CARBOLIC  ACID  PLASTER. 
155 
Heat  the  lac  with  about  one-third  of  the  carbolic  acid  over  a 
slow  fire  till  the  lac  is  completely  melted  ;  then  remove  from 
the  fire  and  add  the  remainder  of  the  acid,  and  stir  briskly  till 
the  ingredients  are  thoroughly  mixed.  Strain  through  muslin, 
and  pour  into  the  machine  for  spreading  plaster ;  and,  when  the 
liquid  has  thickened  by  cooling  to  a  degree  ascertained  by  ex- 
perience, spread  to  the  thickness  of  about  one-fiftieth  of  an  inch. 
Afterwards,  brush  over  the  surface  of  the  plaster  lightly  with  a 
solution  of  gutta  percha  in  about  30  parts  of  bisulphide  of  car- 
bon. When  the  sulphide  has  all  evaporated,  the  plaster  may  be 
piled  in  suitable  lengths  in  a  tin  box,  without  adhering,  or 
rolled  up  and  kept  in  a  canister."  The  coating  of  gutta  percha, 
through,  which  the  acid  permeates  freely,  is  given  to  prevent 
it  adhering  to  the  skin,  as  it  is  desirable  that  such  a  dressing 
should  adhere  very  slightly,  if  at  all.  It  has  this  great  ad- 
vantage over  the  antisepctic  lead  plaster,  that  it  cannot  »be 
softened  either  by  a  watery  or  an  oily  fluid."  If  made  to  contain 
much  less  than  25  per  cent,  of  the  acid,  it  is  brittle,  but  this 
may  be  avoided  by  the  addition  of  spirits  of  wine  in  an  equiv- 
alent quantity,  as  this  sample  contains  12J  per  cent,  of  acid  and 
the  same  of  spirits. 
These  plasters  are  generally  kept  applied  to  the  part  by  means 
of  ordinary  adhesive  plaster  strapped  around  the  edges  of  the 
piece  employed.  But  to  avoid  any  chance  of  germs  getting  access 
to  the  wound,  to  the  adhesive  plaster  before  spreading,  he 
directs  1  per  cent,  of  carbolic  acid  to  be  added. 
Many  other  applications  are  used  in  this  system  of  treatment, 
but  these'  plasters  being  interesting  pharmaceutical  prepara- 
tions, I  have  thought  worthy  of  bringing  under  your  notice 
this  evening. 
The  samples  exhibited  were  prepared  in  the  Hospital  Dis- 
pensary. 
University  College  Hospital^  Dec.  2,  1868. 
In  reply  to  an  inquiry,  Mr.  Martindale  said  there  was  but  little 
loss  of  the  carbolic  acid  by  vaporization  in  making  the  plaster. 
The  plaster  might  be  kept  for  months  without  losing  its  pliable 
condition,  or  sufi'ering  any  material  deterioration  in  strength  or 
quality. — Lond,  Pharm,  Journ,,  Jan.,  1869. 
