108     NEW  INSTRUMENT  FOR  RAPID  FILTRATION  OF  LIQUIDS. 
elastic  ]  iston  to  move  easily  and  yet  tightly  through  its  length, 
makes  an  admirable  air-pump.  The  absence  of  any  liability  to 
dent  or  bruise  in  handling,  or  to  fracture  by  any  ordinary  appli- 
cation of  force,  is  another  recommendation. 
The  air-pump  is  connected  with  a  funnel  by  a  piece  of  elastic 
tube  of  convenient  length.  The  construction  of  the  funnel  is 
shown  in  the  lower  drawing. 
The  upper  section,  a,  has  a  screw  turned  upon  the  outside 
above  its  inferior  margin  ;  this  fits  a  screw  upon  the  inside  of  the 
lower  section,  shown  at  b  ;  the  perforated  diaphragm  c,  of  hard 
rubber,  is  designed  to  be  covered  with  several  layers  of  filtering 
paper  or  cotton  cloth,  or  with  chamois  leather,  or  other  filtering 
medium,  which  is  secured  tightly  in  place  by  the  pressure  of  the 
upper  section  a,  when  screwed  upon  the  lower  section  b;  at  d 
is  shown  a  nipple,  on  to  which  the  elastic  tube  is  slipped  to  con- 
nect the  funnel  with  the  air-pump.  A  washer,  marked  e  in  both 
figures,  serves  to  make  an  air-tight  joint  with  the  receiving  bottle 
into  which  the  funnel  is  designed  to  be  set ;  this  may  conveni- 
ently be  a  quart  salt-mouth  bottle,  if  the  quantity  of  liquid  does 
not  exceed  that  measure ;  but  as  there  is  little  difference  in  the 
width  of  the  mouth  of  the  several  common  sizes,  it  may  be 
adapted  to  almost  any  of  them. 
