Am  jour.  Pharm.)    Pharmaceutical  Use  of  Filter  Press. 
February,  19 17.    >  J 
77 
More  viscous  liquids,  such  as  heavy  elixirs,  light  syrups,  solu- 
tions of  resinous  drugs,  or  preparations  which  contain  large  amounts 
of  glycerin  or  pepsin,  filter  more  slowly  and  require  from  twenty  to 
eighty  pounds  pressure  per  square  inch.  Successful  manipulation 
of  this  class  of  liquids  depends  upon  judicious  use  of  filtering  agent 
and  adjustment  of  the  safety  tube.  The  liquid  will  automatically 
regulate  the  pressure  in  most  cases  and  the  operator  can  judge  the 
condition  of  filtration  by  the  flow  of  nitrate.  It  is  a  mistake  to 
attempt  to  force  the  filtration  by  increasing  the  pressure  as  this  pro- 
cedure nearly  always  results  in  clogging.  It  is  better  to  adjust  the 
volume  delivered  to  that  which  issues  from  the  press  by  shortening 
the  stroke  of  the  pump  and,  in  this  connection,  it  is  well  to  make 
notes  of  the  conditions  and  difficulties  observed  during  the  filtration 
of  a  preparation  for  such  notes  will  save  time  and  trouble  on  future 
batches. 
The  class  of  liquids  which  requires  the  most  art  in  handling  is 
that  which  comprises  the  very  thick,  heavy,  viscous,  or  mucilaginous 
solutions  and  fluids  complicated  by  a  large  amount  of  precipitation, 
particularly  of  starch  or  dextrin.  Trouble  may  always  be  expected 
from  preparations  of  rhubarb,  buchu,  uva  ursi,  senna,  and  gentian 
if,  as  is  frequently  the  case,  the  drugs  have  been  percolated  with 
menstrua  of  low  alcoholic  content.  That  difficulty  can  be  avoided 
by  proper  pharmacy  yet  it  does  occasionally  present  itself.  How- 
ever, all  such  liquids  may  be  successfully  filtered  in  the  press  if  due 
attention  be  paid  to  the  conditions.  It  may  be  necessary  to  age  the 
fluid  first  and  this  is  desirable  where  there  is  precipitation  of  starchy 
matters.  Mucilage  is  the  most  difficult  complication  to  deal  with. 
The  best  and  proper  way  to  eliminate  it  is  to  leave  it  in  the  drug 
in  the  percolator,  for  when  it  gets  into  the  finished  liquid  all  there 
is  left  to  do  is  to  summon  all  available  patience,  use  plenty  of  kiesel- 
guhr,  and  throttle  the  pump  down  to  ten  gallons  per  hour.  In  filter- 
ing liquids  of  this  class  it  may  become  necessary  to  stop  the  opera- 
tion for  the  purpose  of  cleaning  the  chambers,  washing  the  cloths 
and  adjusting  fresh  papers  on  them.  This  removes  a  mass  of  pre- 
cipitate and  gives  the  liquid  a  new  opportunity  to  pass  through.  It 
is  worthy  of  note  that  it  is  practically  impossible  to  filter  such  prepa- 
rations clearly  by  gravity. 
Occasionally  it  will  be  found  advantageous  to  line  the  chambers 
with  a  layer  of  filtering  agent  before  attempting  to  filter  the  prepa- 
ration in  hand.    This  procedure  prevents  the  precipitate  from  enter- 
