﻿Gases 
  by 
  Collision 
  with 
  Low 
  Electric 
  Forces. 
  1039 
  

  

  Experiments 
  with. 
  S0 
  2 
  . 
  

  

  According 
  to 
  Tovvnsend's 
  theory, 
  for 
  any 
  pressure 
  pro- 
  

   vided 
  it 
  is 
  kept 
  constant, 
  the 
  current-electromotive 
  force 
  

   curves, 
  corresponding 
  to 
  different 
  distances 
  between 
  the 
  

   plates, 
  will 
  not 
  cross. 
  

  

  In 
  a 
  paper 
  published 
  in 
  the 
  American 
  Journal 
  of 
  Science, 
  

   vol. 
  xxxiv. 
  Sept. 
  1912, 
  on 
  " 
  Ionization 
  by 
  Collision 
  in 
  Gases 
  

   and 
  Vapours," 
  W. 
  R. 
  Barss 
  claims 
  to 
  have 
  discovered 
  a 
  

   characteristic 
  difference 
  between 
  the 
  behaviour 
  of 
  gases 
  and 
  

   vapours 
  at 
  higher 
  pressures. 
  He 
  says: 
  " 
  The 
  curves 
  at 
  the 
  

   higher 
  pressures 
  in 
  all 
  the 
  vapors 
  employed 
  give 
  evidence 
  

   of 
  some 
  extraordinary 
  but 
  characteristic 
  behaviour. 
  The 
  

   curve 
  for 
  a 
  smaller 
  distance 
  between 
  the 
  plates 
  rises 
  more 
  

   abruptly 
  than 
  for 
  a 
  greater 
  distance; 
  so 
  that 
  the 
  curves 
  for 
  

   two 
  different 
  distances 
  cross 
  each 
  other. 
  As 
  the 
  pressure 
  is 
  

   diminished, 
  this 
  process 
  is 
  somehow 
  reversed, 
  the 
  curves 
  

   becoming 
  approximately 
  parallel 
  and 
  finally 
  diverging 
  as 
  

   the 
  pressure 
  becomes 
  still 
  further 
  reduced. 
  This 
  is 
  contrary 
  

   to 
  the 
  behaviour 
  of 
  gases 
  in 
  so 
  far 
  as 
  we 
  have 
  experimental 
  

   evidence, 
  and 
  is 
  contrary 
  to 
  the 
  facts 
  that 
  would 
  be 
  expected 
  

   from 
  Townsend's 
  theory. 
  

  

  " 
  The 
  theory 
  of 
  ionization 
  by 
  collision 
  as 
  developed 
  for 
  

   gases 
  holds 
  for 
  vapors 
  ionized 
  by 
  alpha 
  particles 
  provided 
  

   the 
  pressure 
  is 
  not 
  too 
  great. 
  As 
  the 
  pressure 
  is 
  increased, 
  

   evidence 
  of 
  irregularity 
  is 
  obtained 
  which 
  seems 
  to 
  point 
  to 
  

   some 
  instability 
  in 
  the 
  molecular 
  structure 
  of 
  vapors, 
  either 
  

   due 
  to 
  the 
  formation 
  of 
  aggregate 
  molecules 
  or 
  to 
  some 
  

   chemical 
  change." 
  

  

  A 
  series 
  of 
  experiments 
  was 
  made 
  with 
  the 
  apparatus 
  

   described 
  above 
  in 
  order 
  to 
  test 
  the 
  results 
  obtained 
  by 
  

   Barss. 
  

  

  The 
  air 
  w 
  r 
  as 
  pumped 
  out 
  of 
  the 
  vessel 
  to 
  a 
  pressure 
  of 
  

   one-tenth 
  of 
  a 
  millimetre, 
  and 
  S0 
  2 
  vapour 
  (previously 
  dried) 
  

   was 
  admitted 
  up 
  to 
  atmospheric 
  pressure. 
  The 
  S0 
  2 
  used 
  

   was 
  supplied 
  in 
  a 
  siphon 
  as 
  commercially 
  pure 
  by 
  A. 
  Boake, 
  

   Roberts 
  &, 
  Co., 
  Ltd., 
  Stratford, 
  London. 
  This 
  was 
  again 
  

   reduced 
  to 
  one-tenth 
  of 
  a 
  millimetre, 
  and 
  again 
  filled 
  with 
  

   S0 
  2 
  . 
  The 
  operation 
  was 
  repeated 
  a 
  third 
  time, 
  and 
  then 
  

   finally 
  the 
  pressure 
  was 
  reduced 
  to 
  16 
  mm. 
  

  

  Barss's 
  experiments 
  were 
  reproduced 
  in 
  every 
  particular, 
  

   pressure 
  16 
  mm., 
  distances 
  between 
  plates 
  *5 
  cm., 
  *8 
  cm., 
  

   1 
  cm., 
  and 
  field-strengths 
  the 
  same. 
  

  

  The 
  results 
  obtained 
  are 
  given 
  in 
  Table 
  II. 
  

  

  Each 
  of 
  the 
  results 
  is. 
  the 
  mean 
  of 
  ten 
  readings 
  taken, 
  and 
  

   the 
  whole 
  set 
  was 
  taken 
  in 
  three 
  days, 
  so 
  that 
  the 
  decay 
  of 
  

   the 
  polonium 
  need 
  not 
  be 
  considered. 
  I 
  

  

  