﻿of 
  a 
  Heterogeneous 
  Reaction. 
  457 
  

  

  V 
  

  

  Wildermann's 
  velocity 
  constants, 
  K, 
  are 
  given 
  in 
  Table 
  V, 
  

  

  K 
  

  

  together 
  with 
  the 
  values 
  of 
  — 
  jr 
  — 
  as 
  calculated 
  for 
  the 
  various 
  

  

  intervals 
  by 
  the 
  method 
  described 
  above. 
  

  

  

  Table 
  V. 
  

  

  

  Results 
  of 
  Wildermann. 
  

  

  

  1-5° 
  17-5° 
  31° 
  40° 
  60° 
  

  

  K 
  = 
  

  

  1-587 
  2-851 
  4-524 
  5-756 
  9'946 
  

  

  A 
  = 
  

  

  1-443 
  1-408 
  1-307 
  1-314 
  

  

  2920 
  3020 
  2550 
  2850 
  

  

  This 
  reaction 
  is 
  not 
  as 
  well 
  adapted 
  for 
  accurate 
  measure- 
  

   ment 
  as 
  the 
  one 
  between 
  cadmium 
  and 
  dissolved 
  iodine, 
  and 
  

   Wildermann's 
  duplicate 
  results 
  show 
  a 
  rather 
  poor 
  agreement. 
  

   The 
  values 
  of 
  A 
  given 
  in 
  the 
  last 
  line 
  of 
  the 
  table 
  are 
  those 
  

  

  T 
  — 
  T 
  

  

  calculated 
  from 
  the 
  equation 
  lnK 
  % 
  — 
  InK^ 
  = 
  A 
  2 
  * 
  , 
  the 
  

  

  2 
  1 
  

  

  integrated 
  form 
  of 
  the 
  van't 
  Hoff 
  equation, 
  d 
  InK/dT 
  — 
  A/T*, 
  

   for 
  the 
  effect 
  of 
  temperature 
  on 
  the 
  velocity 
  of 
  a 
  homogeneous 
  

   reaction. 
  

  

  Wildermann, 
  whose 
  article 
  is 
  throughout 
  an 
  attack 
  on 
  the 
  

   diffusion 
  theory, 
  regards 
  the 
  apparent 
  constancy 
  of 
  A 
  as 
  an 
  

   argument 
  against 
  that 
  theory. 
  The 
  soundness 
  of 
  this 
  argu- 
  

   ment, 
  however, 
  is 
  very 
  doubtful, 
  since 
  there 
  is 
  nothing 
  to 
  show 
  

   that 
  an 
  approximate 
  agreement 
  with 
  an 
  equation 
  of 
  this 
  form 
  

   is 
  in 
  any 
  way 
  incompatible 
  with 
  the 
  mechanism 
  of 
  the 
  reaction 
  

   postulated 
  by 
  the 
  diffusion 
  theory. 
  

  

  Upon 
  calculating 
  the 
  constant 
  A 
  from 
  the 
  reaction 
  veloci- 
  

   ties 
  measured 
  by 
  the 
  author, 
  as 
  given 
  in 
  Table 
  II, 
  we 
  obtain 
  

   the 
  following 
  values, 
  which 
  show 
  a 
  distinct 
  progression 
  and 
  a 
  

   total 
  variation 
  of 
  over 
  20 
  per 
  cent 
  : 
  

  

  0°-15° 
  15°-5° 
  25°-35° 
  35°-45° 
  45°-55° 
  55°-65° 
  

   A= 
  2388 
  2239 
  2069 
  2079 
  1962 
  1902 
  

  

  It 
  is 
  evident 
  that 
  in 
  this 
  case, 
  at 
  least, 
  the 
  experimental 
  results 
  

   do 
  not 
  conform 
  to 
  the 
  van't 
  Hoff 
  equation. 
  

  

  A 
  question 
  of 
  special 
  interest 
  and 
  importance 
  from 
  the 
  

   standpoint 
  of 
  the 
  diffusion 
  theory, 
  is 
  the 
  nature 
  of 
  the 
  relation 
  

   between 
  the 
  observed 
  temperature 
  coefficient 
  of 
  the 
  reaction 
  

   velocity 
  and 
  that 
  of 
  the 
  rate 
  of 
  diffusion 
  of 
  dissolved 
  substances. 
  

   Unfortunately 
  our 
  knowledge 
  of 
  the 
  effect 
  of 
  temperature 
  on 
  

   rates 
  of 
  diffusion 
  is 
  very 
  imperfect, 
  since 
  but 
  few 
  direct 
  meas 
  

  

  