﻿of 
  Water- 
  Vapour 
  by 
  Electric 
  Sjiarks. 
  105 
  

  

  In 
  the 
  above 
  table, 
  experiments 
  1-3 
  when 
  compared 
  with 
  

   4-6 
  show 
  the 
  enormous 
  effect 
  the 
  metal 
  composing 
  tha 
  

   electrodes 
  exerts 
  on 
  the 
  amount 
  of 
  electrolytic 
  gas 
  obtained 
  

   when 
  the 
  stream 
  o£ 
  water- 
  vapour 
  enters 
  the 
  spark-tube 
  at 
  

   the 
  anode 
  and 
  cathode 
  respectively. 
  Experiments 
  1-3 
  com- 
  

   pared 
  with 
  7-8 
  show 
  the 
  difference 
  between 
  thick 
  and 
  thin 
  

   electrodes. 
  In 
  experiments 
  7-8, 
  where 
  the 
  electrodes 
  are 
  

   thick 
  and 
  therefore 
  become 
  only 
  slightly 
  heated, 
  there 
  is 
  a 
  

   very 
  small 
  amount 
  of 
  spray, 
  and 
  consequently 
  the 
  difference 
  

   in 
  the 
  amount 
  of 
  gas 
  collected 
  when 
  the 
  vapour 
  enters 
  at 
  the 
  

   cathode 
  compared 
  with 
  that 
  when 
  it 
  enters 
  at 
  the 
  anode 
  is 
  

   smaller 
  than 
  in 
  experiments 
  1-3. 
  

  

  Experiments 
  1-3 
  and 
  9-10 
  show 
  the 
  effect 
  of 
  large 
  and 
  

   small 
  bulbs 
  round 
  the 
  electrodes. 
  It 
  will 
  be 
  noticed 
  that 
  

   when 
  the 
  bulbs 
  are 
  large, 
  the 
  effect 
  is 
  the 
  same 
  as 
  when 
  the 
  

   electrodes 
  are 
  very 
  thick. 
  This 
  difference 
  between 
  the 
  amount 
  

   of 
  gas 
  collected 
  when 
  the 
  w 
  r 
  ater-vapour 
  enters 
  at 
  the 
  anode 
  

   or 
  cathode 
  can 
  be 
  explained 
  by 
  the 
  catalytic 
  action 
  of 
  the 
  

   platinum 
  spray. 
  

  

  In 
  the 
  first 
  experiment 
  of 
  any 
  series 
  the 
  spark-tube 
  is 
  clean 
  

   and 
  C 
  is 
  made 
  the 
  cathode, 
  as 
  already 
  mentioned. 
  The 
  

   vapour 
  enters 
  at 
  the 
  cathode, 
  is 
  partially 
  decomposed 
  by 
  the 
  

   spark 
  and 
  passes 
  over 
  the 
  anode 
  on 
  its 
  way 
  out 
  of 
  the 
  tube 
  

   at 
  D. 
  The 
  amount 
  of 
  spray 
  and 
  heating 
  at 
  the 
  anode 
  being 
  

   negligible, 
  and 
  the 
  surrounding 
  glass 
  being 
  clean, 
  no 
  re- 
  

   combination 
  of 
  the 
  electrolytic 
  gas 
  produced 
  in 
  the 
  spark 
  

   takes 
  place. 
  

  

  D 
  is 
  next 
  made 
  the 
  cathode 
  ; 
  the 
  electrolytic 
  gas 
  produced 
  

   in 
  the 
  spark 
  passes 
  over 
  its 
  heated 
  surface, 
  from 
  which 
  par- 
  

   ticles 
  of 
  metal 
  are 
  being 
  shot 
  off 
  ; 
  and 
  some 
  recombination 
  of 
  

   the 
  oxygen 
  and 
  hydrogen 
  occurs 
  ; 
  consequently 
  a 
  smaller 
  

   amount 
  is 
  collected 
  than 
  when 
  the 
  cathode 
  was 
  at 
  C. 
  

  

  When 
  the 
  electrodes 
  are 
  thick 
  the 
  heating 
  of 
  the 
  cathode 
  

   is 
  less, 
  and 
  a 
  smaller 
  amount 
  of 
  metal 
  is 
  shot 
  off 
  : 
  there 
  is 
  

   therefore 
  less 
  recombination 
  ; 
  and 
  if 
  a 
  very 
  thick 
  cathode 
  is 
  

   used 
  there 
  may 
  be 
  little 
  difference 
  between 
  the 
  amounts 
  of 
  gas 
  

   collected 
  according 
  as 
  this 
  pole 
  is 
  at 
  C 
  or 
  D. 
  

  

  It 
  will 
  be 
  noticed 
  in 
  the 
  table 
  that 
  in 
  the 
  case 
  of 
  platinum 
  

   each 
  successive 
  pair 
  of 
  experiments 
  gives 
  a 
  low 
  T 
  er 
  value 
  for 
  

   the 
  ratio 
  B/A, 
  that 
  is 
  to 
  say 
  the 
  amount 
  of 
  recombination 
  

   increases 
  every 
  time 
  D 
  is 
  made 
  the 
  cathode. 
  Since 
  the 
  

   amount 
  of 
  spray 
  shot 
  off 
  the 
  cathode 
  does 
  not 
  vary 
  from 
  one 
  

   experiment 
  to 
  the 
  next, 
  this 
  increase 
  of 
  recombination 
  must 
  

   result 
  from 
  the 
  catalytic 
  action 
  of 
  the 
  metallic 
  film 
  which 
  is 
  

   deposited 
  on 
  the 
  walls 
  of 
  the 
  tube. 
  This 
  film 
  becomes 
  denser 
  

  

  