﻿Hrs. 
  

  

  Min. 
  

  

  

  

  22 
  

  

  

  

  27 
  

  

  

  

  46 
  

  

  1 
  

  

  4 
  

  

  1 
  

  

  23 
  

  

  3 
  

  

  18 
  

  

  4 
  

  

  6 
  

  

  4 
  

  

  42 
  

  

  71 
  

  

  12 
  

  

  Volta 
  Electricity 
  of 
  Metals. 
  411 
  

  

  Volts. 
  

  

  . 
  +-515 
  

  

  . 
  + 
  -520 
  

   + 
  •535 
  

  

  . 
  +-535 
  

  

  . 
  +-515 
  

  

  . 
  +*495 
  

  

  . 
  +-495 
  

  

  . 
  +-495 
  

  

  . 
  +*465 
  

  

  The 
  plate 
  was 
  kept 
  in 
  the 
  apparatus 
  all 
  the 
  time 
  and 
  its 
  

   potential 
  taken 
  with 
  a 
  standard 
  gold 
  plate. 
  

  

  § 
  33. 
  In 
  another 
  experiment 
  a 
  tin 
  plate 
  polished 
  on 
  the 
  

   finest 
  glass-paper 
  gave, 
  after 
  h 
  15 
  m 
  , 
  

  

  + 
  -525 
  v.- 
  

   After 
  23 
  h 
  30 
  m 
  it 
  gave 
  

  

  + 
  •535 
  v. 
  

  

  This 
  experiment 
  was 
  made 
  in 
  June, 
  while 
  the 
  previous 
  one 
  

   was 
  made 
  in 
  December. 
  Hence 
  probably 
  the 
  greater 
  rate 
  of 
  

   variation 
  in 
  the 
  former 
  was 
  due 
  to 
  a 
  moister 
  and 
  less 
  pure 
  

   atmosphere. 
  

  

  § 
  34. 
  An 
  old 
  zinc 
  plate 
  which 
  had 
  probably 
  not 
  been 
  

   polished 
  for 
  many 
  years 
  gave 
  

  

  + 
  •37 
  v. 
  

  

  with 
  the 
  standard 
  gold 
  plate. 
  It 
  was 
  next 
  polished 
  on 
  glass- 
  

   paper, 
  and 
  gave 
  

  

  + 
  •75 
  v. 
  

  

  with 
  the 
  same 
  standard. 
  This 
  shows 
  that 
  the 
  ultimate 
  effect 
  

   of 
  exposure 
  is 
  to 
  make 
  the 
  potential 
  of 
  zinc 
  fall. 
  1 
  have 
  found 
  

   that 
  in 
  some 
  cases 
  this 
  fall 
  is 
  preceded 
  by 
  a 
  slight 
  rise, 
  as 
  in 
  

   the 
  case 
  of 
  tin 
  (§§ 
  32, 
  33); 
  but 
  the 
  ultimate 
  effect 
  is 
  in 
  the 
  

   negative 
  direction. 
  

  

  § 
  35. 
  The 
  potential 
  of 
  a 
  silver 
  plate 
  which 
  had 
  been 
  polished 
  

   on 
  glass-paper 
  remained 
  constant 
  for 
  an 
  hour. 
  The 
  experi- 
  

   ment 
  was 
  not 
  continued 
  further. 
  

  

  § 
  36. 
  Aluminium 
  becomes 
  gradually 
  negative 
  in 
  air. 
  In 
  

   one 
  case 
  the 
  potential 
  fell 
  about 
  *18 
  v. 
  in 
  a 
  week. 
  The 
  

   time-change 
  of 
  this 
  metal, 
  mainly 
  on 
  account 
  of 
  its 
  large 
  

   temperature-variation 
  (see 
  Chap. 
  IX.), 
  is 
  rather 
  difficult 
  to 
  

   determine. 
  

  

  § 
  37. 
  An 
  iron 
  plate 
  which 
  had 
  not 
  been 
  cleansed 
  for 
  two 
  

   months 
  rose 
  *05 
  v. 
  when 
  polished. 
  Hence 
  the 
  effect 
  of 
  

   exposure 
  had 
  been 
  to 
  make 
  its 
  potential 
  fall 
  slightly. 
  

  

  § 
  38. 
  I 
  have 
  included 
  these 
  results, 
  for 
  which, 
  as 
  for 
  many 
  

   others 
  like 
  them, 
  I 
  can 
  as 
  yet 
  give 
  no 
  definite 
  explanation, 
  

  

  