XvSer^'Y^iS:}         The  Theory  of  Percolation.  785 
unless  it  is  a  better  solvent  than  either  alcohol  or  water  as  it  "inter- 
feres with  percolation." 
Beringer^  has  devoted  much  attention  to  the  use  of  glycerin  as  a 
solvent  and  preservative.  As  a  result  of  his  work  a  new  class  of  offi- 
cial preparations,  the  fluidgly cerates,  has  been  introduced.  Ripp- 
toe^  has  shown  that  the  fluidglycerates  of  digitalis  and  ergot  are 
very  much  less  active  physiologically  than  the  corresponding  fluid 
extracts. 
When  the  menstruum  has  been  decided  upon  the  drug  is  moistened 
with  a  portion  of  it  and  allowed  to  stand  several  hours  to  swell.  This 
is  done  for  practical  reasons,  viz.,  to  assist  in  packing,  to  allow  a  modi- 
fication of  the  conditions  of  the  drug  constituents,  and  to  insure  the 
saturation  of  every  particle  of  drug  with  menstruum  so  that  the  ac- 
tual percolation  may  affect  all  the  drug  evenly.  Some  drugs  need 
not  be  moistened,^  as  cimicifuga,  cubebs  and  resinous  or  oleoresinous 
drugs  which  are  extracted  with  alcohol,  ether,  chloroform,  or  petro- 
leum ether  and  similar  solvents  and  consequently  do  not  swell  in  the 
percolator  nor  yield  a  viscous  percolate.  I  believe,  however,  that  it 
is  better  to  moisten  a  drug  before  packing  in  all  cases  where  it  is 
practically  and  economically  convenient. 
A  dry  drug  cannot  be  packed  as  evenly  nor  as  firmly  as  one  that 
has  been  moistened  and,  with  uneven  packing,  the  operator  is  doomed 
to  get  irregular  extraction  with  probable  incomplete  exhaustion. 
With  certain  drugs  it  is  often  desirable  to  modify  the  nature  of  the 
conditions  in  which  the  constituents  exist.  Alkaloidal  drugs  are 
often  extracted  with  acid  menstrua  to  increase  the  solubility  of  the 
bases  and  their  rates  of  extraction.  At  other  times  it  is  desired  to 
carry  out  the  percolation  in  an  alkaline  medium,  or  perhaps,  an  alka- 
loid which  exists  as  a  salt  in  the  plant  is  to  be  extracted  with  a  men- 
struum, like  benzol,  in  which  the  free  alkaloid,  but  not  its  salt,  is 
soluble.  Or  some  treatment  is  required  to  render  insoluble  or  to  de- 
stroy an  undesirable  constituent  as  in  the  case  of  cascara  sagrada. 
In  such  cases  it  is  usually  best  to  make  the  modification  at  the 
time  the  diug  is  being  moistened.  Thus  the  quantity  of  acid,  diluted 
with  a  portion  of  menstruum,  is  added  all  at  once  to  the  drug  and 
evenly  distributed  through  it.  With  ergot,  lobelia,  ipecac,  etc., 
this  is  a  stock  method.    In  making  alkaline  a  drug  which  is  to  be 
^  This  Journal,  Vol.  79,410,  (1907);  Vol.  80,  525,  (1908);  Vol,  81,475,  (1909). 
2  This  Journal,  Vol.  81,  84,  (1909). 
'  This  Journal,  Vol.  31,  317,  (1859). 
