﻿452 
  R. 
  G. 
  Van 
  JS 
  r 
  ame 
  — 
  Temperature 
  Coefficient 
  

  

  value 
  of 
  v 
  so 
  found, 
  i. 
  e. 
  its 
  mean 
  value, 
  -J 
  (t\+v 
  2 
  ), 
  for 
  the 
  

   given 
  interval, 
  was 
  used 
  in 
  the 
  calculation 
  of 
  K. 
  This 
  method 
  

   was 
  followed 
  in 
  all 
  cases 
  at 
  35° 
  and 
  higher 
  temperatures. 
  At 
  

   25° 
  a 
  simpler 
  procedure, 
  equivalent 
  in 
  effect, 
  was 
  employed 
  

   instead. 
  (See 
  p. 
  453.) 
  Below 
  25° 
  corrections 
  to 
  v 
  were 
  found 
  

   to 
  be 
  negligibly 
  small 
  and 
  were 
  therefore 
  not 
  applied. 
  

  

  The 
  second 
  error 
  resulting 
  from 
  evaporation, 
  namely, 
  change 
  

   in 
  the 
  iodine 
  concentration, 
  might 
  conceivably 
  be 
  practically 
  

   zero 
  if 
  iodine 
  and 
  water 
  evaporated 
  in 
  nearly 
  the 
  same 
  ratio 
  as 
  

   that 
  in 
  which 
  they 
  were 
  present 
  in 
  the 
  solution. 
  Under 
  the 
  

   conditions 
  obtaining 
  in 
  the 
  present 
  investigation, 
  however, 
  

   evaporation 
  of 
  iodine 
  predominated, 
  blank 
  experiments 
  with- 
  

   out 
  a 
  cadmium 
  disk 
  giving 
  always 
  a 
  positive 
  value 
  of 
  the 
  

   velocity 
  constant. 
  The 
  problem 
  of 
  correcting 
  for 
  errors 
  so 
  

   introduced 
  was 
  encountered 
  in 
  one 
  of 
  the 
  previous 
  investiga- 
  

   tions* 
  and 
  is 
  briefly 
  discussed 
  in 
  the 
  published 
  paper. 
  Al- 
  

   though 
  the 
  corrections 
  needed 
  in 
  that 
  work 
  were 
  rightly 
  

   calculated 
  and 
  properly 
  applied, 
  the 
  discussion 
  as 
  printed 
  

   unfortunately 
  contains 
  a 
  rather 
  obvious 
  error. 
  The 
  following 
  is 
  

   a 
  corrected 
  and 
  more 
  detailed 
  statement 
  of 
  the 
  case 
  :f 
  

  

  Evaporation 
  of 
  the 
  solute, 
  iodine, 
  (assuming 
  constancy 
  of 
  the 
  

  

  liquid 
  surface) 
  obeys 
  the 
  equation 
  — 
  —=- 
  = 
  Kg 
  in 
  which 
  ra 
  is 
  

  

  ciz 
  

  

  the 
  mass 
  of 
  iodine 
  and 
  K' 
  a 
  constant. 
  Simply 
  transformed 
  

   this 
  becomes 
  

  

  - 
  d 
  ^-^K'- 
  (II) 
  

  

  dt 
  v 
  v 
  J 
  

  

  Evaporation 
  of 
  the 
  solvent, 
  water, 
  follows 
  the 
  equation 
  

   dv 
  

   dt 
  

  

  dv 
  

  

  — 
  — 
  - 
  = 
  K" 
  which 
  is 
  equivalent 
  to 
  

  

  + 
  ^ 
  = 
  K* 
  — 
  (III) 
  

  

  dt 
  v 
  v 
  ' 
  

  

  In 
  equation 
  (III) 
  v 
  is 
  a 
  variable, 
  though 
  a 
  constant 
  in 
  (II). 
  

   As 
  an 
  approximation, 
  however, 
  equation 
  (III) 
  may 
  safely 
  be 
  

   integrated 
  upon 
  the 
  assumption 
  that 
  v 
  is 
  constant 
  and 
  equal 
  

   to 
  i[v 
  x 
  —v^ 
  the 
  arithmetical 
  mean 
  of 
  its 
  limits, 
  provided 
  

   that 
  these 
  limits 
  are 
  close 
  together.;}; 
  In 
  the 
  integrated 
  

  

  * 
  This 
  Journal 
  (4), 
  xxxvi, 
  543, 
  1913. 
  

  

  \ 
  To 
  replace, 
  on 
  page 
  545 
  of 
  the 
  article 
  just 
  cited, 
  the 
  second 
  paragraph 
  

   and 
  the 
  first 
  nine 
  lines 
  of 
  the 
  third 
  paragraph. 
  The 
  error 
  referred 
  to 
  occurs 
  

   in 
  the 
  11th 
  line 
  from 
  the 
  bottom 
  of 
  this 
  page, 
  where 
  the 
  word 
  " 
  added" 
  

   should 
  appear 
  in 
  place 
  of 
  " 
  subtracted." 
  

  

  X 
  The 
  error 
  introduced 
  by 
  this 
  approximation 
  when 
  v 
  t 
  and 
  v 
  2 
  differ 
  by 
  

   2 
  per 
  cent 
  is 
  only 
  0*19 
  per 
  cent 
  of 
  the 
  value 
  of 
  K 
  ", 
  which 
  is 
  itself 
  only 
  a 
  cor- 
  

   rection 
  term. 
  In 
  the 
  present 
  series 
  of 
  experiments 
  the 
  effect 
  of 
  this 
  error 
  

   upon 
  the 
  final 
  result 
  was 
  in 
  all 
  cases 
  wholly 
  negligible. 
  

  

  