872 
The  Theory  of  Percolation. 
(  Am.  Jour.  Pharm. 
\     December,  1920. 
the  relationships  between  the  drug,  absorbed  menstruum,  and  the 
precolate  are  upset  when  the  precolate  is  driven  through  the  drug. 
If  a  drug  is  suitable  for  extraction  by  simple  percolation,  then  a 
proper  regard  for  the  conditions  of  fineness  of  powder,  moistening, 
packing,  and  choice  of  menstruum  will  be  sufficient  to  ensure  suc- 
cess without  any  resort  to  external  force.  As  I  have  shown  above, 
the  idea  that  the  precolate  may  be  hastened  through  the  drug  is 
based  upon  erroneous  notions  of  the  principles  of  percolation.  The 
ideal  condition  is  such  a  one  that  the  menstruum  is  in  contact  with 
the  drug  just  long  enough  to  establish  equilibrium  between  the 
factors  present  before  the  liquid  drops  through  the  orifice.  This 
equilibrium  is  not  established  in  any  short  period  of  time  and,  con- 
sequently, any  process  which  does  not  take  this  idea  into  considera- 
tion is  open  to  pharmaceutical  objection.  These  complex  forms 
of  apparatus  have  uniformly  been  rejected  by  pharmacists  and  the 
simple  percolator  still  is  to  be  seen  in  every  establishment  where 
drugs  are  extracted. 
MISCBLLANKOUS  PROCKSSKS  AND  APPARATUS. 
The  following  contains  a  brief  chronological  account  of  a  num- 
ber of  processes  for  percolating  drugs  and  making  fluidextracts  with 
an  indication  of  the  essential  feature  of  each. 
The  well-tube  percolator  of  Squibb  has  already  been  described. 
The  same  idea  is  used  in  a  percolator  made  of  "Appert"  glass. ^ 
Squibb  has  also  described^  an  "automatic"  percolator  the  chief 
feature  of  which  is  an  ingenious  method  for  the  automatic  addition 
of  menstruum  to  the  drug. 
In  1858  appeared  Bashford's  Compound  Percolator  which  is 
provided  with  an  outside  jacket  so  that  it  may  be  operated  to  allow 
hot  percolation.^ 
N.  S.  Thomas^  in  1865  obtained  a  patent  for  a  method  of  prepar- 
ing fluidextracts  which  consists  in  moistening  the  drug  with  suc- 
cessive portions  of  the  menstruum,  macerating,  and  pressing  out 
in  a  tincture  press  after  each  addition.  The  operation  is  continued 
until  the  amount  of  liquid  pressed  out  is  equal  in  volume  to  the 
fluidextract  which  the  given  amount  of  drug  should  furnish.  Squibb^ 
says  the  process  is  an  old  one. 
^  Remington,  "Practice  of  Pharmacy,"  1907,  375. 
2  This  Journal,  Vol.  30,  97,  (1858). 
3  This  Journal,  Vol.  30,  81,  (1858);  from  the  San  Francisco  Bulletin. 
'  This  Journal,  Vol.  37,  81,  (1865). 
5  This  Journal,  Vol.  37,  182,  (1865). 
