﻿108 
  Messrs. 
  A. 
  Holt 
  and 
  E. 
  Hopkinson 
  on 
  Decomposition 
  

  

  It 
  will 
  be 
  seen 
  from 
  these 
  tables 
  that 
  all 
  those 
  metals 
  which 
  

   oxidize 
  when 
  heated 
  in 
  air 
  behave 
  like 
  aluminium. 
  They 
  

   give 
  no 
  spray 
  and 
  cause 
  no 
  recombination 
  of 
  the 
  electrolytic 
  

   gas 
  produced 
  by 
  the 
  spark. 
  They 
  do 
  not 
  appear 
  to 
  be 
  oxidized 
  

   by 
  the 
  water-vapour, 
  but 
  possibly 
  a 
  very 
  thin 
  skin 
  of 
  oxide 
  is 
  

   formed 
  which 
  prevents 
  any 
  metal 
  being 
  shot 
  off 
  the 
  cathode, 
  

   for 
  several 
  of 
  them 
  have 
  been 
  shown 
  by 
  Crookes 
  (Proc. 
  Roy. 
  

   Soc. 
  18^1, 
  vol. 
  1. 
  p. 
  88) 
  to 
  disintegrate 
  in 
  other 
  gases. 
  

  

  Those 
  metals 
  which 
  do 
  not 
  oxidize 
  when 
  heated 
  in 
  air 
  to 
  a 
  

   moderate 
  temperature, 
  or 
  which 
  form 
  a 
  volatile 
  oxide 
  as 
  in 
  

   the 
  case 
  of 
  osmium, 
  behave, 
  with 
  the 
  exception 
  of 
  silver 
  and 
  

   palladium, 
  exactly 
  like 
  platinum. 
  They 
  disintegrate 
  in 
  water- 
  

   vapour 
  and 
  bring 
  about 
  more 
  or 
  less 
  recombination 
  of 
  the 
  

   electrolytic 
  gas. 
  Silver, 
  though 
  spraying 
  readily, 
  does 
  not 
  

   appear 
  to 
  combine 
  oxygen 
  and 
  hydrogen. 
  Palladium 
  behaves 
  

   exceptionally, 
  for 
  the 
  ratio 
  B/A 
  is 
  found 
  to 
  steadily 
  increase 
  

   in 
  each 
  successive 
  pair 
  of 
  experiments, 
  instead 
  of 
  decreasing, 
  

   as 
  in 
  the 
  case 
  of 
  the 
  other 
  metals. 
  

  

  When 
  this 
  metal 
  is 
  in 
  a 
  state 
  of 
  very 
  fine 
  subdivision 
  

   (palladium 
  black), 
  it 
  is 
  known 
  to 
  exert 
  intense 
  catalytic 
  action 
  

   on 
  a 
  mixture 
  of 
  oxygen 
  and 
  hydrogen. 
  The 
  metal 
  rapidly 
  

   becomes 
  heated 
  through 
  the 
  energy 
  with 
  which 
  these 
  gases 
  

   are 
  combined 
  on 
  its 
  surface. 
  

  

  During 
  the 
  experiments 
  with 
  electrodes 
  of 
  this 
  metal, 
  it 
  

   was 
  noticed 
  that 
  the 
  film 
  deposited 
  on 
  the 
  tube 
  about 
  D 
  

   became 
  heated 
  when 
  C 
  was 
  the 
  cathode, 
  a 
  phenomenon 
  not 
  

   observed 
  in 
  the 
  case 
  of 
  any 
  other 
  metal 
  ; 
  and 
  though 
  the 
  

   amount 
  of 
  gas 
  collected 
  when 
  D 
  was 
  the 
  cathode 
  was 
  found 
  

   to 
  diminish 
  in 
  each 
  successive 
  experiment, 
  yet 
  when 
  C 
  was 
  

   the 
  cathode 
  it 
  was 
  found 
  to 
  diminish 
  far 
  more 
  rapidly, 
  espe- 
  

   cially 
  at 
  first, 
  and 
  hence 
  caused 
  the 
  increase 
  in 
  the 
  ratio 
  B/A. 
  

   As 
  the 
  film 
  around 
  D 
  became 
  heated, 
  it 
  was 
  probable 
  that 
  the 
  

   steady 
  diminution 
  in 
  the 
  amount 
  of 
  gas 
  collected 
  in 
  each 
  

   experiment 
  when 
  C 
  was 
  the 
  cathode 
  was 
  the 
  result 
  of 
  

   recombination. 
  To 
  see 
  if 
  this 
  was 
  the 
  case 
  a 
  series 
  of 
  expe- 
  

   riments 
  was 
  carried 
  out 
  in 
  exactly 
  the 
  same 
  manner 
  and 
  with 
  

   the 
  same 
  spark-tube, 
  only 
  when 
  C 
  was 
  the 
  cathode, 
  the 
  

   metallic 
  film 
  round 
  JD 
  was 
  kept 
  cold 
  by 
  water 
  so 
  as 
  to 
  prevent, 
  

   as 
  far 
  as 
  possible, 
  any 
  catalysis. 
  The 
  results 
  then 
  obtained 
  

   were 
  in 
  exact 
  agreement 
  with 
  the 
  other 
  platinum 
  metals 
  

   (tal)ie, 
  p. 
  109). 
  

  

  The 
  observations 
  of 
  Chapman 
  and 
  Lidbury 
  thai 
  the 
  degree 
  

   of 
  separation 
  of 
  the 
  oxygen 
  and 
  hydrogen 
  is 
  less 
  when 
  the 
  

   Stream 
  of 
  water-vapour 
  enters 
  the 
  spark 
  near 
  the 
  anode 
  than 
  

  

  near 
  the 
  cathode 
  can 
  now 
  receive 
  a 
  complete 
  explanation. 
  

   When 
  the 
  vapour 
  enters 
  near 
  the 
  anode 
  the 
  greater 
  part 
  of 
  

  

  