AStemberfi9ia'}    Manufacture  of  Medicinal  Plasters.  423 
"  Melt  the  rubber  at  a  temperature  not  exceeding  1500  C. 
(3020  F.)  ;  add  the  petrol'atum,  and  continue  the  heat  until  the 
rubber  is  dissolved.  Add  the  lead  plaster  to  the  hot  mixture ; 
continue  the  heat  until  it  becomes  liquid,  then  strain,  allow  it  to 
cool,  and  stir  until  it  stiffens." 
The  mass  here  given  was  intended  as  an  adhesive  plaster,  and 
also  to  be  used  as  a  base  or  vehicle  for  belladonna  plasters,  cap- 
sicum plasters,  and  opium  plasters.  In  the  previous  edition  of  the 
Pharmacopoeia  the  base  or  mass  in  most  instances  had  been  a  com- 
bination of  resin  and  lead  plaster  masses.  Masses  of  this  character 
had  been  official  in  several  of  the  previous  revisions.  It  has  been 
stated  that  the  present  mass  was  introduced  for  the  reason  that 
non-rubber  plasters  had  been  entirely  superseded  by  plasters  with 
a  rubber  base,  and  that  while  non-rubber  plasters  had  been  retained 
in  the  U.  S.  Pharmacopoeia  in  the  several  revisions,  they  had 
become  entirely  obsolete,  and  it  was  the  intent  of  this  innovation 
to  improve  the  plaster  mass  so  as  to  make  them  respond  to  the 
requirements  for  an  India  rubber  base  plaster. 
It  has  been  stated  that  the  formula  of  the  Pharmacopoeia  would 
enable  the  pharmacist  to  prepare  and  spread  rubber  base  plasters, 
and  that  as  a  final  result  the  lost  art  of  plaster  spreading  would 
be  restored  to  pharmacy.  Experience,  however,  has  shown  that 
plaster  spreading  in  pharmacy  is  no  more  popular  to-day  than 
when  the  present  edition  of  the  Pharmacopoeia  was  issued,  and, 
indeed,  the  present  mass  of  the  Pharmacopoeia  is  not  as  popular 
as  were  the  plaster  masses  of  the  previous  Pharmacopoeia. 
The  reasons  for  this  condition  are  plain.  The  mass  of  the 
Pharmacopoeia  contains  2  per  cent,  of  rubber,  2  per  cent,  of 
petrolatum,  and  96  per  cent,  of  lead  plaster.  This  falls  far  short 
of  the  requirements  for  an  India  rubber  plaster  mass.  The  India 
rubber  adhesive  plasters,  such  as  are  sold  in  the  market  at  the 
present  time,  contain  from  20  to  50  per  cent,  of  India  rubber ;  the 
medicated  India  rubber  plasters  contain  from  20  to  40  per  cent., 
and  it  is  the  use  of  India  rubber  in  these  proportions  that  gives 
to  India  rubber  plasters  their  peculiar  consistency  and  properties. 
It  is  my  judgment  that  the  finished  plaster  mass  of  the  Pharma- 
copoeia contains  little  or  no  rubber,  as  such.  In  making  up  the 
mass  it  is  required  that  the  rubber  shall  be  melted  at  a  temperature 
of  1500  C.  (3020  P.),  it  is  then  combined  with  petrolatum  and 
lead  plaster  mass.    India  rubber  is  decomposed  at  a  temperature 
