78o 
The  Theory  of  Percolation. 
(  Am.  Jour.  Pharm. 
(    November,  1920. 
product  the  drug  is  extracted  with  an  alcoholic  menstruum  in  which 
the  mucilage  is  insoluble.  In  such  cases  the  drug  may  be  placed  in 
another  classification,  senna  in  class  IV  and  uva  ursi  in  class  II.  IX. 
Acid  drugs.  Licorice,  triticum,  zea  mays,  mostly  extractible  with 
water,  more  easily  with  alkaline  menstrua.  Licorice  is  extracted  with 
dilute  ammonia.  Rhubarb  may  be  extracted  with  water  but  its  con- 
tent of  mucilage  presents  practical  difficulties  so  that  dilute  alcohol 
is  usually  employed.  X.  Miscellaneous  drugs,  requiring  special 
treatment  on  account  of  individual  peculiarities,  prunus  virgiana, 
gentian,  quassia. 
The  class  to  which  a  drug  is  to  be  referred,  then,  will  depend  upon 
the  nature  and  solubility  of  its  active  principle  modified  by  the  solu- 
bilities of  undesirable  ingredients  which  the  plant  may  contain  or  by 
the  exigencies  of  preserving  the  product.  This  classification  is  thus 
strictly  pharmaceutical  and  very  different  from  botanical  or  thera- 
peutical systems.  Drugs  exhibit,  however,  such  individualities  that 
it  is  difficult  to  draw  many  generalizations  about  them. 
This  point  is  particularly  true  in  the  preparation  of  drugs  for  per- 
colation. Squibb  remarked^  that  the  process  of  percolation  differs 
materially  with  every  drug  and  every  menstruum  used.  The  master 
of  percolation  varies  the  details  of  his  process  from  beginning  to  end 
to  suit  the  characteristics  of  the  drug. 
The  extraction  of  a  drug  properly  begins  with  the  grinding  of  the 
crude  material,  proceeds  through  its  moistening,  maceration,  packing 
and  the  actual  percolation  to  the  emptying  of  the  exhausted  marc  into 
the  dreg  still.  As  all  these  steps  are  of  considerable  importance  the 
following  pages  will  bear  a  detailed  discussion  of  each  in  order. 
The  fineness  of  the  drug,  that  is  the  degree  of  comminution  or  the 
size  of  its  particles,  is  a  factor  upon  which  depends,  in  no  small  mea- 
sure, the  success  of  percolation.  Little  has  been  published  on  this 
subject  and  that  has  been  largely  opinion  based  on  practical  experience 
and  not  upon  critical  experiment.  The  general  agreement  is  that  the 
finer  the  drug  powder,  the  more  efficient  the  extraction  and  the 
pharmacopoeia  revels  in  number  sixty  powders.  Squibb ^  thought 
a  number  24  powder  fine  enough  and  Procter^  allowed  as  coarse  pow- 
der as  Nos.  25  to  30  for  mucilaginous  drugs  but  preferred  a  fine 
^  Proc.  A.  Ph.  A.  1869,  305. 
2  This  Journal,  Vol.  30,  97,  (1858).  ; 
2  This  Journal,  Vol.  31,  317,  (1859). 
