﻿388 
  OF 
  A 
  SUCTION 
  AND 
  FORCING 
  AIR 
  PUMP. 
  

  

  the 
  preference 
  to 
  the 
  new 
  instrument, 
  in 
  all 
  cases 
  where 
  a 
  perfect 
  

   exhaustion 
  has 
  been 
  desirable. 
  

  

  Of 
  the 
  three 
  valve 
  cocks, 
  one 
  usually 
  communicates 
  with 
  a 
  gage; 
  

   since, 
  instead 
  of 
  an 
  instrument 
  of 
  that 
  nature 
  permanently 
  associated 
  

   with 
  the 
  pump, 
  and 
  which 
  is 
  subjected 
  to 
  exhaustion 
  by 
  means 
  of 
  a 
  

   lateral 
  communication 
  with 
  the 
  perforation 
  leading 
  to 
  the 
  cavity 
  of 
  the 
  

   receiver, 
  I 
  employ 
  a 
  movable 
  barometer 
  gage, 
  which 
  is 
  made 
  to 
  com- 
  

   municate 
  with 
  the 
  receiver 
  directly. 
  The 
  operator 
  is 
  thus 
  enabled 
  to 
  

   observe 
  the 
  quantity 
  of 
  gas 
  in 
  the 
  receiver, 
  after 
  the 
  communication 
  

   with 
  the 
  air 
  pump 
  is 
  arrested 
  by 
  closing 
  the 
  valve 
  cock 
  through 
  which 
  

   it 
  was 
  established. 
  An 
  exemplification 
  of 
  this 
  method 
  of 
  manipulating 
  

   will 
  be 
  afforded 
  by 
  the 
  apparatus 
  and 
  eudiometrical 
  process, 
  described 
  

   in 
  the 
  next 
  article. 
  

  

  