﻿602 
  Messrs. 
  Cameron 
  and 
  Oettinger 
  on 
  Electromotive 
  

  

  with 
  the 
  results 
  of 
  Dorn 
  and 
  o£ 
  ourselves 
  ; 
  but 
  the 
  change 
  

   produced 
  on 
  making 
  the 
  solution 
  acid 
  or 
  alkaline 
  is, 
  in 
  sign, 
  

   the 
  same 
  which 
  we 
  have 
  found, 
  and 
  which 
  is 
  to 
  be 
  expected 
  

   from 
  the 
  theory 
  quoted 
  in 
  the 
  beginning 
  of 
  this 
  paper. 
  

  

  The 
  theory 
  of 
  Perrin, 
  also, 
  is 
  very 
  different 
  from 
  that 
  from 
  

   which 
  we 
  start. 
  It 
  is 
  akin 
  to 
  the 
  views 
  of 
  Knoblauch_, 
  who 
  

   found 
  that 
  when 
  platinum 
  was 
  brought 
  into 
  contact 
  with 
  solid 
  

   acids 
  or 
  bases, 
  it 
  obtained 
  a 
  positive 
  or 
  negative 
  charge 
  re- 
  

   spectively. 
  The 
  fundamental 
  point 
  of 
  these 
  theoretical 
  views 
  

   is 
  that 
  the 
  governing 
  phenomenon 
  is 
  the 
  diffusion 
  of 
  the 
  ions. 
  

   Knoblauch 
  assumes 
  that 
  the 
  platinum 
  has 
  an 
  infinitely 
  thin 
  

   layer 
  of 
  water 
  on 
  it 
  ; 
  the 
  solid 
  acid 
  or 
  base 
  is 
  dissolved 
  in 
  this 
  

   to 
  a 
  certain 
  extent 
  and 
  diffuses 
  onto 
  the 
  platinum 
  ; 
  the 
  ions 
  

   which 
  diffuse 
  faster 
  first 
  come 
  in 
  contact 
  with 
  the 
  platinum, 
  

   which 
  accordingly 
  becomes 
  charged 
  positively 
  with 
  acids, 
  

   negatively 
  with 
  alkalies. 
  Perrin, 
  following 
  some 
  ideas 
  of 
  

   Langevin, 
  thinks 
  that 
  the 
  faster 
  migrating 
  ions 
  are 
  smaller; 
  

   they 
  are 
  thus 
  enabled 
  to 
  come 
  nearer 
  to 
  the 
  surface 
  of 
  a 
  solid 
  

   insulator 
  surrounded 
  by 
  electrolytically 
  dissociated 
  liquid 
  than 
  

   can 
  the 
  slower 
  moving 
  ions. 
  In 
  the 
  case 
  of 
  such 
  a 
  liquid 
  

   streaming 
  along 
  an 
  insulator 
  he 
  thinks 
  that 
  the 
  faster 
  ions 
  

   come 
  within 
  the 
  last 
  layer 
  held 
  in 
  a 
  state 
  of 
  rest 
  by 
  external 
  

   friction 
  at 
  the 
  surface, 
  while 
  the 
  slower 
  moving 
  and, 
  

   according 
  to 
  his 
  view, 
  larger 
  ions 
  remain 
  in 
  the 
  moving- 
  

   layers 
  of 
  the 
  liquid. 
  This 
  view 
  is 
  applicable 
  to 
  acids 
  and 
  

   alkalies 
  because 
  the 
  hydrogen 
  and 
  hydroxyl 
  ions 
  are 
  espe- 
  

   cially 
  fast 
  ; 
  it 
  is 
  supported 
  by 
  Perrin's 
  experimental 
  data 
  for 
  

   these 
  ions. 
  It 
  of 
  course 
  would 
  bo 
  expected 
  that 
  it 
  holds 
  also 
  

   in 
  other 
  cases 
  where 
  differences 
  of 
  the 
  migration 
  velocities 
  

   exist, 
  but 
  Perrin 
  could 
  not 
  verify 
  this 
  for 
  lithium 
  bromide, 
  

   although 
  he 
  himself 
  emphasized 
  the 
  fact 
  that 
  the 
  lithium 
  ion 
  

   has 
  only 
  half 
  the 
  mobility 
  of 
  that 
  of 
  bromine 
  *. 
  

  

  Contradictory 
  as 
  Perrin's 
  results 
  are 
  to 
  those 
  of 
  Dorn 
  and 
  

   of 
  ourselves, 
  so 
  equally 
  contradictory 
  is 
  his 
  theory 
  to 
  that 
  of 
  

   Lamb, 
  who 
  thinks 
  that 
  the 
  charge 
  is 
  rigidly 
  confined 
  to 
  the 
  

   first 
  layer 
  of 
  solid 
  and 
  last 
  layer 
  of 
  liquid. 
  Helmholtz^s 
  

   theory 
  of 
  the 
  phenomenon 
  is 
  so 
  general 
  that 
  that 
  it 
  may 
  be 
  

   considered 
  in 
  agreement 
  with 
  either 
  standpoint. 
  The 
  most 
  

   important 
  point, 
  however, 
  is 
  that 
  the 
  dift'usion 
  theory 
  cannot 
  

   be 
  assimilated 
  up 
  to 
  the 
  present 
  time 
  with 
  the 
  views 
  which 
  

  

  * 
  The 
  standpoint 
  of 
  Perrin 
  recalls 
  some 
  results 
  obtained 
  by 
  Rutherford 
  

   with 
  ionized 
  gases. 
  He 
  was 
  able 
  to 
  show 
  that 
  such 
  a 
  gas 
  when 
  it 
  passed 
  

   through 
  a 
  narrow 
  metallic 
  tube 
  produces 
  a 
  charge 
  at 
  the 
  surface 
  of 
  the 
  

   metal 
  the 
  sign 
  of 
  which 
  is 
  determined 
  by 
  that 
  of 
  the 
  ion 
  with 
  higher 
  

   diffusion 
  coefficient. 
  

  

  