﻿[ 
  280 
  ] 
  

  

  XXI. 
  The 
  Genesis 
  of 
  Ions 
  by 
  Collision 
  of 
  Positive 
  and 
  Nega- 
  

   tive 
  Ions 
  in 
  a 
  Gas. 
  Experiments 
  on 
  Argon 
  and 
  Helium, 
  

   By 
  E. 
  W. 
  B. 
  Gill, 
  B.A., 
  Christ 
  Church, 
  Oxford, 
  and 
  

   F. 
  B. 
  Pidduck, 
  B. 
  A., 
  Fellow 
  of 
  Queen 
  s 
  College, 
  Oxford*. 
  

  

  THE 
  present 
  paper 
  contains 
  an 
  account 
  of 
  some 
  expe- 
  

   riments 
  in 
  verification 
  of 
  the 
  theory 
  of 
  ionization 
  by 
  

   collision 
  of 
  positive 
  and 
  negative 
  ions 
  f, 
  conducted 
  on 
  the 
  

   monatomic 
  gases 
  argon 
  and 
  helium. 
  

  

  The 
  theory 
  may 
  be 
  summarized 
  as 
  follows: 
  — 
  Let 
  a 
  constant 
  

   electric 
  force 
  be 
  maintained 
  between 
  parallel 
  plate 
  electrodes, 
  

   the 
  distance 
  d 
  (in 
  centimetres) 
  being 
  alterable. 
  A 
  number 
  

   ■n 
  of 
  negative 
  ions 
  are 
  set 
  free 
  per 
  second 
  by 
  ultra-violet 
  

   light 
  from 
  the 
  negative 
  plate, 
  and 
  n 
  ions 
  arrive 
  at 
  the 
  positive 
  

   plate 
  per 
  second. 
  Then 
  if 
  each 
  negative 
  ion 
  produces 
  a 
  ions 
  

   of 
  each 
  kind, 
  and 
  each 
  positive 
  ion 
  ft, 
  in 
  moving 
  through 
  a 
  

   centimetre 
  under 
  the 
  given 
  force, 
  

  

  w 
  a-fte^-M 
  ' 
  • 
  • 
  • 
  • 
  • 
  W 
  

  

  If 
  also 
  X 
  is 
  the 
  electric 
  force 
  in 
  volts 
  per 
  centimetre, 
  and 
  

   p 
  the 
  pressure 
  in 
  millimetres 
  of 
  mercury, 
  

  

  — 
  is 
  a 
  function 
  of 
  — 
  , 
  .... 
  (2) 
  

  

  p 
  p> 
  \ 
  y 
  

  

  — 
  is 
  a 
  function 
  of 
  — 
  (3) 
  

  

  P 
  P 
  

  

  From 
  (1) 
  the 
  sparking 
  distance 
  a 
  is 
  given 
  by 
  

  

  a 
  -#?(«-«« 
  = 
  (4) 
  

  

  The 
  equations 
  (2), 
  (3), 
  and 
  (4) 
  lead 
  to 
  Paschen's 
  law 
  that 
  

   the 
  sparking 
  potential 
  depends 
  only 
  on 
  the 
  mass 
  of 
  gas 
  

   between 
  the 
  electrodes. 
  

  

  On 
  account 
  of 
  the 
  fact 
  that 
  continuous 
  production 
  of 
  new 
  

   gas 
  was 
  inconvenient, 
  the 
  apparatus 
  previously 
  used 
  was 
  

   slightly 
  modified. 
  It 
  was 
  arranged 
  so 
  that 
  after 
  an 
  expe- 
  

   riment 
  the 
  gas 
  could 
  be 
  pumped 
  up 
  into 
  a 
  reservoir, 
  while 
  

   the 
  small 
  residue 
  remaining 
  over 
  was 
  pumped 
  out 
  into 
  the 
  

   air 
  before 
  beginning 
  a 
  fresh 
  experiment. 
  The 
  effect 
  of 
  the 
  

   small 
  leak 
  of 
  the 
  apparatus 
  (about 
  *01 
  mm. 
  in 
  24 
  hours) 
  was 
  

   thus 
  reduced 
  to 
  a 
  minimum. 
  

  

  * 
  Communicated 
  by 
  Prof. 
  J. 
  S. 
  Townsend, 
  F.R.S. 
  

  

  t 
  For 
  previous 
  experiments 
  on 
  other 
  gases, 
  see 
  papers 
  by 
  J. 
  S. 
  

   Townsend, 
  Phil. 
  Mag-. 
  Nov. 
  1903 
  ; 
  J. 
  S. 
  Townsend 
  and 
  H. 
  E.* 
  Hurst, 
  

   Phil. 
  Mag. 
  Dec. 
  1904 
  ; 
  and 
  H. 
  E. 
  Hurst, 
  Fhil. 
  Mag. 
  April 
  1906. 
  

  

  