﻿Volt 
  a 
  Electricity 
  of 
  Metals. 
  

  

  117 
  

  

  of 
  the 
  potentials, 
  copper-water 
  and 
  water-zinc, 
  is 
  not 
  equal 
  to 
  

   copper-zinc, 
  thus 
  proving 
  that 
  the 
  two 
  free 
  surfaces 
  of 
  water 
  

   are 
  not 
  at 
  the 
  same 
  potential. 
  This 
  is 
  directly 
  demonstrated 
  

   by 
  the 
  experiments 
  of 
  Professors 
  Ayrton 
  and 
  Perry, 
  and 
  by 
  

   the 
  results 
  given 
  in 
  Chaps. 
  VI., 
  VII., 
  and 
  X. 
  of 
  this 
  commu- 
  

   nication. 
  

  

  If 
  the 
  intervening 
  layers 
  of 
  non-conductor 
  be 
  removed 
  by 
  

   joining 
  the 
  liquid 
  surfaces 
  so 
  that 
  there 
  is 
  but 
  one 
  mass 
  of 
  

   liquid 
  between 
  the 
  plates, 
  conduction 
  at 
  once 
  tends 
  to 
  reduce 
  

   the 
  whole 
  liquid 
  to 
  the 
  same 
  potential, 
  leaving 
  the 
  contact- 
  

   potential-differences, 
  now 
  unbalanced 
  by 
  the 
  removal 
  of 
  the 
  

   non-conducting 
  medium 
  which 
  was 
  capable 
  of 
  sustaining 
  the 
  

   stress, 
  to 
  act 
  as 
  external 
  electromotive 
  force. 
  This 
  then 
  

   shows 
  the 
  connexion 
  between 
  contact-potentials, 
  measured 
  

   electrostatically 
  by 
  the 
  method 
  described 
  in 
  this 
  paper, 
  and 
  

   the 
  electromotive 
  force 
  of 
  a 
  voltaic 
  cell. 
  

  

  § 
  53. 
  The 
  contact-potential 
  of 
  a 
  liquid 
  with 
  a 
  metal 
  is 
  

   clearly, 
  if 
  the 
  air-potentials 
  be 
  neglected, 
  the 
  difference 
  

   between 
  the 
  potential 
  of 
  the 
  dry 
  metal 
  and 
  that 
  of 
  the 
  metal 
  

   when 
  wet 
  with 
  the 
  liquid 
  ; 
  the 
  same 
  standard 
  plate 
  being 
  

   used 
  as 
  zero 
  of 
  potential 
  in 
  both 
  cases. 
  The 
  results 
  given 
  in 
  

   the 
  tables 
  must 
  no 
  doubt 
  be 
  iu 
  some 
  cases 
  complicated 
  by 
  the 
  

   formation 
  of 
  solid 
  compounds 
  in 
  the 
  interface 
  between 
  liquid 
  

   and 
  metal 
  so 
  that 
  the 
  liquid 
  is 
  no 
  longer 
  in 
  contact 
  with 
  clean 
  

   metal, 
  and 
  the 
  liquid 
  must 
  also 
  displace 
  any 
  film 
  of 
  condensed 
  

   air 
  which 
  may 
  exist 
  on 
  the 
  metal. 
  The 
  latter 
  influence 
  will 
  

   be 
  discussed 
  in 
  Chaps. 
  VIII. 
  and 
  X. 
  

  

  Table 
  III. 
  — 
  Potential 
  of 
  Metals 
  covered 
  with 
  visible 
  

   layer 
  of 
  Alcohol. 
  

  

  Metal. 
  

  

  State 
  of 
  Surface. 
  

  

  Potential 
  with 
  standard 
  

   gold 
  plate. 
  

  

  Dry. 
  

  

  Wet. 
  

  

  Change. 
  

  

  G-old 
  ... 
  

  

  Silver 
  

  

  Filed 
  ; 
  wet 
  with 
  alcohol 
  

  

  volt. 
  

   -•13 
  

  

  +•10 
  

  

  + 
  •61 
  

   

  

  volt. 
  

   +•19 
  

  

  + 
  •18 
  

   + 
  •19 
  

  

  +•74' 
  

   +•74 
  

  

  volt. 
  

   + 
  •32 
  

  

  + 
  •13 
  

  

  + 
  •08 
  

   + 
  09 
  

  

  + 
  •13 
  

   +•13 
  

  

  

  Lead 
  

  

  Scraped 
  thorouorhlv 
  

  

  

  Wet, 
  *1 
  cm. 
  deep 
  

  

  ,, 
  thin 
  film 
  only 
  

  

  

  