﻿and 
  Chemical 
  Reactions 
  in 
  Heterogeneous 
  Systems. 
  569 
  

  

  solid 
  itself, 
  and 
  the 
  increase 
  of 
  the 
  diffusion 
  surface 
  will 
  be 
  

   the 
  same 
  as 
  that 
  of 
  the 
  surface 
  of 
  the 
  solid 
  during 
  corrosion, 
  

   i. 
  e., 
  we 
  gain 
  nothing 
  whatever 
  here 
  bj 
  the 
  assumption 
  of 
  a 
  

   diffusion 
  layer. 
  

  

  The 
  true 
  position 
  of 
  the 
  facts 
  here 
  is, 
  in 
  my 
  opinion, 
  the 
  

   following 
  : 
  — 
  

  

  Surfaces 
  which 
  appear 
  to 
  the 
  naked 
  eye 
  smooth 
  are 
  in 
  reality, 
  

   on 
  inspection 
  with 
  a 
  lens, 
  corroded 
  surfaces, 
  and 
  such 
  surfaces 
  

   are 
  not 
  always 
  essentially 
  smaller 
  than 
  the 
  surface 
  of 
  the 
  

   same 
  solid 
  when 
  its 
  corrosions 
  are 
  perceivable 
  ; 
  influences 
  of 
  

   an 
  opposite 
  kind 
  may 
  often 
  counteract 
  one 
  another 
  : 
  on 
  the 
  

   other 
  hand, 
  I 
  must 
  assert 
  that 
  very 
  often 
  we 
  find 
  an 
  increase 
  

   of 
  the 
  velocity 
  constant 
  with 
  the 
  increase 
  of 
  corrosion, 
  when 
  

   this 
  is 
  still 
  very 
  far 
  below 
  the 
  values 
  mentioned 
  by 
  Nernst 
  and 
  

   Brunner, 
  and 
  I 
  find 
  that 
  repeated 
  polishing 
  of 
  the 
  surfaces 
  is 
  

   in 
  this 
  region 
  imperative. 
  

  

  Part 
  II. 
  

  

  (i.) 
  I 
  now 
  pass 
  to 
  the 
  most 
  important 
  and 
  most 
  direct 
  test 
  

   of 
  the 
  diffusion 
  theory. 
  This 
  is 
  given 
  to 
  us 
  by 
  the 
  investi- 
  

   gation 
  : 
  — 
  (1) 
  of 
  the 
  speed 
  of 
  solution 
  of 
  different 
  modifications 
  

   of 
  the 
  same 
  substance 
  in 
  the 
  same 
  solvent 
  ; 
  (2) 
  of 
  the 
  speed 
  of 
  

   solution 
  of 
  the 
  same 
  crystal, 
  cut 
  in 
  different 
  directions 
  to 
  its 
  

   axis, 
  in 
  the 
  same 
  solvent. 
  Because 
  if 
  the 
  velocity, 
  with 
  which 
  

   a 
  solid 
  dissolves, 
  depends, 
  as 
  we 
  are 
  told, 
  upon 
  the 
  speed 
  of 
  

   diffusion 
  of 
  its 
  saturated 
  solution 
  from 
  the 
  solid 
  into 
  the 
  rest 
  

   of 
  the 
  solution_, 
  and 
  if 
  the 
  saturated 
  solution 
  is 
  formed 
  

   instantaneously 
  at 
  the 
  solid, 
  then 
  all 
  the 
  CaS04 
  + 
  2HoO 
  of 
  

   the 
  different 
  Gypsums 
  giving 
  the 
  same 
  saturated 
  solution"^ 
  

   must 
  dissolve 
  with 
  the 
  same 
  speed, 
  and 
  the 
  same 
  crystal 
  

   Selenite 
  must 
  dissolve 
  in 
  different 
  directions 
  of 
  its 
  axis 
  with 
  

   the 
  same 
  speed. 
  If 
  this 
  is 
  not 
  the 
  case, 
  this 
  is 
  the 
  most 
  decisive 
  

   and 
  direct 
  proof 
  one 
  can 
  possibly 
  imagine, 
  that 
  these 
  funda- 
  

   mental 
  assumptions 
  of 
  the 
  diffusion 
  theory 
  do 
  not 
  hold 
  good, 
  

   and 
  the 
  luhole 
  diffusion 
  theory 
  tumbles 
  to 
  the 
  ground. 
  Bruner 
  

   and 
  Tolloczko 
  found 
  (Zeitsch. 
  filr 
  anorg. 
  Chemie, 
  1901, 
  

   p. 
  325) 
  for 
  Alabaster, 
  the 
  velocity 
  constant 
  A 
  = 
  0*00230 
  

   (Y 
  = 
  2000 
  cc, 
  /= 
  22-91 
  cm.^, 
  number 
  of 
  revolutions 
  400) 
  

   and 
  for 
  Marienglass 
  or 
  Selenite 
  A 
  = 
  0-00079 
  (V 
  = 
  2400 
  cc, 
  

   /=20*9 
  cm.^ 
  number 
  of 
  revolutions 
  400), 
  i.e. 
  A 
  Alabaster 
  : 
  

   A 
  Marienglass 
  = 
  3*44 
  : 
  1. 
  In 
  Zeitsch. 
  fur 
  anorg. 
  Chemie, 
  

   1903, 
  pp. 
  29, 
  30, 
  they 
  try 
  to 
  get 
  over 
  this 
  difficulty. 
  They 
  

  

  * 
  See 
  the 
  investigations 
  of 
  Kohlrausch 
  and 
  Kose 
  and 
  others. 
  

   Phil 
  Mag. 
  S. 
  6. 
  Vol. 
  18. 
  Xo. 
  106. 
  Oct. 
  1909. 
  2 
  Q 
  

  

  