AmAJp°rH;iP8S8arm'}       Assay  of  Belladonna  Plasters.  185 
lumps,  then  precipitate  the  rubber  by  addition  of  20  c.c.  of  alcohol 
and  proceed  as  before,  adding  the  chloroform-alcohol  solution  to 
that  in  the  separator.  Repeat  this  procedure  once  more  or  until  all 
mass  is  removed  from  cloth  and  beaker.  Dry  the  cloth  at  a  low 
heat,  cool,  and  weigh  it.  The  chloroform-alcohol  solution  is  of  a 
light-yellowish  or  brownish  color,  the  depth  of  color  depending 
mainly  on  the  proportion  of  extract  of  belladonna  (or  scopolia) 
present.  If  the  plaster  contains  leaf  extract,  the  solution  is,  of 
course,  green.  It  is  nearly  always  more  or  less  turbid  from  minute 
particles  of  rubber  held  suspended,  which  do  not  settle  to  the  bot- 
tom except  upon  standing  for  some  time.  This  suspended  matter 
separates  out  during  the  next  stage  of  the  process  and  introduces 
complications.  Filtration  is  impracticable,  as  the  filter  soon  becomes 
covered  with  an  impervious  layer  of  rubber.  When  the  chloroform 
mixture  and  alcohol  are  shaken  vigorously  in  a  stoppered  flask,  in- 
stead of  stirring  in  a  beaker  with  a  rod,  the  supernatant  solution 
will,  as  a  rule,  be  nearly  clear,  but  a  portion  of  the  precipitated  rub- 
ber will  be  in  a  light,  flocculent  condition,  so  that  only  a  part  of  the 
liquid  can  be  decanted  without  carrying  a  considerable  quantity  of 
rubber  with  it.  The  other  plan  was,  upon  the  whole,  considered  the 
best,  particularly  as  the  presence  of  this  small  amount  of  rubber 
does  not  materially  affect  the  accuracy  of  the  method,  but  merely 
necessitates  a  little  more  care  in  the  manipulation.  The  quantity 
depends  to  some  extent  on  the  proportion  of  alcohol  used  to  pre- 
cipitate the  rubber  from  the  chloroform.  Although  nearly  all  of  the 
rubber  is  precipitated  by  a  volume  of  alcohol  one-half  that  of  the 
chloroform,  it  was  found  that  practically  4  volumes  of  alcohol  are 
required  to  insure  a  maximum  precipitation  from  5  volumes  of  chloro- 
form. When  this  proportion  of  alcohol  is  used,  the  rubber  carried 
over  into  the  next  stage  of  the  process  is  too  small  in  amount  to 
influence  the  result. 
To  the  combined  chloroform-alcohol  solutions  in  the  separator  add 
20  c.c.  of  water  containing  2  per  cent,  of  sulphuric  or  hydrochloric  acid 
and  agitate  by  a  gentle  rotatory  motion  and  inversion  of  the  separator 
during  five  minutes.  Vigorous  shaking  causes  emulsification.  After 
complete  separation  of  the  liquids  draw  off  the  chloroform  solution 
into  another  separator,  together  with  any  solid  matter  that  may 
have  separated  during  the  agitation  and  collected  at  the  line  of  con- 
tact  of  the  two  liquids.  Pour  out  from  the  top  into  a  third  separator 
