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  XCIV. 
  On 
  Ionization 
  in 
  various 
  Gases. 
  By 
  E. 
  Parr 
  

   Metcalfe, 
  B.Sc. 
  (Loud.); 
  1851 
  Exhibition 
  Scholar^ 
  Em- 
  

   manuel 
  College^ 
  Cambridge* 
  . 
  

  

  [Plate 
  XXIX.] 
  

  

  THE 
  relative 
  ionizations 
  produced, 
  under 
  similar 
  con- 
  

   ditions, 
  in 
  a 
  large 
  number 
  o£ 
  elementary 
  and 
  compound 
  

   gases, 
  have 
  been 
  measured 
  by 
  several 
  investigators 
  f. 
  The 
  

   results 
  which 
  have 
  been 
  obtained 
  seemed 
  to 
  suggest 
  that 
  the 
  

   ionization 
  per 
  molecule 
  may 
  be 
  the 
  sum 
  of 
  the 
  ionizations 
  

   contributed 
  by 
  the 
  atoms 
  composing 
  the 
  molecules, 
  the 
  con- 
  

   tribution 
  of 
  each 
  atom 
  being 
  characteristic 
  of 
  that 
  atom 
  and 
  

   not 
  influenced 
  by 
  the 
  manner 
  of 
  the 
  chemical 
  linkage 
  or 
  by 
  

   the 
  presence 
  of 
  the 
  other 
  atoms 
  in 
  the 
  molecule. 
  It 
  was 
  

   mainly 
  with 
  the 
  object 
  of 
  gaining 
  further 
  evidence 
  on 
  this 
  

   subject 
  that 
  the 
  work 
  now 
  described 
  was 
  undertaken. 
  

  

  The 
  system 
  adopted 
  was 
  that 
  of 
  obtaining 
  values 
  for 
  the 
  

   ionization 
  per 
  molecule 
  for 
  members 
  of 
  complete 
  sequences 
  

   of 
  three 
  or 
  more 
  different 
  compounds 
  of 
  the 
  same 
  two 
  

   elements. 
  The 
  two 
  sequences 
  which 
  first 
  suggested 
  them- 
  

   selves 
  were 
  Og, 
  OO2, 
  CO 
  and 
  Ng, 
  N2O, 
  NO. 
  In 
  these 
  no 
  

   values 
  existed 
  for 
  the 
  ionization 
  in 
  CO 
  and 
  NO. 
  A 
  beginning- 
  

   was 
  accordingly 
  made 
  with 
  these 
  two 
  compounds. 
  The 
  

   sequence 
  next 
  dealt 
  with 
  was 
  that 
  of 
  the 
  paraffin 
  gases, 
  

   values 
  being 
  obtained 
  for 
  the 
  first 
  four 
  members. 
  

  

  Before 
  proceeding 
  with 
  these 
  systematic 
  determinations, 
  

   careful 
  measurements 
  were 
  made 
  of 
  the 
  ionization 
  in 
  hydrogen, 
  

   by 
  way 
  of 
  gaining 
  experience 
  of 
  the 
  w^orking 
  of 
  the 
  apparatus, 
  

   and 
  as 
  a 
  check 
  on 
  the 
  accuracy 
  of 
  the 
  method 
  employed. 
  

   Three 
  values 
  of 
  this 
  constant 
  have 
  already 
  been 
  recorded, 
  

   two 
  by 
  Strutt 
  and 
  one 
  by 
  Bragg. 
  With 
  these 
  the 
  values 
  now 
  

   found 
  are 
  in 
  fair 
  agreement. 
  

  

  On 
  the 
  completion 
  of 
  the 
  paraffin 
  sequence, 
  the 
  apparatus 
  

   was 
  working 
  so 
  satisfactorily 
  that 
  a 
  continuation 
  was 
  made 
  

   with 
  helium, 
  hydrogen 
  chloride, 
  and 
  bromine, 
  in 
  this 
  order. 
  

  

  The 
  ionizing 
  agent 
  used 
  was 
  the 
  radiation 
  from 
  thin 
  layers 
  

   of 
  uranium 
  oxide 
  ; 
  and 
  the 
  effect 
  may 
  be 
  considered 
  as 
  being 
  

   entirely 
  due 
  to 
  the 
  bombardment 
  of 
  the 
  molecules 
  of 
  gas 
  by 
  

   a-particles 
  ; 
  the 
  influence 
  of 
  other 
  radiation 
  under 
  these 
  condi- 
  

   tions 
  is 
  negligible 
  in 
  comparison 
  with 
  the 
  experimental 
  error. 
  

  

  In 
  assigning 
  the 
  apparatus 
  for 
  the 
  work 
  the 
  writer's 
  aim 
  

   was 
  to 
  obtain 
  as 
  large 
  an 
  ionization- 
  current 
  as 
  possible 
  at 
  low 
  

  

  * 
  Communicated 
  bv 
  Sir 
  J. 
  J. 
  Thomson. 
  

  

  t 
  Strutt, 
  Phil. 
  Trans. 
  A. 
  cxcvi. 
  p. 
  507, 
  1900 
  ; 
  Rov. 
  Soc. 
  Proc. 
  1903, 
  

   p. 
  208. 
  Bragg-, 
  Phil. 
  Mag. 
  1906, 
  May, 
  and 
  1907, 
  March 
  ; 
  also 
  Trans. 
  Roy. 
  

   Soc. 
  S. 
  Australia, 
  1900. 
  Kleeman, 
  Roy. 
  Soc. 
  Proc. 
  A. 
  Ixxix. 
  p. 
  220. 
  

   Laby, 
  Roy. 
  Soc. 
  Proc. 
  A. 
  Ixxix. 
  p. 
  206. 
  

  

  