422  Manufacture  of  Medicinal  Plasters.    { ^dmh^mlo 
plaster,  will  at  once  agree  as  to  the  superior  keeping  qualities  of 
an  India  rubber  plaster.  In  the  writer's  practice  he  has  known 
India  rubber  base  plasters  to  keep  perfectly  for  fifteen  years. 
The  making  of  India  rubber  plasters  is  hardly  within  the 
province  of  a  retail  pharmacist.  In  fact,  it  is  an  art  which  requires 
the  installation  of  large  and  expensive  apparatus.  The  process 
has  often  been  described.  It  is  perhaps  sufficient  to  state  that  the 
processes  outlined  in  the  United  States  Dispensatory  are  sub- 
stantially correct. 
Rubber  plasters,  for  the  most  part,  are  made  by  combining 
India  rubber,  two  parts,  with  burgundy  pitch,  one  part,  and  to  this 
is  added  gum,  olibanum,  galbanum,  wax,  sometimes  olive  oil,  fillers, 
such  as  orris  root,  to  complete  the  mass.  Masses  of  this  character 
vary  with  each  individual  plaster  or  medication,  an  acceptable 
plaster  being  one  which  shall  contain  at  least  33      per  cent,  rubber, 
The  rubber  to  be  used  in  a  plaster  mass  is  crushed,  washed  in 
alkaline  water  to  remove  the  natural  acids,  resins,  dirt,  etc.,  it  is 
then  ground  until  plastic,  and  combined  with  the  gums  and  with 
the  medicaments.  The  process  of  crushing,  grinding,  and  mixing 
is  conducted  by  means  of  large  iron  rollers,  an  essential  feature 
of  the  process  being  the  use  of  great  pressure  instead  of  the  heat 
employed  in  the  ordinary  process  of  plaster  making.  The  plasters 
are  finally  spread  upon  the  cloth  by  means  of  heavy  iron  rollers, 
on  an  apparatus  known  as  a  calender.  In  the  writer's  laboratory 
this  calender  weighs  20,000  pounds,  and  here  the  spreading  is 
accomplished  by  pressure  and  the  avoidance  of  heat.  The  finished 
plaster  after  being  spread  is  allowed  to  stand  or  set.  It  is  then 
wound  upon  cylinders,  cut  into  shapes  and  lengths,  such  as  rolls 
of  varying  widths  and  lengths,  or  into  the  ordinary  size,  5  x  7^2 
inches,  the  latter  usually  being  perforated. 
In  the  eighth  revision  of  the  Pharmacopoeia  a  notable  change 
was  made  in  the  formula  for  plasters  by  introducing  a  new  mass 
under  the  title  of  "  Emplastrum  Adhaesivum  "  as  follows : 
Emplastrum  Adh^sivum 
Adhesive  Plaster 
Rubber,  cut  in  small  pieces,  twenty  grammes   20  Gin. 
Petrolatum,  twenty  grammes    20  Gm. 
Lead  plaster,  nine  hundred  and  sixty  grammes   960  Gm. 
To  make  one  thousand  grammes   1000  Gm. 
