﻿Volta 
  Electricity 
  of 
  Metals. 
  405 
  

  

  In 
  nnother 
  experiment 
  two 
  coppers 
  which 
  had 
  been 
  polished 
  

   on 
  medium 
  emery-cloth 
  (Davies's 
  No. 
  1\) 
  gave, 
  with 
  the 
  

   standard 
  plate, 
  

  

  (a) 
  -'11 
  v. 
  

  

  (b) 
  --06 
  v. 
  

  

  When 
  slightly 
  burnished 
  by 
  rubbing 
  them 
  together, 
  they 
  

   gave 
  

  

  (a) 
  -'02 
  v. 
  

  

  (b) 
  -'02 
  v. 
  

  

  Thus, 
  smoothing 
  by 
  mutual 
  friction 
  made 
  both 
  more 
  positive. 
  

   The 
  amount 
  of 
  the 
  change 
  is 
  not 
  great, 
  either 
  in 
  potential 
  or 
  

   in 
  smoothness, 
  as 
  it 
  is 
  very 
  difficult 
  to 
  polish 
  copper 
  on 
  copper, 
  

   but 
  the 
  direction 
  of 
  change 
  is 
  the 
  same 
  as 
  previously 
  found, 
  

   namely, 
  a 
  smooth 
  surface 
  is 
  more 
  positive 
  than 
  a 
  sharply 
  

   scratched 
  one. 
  

  

  § 
  17. 
  On 
  account 
  of 
  the 
  difficulty 
  of 
  obtaining 
  a 
  burnished 
  

   surface 
  by 
  simply 
  rubbing 
  two 
  pieces 
  of 
  the 
  same 
  metal 
  

   together, 
  I 
  tried 
  another 
  form 
  of 
  experiment 
  in 
  which 
  the 
  

   possible 
  effect 
  of 
  the 
  material 
  of 
  the 
  polishing 
  agent 
  is 
  elimi- 
  

   nated 
  by 
  using 
  the 
  same 
  tool 
  to 
  produce 
  different 
  states 
  of 
  

   surface. 
  Thus 
  a 
  copper 
  plate 
  was 
  scratched 
  very 
  roughly 
  

   with 
  a 
  steel 
  tool, 
  and 
  gave 
  

  

  -•07 
  v. 
  

  

  with 
  the 
  standard 
  plate, 
  then 
  burnished 
  slightly 
  with 
  the 
  

   same 
  tool 
  it 
  gave 
  

  

  -•02 
  v. 
  

  

  It 
  had 
  thus 
  risen 
  *05 
  v. 
  on 
  account 
  of 
  the 
  alteration 
  pro- 
  

   duced 
  in 
  smoothing; 
  its 
  surface. 
  Thus 
  these 
  results 
  also 
  con- 
  

   firm 
  the 
  conclusion 
  given 
  in 
  § 
  14. 
  

  

  § 
  18. 
  It 
  should 
  be 
  noticed 
  that 
  although 
  individual 
  results 
  

   occasionally 
  appear 
  to 
  conflict, 
  the 
  average 
  value 
  of 
  the 
  

   potential 
  of 
  any 
  given 
  metal 
  when 
  polished 
  with 
  a 
  certain 
  

   agent 
  is 
  almost 
  always 
  in 
  proportion 
  to 
  the 
  smoothness 
  of 
  

   the 
  surface 
  produced. 
  However 
  much 
  one 
  may 
  try, 
  it 
  is 
  

   impossible 
  to 
  get 
  exactly 
  the 
  same 
  state 
  of 
  surface 
  over 
  again, 
  

   but 
  by 
  taking 
  the 
  average 
  of 
  a 
  considerable 
  number 
  of 
  experi- 
  

   ments 
  with 
  one 
  polishing 
  agent, 
  a 
  general 
  value 
  is 
  got 
  which 
  

   represents 
  the 
  potential 
  given 
  by 
  the 
  plate 
  in 
  a 
  certain 
  state 
  

   of 
  polish. 
  It 
  is 
  so 
  arranged 
  that 
  the 
  sharply 
  scratched 
  sur- 
  

   faces 
  come 
  at 
  the 
  head 
  of 
  the 
  table, 
  and 
  each 
  succeeding 
  

   polishing 
  agent 
  in 
  the 
  list 
  produces 
  a 
  smoother 
  surface. 
  

  

  § 
  19. 
  It 
  should 
  be 
  observed 
  that 
  with 
  soft 
  metals 
  such 
  as 
  

   tin, 
  different 
  polishers 
  produce 
  but 
  little 
  change 
  in 
  the 
  contact 
  

   potential. 
  This, 
  though 
  at 
  first 
  sight 
  apparently 
  contrary 
  to 
  

  

  