Am.  Jour.  Pharm. ) 
November,  1920.  ) 
The  Theory  of  Percolation. 
powder.^  CampbelP  recommends  a  No.  40  powder.  Lloyd^ 
showed  mathematically  the  probability  of  greater  efficiency  in  ex- 
traction the  finer  the  drug  powder  and  Rosen wasser'^  developed  the 
same  conclusion.    The  following  figures^  for  the  yield  of  extract  by 
Menstruum.  Coarse  Powder.  Fine  Powder. 
Cold  water  32  . 94-39  •  82  per  cent.  35  . 25-35  •  42  per  cent. 
Boiling  water  40 . 19-41  22        "  38 . 68-38 .91  " 
Dilute  alcohol  38.57-41-3         "  40.3 
68  per  cent.  al.  36  32-39. 31       "  39.1  " 
maceration  of  gentian  of  different  fineness  and  with  various  menstrua 
show  a  difference:  FeiP  reported  31,5  per  cent,  extract  from  gentian 
by  percolation.  The  figures  in  the  above  table  show  more  uniform 
results  in  extract  yield  from  the  finely  powdered  drug  yet  with 
every  menstruum  the  coarse  drug  yielded  more  extract  than  the 
fine  which  is  quite  contrary  to  expectation. 
In  considering  the  differences  in  different  degrees  of  fineness  the 
time  factor  has  again  always  been  neglected.  Any  menstruum  will 
pass  more  quickly  through  a  coarse  drug  than  through  one  that  is 
finely  powdered  and  is,  therefore,  in  contact  with  the  drug  and  able 
to  exert  its  solvent  action  for  a  much  shorter  period  of  time.  In  my 
own  experience  I  have  known  two  weeks  to  elapse  after  flooding  a 
percolator  which  contained  83  pounds  of  gentian  in  No.  60  powder 
before  the  percolate  appeared.  There  is  need  of  some  careful  in- 
vestigation to  furnish  data  in  which  all  the  factors  are  included. 
The  results  quoted  above  were  obtained  by  maceration  so  that  the 
time-contact  factor  is  eliminated  from  the  figures  and  they  show  a 
slight  favor  towards  the  coarse  drug.  If  this  time-contact  factor 
were  eliminated  in  percolating  powders  of  the  same  drug  of  different 
degrees  of  fineness,  by  commencing  the  percolations  after  the  same 
elapse  of  time  after  packing  and  adjusting  the  rate  of  flow  of  perco- 
late to  the  same  volume  per  hour  for  all  cases  the  results  furnished 
would  contain  no  interfering  factor  and  such  data  would  serve  as 
a  basis  for  really  valuable  conclusions  upon  the  relative  merits  of 
different  degrees  of  fineness. 
1  This  Journal,  Vol.  36,  i,  (1864). 
2  This  Journal,  Vol.  41,  384,  (1869). 
3  Proc.  A.  Ph.  A.  1879,  682. 
4  Proc.  A.  Ph.  A.  1882,  519. 
6  Proc.  A.  Ph.  A.  1906,  746. 
^  Proc.  A.  Ph.  A.  1906,  433. 
