﻿Volta 
  Electricity 
  of 
  Metals. 
  423 
  

  

  § 
  62. 
  A 
  tin 
  plate 
  was 
  polished 
  on 
  clean 
  glass-paper, 
  and 
  

   gave 
  with 
  a 
  copper 
  plate 
  

  

  + 
  •40 
  v., 
  

  

  tin 
  being 
  positive. 
  Fifteen 
  minutes 
  later 
  the 
  potential 
  of 
  the 
  

   plates 
  had 
  not 
  altered. 
  I 
  now 
  put 
  the 
  tin 
  into 
  the 
  bell-jar 
  

   and 
  turned 
  on 
  the 
  oxygen. 
  After 
  it 
  had 
  soaked 
  for 
  47 
  

   minutes 
  it 
  was 
  taken 
  out 
  and 
  compared 
  with 
  the 
  same 
  copper 
  

  

  plate. 
  It 
  gave 
  

  

  Time. 
  Contact-potential. 
  

   h. 
  m. 
  v. 
  

  

  5 
  +-32 
  

  

  13 
  +'32 
  

  

  35 
  +-35 
  

  

  Thus 
  the 
  variation 
  of 
  tin 
  appears 
  to 
  be 
  in 
  the 
  negative 
  direc- 
  

   tion, 
  like 
  that 
  of 
  platinum. 
  

  

  § 
  63. 
  A 
  silver 
  plate, 
  polished 
  on 
  glass-paper, 
  gave 
  with 
  a 
  

   standard 
  copper 
  plate 
  

  

  -•04 
  v., 
  

  

  and 
  remained 
  constant 
  during 
  an 
  hour. 
  It 
  was 
  then 
  put 
  into 
  

   oxygen 
  for 
  15 
  minutes, 
  and 
  when 
  taken 
  out 
  its 
  potential 
  was 
  

   found 
  to 
  be 
  

  

  rp" 
  

  

  lime, 
  

   h. 
  m. 
  

   3 
  

  

  Contact-potential. 
  

   v. 
  

   -f-02 
  

  

  19 
  

  

  -•01 
  

  

  40 
  

  

  -•02 
  

  

  45 
  

  

  -•02 
  

  

  59 
  

  

  —03 
  

  

  Thus 
  by 
  immersion 
  in 
  oxygen 
  for 
  15 
  minutes 
  it 
  had 
  risen 
  

   *06 
  v., 
  and 
  had 
  fallen 
  to 
  nearly 
  its 
  original 
  value 
  in 
  an 
  hour 
  

   in 
  air. 
  

  

  § 
  64. 
  Silver 
  polished 
  on 
  clean 
  " 
  fine 
  " 
  glass-paper 
  gave 
  

   with 
  a 
  standard 
  copper 
  

  

  -•095 
  v. 
  

  

  After 
  it 
  had 
  been 
  24 
  minutes 
  in 
  oxygen 
  it 
  gave 
  in 
  air 
  

  

  + 
  •015 
  v., 
  

   and 
  1 
  2 
  minutes 
  later 
  

  

  + 
  •010 
  v., 
  

  

  showing 
  that 
  the 
  potential 
  had 
  in 
  24 
  minutes 
  in 
  oxygen 
  

   become 
  "110 
  more 
  positive. 
  

  

  § 
  65. 
  It 
  is 
  noticeable 
  that 
  the 
  amount 
  of 
  change 
  in 
  these 
  

   experiments 
  on 
  silver 
  is 
  to 
  some 
  extent 
  proportionate 
  to 
  the 
  

  

  