188  Assay  of  Belladonna  Plasters.  {^•l^S™* 
partially  fades  upon  shaking,  as  the  liberated  alkaloid  is  taken  up  by 
the  chloroform.  If  this  is  not  kept  in  mind,  the  neutral  point  may 
be  overstepped.  The  endreaction  should  be  placed  at  the  point 
where  the  color  changes  throughout  the  liquid,  although  it  may  dis- 
appear after  further  shaking  or  stirring. 
ASSAY  OF  COMMERCIAL  SAMPLES. 
Eleven  samples,  comprising  the  products  of  six  manufacturers, 
were  obtained,  with  the  double  purpose  of  testing  the  general  appli- 
cability of  the  assay  method  and  to  learn  the  alkaloidal  strengths 
of  the  various  plasters  offered  in  the  market.  All  prominent  Ameri- 
can manufacturers  are  represented,  and  one  foreign  plaster  is 
included.  The  plasters  were  all  purchased  in  the  open  market. 
The  results  given  in  the  appended  table  fully  corroborate  previous 
statements  to  the  effect  that  a  great  variation  in  strength  exists.  Only 
three  samples  in  the  list,  all  of  them  the  products  of  one  firm,  conform 
to  the  U.S. P.  standard  of  strength ;  all  others  are  much  below  it. 
The  assay  scheme,  as  detailed  in  the  preceding  pages,  was  found 
suitable  for  all  plasters  of  American  manufacture,  but  a  modification 
was  required  for  the  foreign  sample.  That  portion  of  it  insoluble  in 
the  mixture  of  chloroform  and  alcohol  could  not  be  made  to  agglu- 
tinate, even  on  the  addition  of  a  large  quantity  of  rubber  dissolved 
in  chloroform.  The  most  uniform  results  were  obtained  by  making 
the  chloroform-alcohol  solution  up  to  a  definite  volume  and  filtering 
an  aliquot  part  of  it.  In  other  respects  no  change  in  the  method 
was  required. 
All  porous  plasters  examined  were  uniform  in  square  measure, 
5x7^  inches,  and  in  the  table  the  average  weight  of  the  mass  in 
one  plaster  is  given,  except  in  the  cases  of  plasters  put  up  in  rolls. 
Weight  of  Mass  in 
Per  Cent,  of  Alkaloid  One  Plaster,  in 
No.                                                                in  Mass.  Grammes. 
1  •  •  •  0-586  ;  0-594  ;  0-587  ;  0-571.  8-55 
2  0*407  ;  0*403  ;  0*400  ;  0-416.  8-7 
3  •                0*509 ;  0-497-  — 
4                                                            o-ii2 ;  o*io8.  8-65 
5                                                            0-103 \  o'lio.   
6                                                            0*060 ;  0*058.  8'2 
7                                                            0*084;  0*081.  7*35 
8                                                          0*125  ;  0-116.  3*25 ! 
9                                                            0*098 ;  0*101.  8*35 
10                                                            0*042 ;  0*047.  57 
11                                                  0*095;  0*093;  0-096.   
