THE  PROCESS  OF  PERCOLATION  OR  DISPLACEMENT.  357 
Contrary  to  the  prescribed  rules  in  this  particular,  my  plan 
is  to  add  just  sufficient  of  the  solvent  to  dampen  the  powder, 
scarcely  destroying  its  pulverulent  condition,  regardless  whether 
the  substance  be  liable  to  much  swelling  on  imbibing  the  liquid, 
or  not  ;  the  object  being  to  enable  it  to  pack  properly,  and  at 
the  same  time  to  contain  sufficient  moisture  to  produce  capillary 
attraction  to  conduct  the  liquid ;  by  which  means  the  fluid  with 
which  the  powder  was  moistened,  on  the  subsequent  addition  of 
the  menstruum  to  the  packed  powder  in  the  percolator,  is  driven 
forward  very  highly  charged  with  soluble  matter,  and  escapes  at 
once,  perfectly  dear,  followed  in  regular  and  uniform  succession 
by  liquid  more  or  less  strong  as  it  advances  ;  and  in  a  compara- 
tively short  time — frequently  several  hours  less  than  is  directed 
for  previous  maceration  by  the  Pharmacopoeia — the  powder  will 
be  left  in  the  displacer  completely  exhausted  of  its  soluble  mat- 
ter. 
By  this  means  highly  concentrated  solutions  are  obtained — 
an  advantage  gained  by  this  small  addition  of  liquid  to  the  pow- 
der at  first,  in  connection  with  the  manner  of  packing,  which 
will  be  referred  to  presently — and  may  be  explained  thus :  the 
quantity  of  liquid  absorbed  being  minute,  on  the  subsequent 
addition  of  the  menstruum  it  is  displaced,  and  other  particles 
becoming  saturated  in  quick  succession,  dispose  the  substance 
to  yield  up  its  soluble  matter  to  the  least  possible  amount  of 
solvent.  The  liquid,  by  this  means  of  treatment,  having  per- 
meated the  particles  of  the  mass,  without  having  had  any  of  the 
particles  diffused  or  suspended  in  it,  will  necessarily  escape  from 
the  instrument  perfectly  clear,  as  already  stated,  and  almost  of 
a  syrupy  consistence  ;  and,  for  obvious  reasons,  should  not  be 
returned  to  the  mass,  as  is  frequently  requisite  when  the  usual 
manner  of  previous  maceration  is  resorted  to. 
The  manner  of  adding  the  liquid  may  be  worthy  of  some 
notice.  I  found  it  best  to  distribute  the  liquid  over  the  powder 
in  portions,  the  quantity  generally  not  more  than  one  fourth  of 
the  substance  under  treatment,  frequently  less,  especiilly  with 
such  substances  as  rhubarb,  gentian,  &c,  and  with  my  fingers 
or  whole  hand,  according  to  the  quantity,  rub  it  through  the 
powder  uniformly,  the  state  of  this  being  the  guide  for  the  pro- 
per quantity,  which  should  never  be  sufficient  to  produce  a  soft 
