Am.  Jour.  Pharm.  ) 
November,  1920.  ) 
The  Theory  of  Percolation. 
779 
uncleanly,  heavy,  and  not  strong  enough  to  withstand  the  great 
pressure  developed  by  a  swelling  drug  unless  reinforced  by  many  iron 
hoops. 
THK  DRUG  AND  ITS  PREPARATION  I^OR  PKRCOI^ATlON. 
Plant  drugs  may  be  classified  in  a  variety  of  ways  but,  for  our  pur- 
poses, their  behavior  toward  solvents  is  the  criterion  of  their  relation- 
ships. From  this  point  of  view  we  may  propose  the  following  classi- 
fication. I.  Resinous  drugs,  cimicifuga,  cannabis,  balm  of  gilead, 
whose  active  principles  are  usually  extracted  only  by  strong  alcohol. 
II.  Terpene  drugs,  peppermint,  buchu,  thyme,  whose  active  principle 
is  a  terpene  or  a  terpene  derivative  demanding  a  menstruum  rich  in 
alcohol-  III.  Alkaloidal  drugs,  gelsemium,  nuxvomica,  belladonna; 
the  menstruum  depends  upon  the  individual  solubility  of  the  alka- 
loid and  the  condition  in  which  it  exists  in  the  plant.  In  general 
strong  alcohol  is  needed  for  those  plants  which  contain  free  alkaloids ; 
dilute  alcohhol  is  employed  where  the  alkaloid  exists  as  a  salt.  Acid 
menstrua  are  often  employed  in  the  extraction  of  this  class  of  drugs, 
e.g.,  ergot,  lobelia,  sanguinaria.  IV.  Glucosidal  drugs.  The  solu- 
bilities of  the  glucosides  vary  widely  from  insolubility  to  free  solu- 
bility in  water  and  dilute  alcohol.  Menstrua  employed  for  this  class 
vary  from  water  in  the  case  of  cascara  to  alcohol  for  strophanthus. 
The  majority  of  them  may,  however,  be  extracted  with  dilute  alcohol. 
V.  Oleoresinous  drugs.  Pepper,  parsley,  aspidium.  These  drugs 
are  extracted  with  ether  or  the  less  expensive  acetone,  for  the  loss  of 
solvent  through  evaporation  may  be  quite  large  in  spite  of  precau- 
tions. VI.  Tannin- containing  drugs.  Kino,  rubus,  krameria.  These 
drugs  are  extractible  with  water.  However,  aqueous  solutions  of  their 
extracts  are  apt  to  gelatinize  so  the  drugs  are  extracted  with  menstrua 
containing  alcohol  and  glycerin  is  added  to  the  first  portions  of  per- 
colate. Sometimes  glycerin  is  used  in  the  menstruum.  VII.  Sa- 
ponin drugs,  quillaja,  sarsaparilla,  squills,  senega.  The  saponins 
are  soluble  in  water  and  insoluble  in  cold  alcohol.  The  menstruum 
usually  used  is  diluted  alcohol,  the  alcohol  being  employed  as  a  pre- 
servative. Diluted  acetic  acid  is  of  course,  a  favorite  menstruum 
for  squills.  VIII.  Mucilaginous  drugs.  A.  Elm,  chondrus;  B. 
senna,  uva  ursi.  These  drugs  are  extracted  in  two  ways  according 
whether  the  mucilage  is  desired  or  not.  A.  Where  the  mucilaginous 
substance  is  to  be  extracted  the  drug  is  treated  with  hot  water  but  is 
not  usually  percolated.    B.  If  the  mucilage  is  undesirable  in  the 
