290 
Rapid  Filtration 
J  Am.  Jour.  Pharm. 
I      July,  1876. 
funnel  approaches  as  nearly  a  perfect  cone  as  possible.  In  this  case 
the  transition  of  the  cone  into  the  tube  is  marked  by  a  distinct 
angle,  formed  by  the  meeting  of  two  straight  lines.  The  opening  at 
the  bottom  of  the  funnel  must  not  be  too  large,  its  diameter  should 
not  surpass  \  inch. 
A  filter  inserted  into  a  funnel  of  50  degrees,  moistened  and  brought 
in  perfect  contact  with  the  glass  by  pressing  with  the  finger,  will  stand 
the  pressure  of  a  column  of  water  ij  feet  high  with  safety.  Filters 
supported  by  funnels  of  30  degrees  did  not  rupture  by  the  weight  of  a 
column  of  water  3  feet  high.  Funnels  over  50  degrees  require  the 
introduction  of  another  but  smaller  paper  filter,  inside  of  which,  and 
over-reaching  it,  the  main  filter  is  inserted. 
1.  The  filtering  tube  (see  sketch  C)  consists  of  a  wider  upper  part, 
carrying  the  funnel,  and  a  lower  narrower  part,  reaching  almost  to  the 
bottom  of  the  receptacle,  and  dipping  into  the  filtered  liquid.  By 
srarefaction  of  the  air  in  C>  the  filtered  liquid  is  raised  to  a  certain  height, 
and  therefrom  results  an  increased  pressure  on  the  liquid  in  the  funnel, 
