﻿Oil 
  

  

  420 
  Dr. 
  J. 
  Erskine- 
  Murray 
  

  

  After 
  detailing 
  some 
  experiments 
  in 
  which 
  the 
  plates 
  were 
  

   coated 
  with 
  the 
  gases 
  by 
  electrolysis, 
  Lord 
  Kelvin 
  concludes 
  : 
  

   " 
  Thus 
  in 
  the 
  case 
  of 
  polarization 
  by 
  oxygen, 
  as 
  well 
  as 
  in 
  the 
  

   case 
  of 
  polarization 
  by 
  hydrogen, 
  the 
  effect 
  of 
  exposure 
  to 
  

   the 
  dry 
  gas 
  was 
  considerably 
  greater 
  than 
  the 
  effect 
  of 
  elec- 
  

   troplating 
  the 
  platinum 
  with 
  the 
  gas 
  by 
  the 
  electromotive 
  

   force 
  of 
  one 
  volt."" 
  

  

  The 
  large 
  effects 
  on 
  contact-potential 
  produced 
  by 
  films 
  

   formed 
  from 
  gases 
  are 
  clearly 
  shown 
  in 
  these 
  experiments 
  of 
  

   Lord 
  Kelvin's. 
  It 
  is 
  well 
  known 
  that 
  platinum 
  and 
  other 
  

   metals 
  have 
  the 
  property 
  of 
  occluding 
  large 
  quantities 
  of 
  gas 
  

   in 
  their 
  surface 
  layers, 
  and 
  that 
  the 
  condensed 
  gas 
  is 
  possibly 
  

   in 
  the 
  liquid 
  state, 
  which 
  would 
  account 
  for 
  the 
  similarity 
  

   between 
  the 
  effects 
  of 
  liquids 
  and 
  of 
  gases 
  on 
  metals. 
  

  

  § 
  56. 
  The 
  plates 
  with 
  which 
  my 
  first 
  experiments 
  on 
  this 
  

   subject 
  were 
  made 
  were 
  of 
  " 
  high 
  conductivity 
  M 
  copper. 
  They 
  

   had 
  been 
  polished 
  on 
  fine 
  glass-paper 
  five 
  hours 
  before, 
  and 
  

   their 
  mutual 
  potential 
  had 
  remained 
  constant 
  at 
  

  

  •02 
  volt 
  

  

  for 
  four 
  hours. 
  The 
  lower 
  plate 
  was 
  then 
  put 
  into 
  a 
  glass 
  vessel? 
  

   into 
  which 
  oxygen 
  gas 
  was 
  admitted 
  from 
  a 
  cylinder, 
  and 
  the 
  

   oxygen, 
  which 
  was 
  of 
  Messrs. 
  Brings 
  manufacture, 
  guaranteed 
  

   93-95 
  per 
  cent, 
  oxygen 
  (nitrogen 
  is 
  usually 
  the 
  only 
  

   impurity), 
  was 
  allowed 
  to 
  stream 
  through 
  the 
  glass 
  vessel 
  

   containing 
  the 
  plate 
  for 
  some 
  minutes, 
  and 
  the 
  exit 
  and 
  inlet 
  

   of 
  the 
  vessel 
  were 
  then 
  closed. 
  Forty-five 
  minutes 
  later 
  the 
  

   plate 
  was 
  taken 
  out 
  and 
  its 
  potential 
  again 
  measured 
  with 
  

   the 
  other 
  plate, 
  which 
  had 
  remained 
  in 
  air 
  during 
  the 
  interval. 
  

   Counting 
  time 
  from 
  the 
  moment 
  at 
  which 
  the 
  plate 
  was 
  taken 
  

   out 
  of 
  the 
  oxygen, 
  the 
  potential 
  varied 
  as 
  shown 
  below, 
  the 
  

   oxygenized 
  plate 
  being 
  positive 
  to 
  the 
  other 
  in 
  all 
  cases 
  : 
  — 
  

  

  Time. 
  

  

  C 
  ontact-potential 
  

  

  h. 
  m. 
  

  

  v. 
  

  

  3 
  

  

  •12 
  

  

  19 
  

  

  •08 
  

  

  30 
  

  

  •06 
  

  

  17 
  20 
  

  

  •03 
  

  

  Thus 
  the 
  effect 
  of 
  increasing 
  the 
  proportion 
  of 
  oxygen 
  in 
  the 
  

   surface 
  film 
  was 
  to 
  make 
  the 
  copper 
  more 
  positive. 
  

  

  § 
  57. 
  This 
  variation 
  is 
  in 
  the 
  opposite 
  direction 
  to 
  that 
  

   found 
  by 
  Lord 
  Kelvin 
  for 
  platinum 
  which 
  has 
  been 
  soaked 
  in 
  

   oxygen. 
  In 
  order 
  to 
  make 
  sure 
  that 
  this 
  difference 
  was 
  not 
  

   the 
  effect 
  of 
  some 
  impurity 
  in 
  the 
  oxygen, 
  I 
  repeated 
  his 
  

  

  