﻿386 
  OF 
  A 
  SUCTION 
  

  

  opened. 
  Between 
  the 
  apertures 
  thus 
  alternately 
  opened 
  and 
  shut, 
  and 
  

   the 
  valve 
  cock 
  A, 
  a 
  communication 
  is 
  made 
  by 
  means 
  of 
  a 
  forked 
  

   leaden 
  pipe, 
  communicating 
  with 
  the 
  valve 
  cock 
  at 
  A, 
  and 
  with 
  the 
  

   apertures 
  at 
  B 
  and 
  C. 
  The 
  valve 
  cock, 
  by 
  means 
  of 
  a 
  gallows 
  screw 
  

   D, 
  communicates, 
  when 
  desirable, 
  with 
  any 
  receiver 
  by 
  another 
  flexible 
  

   leaden 
  pipe 
  P. 
  

  

  Two 
  other 
  analogous 
  and 
  corresponding 
  apertures 
  E 
  R, 
  which 
  com- 
  

   municate 
  in 
  like 
  manner 
  with 
  a 
  valve 
  cock 
  G, 
  are 
  furnished 
  with 
  two 
  

   valves 
  opening 
  outwards. 
  These, 
  when 
  not 
  subjected 
  to 
  any 
  pressure 
  

   from 
  within 
  the 
  chamber, 
  are 
  kept 
  in 
  their 
  places 
  by 
  spiral 
  springs. 
  

   They 
  act 
  as 
  valves 
  of 
  efflux, 
  and, 
  like 
  the 
  valves 
  in 
  other 
  condensers, 
  

   are 
  opened 
  by 
  the 
  pressure 
  of 
  the 
  air 
  condensed 
  by 
  the 
  piston 
  as 
  it 
  ap- 
  

   proaches 
  them, 
  and 
  are 
  shut 
  by 
  the 
  springs 
  when 
  the 
  piston 
  moves 
  in 
  

   the 
  opposite 
  direction. 
  It 
  is 
  well 
  known, 
  however, 
  that 
  this 
  mode 
  of 
  

   opening 
  valves, 
  if 
  unassisted, 
  always 
  allows 
  a 
  small 
  portion 
  of 
  condensed 
  

   air 
  to 
  remain 
  in 
  that 
  portion 
  of 
  the 
  chamber 
  and 
  of 
  the 
  passage 
  lead- 
  

   ing 
  to 
  the 
  valve, 
  which 
  the 
  piston 
  cannot 
  be 
  made 
  to 
  occupy 
  entirely. 
  

   This 
  disadvantage 
  is 
  diminished 
  in 
  the 
  case 
  of 
  the 
  valves 
  which 
  I 
  am 
  

   describing. 
  A 
  stem 
  proceeding 
  from 
  each 
  valve 
  enters 
  the 
  chamber 
  

   so 
  far, 
  as 
  that 
  the 
  piston 
  cannot 
  finish 
  the 
  stroke 
  without 
  coming 
  in 
  

   contact 
  with 
  the 
  stem, 
  and 
  moving 
  the 
  valve 
  sufficiently 
  to 
  allow 
  the 
  

   air 
  to 
  escape, 
  without 
  suffering 
  any 
  resistance 
  from 
  the 
  valve 
  and 
  its 
  

   spring. 
  

  

  The 
  means 
  by 
  which 
  the 
  apertures 
  of 
  the 
  suction 
  valves 
  communi- 
  

   cate 
  with 
  a 
  valve 
  cock 
  A, 
  and 
  may 
  be 
  made 
  to 
  communicate 
  with 
  the 
  

   receiver 
  through 
  the 
  pipe 
  P, 
  have 
  been 
  explained. 
  By 
  like 
  means 
  the 
  

   communication, 
  existing 
  between 
  the 
  apertures 
  of 
  the 
  valves 
  of 
  efflux 
  

   and 
  a 
  valve 
  cock 
  G, 
  may 
  be 
  extended 
  from 
  this 
  valve 
  cock 
  to 
  any 
  

   receiver. 
  In 
  fact, 
  it 
  is 
  only 
  necessary 
  to 
  vary 
  the 
  situation 
  or 
  number 
  

   of 
  the 
  pipes, 
  by 
  which 
  communications 
  with 
  the 
  chamber 
  are 
  effected, 
  

   in 
  order 
  to 
  cause 
  the 
  apparatus 
  to 
  perform 
  the 
  part 
  of 
  an 
  air 
  pump, 
  

   a 
  condenser, 
  or 
  both. 
  When 
  employed 
  to 
  transfer 
  air, 
  it 
  would 
  be 
  

   more 
  correctly 
  designated 
  as 
  a 
  forcing 
  air 
  pump, 
  than 
  as 
  a 
  condenser. 
  

  

  The 
  disk 
  of 
  brass 
  in 
  front 
  of 
  the 
  pump, 
  serves 
  as 
  an 
  air 
  pump 
  plate, 
  

   when 
  connected 
  with 
  the 
  pump 
  by 
  means 
  of 
  the 
  pipe 
  P, 
  as 
  represented 
  

   in 
  the 
  drawing. 
  It 
  is 
  supported 
  on 
  a 
  hollow 
  brass 
  cylinder, 
  furnished 
  

  

  