1 84  Assay  of  Belladonna  Plasters.  \Km'Ll™\Xm™' 
mixed  with  four  parts  of  the  rubber  compound.  The  mass  should 
assay  0-502  per  cent.;  the  amount  found  was  0-493  an<^  0-500  per 
cent. 
The  incorporation  of  the  extracts  with  the  rubber  mixture  was 
accomplished  by  working  them  up  together  in  the  hands,  pulling 
out,  twisting,  etc.  This  was  continued  until  the  mass  had  a  per- 
fectly uniform  appearance.  Small  losses  of  one  or  the  other  ingre- 
dient, through  adhering  to  the  hands,  were  prevented  by  rubbing  a 
very  little  petrolatum  on  the  fingers  from  time  to  time.  After 
admixture  the  mass  was  weighed  and  found  to  have  suffered  no 
change  in  weight  through  loss  or  gain  of  moisture.  Disintegration 
of  the  mass,  when  in  form  of  lumps,  is  very  much  slower  than  is 
the  case  with  spread  plasters.  It  was  found  best  to  drop  it  in  small 
pieces  separately  into  the  chloroform,  as  otherwise  the  fragments 
reunite  into  one  large  lump,  greatly  retarding  solution. 
The  above  stated  results  indicating  the  method  to  be  reasonably 
accurate  and  reliable,  it  was  accepted  as  the  best  available  for  the 
valuation  of  commercial  belladonna  plasters  containing  rubber. 
THE  ASSAY  METHOD  IN  DETAIL. 
If  the  plaster  to  be  assayed  approximates  the  U.S. P.  standard  of 
strength,  one  plaster,  or  about  8  grammes  of  mass,  is  sufficient  for 
each  determination ;  if  weaker,  correspondingly  more  should  be 
taken,  if  accurate  results  are  expected.  The  quantities  of  solvents, 
etc.,  given  are  suitable  for  one  plaster  of  ordinary  size.  Weigh  the 
plaster  after  removing  all  cloth  except  that  upon  which  the  mass  is 
spread,  cut  it  into  strips,  and  place  it  into  a  beaker  of  100  c.c.  capa- 
city with  50  c.c.  of  chloroform  and  10  drops  of  10  per  cent,  ammo- 
nia water.  Stir  with  a  glass  rod  until  the  mass  is  entirely  removed 
from  the  cloth,  which  usually  requires  five  to  ten  minutes.  Heating 
is  unnecessary  and  is  apt  to  cause  loss  of  alkaloid  by  saponification. 
Decant  the  chloroform  mixture  into  a  beaker  of  similar  size  and  add 
to  it  40  c.c.  of  91  per  cent,  (by  weight)  alcohol.  Stir  gently  until 
all  rubber  has  separated  in  compact  form,  then  leave  it  undisturbed 
for  a  few  minutes  and  pour  off  the  supernatant  liquid  into  a  separa- 
tor of  at  least  250  c.c.  capacity.  Wash  the  cloth  in  the  first  beaker 
with  25  c.c.  of  chloroform  and  5  drops  of  ammonia  water,  decant  the 
washings  into  the  second  beaker,  and  redissolve  with  them  the  pre- 
cipitated rubber.    Stir  this  mixture  until  it  is  perfectly  free  from 
