Am.  Jour.  Pharm.  | 
December,   1920.  ) 
The  Theory  of  Percolation. 
871 
merely  modifications  of  Real's  apparatus.  In  this  category  belong 
the  methods  of  Wuertzer,^  Brandes,"  Beindorf,"^  Rosenwasser^, 
Berry/^  Hallberg's  peerless  percolator/^  A.  I.  Cohen, ^  and  of  B. 
S.  Procter.^ 
A  second  class  utilizes  air  pressure  applied  to  the  surface  of  the 
drug.  Pumps  of  various  kinds  are  employed  by  Semelbauer,^  in 
three  forms  of  apparatus  suggested  by  Romershausen,^'^  by  Sig- 
noret/^  Allen,  ^"^  Nunn,'"^  and  by  Lenz.^^  Marpmann,^'^  Phillips, 
and  Cowley ^'^  utilize  air  pressure  obtained  by  the  force  of  a  column  of 
liquid  acting  on  an  enclosed  volume  of  air.  The  elaborate  method 
of  Duffield,^^  Fairthorne,^'*  and  Thompson, -°  include  exhaustion  of 
the  drug,  vacuum  maceration,  and  expulsion  of  the  percolate  by 
compressed  air. 
The  third  class  accomplishes  the  pressure  by  applying  suction  to 
the  bottom  of  the  percolator.  Maben^^  employs  an  ordinary  water 
pump  or  aspirator;  Arthur'-"'  uses  an  exhausting  syringe,  and  Platt^^ 
a  Sprengel  pump. 
It  must  be  borne  in  mind  that  any  process  which  employs  pres- 
sure other  than  that  produced  by  the  natural  effect  of  gravity  upon 
the  menstruum  is  not  a  true  process  of  simple  percolation  because 
^  Rep.  der  Pharni.  7,  230,  (1S19). 
-  Ihid.    7,    234,    (1819).  • 
Mag.  filr  d.  Pharm.  9,   185,  (1826). 
This  Journal,  Vol.  53,  567,  (1881). 
This  Journal,  Vol.  55,  587,  (1883). 
6  West.  Drug.  15,  46,  (1^93);  Proc.  A.  Ph.  A.  1893.  383. 
'  Merck's  Report,  1899,  4;  Proc.  A.  Ph.  A.  1899,  383. 
^  Pharm.  Jour.  36,  641,  (1877);  This  Journal,  Vol.  49,  372,  (1877). 
Rep.  der  Pharm.  3,  88,  U817). 
Ihid.  6,  316,  (1819). 
"  This  Journal,  Vol.  33.  319,  (1861). 
^' Pharm.  Rec.  7,  6,  66,  (1887). 
^'■^  Pharm.  Jour.  1898,  981. 
Ber.  d.d.  Pharm.  Ges.  15,  137,  (1905). 
'•^  Pharm.  Centr.  29,  507,  (1888). 
Pharm.  Rec.  8,  213,  (1888). 
Pharm.  Jour.  1898,  418. 
This  Journal,  Vol.  41,  2,  (1869). 
'■'  This  Journal,  Vol.  54,  236,  (1882). 
This  Journal,  Vol.  55,  537,  (1883). 
'-'  Pharm.  Jour.  46,  941,  (1887). 
'^'^  Pharm.  Jour.  49,  850,  (1889). 
Pharm.  lira,  1892,  1  13;  Proc.  A.  Ph.  A.  1892,  403. 
