76 
Pharmaceutical  Use  of  Filter  Press.  J°ur-  pharm- 
3  .February,  19 17. 
paper  used  should  be  of  good  quality  and  fine  weave.  Fine  gray 
filter  paper  answers  well.  It  is  of  the  highest  importance  that  cloth 
and  paper  fit  well  and  lie  smoothly  on  the  plates ;  wrinkles  and  up- 
turned corners  prevent  the  proper  closing  of  the  press  and  furnish 
channels  for  the  escape  of  liquid.  It  is  also  important  that  the  press 
be  closed  as  tightly  as  possible  to  prevent  spurting  from  the 
chambers. 
During  the  filtration  the  chambers  become  filled  with  a  mixture 
of  filtering  agent  and  precipitate :  in  most  cases  it  is  possible  to  add 
just  sufficient  talc  or  kieselguhr  to  the  liquids  to  fill  the  chambers 
as  the  last  of  the  liquid  enters  and  this  can  be  determined  by  experi- 
ment; however,  should  the  chambers  fill  before  the  liquid  is  all 
through,  the  press  should  be  drained  by  pumping  air  into  it  and  then 
should  be  cleaned  and  readjusted. 
The  amount  of  material  left  in  the  chamber  after  filtration  de- 
pends largely  upon  the  nature  of  the  filtering  agent  used.  We  em- 
ploy kieselguhr  almost  exclusively,  for  reasons  given  below,  and  find 
that  each  chamber  when  filled  under  pressure  will  hold  18  ounces 
(av.)  of  dry  kieselguhr  which  will  absorb  and  hold  28  ounces  (av.) 
of  liquid.    We  have  no  figures  for  other  agents. 
The  absorption  of  liquid,  as  we  stated  above,  constitutes  one  of 
the  disadvantages  of  the  filter  press  and  yet  it  is  no  larger,  for  a 
given  volume  of  liquid,  than  the  absorption  in  ordinary  gravity  filtra- 
tion. The  absorbed  liquid  may  be  recovered  by  pumping  a  small 
quantity  of  water  through  the  press,  but  that  method  involves  phar- 
maceutical difficulties.  We  drain  the  press  by  pumping  air  into  it, 
thereby  forcing  a  large  quantity  of  the  absorbed  material  out ;  that 
which  remains  behind  is  lost. 
It  may  be  said  that  every  liquid  to  be  filtered  presents  a  new 
problem  and  requires  individual  treatment  but,  for  practical  pur- 
poses, we  can  divide  preparations  into  four  classes,  three  of  which 
depend  upon  the  viscosity  of  the  liquid  which,  in  turn,  depends  upon 
the  nature  of  the  ingredients  present  and  the  character  and  amount 
of  precipitation. 
The  least  troublesome  class  of  liquids  comprises  the  very  fluid 
elixirs  and  solutions,  such  as  simple  elixir,  essence  of  pepsin,  elixir 
of  iron,  quinine,  and  strychnine  phosphates,  and  the  various  elixirs 
of  "lactated"  pepsin.  These  preparations  commonly  filter  rapidly 
without  elevation  of  pressure  and  with  little  decrease  in  the  rate  of 
filtration. 
