﻿Volta 
  Electricity 
  of 
  Metals, 
  

  

  419 
  

  

  Hot 
  sensibly 
  different 
  in 
  different 
  gases 
  so 
  long 
  as 
  the 
  metals 
  

   are 
  not 
  chemically 
  affected, 
  and 
  is 
  not 
  sensibly 
  altered 
  by 
  a 
  

   great 
  reduction 
  of 
  pressure. 
  The 
  body 
  of 
  the 
  gas 
  may 
  

   possibly 
  have 
  some 
  influence, 
  but 
  the 
  variations 
  which 
  have 
  

   frequently 
  been 
  attributed 
  to 
  it 
  may 
  usually 
  be 
  more 
  satis- 
  

   factorily 
  explained 
  as 
  being 
  due 
  to 
  change 
  in 
  the 
  film 
  in 
  

   contact 
  with 
  the 
  metallic 
  surface. 
  In 
  the 
  case 
  of 
  a 
  gas 
  which 
  

   acts 
  vigorously 
  on 
  the 
  metal 
  at 
  ordinary 
  temperatures 
  the 
  

   film 
  is 
  permanent, 
  and 
  is 
  probably 
  a 
  solid 
  compound 
  ; 
  in 
  

   other 
  cases 
  it 
  is 
  not 
  permanent, 
  and 
  hence 
  probably 
  not 
  solid. 
  

   § 
  55. 
  In 
  'Nature' 
  for 
  1881, 
  Lord 
  Kelvin 
  describes 
  some 
  

   very 
  important 
  experiments 
  on 
  this 
  subject. 
  As 
  these 
  appear 
  

   to 
  be 
  but 
  little 
  known 
  I 
  shall 
  give 
  some 
  extracts 
  from 
  his 
  

   paper 
  before 
  describing 
  my 
  own 
  results. 
  Under 
  the 
  date 
  

   November 
  23, 
  1880, 
  Lord 
  Kelvin 
  says 
  : 
  — 
  u 
  I 
  have 
  found 
  that 
  

   a 
  dry 
  platinum 
  disk, 
  kept 
  for 
  some 
  time 
  in 
  dry 
  hydrogen 
  

   gas, 
  and 
  then 
  put 
  into 
  its 
  position 
  in 
  dry 
  atmospheric 
  air 
  in 
  the 
  

   Volta-condenser, 
  becomes 
  positive 
  to 
  another 
  platinum 
  disk 
  

   which 
  had 
  not 
  been 
  so 
  treated, 
  but 
  had 
  simply 
  been 
  left 
  

   undisturbed 
  in 
  the 
  apparatus. 
  The 
  positive 
  quality 
  thus 
  

   produced 
  by 
  the 
  hydrogen 
  diminishes 
  gradually, 
  and 
  becomes 
  

   insensible 
  after 
  two 
  or 
  three 
  days. 
  P.S. 
  — 
  On 
  December 
  24, 
  

   1880, 
  one 
  of 
  the 
  platinum 
  plates 
  in 
  the 
  Volta-condenser 
  was 
  

   taken 
  out 
  ; 
  placed 
  in 
  dried 
  oxygen 
  gas 
  for 
  forty-five 
  minutes; 
  

   taken 
  out, 
  carried 
  by 
  hand, 
  and 
  replaced 
  in 
  the 
  Volta-con- 
  

   denser 
  at 
  12.30 
  on 
  that 
  day. 
  It 
  was 
  then 
  found 
  to 
  be 
  

   negative 
  to 
  the 
  platinum 
  plate, 
  which 
  had 
  been 
  left 
  undis- 
  

   turbed. 
  The 
  amount 
  of 
  the 
  difference 
  was 
  about 
  '33 
  of 
  a 
  

   volt. 
  The 
  plates 
  were 
  left 
  undisturbed 
  for 
  seventeen 
  minutes 
  

   in 
  the 
  condenser, 
  and 
  were 
  tested 
  again, 
  and 
  the 
  difference 
  

   was 
  found 
  to 
  have 
  fallen 
  to 
  '29 
  of 
  a 
  volt. 
  At 
  noon 
  on 
  the 
  

   25th 
  they 
  were 
  again 
  tested, 
  and 
  the 
  difference 
  found 
  to 
  be 
  

   *18. 
  The 
  difference 
  had 
  been 
  tested 
  from 
  time 
  to 
  time 
  since 
  

   that 
  day, 
  the 
  plates 
  having 
  been 
  left 
  in 
  the 
  condenser 
  undis- 
  

   turbed 
  in 
  the 
  intervals. 
  The 
  following 
  table 
  shows 
  the 
  whole 
  

  

  series 
  ot 
  these 
  results 
  : 
  Electric 
  difference 
  between 
  surfaces 
  of 
  

  

  a 
  platinum 
  plate 
  in 
  natural 
  con- 
  

   dition, 
  and 
  a 
  platinum 
  plate 
  after 
  

   45 
  minutes' 
  exposure 
  to 
  dry 
  oxygen 
  

   gas. 
  

  

  •33 
  of 
  a 
  volt. 
  

  

  •29 
  

  

  •18 
  

   •116 
  

   •097 
  

   •047 
  

   •042 
  

   •020 
  

  

  Time. 
  

   Dec. 
  24, 
  12.30 
  p.m. 
  

  

  „ 
  24, 
  12.47 
  p.m. 
  

  

  „ 
  25, 
  noon 
  . 
  . 
  

  

  „ 
  27, 
  noon 
  , 
  . 
  

  

  „ 
  28, 
  11.20 
  a.m. 
  

  

  „ 
  31, 
  noon 
  

   Jan. 
  4, 
  11 
  a.m. 
  . 
  

  

  „ 
  11, 
  11.40 
  A.M. 
  

  

  >» 
  

  

  