﻿412 
  Dr. 
  J. 
  Erskine-Murray 
  on 
  

  

  in 
  the 
  hope 
  that 
  they 
  may 
  serve 
  as 
  a 
  basis 
  for 
  future 
  expe- 
  

   riment 
  and 
  generalization. 
  The 
  great 
  difficulty 
  in 
  all 
  such 
  

   experiments 
  on 
  contact 
  electricity 
  is 
  to 
  define 
  the 
  circum- 
  

   stances 
  and, 
  with 
  them, 
  the 
  causes 
  of 
  any 
  given 
  variation. 
  

  

  VI. 
  Very 
  Thin 
  Liquid 
  Films 
  on 
  Metals. 
  

   § 
  39. 
  In 
  the 
  earlier 
  experiments 
  it 
  was 
  found 
  that, 
  as 
  a 
  

   rule, 
  copper 
  polished 
  on 
  glass-paper 
  or 
  emery-cloth 
  was 
  about 
  

   '20 
  v. 
  negative 
  to 
  the 
  standard 
  alcohol- 
  washed 
  gold 
  plate. 
  

   On 
  comparing 
  this 
  value 
  with 
  M. 
  Pellat's 
  results* 
  I 
  found 
  

   that 
  his 
  value 
  for 
  copper 
  was 
  about 
  "20 
  positive 
  to 
  the 
  same 
  

   standard. 
  I 
  at 
  once 
  determined 
  to 
  try 
  his 
  method 
  of 
  cleansing 
  

   the 
  plate 
  so 
  as 
  to 
  find 
  if 
  the 
  difference 
  (*40 
  volt) 
  were 
  due 
  to 
  

   that 
  alone. 
  For 
  this 
  purpose 
  a 
  copper 
  plate 
  was 
  carefully 
  

   polished 
  on 
  glass-paper. 
  It 
  gave, 
  with 
  the 
  standard, 
  

  

  -•20 
  v. 
  

  

  It 
  was 
  then 
  washed 
  with 
  alcohol 
  and 
  allowed 
  to 
  dry 
  in 
  air. 
  

  

  It 
  now 
  gave 
  ->~ 
  

  

  ° 
  +'22 
  v. 
  

  

  with 
  the 
  same 
  standard. 
  The 
  change 
  due 
  to 
  the 
  treatment 
  is 
  

  

  therefore 
  + 
  *42 
  volt, 
  and 
  continues 
  permanent 
  many 
  hours. 
  

  

  § 
  40. 
  A 
  plate 
  of 
  thickly 
  oxidized 
  copper 
  giving, 
  with 
  the 
  

  

  standard 
  plate, 
  _ 
  . 
  

  

  r 
  —'24 
  v. 
  

  

  gave, 
  after 
  it 
  had 
  been 
  washed 
  with 
  alcohol 
  and 
  allowed 
  to 
  

  

  dr 
  * 
  -00 
  v. 
  

  

  a 
  rise 
  of 
  *24 
  volt. 
  

  

  § 
  41. 
  A 
  zinc 
  plate, 
  when 
  cleaned 
  on 
  glass-paper, 
  gave 
  

  

  + 
  •61 
  v. 
  

   It 
  was 
  then 
  washed 
  with 
  alcohol, 
  and 
  when 
  apparently 
  quite 
  

  

  dry 
  gave 
  , 
  n 
  . 
  

  

  J 
  fe 
  -f 
  • 
  94 
  v., 
  

  

  remaining 
  constant 
  at 
  this 
  value 
  for 
  many 
  hours. 
  The 
  rise 
  

   in 
  this 
  case 
  is 
  '33 
  volt. 
  

  

  § 
  42. 
  The 
  results 
  of 
  many 
  similar 
  experiments 
  made 
  with 
  

   alcohol 
  and 
  other 
  liquids 
  on 
  gold, 
  silver, 
  zinc, 
  copper, 
  iron, 
  

   tin, 
  lead, 
  and 
  aluminium 
  will 
  be 
  found 
  in 
  Table 
  II. 
  It 
  is 
  

   notable 
  that 
  in 
  almost 
  every 
  case 
  the 
  contact-potential 
  of 
  a 
  

   metal 
  which 
  has 
  been 
  polished 
  on 
  a 
  hard 
  dry 
  material 
  rises 
  at 
  

   least 
  *15 
  volt 
  in 
  consequence 
  of 
  alcohol 
  washing, 
  and 
  that 
  

   this 
  change 
  is 
  nearly 
  permanent 
  for 
  many 
  hours 
  after 
  the 
  

   plate 
  appears 
  to 
  be 
  quite 
  dry. 
  

  

  § 
  43. 
  It 
  may 
  be 
  remarked 
  that, 
  as 
  M. 
  Pellat 
  appears 
  to 
  

   have 
  invariably 
  washed 
  the 
  metal 
  with 
  alcohol 
  before 
  making 
  

   a 
  measurement 
  of 
  its 
  potential, 
  his 
  results 
  do 
  not 
  apply 
  

   * 
  Ann. 
  de 
  Chimie 
  et 
  de 
  Physique, 
  1881. 
  

  

  