﻿Volla 
  Electricity 
  of 
  Metals. 
  415 
  

  

  potential 
  remaining 
  the 
  same 
  ; 
  i, 
  e. 
  tlie 
  lead 
  plate 
  gave 
  with 
  

   the 
  water 
  in 
  the 
  leaden 
  dish, 
  

  

  + 
  •10 
  v., 
  

  

  water 
  in 
  leaden 
  dish 
  being 
  negative. 
  

  

  § 
  48. 
  The 
  plate 
  and 
  dish 
  were 
  again 
  scraped, 
  and 
  this 
  time 
  

   they 
  gave 
  

  

  + 
  •05 
  v., 
  

  

  the 
  plate 
  being 
  positive. 
  Water 
  was 
  next 
  poured 
  into 
  the 
  

   dish, 
  which 
  gave, 
  with 
  the 
  dry 
  lead 
  plate, 
  

  

  + 
  •09 
  v., 
  

  

  the 
  water 
  in 
  the 
  dish 
  being 
  negative 
  as 
  before. 
  The 
  dish 
  was 
  

   now 
  removed 
  and 
  a 
  standard 
  gold 
  plate 
  put 
  in 
  its 
  place 
  ; 
  with 
  

   this 
  the 
  lead 
  plate 
  gave 
  

  

  + 
  •52 
  v., 
  

  

  the 
  lead 
  being 
  positive. 
  Thus 
  water 
  in 
  contact 
  with 
  lead 
  is 
  

   about 
  *09 
  v. 
  negative 
  to 
  dry 
  lead. 
  

  

  § 
  49. 
  Turpentine 
  seems 
  to 
  produce 
  opposite 
  effects 
  on 
  zinc 
  

   and 
  copper, 
  i. 
  e. 
  copper 
  becomes 
  more 
  negative 
  and 
  zinc 
  

   more 
  positive 
  when 
  wet. 
  Thus 
  copper 
  and 
  zinc 
  which 
  had 
  

   been 
  dry-polished 
  gave 
  with 
  one 
  another 
  

  

  •77 
  v., 
  

   zinc 
  positive. 
  

  

  With 
  the 
  zinc 
  wet 
  with 
  turpentine, 
  

  

  •96 
  v. 
  

  

  And 
  with 
  both 
  zinc 
  and 
  copper 
  wet 
  about 
  

  

  1-20 
  v. 
  

  

  Their 
  potential-difference 
  increased 
  somewhat 
  as 
  the 
  turpentine 
  

   dried 
  up 
  ; 
  and 
  when 
  apparently 
  quite 
  dry 
  its 
  value 
  was 
  still 
  

   at 
  least 
  

  

  1-20 
  v., 
  

  

  the 
  plates, 
  however, 
  smelt 
  strongly 
  of 
  turpentine, 
  showing 
  

   that 
  an 
  invisible 
  layer 
  remained 
  on 
  their 
  surfaces. 
  

  

  § 
  50. 
  A 
  crystal 
  of 
  copper 
  sulphate 
  gave, 
  with 
  a 
  standard 
  

   gold 
  plate, 
  

  

  + 
  '02 
  v., 
  

  

  copper 
  sulphate 
  positive. 
  This 
  result 
  was 
  obtained 
  in 
  con- 
  

   nexion 
  with 
  some 
  experiments 
  on 
  the 
  contact-potential 
  of 
  an 
  

   aqueous 
  solution 
  of 
  copper 
  sulphate. 
  It 
  was 
  found 
  that 
  such 
  

   a 
  solution 
  in 
  a 
  copper 
  dish 
  gave 
  about 
  +*07 
  volt 
  with 
  a 
  dry 
  

   standard 
  gold 
  plate, 
  the 
  solution 
  being 
  positive. 
  Blotting- 
  

  

  2 
  F 
  2 
  

  

  