234   THE  MOST  CORRECT  METHODS  FOR  PREPARING  EXTRACTS. 
Of  20  pounds  fresh  herb  of  Aconitum  Napellus,  one  half  was 
dried  at  30°  C.  (86°  F.,)  leaving  2 J  pounds,  which  furnished  3J 
ounces  extract;  of  the  remaining  10  pounds  fresh  herb  4-|  ounces 
extract  was  obtained  in  the  same  manner ;  but  the  extract  from 
the  dried  herb  contained  0.322  grms.,  the  other  only  0.202 
grms.  of  nearly  pure  aconitine.  It  will,  therefore,  be  prefer- 
able for  pharmaceutists  to  prepare  the  narcotic  extracts  for  their 
own  use,  as  from  good  dry  herbs  they  will  be  sure  of  obtaining 
a  more  active  extract. 
The  quantity  of  the  exhausting  menstruum  is  a  great  object, 
as  with  an  increase  of  it  the  solution  must  be  exposed  for  a 
longer  time  to  heat  and  air.  But  also  the  mode  of  extracting 
must  be  kept  in  view.  Mohr's  press  box  and  his  displacement 
apparatus  are  recommended  for  the  various  processes.  For  the 
cold  displacement  the  authors  have  constructed  a  suction  pump, 
which  from  the  receiving  vessel  withdraws  the  air,  so  that  the 
pressure  of  the  atmosphere  forces  the  liquid  in  the  percolator 
through  the  finely  powdered  substance.  Before  evaporation  the 
liquids  are  to  be  decanted  or  strained,  by  which  precaution  a 
burning  of  the  extracts  is  prevented,  and  the  liability  to  fer- 
ment lessened. 
For  the  evaporation  of  larger  quantities  of  liquids,  the  authors 
have  constructed  a  peculiar  apparatus,  consisting  of  a  copper 
boiler,  into  which  a  smaller  copper  kettle  is  fitted.  Water  is 
heated  in  the  boiler  and  the  steam  passed  under  a  well  tinned 
evaporating  trough  ;  the  liquid  after  having  been  heated  in  the 
kettle,  is  drawn  into  a  reservoir,  from  whence  it  runs  into  the 
trough,  which  is  divided  by  partitions  running  alternately  from 
both  sides  of  the  trough,  to  within  a  short  distance  of  the  oppo- 
site side;  the  trough  stands  on  an  inclined  plane,  the  lower  end 
of  which  is  by  means  of  a  pipe  connected  with  the  kettle.  The 
advantages  of  this  arrangement  are,  that  the  liquid  is  constantly 
kept  in  motion,  the  temperature  never  rises  above  70°  C,  (158° 
F.,)  and  that  by  the  continued  evaporation  the  access  of  air  is 
almost  entirely  prevented.  For  smaller  quantities,  porcelain 
evaporating  dishes  are  used,  heated  by  a  water  bath. 
The  authors  distinguish  four  different  degrees  of  the  consis- 
tency of  extracts  :  1,  consistence  of  extr.  graminis,  1340  grs.  of 
which  fill  a  1000  gr.  flask  at  14°  C,  (58°  F.,)  %  consistence  of 
