Am.  Jour.  Pharm.  ) 
November,  1920.  ) 
The  Theory  of  Percolation. 
789 
tion  produces  a  much  more  saturated  first  percolate.  Taylor^  pub- 
lished figures  showing  the  effect  of  maceration  on  yellow  cinchona 
using  four  troy  ounces  of  drug  and  a  menstruum  of  diluted  alcohol. 
He  macerated  individual  samples  for  one-half  hour,  forty-eight  hours, 
and  four  days  and  his  results  are  plotted  in  Chart.  A.  This  shows 
clearly  the  increased  concentration  due  to  maceration  and  the  rapid- 
ity of  exhaustion  after  it.  By  two  days'  maceration  he  was  able  to 
extract  as  much  in  20  fluidounces  as  were  extracted  in  100  fl.  oz. 
after  the  half  hour's  maceration;  and  12  fl.  oz.  of  percolate  from  the 
four  day  experiment  contained  slightly  more  extract.  Robbins' 
experiments  show  the  same  effect.  ^  Kdel  also  advocated  lengthy 
maceration.^  The  following  figures  were  obtained  by  the  writer: 
the  first  drippings  from  the  percolator  were  collected  and  analyzed, 
the  apparatus  was  closed  and  allowed  to  macerate  and  the  first  100 
mils  of  percolate  collected  after  the  maceration  was  completed. 
Poke  root  gave  16.14  Gm.  of  dry  extract  per  100  mils  of  first  drippings; 
after  three  days'  maceration,  18.888  Gm.  Passiflora  gave  13.636  Gm. 
of  extract  per  100  mils  of  first  drippings;  after  five  days'  maceration 
15.44  Gm. 
The  optimum  length  of  maceration  does  not  seem  to  have  been 
investigated.  The  increase  in  extract  content  is  not,  apparently, 
proportional  to  the  time  of  maceration  but  diminishes  as  time  pro- 
ceeds. The  equilibrium  point  would  probably  not  be  reached  for 
weeks  or  even  months.  It  becomes,  then,  a  question  of  judgment  to 
decide  when  the  gain  in  extract  becomes  too  small  to  justify  the  ex- 
penditure of  time  and  this  must  be  decided  by  each  operator  for  him- 
self. 
At  the  end  of  the  period  of  maceration  the  stopcock  of  the  perco- 
lator is  opened  and  the  collection  of  the  percolate  begins.  At  this 
point  we  have  in  the  percolator  three  distinct  phases, the  partly  ex- 
hausted drug,  the  absorbed  menstruum,  wetting  the  drug  with  what- 
ever extractive  that  menstruum  has  dissolved,  and  the  precolate  or 
partly  saturated  menstruum  distinct  from  that  which  has  been 
absorbed  by  the  drug.  Outside  the  percolator  we  have  a  fourth 
phase,  the  percolate. 
The  absorbed  menstruum  may  claim  our  immediate  attention. 
1  Proc.  A.  Ph.  A.  1869,  390. 
2  This  Journal,  Vol.  50,  329,  (1878). 
3  West.  Drug.   1893,  218. 
^  This  term  is  not  used  in  the  physico-chemical  sense. 
