dahlke's  filter  for  chemical  liquids. 
229 
DAHLKE'S  FILTER  FOR  CHEMICAL  LIQUIDS. 
The  filtering  medium  patented  by  Mr.  Dahlke  was  noticed  by 
us  at  considerable  length  in  a  former  number.*  We  are  glad 
to  learn  that  the  favorable  estimate  we  expressed  respecting  its 
value  is  likely  to  be  brought  to  a  very  extended  trial,  Mr.  Dahlke 
having  organized  a  company  for  the  purpose  of  working  out  the 
patent  to  the  fullest  extent.  The  managers  have  already  re- 
ceived orders  to  fit  up  the  whole  of  the  General  Post  Office  with 
filters  similar  to  those  supplied  to  the  Drinking  Fountain  Asso. 
ciation. 
But  our  immediate  object  is  an  ingenious  adaptation  of  the 
material  to  the  purification  of  chemical  liquids,  for  which  it  is 
more  especially  adapted,  as  being  composed  of  silica  and  carbon  ; 
it  is  unacted  upon  by  any  ordinary  re-agents ;  and  possessing 
the  capability  of  being  made  of  any  required  porosity,  it  can 
be  used  in  filtering  to  any  required  degree  of  mechanical  purity. 
In  ordinary  cases,  a  separate  filter  is  required  for  each  liquid 
that  has  to  be  purified,  entailing  a  necessity  for  a  considerable 
number  of  filters.  The  inconvenience,  which  is  very  great  when 
many  liquids  have  to  be  dealt  with,  is  entirely  obviated  by  the 
ingenuity  of  Mr.  Dahlke ;  as  he  has  devised  a  plan,  shown  in 
the  annexed  engraving,  by  which  one  filter  will  answer  for  a 
considerable  number  of  liquids  ;  all  that  is  requisite  being  to 
remove  the  block  of  silicated  carbon  and  replace  it  by  a  second, 
or  even  by  another  filtering  substance. 
Thus  one  block  of  the  filtering  medium 
can  be  kept  for  each  liquid,  or  for  each 
class  of  liquids ;  and,  hence,  used  with 
economy,  and  without  the  chance  of  con- 
taminating a  simple  medicine  with  any 
other  of  a  poisonous  or  acrid  character. 
To  produce  rapid  action,  a  syphon,  B,  is 
employed,  which  is  brought  into  action  by 
means  of  a  syringe,  C,  attached  to  it  and 
the  vessel.  Therefore,  neither  quantity 
nor  weight  of  the  liquid  to  be  filtered  will 
have  any  influence  on  the  rapidity  of  the  filtration. 
*yol.  i.  p.  313. 
