﻿of 
  Water-Vapour 
  by 
  Electric 
  Sparks. 
  93 
  

  

  proved, 
  therefore, 
  that 
  an 
  electric 
  current 
  is 
  conducted 
  

   through 
  water-vapour 
  in 
  a 
  similar 
  manner 
  as 
  through 
  liquid 
  

   water. 
  

  

  J. 
  J. 
  Thomson 
  (' 
  Recent 
  Researches 
  in 
  Electricity 
  and 
  

   Magnetism/ 
  Appendix), 
  in 
  repeating 
  the 
  experiments 
  o£ 
  

   Perrot, 
  found 
  that 
  the 
  pole 
  at 
  which 
  the 
  excess 
  of 
  oxygen 
  or 
  

   hydrogen 
  appeared 
  depended 
  on 
  the 
  length 
  of 
  the 
  spark, 
  for 
  

   when 
  it 
  was 
  extremely 
  short 
  and 
  resembling 
  an 
  arc 
  the 
  

   hydrogen 
  was 
  found 
  at 
  the 
  anode 
  and 
  the 
  oxygen 
  at 
  the 
  

   cathode 
  ; 
  whereas 
  with 
  a 
  long 
  spark, 
  the 
  excess 
  of 
  hydrogen 
  

   appeared 
  at 
  the 
  cathode 
  and 
  the 
  excess 
  of 
  oxygen 
  at 
  the 
  

   anode. 
  A 
  critical 
  position 
  could 
  be 
  found 
  between 
  long 
  and 
  

   short 
  sparks 
  at 
  which 
  the 
  excess 
  of 
  hydrogen 
  was 
  sometimes 
  

   collected 
  at 
  the 
  anode 
  and 
  sometimes 
  at 
  the 
  [cathode. 
  If, 
  

   under 
  these 
  circumstances, 
  Ley 
  den 
  jars 
  were 
  introduced 
  into 
  

   the 
  circuit, 
  the 
  hydrogen 
  always 
  appeared 
  at 
  the 
  anode 
  and 
  

   the 
  oxygen 
  at 
  the 
  cathode, 
  while 
  the 
  critical 
  spark-length 
  was 
  

   found 
  to 
  be 
  increased. 
  This 
  was 
  explained 
  by 
  Thomson 
  by 
  

   supposing 
  that 
  the 
  separation 
  of 
  the 
  oxygen 
  and 
  hydrogen 
  

   was 
  the 
  result 
  of 
  the 
  motion 
  of 
  charged 
  hydrogen 
  towards 
  

   one 
  pole 
  and 
  oppositely 
  charged 
  oxygen 
  towards 
  the 
  other, 
  

   the 
  charges 
  on 
  the 
  molecules 
  of 
  the 
  gases 
  being 
  different 
  

   when 
  the 
  discharge 
  resembled 
  an 
  arc 
  or 
  spark. 
  

  

  In 
  a 
  separate 
  series 
  of 
  experiments 
  he 
  showed 
  that 
  there 
  

   was 
  an 
  alteration 
  in 
  the 
  sign 
  of 
  the 
  charges 
  on 
  the 
  molecules 
  

   of 
  these 
  gases 
  when 
  the 
  discharge 
  changed 
  from 
  an 
  arc 
  to 
  a 
  

   spark, 
  or 
  vice 
  versa. 
  

  

  More 
  recently, 
  Chapman 
  and 
  Lidbury 
  (J. 
  0. 
  S. 
  Trans. 
  

   1902, 
  p. 
  1301) 
  noticed 
  that 
  the 
  position 
  in 
  which 
  the 
  water- 
  

   vapour 
  entered 
  the 
  spark 
  had 
  a 
  marked 
  effect 
  on 
  the 
  separa- 
  

   tion 
  of 
  the 
  products 
  of 
  decomposition, 
  for 
  the 
  excess 
  of 
  oxygen 
  

   always 
  appeared 
  at 
  the 
  pole 
  situated 
  furthest 
  from 
  the 
  point 
  

   at 
  which 
  the 
  current 
  of 
  vapour 
  entered. 
  It 
  followed, 
  there- 
  

   fore, 
  that 
  a 
  position 
  could 
  be 
  found 
  at 
  which 
  there 
  was 
  no 
  

   separation, 
  pure 
  electrolytic 
  gas 
  being 
  collected 
  at 
  either 
  

   pole. 
  They 
  further 
  observed 
  that 
  when 
  the 
  vapour 
  entered 
  

   near 
  the 
  anode, 
  the 
  amount 
  of 
  separation 
  of 
  the 
  oxygen 
  and 
  

   hydrogen 
  was 
  very 
  much 
  less 
  than 
  when 
  it 
  entered 
  near 
  the 
  

   cathode. 
  Their 
  experiments 
  led 
  to 
  the 
  conclusion 
  that 
  it 
  was 
  

   not 
  possible 
  to 
  give 
  a 
  complete 
  explanation 
  of 
  the 
  phenomena 
  

   by 
  an 
  hypothesis 
  based 
  solely 
  on 
  the 
  theory 
  of 
  electrolysis 
  in 
  

   liquids. 
  

  

  While 
  carrying 
  out 
  another 
  investigation, 
  one 
  of 
  us 
  noticed 
  

   that 
  oxygen 
  and 
  hydrogen 
  could 
  be 
  separated 
  to 
  a 
  consider- 
  

   able 
  extent 
  by 
  the 
  difference 
  between 
  the 
  rates 
  at 
  which 
  they 
  

   diffused 
  through 
  water-vapour 
  at 
  low 
  pressure. 
  

  

  