﻿Volt 
  a 
  EUctricity 
  of 
  Metals. 
  403 
  

  

  § 
  10. 
  The 
  results 
  given 
  are 
  not 
  in 
  the 
  order 
  in 
  which 
  they 
  

   were 
  obtained, 
  but 
  are 
  classified 
  in 
  such 
  a 
  way 
  as 
  to 
  show 
  

   more 
  clearly 
  their 
  true 
  import, 
  and 
  those 
  of 
  many 
  experi- 
  

   ments 
  which 
  are 
  not 
  mentioned 
  in 
  the 
  text 
  will 
  be 
  found 
  in 
  

   the 
  tables. 
  

  

  III. 
  Effects 
  of 
  different 
  Methods 
  of 
  Cleansing 
  the 
  

   Metallic 
  Surfaces. 
  

  

  § 
  11. 
  It 
  seems 
  probable 
  that 
  the 
  very 
  conflicting 
  results 
  

   obtained 
  by 
  different 
  experimenters 
  for 
  the 
  potential-difference 
  

   of 
  any 
  given 
  pair 
  of 
  metals, 
  in 
  air, 
  must 
  be 
  due, 
  to 
  a 
  large 
  

   extent, 
  to 
  differences 
  in 
  the 
  methods 
  by 
  which 
  the 
  surfaces 
  

   have 
  been 
  prepared. 
  In 
  order 
  to 
  obtain 
  a 
  metallic 
  surface 
  as 
  

   free 
  as 
  possible 
  from 
  all 
  contamination 
  it 
  is 
  clear 
  that 
  a 
  hard 
  

   polishing 
  agent, 
  such 
  as 
  a 
  clean 
  steel 
  file, 
  or 
  emery-cloth, 
  or 
  

   glass-paper, 
  must 
  be 
  used, 
  as 
  a 
  softer 
  material 
  leaves 
  more 
  of 
  

   itself 
  on 
  the 
  plate. 
  A 
  liquid 
  is 
  quite 
  unsuitable, 
  since 
  every 
  

   particle 
  of 
  the 
  metal 
  probably 
  retains 
  particles 
  of 
  the 
  liquid 
  

   adhering 
  to 
  it. 
  Thus 
  the 
  smell 
  of 
  a 
  liquid 
  remains 
  long 
  after 
  

   the 
  plate 
  appears 
  to 
  be 
  quite 
  dry 
  ; 
  and 
  it 
  has 
  been 
  found 
  that 
  

   such 
  a 
  film 
  as 
  must 
  exist 
  to 
  cause 
  the 
  odour 
  is 
  quite 
  sufficient 
  

   to 
  alter 
  the 
  potential 
  very 
  considerably. 
  

  

  § 
  12. 
  In 
  order 
  to 
  obtain 
  uniformity 
  of 
  action 
  the 
  clean 
  

   glass-paper 
  or 
  emery-cloth 
  used 
  to 
  polish 
  a 
  plate 
  was 
  fixed 
  on 
  

   a 
  wooden 
  roller 
  made 
  to 
  revolve 
  with 
  a 
  circumferential 
  velocity 
  

   of 
  about 
  100 
  centim. 
  per 
  second. 
  Care 
  was 
  taken 
  to 
  hold 
  the 
  

   plate 
  so 
  that 
  the 
  scratches, 
  caused 
  by 
  the 
  polisher, 
  should 
  all 
  

   be 
  parallel. 
  Thus 
  little 
  or 
  no 
  grit 
  could 
  lodge 
  in 
  the 
  surface, 
  

   which 
  would 
  have 
  occurred, 
  had 
  the 
  scratches 
  crossed 
  one 
  

   another. 
  A 
  record 
  was 
  kept 
  of 
  the 
  nature 
  of 
  the 
  polishing 
  

   agent 
  in 
  every 
  case. 
  A 
  piece 
  of 
  glass-paper, 
  or 
  other 
  polisher, 
  

   was 
  seldom 
  used, 
  more 
  than 
  once 
  or 
  twice, 
  and 
  was 
  never 
  used 
  

   for 
  any 
  different 
  metal. 
  

  

  § 
  13. 
  M. 
  Pellat 
  found 
  that 
  every 
  change 
  in 
  the 
  smoothness 
  

   of 
  a 
  surface 
  is 
  accompanied 
  by 
  a 
  change 
  in 
  its 
  contact 
  poten- 
  

   tial 
  ; 
  but 
  as 
  his 
  experiments 
  were 
  limited 
  to 
  metals 
  washed 
  

   with 
  alcohol, 
  it 
  was 
  of 
  interest 
  to 
  extend 
  them 
  to 
  more 
  general 
  

   cases. 
  Thus 
  a 
  plate 
  of 
  zinc 
  which 
  had 
  been 
  polished 
  on 
  clean 
  

   glass-paper, 
  and 
  had 
  therefore 
  a 
  surface 
  sharply 
  scratched 
  in 
  

   parallel 
  lines, 
  was 
  found 
  to 
  be 
  

  

  •70 
  volt 
  

  

  positive 
  to 
  the 
  standard 
  gold 
  plate. 
  It 
  was 
  next 
  burnished 
  

   with 
  a 
  tool 
  of 
  hardened 
  steel, 
  and 
  with 
  the 
  same 
  standard 
  

   plate 
  it 
  now 
  gave 
  

  

  •94 
  volt. 
  

  

  