314  Acetic  Acid  in  Extracting  Drugs.     { Am- jjg^f rm- 
of  the  test-tube  has  five  small  holes  that  cannot  be  shown,  and  a 
small  rubber  band  is  better  to  hold  the  syphon  in  place  than  the 
wedge  as  shown.  The  apparatus  is  easily  made  up  from  laboratory 
materials  by  any  fairly  expert  glass-worker,  though  it  may  be 
cheaper  to  pay  Greiner  a  dollar  and  a  half  for  it.  It  is  simply  a 
modification  on  a  small  scale  of  the  writer's  syphon  percolator,  now 
so  many  years  in  successful  use,  in  all  sizes  up  to  100  gallons  (see 
Proceedings  of  the  Amer.  Pharm.  Assoc.  for  1872).  It  is  the  best 
form  of  percolator  because  it  best  applies  the  mechanical  conditions 
requisite  for  complete  exhaustion.  That  is,  the  whole  mass  of  powder 
to  be  extracted  is,  from  first  to  last,  kept  completely  filled,  inside 
the  particles  and  between  them,  with  the  extracting  menstruum  and 
counterbalanced  to  an  equilibrium  by  liquid  that  has  already  passed 
through  the  saturated  powder.  The  syphon  draws  off  the  liquid 
from  near  the  surface  of  this  outer  column  at  a  rate  controlled  by 
the  depth  to  which  the  end  is  immersed,  and  by  the  head  of  men- 
struum supplied  to  the  powder  on  top.  The  inverted  bottle  of 
menstruum  supplies  a  nearly  continuous  feed  from  a  nearly  constant 
level.  The  whole  mass  being  full  of  liquid,  the  outside  column 
nearly  level  with  the  inside  supply,  the  syphon  is  filled,  put  in  place 
and  held  in  position,  where  by  raising  or  lowering  it  is  made  to 
deliver  from  three  to  five  drops  per  minute.  Now,  in  this  position 
the  laws  of  hydrostatics  require  that  the  first  drop  that  falls  from 
the  syphon  sets  the  whole  mass  of  liquid  in  motion,  but  with  such 
extreme  slowness  in  the  powder  that  friction  is  reduced  to  a  mini- 
mum, and  the  liquid  in  the  particles  descends  at  a  rate  approaching 
that  between  the  particles,  thus  securing  a  displacement  of  the  solu- 
ble parts  of  the  powder  with  the  least  obstruction  from  the  insoluble 
parts.  If  the  rate  of  descent  could  be  made  so  slow  as  to  eliminate 
friction,  then  each  stratum  of  solvent  liquid  would  descend  as  a 
piston  and  complete  exhaustion  would  be  attained  with  the  smallest 
quantity  of  solvent. 
Ten  grammes  of  the  powdered  cinchona  in  a  capacious  capsule  is 
moistened  with  10  c.c.  of  10  per  cent,  acetic  acid,  the  lumps  all  well 
broken  up,  the  moist  powder  packed  firmly  in  some  form  of  perco- 
lator and  percolated  to  complete  exhaustion  with  10  percent,  acetic 
acid.  If  this  exhaustion  be  done  in  the  extractor  figured  above, 
about  thirty-six  hours'  time  will  be  required  and  the  percolate  will 
measure  180  to  200  c.c.    The  degree  of  exhaustion  is  judged  by  the 
