Am.  Jour.  Pharm.  ) 
December,  1920.  J 
The  Theory  of  Percolation. 
86i 
marc  on  water  introduced  below  and  Elborne^  later  advocated  the 
same  .  idea. 
As  early  as  1836,  however,  the  use  of  water  to  "displace"  alcohol 
from  marcs  was  questioned  by  Soubeiran^  who  showed  that,  con- 
trary to  the  earlier  idea,  the  displacing  water  mixes  with  the  alco- 
hol of  the  menstruum.  Indeed  it  is  doubtful  whether  much  more 
than  three-fourths  of  the  residual,  alcohol  can  be  recovered  by  this 
process,  for  the  quantity  of  water  necessary  even  to  approximate  a 
complete  washing  out  of  the  menstruum  is  impracticably  great 
and  the  last  portions  are  too  weak  in  alcohol  to  allow  economical 
handling.  The  following  case,  from  the  writer's  experience,  will 
serve  as  an  illustration.  Twelve  pounds  of  coarsely  ground  drug 
were  moistened,  packed,  and  percolated  in  the  usual  way  with 
twelve  gallons  of  diluted  alcohol.  When  the  percolator  had  drained 
the  residual  menstruum  was  displaced  with  water  and  the  issuing 
liquid  tested  from  time  to  time  for  the  presence  of  alcohol.  After 
thirty  gallons  of  water  had  passed  through  the  marc  the  next  por- 
tion of  liquid  gave  strong  evidence  of  the  presence  of  alcohol.  It 
may  be  somewhat  roughly  calculated  that,  at  the  end  of  the  per- 
colation, the  marc  contained  six  pints  of  alcohol  and  that,  therefore, 
forty  times  its  volume  of  water  was  insufficient  to  wash  it  completely 
from  the  drug  fibre.  In  addition  to  its  general  inefficiency  the  prac- 
tise of  washing  alcohol  out  with  water  is  not  applicable  to  muci- 
laginous drugs  like  senna,  buchu,  gentian,  or  rhubarb  which  form 
a  gelatinous  mass  within  the  percolator  as  soon  as  a  portion  of  the 
alcohol  has  been  rem^oved  and  this  effectually  terminates  the  pro- 
cess. 
HOT  PERCOLATION. 
It  is  usually  possible  to  hasten  the  process  of  percolation  by 
employing  a  hot  menstruum  and  several  forms  of  apparatus  have 
been  devised  for  this  purpose.  In  general  this  procedure  offers 
no  advantages  over  the  ordinary  cold  process  except  shortening  the 
time.  Hot  solvents,  too,  frequently  dissolve  substances  which  are 
insoluble  in  the  cold  solvent  and  which  are  deposited  with  more 
or  less  promptness  as  soon  as  the  percolate  reaches  the  room- 
temperature.  Alcohol,  for  instance,  dissolves  saponins,  waxes, 
hydrocarbons,  and  phytosterols  when  hot  and  deposits  them  on 
'  New  Remedies,  9,  32,3,  (1880);  from  Pluirni.  Jour. 
^  This  Journal,  Vol.  10,  221,  (1838);  from  Bui.  C,en.  dc  Thenipie. 
