306     ON  SOME  PREPARATIONS  OF  THE  U.  S.  PHARMACOPCEIA. 
enclosed  in  the  sheathing  of  resin  and  being  insoluble  in  it,  it  is' 
only  the  exterior  layer  that  acts  by  contact. 
Emplastrum  Arnicoe. — Alcoholic  extract  of  arnica  incorpo- 
rates easily  and  completely  with  resin  plaster,  and  forms  a  com- 
pound adherent  and  efficient  as  a  strengthening  plaster.  The 
plaster  in  this  form  was  originally  suggested  by  the  author  of 
this  paper  in  this  Journal  for  September,  1855,  (vol.  3d,  514, 
3d  series),  but  the  strength  as  there  recommended  was  quite 
different,  the  extract  obtained  from  twelve  troy  ounces  of  arnica 
flowers  was  incorporated  with  twenty-two  troy  ounces  of  resin 
plaster.  Now,  arnica  flowers,  with  the  menstruum  there  recom- 
mended, (alcohol  36°  B.  three  parts,  water  one  part,)  yield  33 
per  cent,  of  soft  extract,  consequently,  in  the  original  recipe,  the 
plaster  consisted  of  four  parts  of  extract  to  twenty-two  parts  of 
resin  plaster.  One  part  of  the  officinal  plaster  therefore  repre- 
sents one  part  of  the  flowers,  and  is  a  rather  expensive  prepara- 
tion, taken  in  connection  with  the  cost  of  the  waste  of  alcohol, 
etc. 
Emplastrum  OpiL — This  preparation  differs  from  the  old  one 
in  being  made  with  the  aqueous  extract  of  opium, — a  quantity 
equivalent  to  the  opium  of  the  old  recipe.  When  an  extract  is 
made  with  water  and  alcohol  so  as  to  get  all  the  soluble  matter, 
the  resulting  plaster  fully  represents  the  drug  and  has  its  odor, 
whilst  it  is  perfectly  free  from  particles  of  opium  not  unusually 
observed  in  the  plaster  of  the  old  recipe. 
Emplastrum  Picis  Canadensis  is  a  new  officinal,  being  a  mix- 
ture of  one  part  of  wax  and  twelve  parts  of  Canada  pitcjh., 
strained. 
Emplastrum  Picis  cum  Cantliaride  has  been  reduced  in 
strength  from  the  proportion  of  one  part  of  cerate  to  seven  of 
Burgundy  pitch  to  that  of  one  part  to  twelve  of  pitch.  This 
change  was  made  in  view  of  the  frequent  excessive  action  of 
the  old  plaster,  which  had  often  to  be  reduced  in  strength. 
The  subjects  of  extracts  and  fluid  extracts  come  next  in  order 
and  will  be  remarked  on  in  the  next  number. 
(To  be  continued.) 
