  first  portion  of  filtrate  (10-15  cc.)  that  passes  after 
this  has  been  done  must  be  returned  also,  but  the  succeeding  portion 
is  to  be  tested  again  with  Mayer's  reagent.  As  soon  as  the  precipitation 
ceases  to  be  copious,  the  reagent  is  to  be  added  only  0*1  cc.  at  a  time, 
and  nearly  the  whole  of  the  fluid  allowed  to  pass  through  the  filter 
before  testing  again.  Filtration  is  generally  rapid,  so  that  the  entire 
operation  consumes  but  a  short  time,  and  it  is  easy  to  carry  on  several 
titrations  at  once,  where  a  series  of  assays  are  to  be  made.  The  time 
actually  occupied  in  such  an  assay  is  scarcely  more  than  half  an  hour, 
and  the  manipulations  require  no  especial  skill.  The  result  is  easily 
calculated,  by  merely  multiplying  the  number  of  cc.  of  reagent  con- 
sumed by  0*378,  the  product  expressing  the  percentage  of  emetin  in 
the  drug.  It  is  customary  to  calculate  the  result  upon  the  dry  drug, 
but  for  commercial  purposes  there  is  no  advantage  in  doing  this.  It 
is  easy,  however,  to  obtain  the  corrected  figure,  if  at  the  same  time 
that  the  powder  is  w^eighed  for  the  assay,  a  second  portion  of  one  gram 
is  also  weighed  for  estimation  of  moisture.  This  is  to  be  dried  at  a 
temperature  not  exceeding  105°C.  (221  °F.),  as  long  as  it  continues  to 
lose  weight.  In  this  way,  it  will  be  found  that  the  powder  generally 
contains  5  to  8  per  cent,  of  moisture. 
Suppose  the  drug  to  have  contained  6*5  per  cent,  moisture,  and  to 
have  indicated  in  the  assay  2*4  per  cent,  emetine.  The  corrected  per 
cent,  will  be  found  by  solving  the  proportion  100 — 6*5:100:  :2*4:x, 
and  will  be,  therefore,  2*4^*935=2*57  per  cent. 
To  what  extent,  however,  can  we  put  confidence  in  these  results? 
We  find,  in  most  cases,  that  results  obtained  by  titration  with  Mayer's 
reagent  vary  very  greatly  according  to  the  dilution  of  the  fluid.  It  is 
therefore  necessary,  in  order  to  obtain  results  of  any  value,  to  be  care- 
ful that  the  proportion  of  alkaloid  contained  in  the  solution  shall  not 
vary  materially  from  a  fixed  standard,  and  it  is  equally  necessary  to 
employ  always  in  the  assay  the  same  proportion  of  free  acid.  It  is, 
indeed,  often  necessary  to  make  two  titrations,  the  first  merely  to  as- 
certain approximately  the  amount  of  alkaloid  present  in  order  to  de- 
termine what  should  be  the  volume  of  the  fluid  to  be  titrated,  and  a 
third  experiment  even  may  become  necessary.    Emetine  is,  however. 
