Am.  Jour.  Pharm.  \ 
November,  1920.  j 
The  Theory  of  Percolation. 
777 
was  also  advocated  by  Graham ^  and  Cohen. ^  Squibb,^  Parrish/ 
Lloyd,^  and  Remington,^  have  considered  the  more  cyHndrical  shapes 
superior  to  the  funnel  and  have  discountenanced  the  use  of  the  latter 
except  for  dilute  preparations  such  as  tinctures  and  wines. 
There  is  one  factor  in  this  connection  which  has  not  been  investi- 
gated and,  indeed,  which  has  too  often  been  neglected  in  studies  on 
extraction.  That  is  the  time  factor.  It  is  obvious  that  a  given 
volume  of  menstruum  will  pass  through  a  drug  packed  in  a  funnel 
much  more  rapidly  than  it  will  pass  through  the  same  amount 
of  drug  packed  in  a  long,  narrow  percolator.  Under  such  con- 
ditions we  cannot  expect  the  percolate  from  the  funnel  to  contain 
as  large  a  proportion  of  dissolved  matter  as  that  from  the  less  tapered 
vessel,  but  we  do  not  know  what  the  relation  between  equal  quanti- 
ties of  percolate  from  the  two  or  three  forms  would  be  if  the  flow 
from  the  funnel  were  retarded  to  the  same  rate  as  that  from  the 
other  apparatus,  both  delivering  the  same  volume  of  percolate  in  the 
same  time.  Inasmuch  as,  within  certain  limits,  the  concentration 
of  the  first  portions  of  percolate  depend  upon  the  length  of  time  the 
menstruum  has  been  in  contact  with  the  drug,  the  time  factor  is  of 
great  importance  in  comparing  such  percolators  as  these  and,  on  ac- 
count of  the  neglect  of  it,  the  whole  subject  demands  further  inves- 
tigation. 
In  the  hands  of  the  inexpert  or  the  careless  operator  the  Oldberg 
or  nearly  cylindrical  percolator  will  doubtless  give  more  uniform  re- 
sults and  a  more  concentrated  first  percolate  such  as  is  used  for  the 
reserved  portion  in  the  manufacture  of  fluidextracts.  The  conical 
form  will  prove  nearly  as  efficient  and  has  the  advantage  of  being 
more  easily  unpacked. 
Modifications  of  these  three  shapes  have  been  introduced  from 
time  to  time  to  adapt  them  to  special  purposes.  Many  forms  of 
closed  percolators  have  been  described  for  use  with  volatile  solvents 
such  as  ether,  chloroform,  benzine,  or  acetone,  designed  especially 
to  minimize  loss  of  the  solvent  through  evaporation.  Gilbertson's 
apparatus^  was  one  of  the  first  of  these  and  it  is  very  compact  and 
^  This  Journal,  Vol.  31,  354,  (1859). 
2  This  Journal,  VoL  44,  8,  (1872). 
3  This  Journal,  Vol.  38,  109,  (1866). 
*  This  Journal,  Vol.  31,  327,  (1859). 
1^  Proc.  A.  Ph.  A.  1877,  405. 
•  Drug.  Circ.  1884,  148. 
T  Pharm.  Jour,  i,  591,  (1842). 
