﻿Van 
  Name 
  and 
  Rill 
  — 
  Alcohol 
  and 
  Cane 
  Sugar. 
  545 
  

  

  it 
  necessary 
  to 
  take 
  this 
  effect 
  into 
  account. 
  As 
  is 
  evident 
  

   from 
  the 
  equation, 
  loss 
  of 
  solvent 
  (alcohol 
  and 
  water) 
  tends 
  to 
  

   affect 
  the 
  calculated 
  velocity 
  constants 
  in 
  two 
  ways 
  .; 
  by 
  decreas- 
  

   ing 
  the 
  volume 
  w, 
  and 
  by 
  increasing 
  the 
  concentration 
  of 
  

   iodine 
  c. 
  When 
  the 
  last 
  effect 
  is 
  small, 
  however, 
  it 
  may 
  be 
  

   neutralized 
  or 
  reversed 
  by 
  the 
  evaporation 
  of 
  the 
  iodine 
  itself. 
  

   Since 
  the 
  corrections 
  to 
  be 
  applied 
  are 
  only 
  small, 
  no 
  appreci- 
  

   able 
  error 
  is 
  introduced 
  by 
  assuming 
  that 
  the 
  free 
  surface 
  of 
  

   the 
  liquid 
  has 
  a 
  constant 
  area," 
  and 
  that 
  the 
  volume, 
  therefore, 
  

  

  decreases 
  at 
  a 
  constant 
  rate, 
  or 
  rr 
  = 
  Const. 
  The 
  rate 
  of 
  

  

  at 
  

  

  change 
  in 
  volume 
  was 
  determined 
  either 
  by 
  re-measuring 
  the 
  

  

  volume 
  at 
  the 
  end 
  of 
  the 
  experiment 
  or 
  by 
  special 
  blank 
  

  

  experiments 
  under 
  like 
  conditions. 
  Knowing 
  the 
  loss 
  per 
  

  

  minute, 
  the 
  average 
  volume 
  during 
  each 
  reaction 
  period 
  was 
  

  

  calculated 
  by 
  deducting 
  the 
  loss 
  which 
  had 
  occurred 
  up 
  to 
  the 
  

  

  middle 
  of 
  that 
  period. 
  The 
  true 
  volumes, 
  so 
  found, 
  have 
  been 
  

  

  used 
  in 
  the 
  calculations 
  of 
  all 
  experiments 
  in 
  which 
  the 
  alcohol 
  

  

  was 
  0*5 
  molar 
  or 
  stronger. 
  Below 
  this 
  concentration 
  the 
  

  

  changes 
  in 
  volume 
  due 
  to 
  evaporation 
  were 
  negligibly 
  small. 
  

  

  The 
  effect 
  of 
  evaporation 
  upon 
  the 
  iodine 
  concentration 
  is 
  

  

  the 
  resultant 
  of 
  two 
  parts 
  : 
  (I), 
  evaporation 
  of 
  solvent, 
  which 
  

  

  dc 
  

  

  can 
  easily 
  be 
  shown 
  to 
  yield 
  the 
  expression 
  + 
  -=- 
  = 
  kc 
  % 
  . 
  a 
  re- 
  

  

  1 
  at 
  

  

  action 
  of 
  the 
  second 
  order; 
  and 
  (II), 
  evaporation 
  of 
  iodine, 
  

  

  dc 
  

  

  which 
  obeys 
  the 
  first 
  order 
  reaction 
  equation 
  — 
  '-=- 
  = 
  Jc'c. 
  

  

  The 
  changes 
  in 
  concentration 
  resulting 
  from 
  (I) 
  may 
  be 
  cal- 
  

   culated 
  from 
  the 
  rate 
  of 
  evaporation. 
  Although 
  this 
  reaction 
  is 
  

   of 
  a 
  higher 
  order 
  than 
  the 
  main 
  reaction, 
  we 
  have 
  found 
  that 
  in 
  

   our 
  experiments, 
  owing 
  to 
  the 
  short 
  reaction 
  periods 
  and 
  small 
  

   changes 
  involved, 
  the 
  resulting 
  change 
  in 
  the 
  value 
  of 
  each 
  

   velocity 
  constant 
  is, 
  under 
  given 
  conditions, 
  a 
  practically 
  con- 
  

   stant 
  amount, 
  which 
  can 
  easily 
  be 
  calculated 
  and 
  subtracted, 
  as 
  

   a 
  uniform 
  correction, 
  from 
  each 
  velocity 
  constant 
  of 
  a 
  given 
  

   experiment. 
  To 
  obtain 
  corrections 
  for 
  (II) 
  the 
  evaporation 
  of 
  

   iodine, 
  blank 
  experiments 
  were 
  made 
  using 
  no 
  cadmium 
  disk, 
  

   and 
  the 
  constant 
  calculated 
  in 
  the 
  ordinary 
  way. 
  Three 
  such 
  

   experiments. 
  A, 
  with 
  a 
  solution 
  containing 
  0*25 
  molar 
  alcohol 
  ; 
  

   B. 
  with 
  cane 
  sugar, 
  0*25 
  molar 
  ; 
  and 
  C, 
  without 
  either 
  alcohol 
  

   or 
  sugar, 
  gave 
  the 
  following 
  results 
  : 
  

  

  A. 
  K=0'051, 
  0-032, 
  0-044, 
  0-067, 
  0*070, 
  average 
  0-053 
  

  

  B. 
  K=0-0-*0, 
  0-024, 
  0*051, 
  (V037, 
  0-055, 
  " 
  0-039 
  

  

  C. 
  K 
  = 
  0-039, 
  0-044, 
  0-055, 
  0"044, 
  0*07*7, 
  " 
  0-052 
  

  

  * 
  In 
  reality 
  it 
  increases 
  slightly 
  as 
  the 
  volume 
  decreases, 
  owing 
  to 
  the 
  eon- 
  

   cavity 
  produced 
  by 
  the 
  rotary 
  stirring. 
  

  

  