776 
The  Theory  of  Percolation. 
( Am.  Jour.  Pharm. 
\    November,  1920. 
drug,  as  in  the  manufacture  of  several  gallons  of  a  fluidextract,  the 
difficulty  in  unpacking  a  narrow,  slightly  tapering  percolator  is  so 
great  that  the  conical  shape  is  used  almost  exclusively  in  such  opera- 
tions although  its  diameter  is  very  much  larger  in  proportion  to  its 
capacity.  For  such  purposes  a  percolator  as  designed  by  A.  B. 
Taylor^  where  the  length  is  twice  the  largest  and  four  times  the  small- 
est diameter  will  serve  excellently. 
The  use  of  the  funnel  shaped  percolator  has  provoked  much  dis- 
cussion. The  diameter  of  the  percolator  changes  so  greatly  from  the 
bottom  upwards  that  the  topmost  layers  of  drug,  which  receive  the 
fresh  menstruum,  are  in  contact  with  a  much  smaller  amount  per  unit 
weight  than  the  lower  layers.  The  lower  layers  are  acted  upon  by 
the  most  saturated  menstruum  the  solvent  powers  of  which  are  less 
than  those  of  the  fresh  menstruum  and,  in  the  funnel  percolator,  the 
effect  of  the  narrowing  diameter  is  to  force  this  partly  saturated 
menstruum  into  longer  contact  with  the  drug  than  is  the  case  higher 
up.  The  result  is  that,  as  the  menstruum  becomes  laden  with  ex- 
tractive and  consequently  weaker  in  solvent  powers,  it  is  forced  to 
lie  in  contact  with  unit  weight  of  drug  for  a  longer  time  and  this  effect 
is  distributed  throughout  the  percolator  in  proportion  to  the  diam- 
eter. The  great  advantage  of  the  funnel  percolator  has  been  con- 
sidered to  be  the  fact  that  its  taper  will  permit  a  drug  which  swells 
much  during  percolation  to  push  its  way  upward  instead  of  packing 
very  firmly  in  the  percolator  as  will  happen  in  percolators  of  slight 
taper. 
Campbell  used  the  funnel  percolator  in  his  method  for  the  prep- 
aration of  fluidextracts  without  heat^  which  was  approved  by  A.  B. 
Taylor^  and  Kennedy, although  Reynolds,^  King,®  and  Archibald'^ 
were  unable  to  exhaust  the  drug  thoroughly  with  the  small  quantity 
of  menstruum  permitted  by  Campbell's  process.  Taylor's  experi- 
ments showed,  however,  that  a  very  concentrated  first  percolate 
could  be  obtained  with  a  funnel  percolator  if  four  days  were  allowed 
for  the  preliminary  maceration.    The  use  of  this  type  of  apparatus 
^  Proc.  A.  Ph.  A.  1869,  390. 
2  This  Journal,  Vol.  41,  384,  (1869);  Vol.  42,  17,  (1870). 
^  Proc.  A.  Ph.  A.  1869,  390.    This.  Journal,  Vol.  42,  150,  (1870). 
^  This  Journal,  Vol.  42,  62,  (1870).    .  . 
^  This  Journal,  Vol.  41,  525,  (1869).  ,  .... 
'This  Journal,  Vol.  42,  29,  (1870).  .  . 
This  Journal,  Vol.  42,  117,  (1870). 
