﻿of 
  a 
  Heterogeneous 
  Reaction. 
  453 
  

  

  equation 
  below, 
  v 
  is 
  understood 
  to 
  have 
  this 
  special 
  value. 
  

   Integrated 
  for 
  constant 
  v, 
  equations 
  (II) 
  and 
  (III) 
  yield, 
  respec- 
  

   tively, 
  R 
  '.' 
  =■ 
  -7— 
  In 
  — 
  - 
  , 
  and 
  — 
  K" 
  = 
  -r— 
  In 
  — 
  , 
  both 
  identical 
  

   J 
  ' 
  At 
  c 
  9 
  At 
  c 
  2 
  

  

  in 
  form 
  with 
  the 
  velocity 
  equation 
  for 
  the 
  main 
  reaction. 
  Hence 
  

   when 
  the 
  three 
  processes, 
  reaction 
  of 
  iodine 
  with 
  the 
  metal, 
  

   evaporation 
  of 
  iodine, 
  and 
  evaporation 
  of 
  water, 
  all 
  occur 
  at 
  

   once, 
  the 
  reaction 
  velocity 
  as 
  calculated 
  by 
  equation 
  (I) 
  from 
  

   the 
  change 
  in 
  the 
  iodine 
  concentration, 
  will 
  be 
  equal 
  to 
  

   K 
  + 
  K' 
  — 
  K" 
  . 
  To 
  calculate 
  K 
  we 
  have 
  only 
  to 
  subtract 
  

   (ir 
  — 
  K") 
  which 
  is 
  evidently 
  the 
  reaction 
  velocity 
  as 
  observed 
  

   in 
  a 
  blank 
  experiment 
  (without 
  cadmium 
  disk) 
  under 
  like 
  con- 
  

   ditions. 
  

  

  This 
  was 
  the 
  method 
  used 
  here. 
  Table 
  I 
  gives 
  the 
  values 
  

  

  dl) 
  -w-r 
  

  

  of 
  — 
  -=- 
  (in 
  cm 
  3 
  per 
  minute), 
  and 
  of 
  K' 
  — 
  K" 
  , 
  as 
  actually 
  

   oit 
  

  

  observed 
  and 
  used 
  in 
  applying 
  the 
  corrections 
  for 
  evapora- 
  

   tion. 
  

  

  Table 
  I. 
  

   25° 
  35° 
  45° 
  55° 
  65° 
  

  

  ^-=0-03 
  0-16 
  0-36 
  0*63 
  to 
  0-66 
  1*14 
  to 
  1-33 
  

  

  dt 
  

  

  IT 
  — 
  K" 
  = 
  0'05 
  0-13 
  0-18 
  0-36 
  0'64 
  

  

  At 
  0° 
  and 
  15° 
  no 
  corrections 
  were 
  required. 
  At 
  25° 
  the 
  

  

  dv 
  

  

  value 
  of 
  t 
  was 
  so 
  small 
  that 
  the 
  individual 
  values 
  of 
  v 
  were 
  

  

  dt 
  

  

  not 
  corrected, 
  but 
  instead 
  a 
  correction, 
  calculated 
  to 
  be 
  equiva- 
  

   lent 
  in 
  effect, 
  was 
  applied 
  to 
  the 
  observed 
  average 
  value 
  of 
  K. 
  

   This 
  called 
  for 
  a 
  decrease 
  in 
  K 
  of 
  less 
  than 
  two 
  units 
  in 
  the 
  

   second 
  decimal 
  place. 
  

  

  Results 
  of 
  Reaction 
  Velocity 
  Measurements. 
  — 
  Table 
  II 
  gives 
  

   the 
  results 
  of 
  the 
  whole 
  series 
  of 
  reaction 
  velocity 
  measure- 
  

   ments. 
  The 
  numbers 
  in 
  the 
  first 
  column 
  show 
  the 
  order 
  in 
  

   which 
  the 
  experiments 
  were 
  performed. 
  Determinations 
  were 
  

   begun 
  at 
  25° 
  and 
  then 
  repeated 
  from 
  time 
  to 
  time, 
  particularly 
  

   after 
  any 
  prolonged 
  interruption, 
  so 
  as 
  to 
  detect 
  any 
  accidental 
  

   changes 
  in 
  the 
  adjustments 
  of 
  the 
  apparatus. 
  In 
  this 
  way, 
  

   during 
  the 
  course 
  of 
  investigation, 
  fifteen 
  duplicate 
  experi- 
  

   ments 
  were 
  made 
  at 
  25°, 
  of 
  which, 
  however, 
  only 
  eight 
  — 
  those 
  

   which 
  on 
  consideration 
  of 
  the 
  sources 
  of 
  error 
  appeared 
  to 
  be 
  

   most 
  trustworthy 
  — 
  are 
  included 
  in 
  the 
  table 
  as 
  representative 
  

   of 
  the 
  whole 
  series. 
  The 
  mean 
  value 
  of 
  K 
  (corrected) 
  for 
  the 
  

   eight 
  is 
  7*62. 
  For 
  the 
  whole 
  fifteen 
  it 
  was 
  7*64, 
  a 
  compara- 
  

  

  