•  ON  ARNICA  PLASTER.  247 
Mix  the  alcohol  and  water  and  moisten  the  powder  with  a  pint 
of  the  mixture ;  then  pack  it  firm  in  a  cylindrical  percolator,  and 
gradually  pour  on  the  remainder  of  the  mixture.  Continue  the 
percolation  with  diluted  alcohol  until  six  pints  of  tincture  have 
passed.  Lastly,  evaporate  this  by  means  of  a  water-bath  to  the 
proper  consistence. 
This  process  yielded  20  per  cent,  of  the  extract.  In  making 
the  second  extract  I  have  been  guided  by  the  formula  given  by 
Prof.  Procter,  in  the  Amer.  Jour,  of  Pharmacy,  iii.  series,  vol. 
iii.  No.  vi.,  as  follows : 
Arnica  flowers,  twelve  troyounces. 
Alcohol,  three  pints. 
Water,  one  pint. 
Mix  the  alcohol  and  water,  and  pour  two  pints  of  the  mixture 
over  the  arnica,  previously  finely  bruised.  Allow  it  to  stand  for 
48  hours,  pack  it  firmly  in  a  percolator,  and  pour  on  the  remain- 
der of  the  mixture  until  three  pints  are  obtained.  Evaporate 
this  tincture  in  a  water-bath  (or  still)  till  reduced  to  a  soft  resin- 
ous extract. 
This  extract  I  evaporated  still  further,  in  order  to  obtain  it, 
as  near  as  possible,  of  the  same  consistence  as  the  preceding. 
The  yield  of  this  process  was  16  per  cent,  or  4  per  cent,  less 
than  the  oflicinal.  But  whether  the  20  per  cent,  of  the  officinal 
process  is  of  more  medicinal  value  than  the  16  per  cent,  of  Prof. 
Procter's  process,  I  am  unable  to  say  at  present. 
I  will  now  proceed  to  the  preparation  of  the  plaster. 
Plaster  No.  I.  was  prepared  according  to  the  officinal  formula, 
as  follows :    Take  of 
Alcoholic  extraet  of  arnica  a  troyounce  and  a  half. 
Resin  plaster,  three  troyounces. 
Add  the  extract  to  the  plaster,  previously  melted  by  means  of  a 
water-bath,  and  mix  them. 
The  plaster  thus  prepared  has  a  deep  yellowish-brown  color 
and  is  adhesive,  spreads  readily,  though  somewhat  soft,  more  so 
than  desirable  at  the  temperature  of  the  skin. 
Plaster  No.  II.  was  made  by  taking  of  alcoholic  extract  of 
arnica,  a  troyounce  ;  resin  plaster,  two  troyounces ;  Burgundy 
