154 
CARBOLIC  ACID  PLASTER. 
preparation.  He  next  tried  a  carbolic  acid  plaster,  made  by 
mixing  emplastrum  plumhi  with  one-fourth  of  beeswax  to  give  it 
sufficient  consistence,  and  carbolic  acid  in  the  proportion  of  one- 
tenth  of  the  whole.  This  is  spread  on  calico,  in  a  layer  of  about 
one-twentieth  of  an  inch.  It  is,  however,  inconveniently  soft, 
and  cannot  be  kept  spread  in  stock.  He  says,  "  I  have  since 
found  that  by  increasing  the  proportion  of  litharge,  the  lead- 
soap  may  be  made  to  any  degree  of  firmness  that  may  be  de- 
sired, provided  that  water  be  not  used  in  the  manufacture.  When 
the  litharge  and  olive-oil  are  in  the  proportions  directed  by  the 
Pharmacopoeia,  a  certain  quantity  of  water  must  be  added  to 
promote  the  combination  of  the  fatty  acids  with  the  oxide  of 
lead,  and  even  then  the  process  is  a  very  tedious  one.  But  it 
is  an  interesting  fact,  chemically,  that  if  the  litharge  is  used  in 
about  four  times  the  Pharmacopoeial  proportion,  although  no 
water  be  employed,  the  combination  proceeds  under  a  brisk  heat 
with  great  rapidity.  It  is  upon  this  fact  the  following  method 
of  manufacture  is  based  : — 
"  Take  of 
Olive-oil  12  parts  (by  measure). 
Litharge  (finely  ground),  12  parts  (by  weight). 
Beeswax,  3  parts  (by  weight). 
Crystallized  carbolic  acid,  2i  parts  (by  weight). 
Heat  half  the  olive-oil  over  a  slow  fire,  then  add  the  litharge 
gradually,  stirring  constantly  till  the  mass  becomes  thick  or  a 
little  stiff*;  then  add  the  other  half  of  the  oil,  stirring  as  before, 
till  it  becomes  again  thick.  Then  add  the  wax  gradually,  till 
the  liquid  again  thickens.  Remove  from  the  fire,  and  add  the 
acid,  stirring  briskly  till  thoroughly  mixed.  Cover  up  close  and 
set  aside,  to  allow  all  the  residual  litharge  to  settle  ;  then  pour 
off"  the  fluid,  and  spread  upon  calico  to  the  proper  thickness. 
The  plaster  made  in  this  way  can  be  spread  by  machine,  and 
kept  rolled  in  stock ;  and,  if  in  a  well-fitting  tin  canister,  will 
retain  its  virtues  for  any  length  of  time." 
But  for  almost  all  purposes  the  antiseptic  lead  plaster  is 
superseded  by  his  lac  plaster,  which  is  made  in  this  manner : — 
"  Take  of  Shellac,  3  parts. 
Crystallized  carbolic  acid,  1  part. 
