ON  PERCOLATION  OR  DISPLACEMENT. 
319 
as  in  examples  where  the  proportion  is  less,  for  the  reason  that 
the  proper  capillary  action  is  interfered  with.  To  give  an  ex- 
treme example  in  illustration,  it  would  not  be  proper  or  possible 
to  displace  finely  powdered  gum  or  sugar  with  water,  or  guaiac 
or  mastic  with  alcohol ;  but  by  associating  with  these  powders  a 
a  sufficient  quantity  of  insoluble  matter  in  powder,  the  condition 
of  porosity  being  established,  the  process  would  go  on.  But 
the  range  of  fineness  should  not  be  very  great  in  small  regular 
operations ;  and  where  the  state  of  division  is  properly  attended 
to  there  need  be  no  difficulty  in  regulating  the  porosity  of  the 
mass  and  consequent  passage  of  the  liquid. 
It  is  an  excellent  custom  to  keep  a  set  of  sieves  for  the  pre- 
paration of  powders  for  this  purpose,  so  that  the  degree  of  fine- 
ness of  powders  for  percolation  can  be  easily  regulated,  and  it 
will  be  a  point  worthy  of  consideration  by  the  revising  commit- 
tee of  the  Pharmacopoeia,  whether  some  more  definite  directions 
as  regards  the  state  of  division  of  drugs  for  displacement,  cannot 
be  given  than  at  present, — Dr.  Squibb  suggests  that  a  sieve  of 
24  meshes  to  the  linear  inch  produces  a  powder  of  the  right 
fineness, — Prof.  Grahame  considers  the  range  should  be  from 
40  to  60  meshes  to  the  inch,  I  believe  the  range  should  be 
greater  to  include  large  and  small  operations,  20  to  60  meshes 
to  the  inch.  Where  the  menstruum  is  ethereal  or  alcoholic  (50  to 
95  per  cent,  in  strength,)  the  finer  powder  will  be  found  very 
suitable,  even  in  a  cylindrical  percolator,  unless  the  powder  is 
highly  resinous,  in  which  case,  either  the  powder  must  be  coarse, 
or  if  fine,  must  be  admixed  with  an  inert  powder  like  sand  to 
give  the  requisite  porosity.  When,  however,  very  dilute  alcohol 
or  water  is  used,  a  powder  40  to  the  inch  will  be  found  fine 
enough,  and  if  the  substance  is  mucilaginous,  25  to  30  meshes 
will  be  found  sufficient.  But  whatever  degree  of  division  is 
adopted  let  it  be  as  uniform  as  possible,  and  not  consist  of  fine 
cellular  tissue  mixed  with  long  coarse  fibres,  the  result  of  simple 
contusion  as  is  often  the  case.  Until  apothecaries  will  con- 
scientiously assume  this  trouble  and  care,  they  will  not  be  able 
to  derive  the  beautiful  and  satisfactory  results  from  this  process, 
which  it  so  abundantly  affords. 
This  brings  us  to  the  second  stage  of  the  process,  viz.,  the 
manner  of  packing  the  material  in  the  apparatus,  as  regards  its 
