PREPARATIONS  OF  THE  U.  S.  PHARMACOPEIA,  1860.  395 
intended  as  a  means  of  making  the  Plaster  of  Arnica.  It  is 
made  by  distilling  the  alcohol,  by  means  of  a  water  bath  heat, 
from  a  tincture  of  arnica  made  by  percolation  with  two  parts  al- 
cohol to  one  of  water.  By  careful  manipulation  three-fourths  of 
the  alcohol  used  in.  this  formula  may  be  recovered. 
Extractum  Cannabis  Purification. — It  is  presumable  that  the 
commercial  extract  of  Indian  Hemp  is  made  by  processes  va- 
riable in  their  details,  as  it  is  found  to  differ  materially  at  one 
time  and  another,  both  as  regards  its  medicinal  activity  and  the 
proportion  of  matter  insoluble  in  alcohol  in  the  extract.  Whence 
comes  this  brown  residue  in  the  commercial  extract  ?  We  find 
the  best  reason  for  its  presence  in  the  manner  of  making  on  a 
large  scale.  The  hemp  is  put  in  a  still,  rectified  spirit  (alcohol 
U.  S.  P.)  is  poured  on,  and  the  heat  applied  until  the  drug  is 
well  decocted,  probably  decanting  the  first  hot  liquors,  adding 
more  spirit,  and  again  decocting.  During  this  process  the  alco- 
holic strength  of  the  menstruum  is  altered  by  the  volatilization 
of  a  part  of  the  alcohol,  and  consequently  other  matter  beside 
the  resin,  of  an  extractive  nature,  is  taken  up  and  remains  in  the 
final  product  on  distilling  off  the  alcohol  from  the  tinctures.  The 
only  other  way  to  account  for  its  presence  is  designedly  using 
diluted  alcohol  at  the  end  of  the  process  with  the  intention  of 
getting  a  larger  product. 
The  London  process  for  extract  of  Indian  hemp  directs  it  to 
be  made  by  macerating  powdered  Indian  hemp  in  five  parts  of 
rectified  spirit  without  heat,  pressing  and  evaporating  in  a  still 
to  the  state  of  an  extract.  It  is  very  probable  that  this  extract 
will  dissolve  without  appreciable  residue. 
The  U.  S.  Pharmacopoeia  of  1860  directs  nearly  equal  parts 
of  the  commercial  extract  of  Indian  hemp  and  alcohol  to  be  rub- 
bed together  until  they  are  mixed,  six  parts  more  of  alcohol  add- 
ed and  mixed,  and  then,  after  standing  24  hours,  filtered,  and 
evaporated  at  160°  to  dryness.  When  equal  parts  are  rubbed 
together  a  thick  syrupy  solution  of  the  soluble  portion  of  the 
extract  is  effected,  with  which,  by  continued  malaxation,  the  in- 
soluble portion  will  form  a  semifluid  mixture,  but  as  soon  as  the 
remainder  of  the  alcohol  is  added  the  brown  extractive,  not  being 
