r 
178  METHOD  OF  HASTENING  FILTRATIONS. 
draw  your  attention  to  it  once  more,  and  to  subjoin  a  sketch  of 
the  arrangements  proposed  by  him,  selecting  the  obviously 
best  modification. 
The  funnel  is  elongated,  by  means  of  an  elastic  joint,  into  a 
long  glass  tube,  having  a  kind  of  loop  in  its  upper  part,  which 
serves  to  keep  a  constant  column  of  liquid  in  the  'tube,  and 
causes  it  to  act  as  an  aspirator. 
Having  used  this  contrivance  constantly  for  many  weeks,  I 
can  but  fully  confirm  Dr.  Picard's  final  statements,  of  which, 
therefore,  I  beg  to  subjoin  a  translation  : 
1.  The  column  of  water  not  exceeding  one  foot  in  length, 
there  is  never  any  danger  of  a  filter  breaking. 
2.  The  funnels  should  not  have  a  bulge,  but  they  should  be 
exactly  conical,  so  that  the  paper  filter  lies  everywhere  close 
on  the  glass,  without  any  creases  or  other  irregularities ;  it 
must  then  be  wetted,  and  all  air-bubbles  between  the  glass  and 
paper  must  be  pressed  out  with  the  finger.  This  preparation 
is  indispensable. 
3.  If  the  last- mentioned  condition  is  fulfilled,  the  rate  of 
filtration  is  ten  or  twelve  times  quicker  than  without  the  bent 
tube.  If  that  condition  is  not  completely  fulfilled,  but  if  some 
air  is  sucked  between  glass  and  paper,  so  that  a  row  of  beads 
is  generated  in,  the  aspirating  tube,  instead  of  a  continuous 
column  of  liquor,  then  the  rate  sinks  to  four  or  five  times  the 
ordinary  one ;  but  even  with  filters  badly  made  on  purpose  it 
only  comes  down  to  three  times. 
I  may  be  allowed  to  add  that  hot  liquids  are  found  to  work 
far  better  than  cold  ones,  in  spite  of  the  counter  pressure  of 
their  vapors,  and  that  in  no  instance  have  I  noticed  any 
increase  in  the  tendency  of  some  precipitates  to  pass  through 
the  filter, — a  disadvantage  which  can  easily  be  avoided  by 
using  the  denser  Swedish  filtering  paper,  since  in  the  new  ar- 
rangement the  latter  is  no  more  objectionable  on  account  of  the 
slowness  of  its  working. 
I  am,  &c.         Geo.  Lunge,  Ph.  D. 
South  Shields,  January,  3.  1866. 
. — Chem.  Ne>ws,  Jan.  12,  1866, 
