﻿R. 
  8. 
  Dean 
  — 
  Electron 
  Theory 
  of 
  Passivity. 
  123 
  

  

  Akt. 
  V. 
  — 
  An 
  Electron 
  Theory 
  of 
  Passivity; 
  by 
  Reginald 
  

  

  S. 
  Dean. 
  

  

  Starting 
  from 
  Drude's 
  electron 
  theory 
  of 
  metals 
  it 
  is 
  

   possible 
  to 
  derive 
  a 
  relation 
  giving 
  the 
  contact 
  potential 
  

   in 
  terms 
  of 
  certain 
  characteristic 
  constants 
  and 
  the 
  elec- 
  

   tron 
  numbers 
  of 
  the 
  concerned 
  metals. 
  This 
  has 
  been 
  

   done 
  by 
  Langmuir 
  1 
  who 
  gives 
  the 
  formula 
  

  

  N 
  

   V 
  — 
  V 
  = 
  P 
  — 
  P 
  4-— 
  - 
  

  

  X 
  2 
  

  

  where 
  Pj 
  and 
  P 
  2 
  represent 
  the 
  so-called 
  electron 
  affinities 
  

   and 
  Nj 
  and 
  N 
  2 
  the 
  electron 
  concentrations 
  of 
  the 
  con- 
  

   cerned 
  metals. 
  

  

  The 
  contact 
  potential 
  is 
  only 
  a 
  constant 
  therefore 
  if 
  

   Nj 
  and 
  N 
  2 
  are 
  constants 
  ; 
  if 
  this 
  is 
  not 
  the 
  case 
  the 
  expres- 
  

   sion 
  only 
  holds 
  if 
  Nj 
  and 
  N 
  2 
  represent 
  the 
  electron 
  num- 
  

   bers 
  of 
  the 
  surface 
  layer. 
  If 
  it 
  were 
  possible 
  to 
  maintain 
  

   a 
  surface 
  layer 
  with 
  a 
  greater 
  or 
  less 
  electron 
  concentra- 
  

   tion 
  than 
  the 
  mass 
  of 
  the 
  metal 
  we 
  should 
  then 
  have 
  a 
  

   condition 
  of 
  abnormal 
  contact 
  potential. 
  In 
  case 
  the 
  sur- 
  

   face 
  were 
  less 
  concentrated 
  in 
  electrons 
  than 
  the 
  main 
  

   body 
  of 
  the 
  metal, 
  we 
  should 
  have 
  a 
  condition 
  of 
  

   ennobling. 
  Such 
  a 
  surface 
  condition 
  would 
  explain 
  many 
  

   of 
  the 
  peculiarities 
  of 
  the 
  so-called 
  passive 
  metals. 
  

  

  The 
  production 
  of 
  passivity 
  by 
  oxidizing 
  agents 
  and 
  

   anodic 
  polarization 
  can 
  be 
  explained 
  in 
  this 
  way 
  since 
  

   oxidation 
  is 
  in 
  effect 
  the 
  removal 
  of 
  electrons. 
  

  

  The 
  various 
  phenomena 
  of 
  ennobling 
  characteristic 
  of 
  

   passive 
  surfaces 
  are 
  all 
  to 
  be 
  explained 
  from 
  raised 
  con- 
  

   tact 
  potential 
  or 
  the 
  closely 
  connected 
  electrode 
  poten- 
  

   tial. 
  

  

  The 
  low 
  photo-electric 
  emission 
  of 
  passive 
  iron 
  as 
  

   observed 
  by 
  Allen 
  2 
  is 
  in 
  direct 
  accord 
  with 
  a 
  surface 
  layer 
  

   lower 
  in 
  electrons. 
  

  

  There 
  remain, 
  however, 
  three 
  things 
  which 
  must 
  be 
  

   accounted 
  for 
  to 
  make 
  an 
  electron 
  theory 
  of 
  passivity 
  

   probable: 
  (1) 
  the 
  maintenance 
  of 
  an 
  electron 
  deficient 
  

   surface; 
  (2) 
  the 
  characteristic 
  occurrence 
  of 
  passivity 
  in 
  

   the 
  metals 
  of 
  the 
  iron 
  group 
  ; 
  (3) 
  the 
  effect 
  of 
  magnetism 
  

   on 
  passivity. 
  

  

  1 
  1. 
  Langmuir, 
  Trans. 
  Amer. 
  Electrochem. 
  Soc, 
  p. 
  144, 
  1916. 
  

   2 
  H. 
  S. 
  Allen, 
  Proc. 
  Koy. 
  Soc. 
  London, 
  88, 
  70, 
  1913. 
  

  

  