Am.  Jour.  Pharm.  \ 
July, 1883.  J 
Faots  Concerning  Filtration. 
351 
my  opinion,  the  most  suitable ;  for  larger  sizes  the  French  stout  plaited 
or  plain  papers,  taken  in  all  their  qualities,  give  the  best  results.  The 
Prench  also  make  a  paper  specially  suitable  for  syrups,  thick  to  sup- 
port the  weight,  and  yet  sufficiently  pervious  to  allow  of  fairly  rapid 
filtration.  I  find,  however,  in  very  large  sizes,  a  double  sheet  of 
Khenish  paper  in  an  inverted  case  of  linen,  as  already  described, 
answers  even  better. 
Some  fabrics,  such  as  swansdown,  close  textured  twilled  calico,  etc., 
filter  as  brightly  as  paper  does,  and  may  be  used  for  that  purpose  as 
distinct  from  ordinary  straining,  provided  the  solid  particles  separate 
from  the  liquid  in  which  they  are  suspended  with  ease,  but  when  this 
is  not  the  case  they  are  of  much  less  value ;  indeed,  with  paper  as  a 
medium,  slimy  deposits  present  considerable  difficulty.  Pepsin  wine, 
prepared  from  the  fresh,  undried  pepsin,  might  be  regarded  as  typical 
•of  this  class  of  liquids ;  the  tendency  being  to  choke  ^up  the  pores  of 
the  filter  almost  immediately  the  operation  commences.  In  such  cases 
some  kind  of  coarse  straining  material  placed  within  the  paper  cone 
helps  materially  to  obviate  the  difficulty.  Hair  cloth  and  thin  coarse 
flannel  answer  well  for  this  purpose ;  they  operate  by  collecting  on 
their  rough  projecting  surfaces  the  larger  proportion  of  the  undissolved 
slimy  matter,  without  becoming  sufficiently  choked  up  to  materially 
impede  the  progress  of  the  operation. 
Succus  taraxaci,  as  expressed  from  the  root  and  mixed  with  spirit 
according  to  the  B.  P.  instructions,  is  typical  of  a  ^class  containing  a 
large  quantity  of  starchy  matter  and  where  subsidence  in  a  closed  vessel 
previous  to  filtration  is  of  great  service.  The  liquor  from  poppy 
capsules,  in  the  process  of  preparing  syrupus  papaveris  alb.,  furnishes 
us  with  an  example  of  a  liquid  containing  a  large  quantity  of  albumin- 
ous matter  and  mucilage  which,  when  coagulated  by  spirit,  has  to  be 
filtered  ofi",  and  here  again  subsidence  in  a  closed  vessel  helps  the  sepa- 
ration materially.  The  greater  portion  of  the  liquor  can,  after  a  time, 
be  poured  almost  bright  into  the  filter,  and  the  remaining  soft  mass 
can  with  care  be  slowly  pressed  almost  dry ;  the  chief  difficulty  in  this 
latter  operation  being  to  press  sufficiently  slowly  to  separate  the  liquid 
from  the  solid,  and  yet  not  to  expose  it  to  the  air  long  enough  to  lose 
much  spirit  by  evaporation,  as  in  that  case  some  of  the  solid  portion 
would  be  again  taken  up  in  imperfect  solution. 
For  removing  suspended  particles  from  strong  acids,  spun  glass, 
known  as    glass  wool,'^  answers  best,  but  this  might  be  regarded  as 
