﻿jR. 
  G. 
  Van 
  Name 
  — 
  Temperature 
  Coefficient. 
  449 
  

  

  Art. 
  XL. 
  — 
  On 
  the 
  Temperature 
  Coefficient 
  of 
  a 
  Hetero- 
  

   geneous 
  Reaction 
  ; 
  by 
  R. 
  Gr. 
  Van 
  j^ame. 
  

  

  [Contributions 
  from 
  the 
  Kent 
  Chemical 
  Laboratory 
  of 
  Yale 
  Univ. 
  — 
  cclxxxviii. 
  J 
  

  

  In 
  the 
  course 
  of 
  a 
  series 
  of 
  studies 
  on 
  the 
  rates 
  of 
  solution 
  of 
  

   metals, 
  the 
  results 
  of 
  which 
  have 
  been 
  published 
  in 
  four 
  pre- 
  

   vious 
  papers,* 
  the 
  writer 
  has 
  found 
  that 
  certain 
  of 
  these 
  reac- 
  

   tions 
  are 
  exceptionally 
  well 
  adapted 
  for 
  accurate 
  measurements 
  

   of 
  reaction 
  velocity, 
  having 
  distinct 
  advantages 
  in 
  this 
  respect 
  

   over 
  most 
  other 
  types 
  of 
  heterogeneous 
  reactions. 
  

  

  Since 
  our 
  knowledge 
  of 
  the 
  effect 
  of 
  temperature 
  on 
  the 
  

   velocity 
  of 
  heterogeneous 
  reactions 
  is 
  rather 
  limited, 
  it 
  has 
  

   seemed 
  desirable 
  to 
  utilize 
  the 
  experience 
  gained 
  through 
  the 
  

   work 
  above 
  mentioned, 
  in 
  the 
  careful 
  measurement 
  of 
  the 
  

   temperature 
  coefficient 
  of 
  the 
  velocity 
  of 
  a 
  single 
  reaction 
  of 
  

   this 
  type 
  over 
  a 
  considerable 
  range 
  of 
  temperature. 
  For 
  this 
  

   purpose 
  the 
  reaction 
  between 
  cadmium 
  and 
  a 
  water 
  solution 
  of 
  

   iodine 
  in 
  potassium 
  iodide 
  has 
  been 
  selected, 
  and 
  the 
  velocity 
  

   determined 
  at 
  seven 
  temperatures 
  covering 
  the 
  range 
  from 
  

   0° 
  to 
  65°. 
  

  

  The 
  choice 
  of 
  this 
  reaction 
  was 
  due 
  not 
  only 
  to 
  the 
  excep- 
  

   tional 
  convenience 
  and 
  accuracy 
  with 
  which 
  iodine 
  can 
  be 
  

   titrated, 
  but 
  also 
  to 
  the 
  fact 
  that 
  cadmium 
  can 
  easily 
  be 
  

   obtained 
  practically 
  free 
  from 
  objectionable 
  impurities, 
  can 
  

   readily 
  be 
  rolled 
  out 
  into 
  sheets, 
  and 
  when 
  so 
  rolled 
  has 
  a 
  very 
  

   finely 
  crystalline 
  structure, 
  so 
  that 
  it 
  dissolves 
  in 
  the 
  iodine 
  

   solution 
  without 
  any 
  appreciable 
  roughening 
  of 
  the 
  surface, 
  

   thus 
  preserving 
  a 
  constant 
  surface 
  area. 
  

  

  The 
  procedure 
  employed 
  did 
  not 
  differ 
  in 
  any 
  essential 
  

   respect 
  from 
  that 
  described 
  in 
  an 
  earlier 
  paper,f 
  and 
  therefore 
  

   calls 
  for 
  no 
  general 
  description. 
  A 
  few 
  points, 
  however, 
  which 
  

   are 
  only 
  very 
  briefly 
  or 
  incompletely 
  treated 
  in 
  the 
  previous 
  

   articles, 
  will 
  be 
  taken 
  up 
  in 
  detail 
  here. 
  The 
  following 
  data 
  

   apply 
  to 
  all 
  the 
  experiments 
  : 
  Reaction 
  vessel, 
  a 
  thin 
  beaker 
  

   ll 
  cm 
  in 
  internal 
  diameter. 
  Diameter 
  of 
  cadmium 
  disk 
  38'3 
  mm 
  , 
  

   thickness 
  0*5 
  mm 
  . 
  Composition 
  of 
  liquid 
  : 
  KI, 
  0*5 
  molar 
  ; 
  

   H 
  2 
  S0 
  4 
  , 
  O'Ol 
  molar 
  ; 
  I 
  2 
  (at 
  start) 
  about 
  O02 
  molar. 
  Volume 
  of 
  

   liquid, 
  600 
  cm 
  3 
  at 
  start, 
  20 
  cm 
  3 
  taken 
  for 
  each 
  titration. 
  

   Thiosulphate 
  used 
  in 
  titrations, 
  0*02 
  normal. 
  Rate 
  of 
  stirring 
  

   200 
  revolutions 
  per 
  minute. 
  

  

  Experiments 
  were 
  conducted 
  at 
  0°, 
  15°, 
  25°, 
  35°, 
  45°, 
  55°, 
  

   and 
  65°. 
  Only 
  at 
  25° 
  was 
  the 
  temperature 
  found 
  to 
  be 
  prac- 
  

  

  * 
  Van 
  Name 
  and 
  Edgar, 
  this 
  Journal 
  (4), 
  xxix, 
  237, 
  1910; 
  Van 
  Name 
  and 
  

   Bosworth, 
  ibid. 
  (4), 
  xxxii, 
  207, 
  1911 
  ; 
  Van 
  Name 
  and 
  Hill, 
  ibid. 
  (4), 
  xxxvi, 
  

   543, 
  1913, 
  and 
  (4), 
  xlii, 
  301, 
  1916. 
  

  

  f 
  The 
  second 
  of 
  the 
  articles 
  cited 
  in 
  the 
  preceding 
  foot-note. 
  

  

  