﻿450 
  R. 
  G. 
  Van 
  Name 
  — 
  Temperature 
  Coefficient 
  

  

  tically 
  the 
  same 
  in 
  the 
  reaction 
  beaker 
  as 
  in 
  the 
  water 
  of 
  the 
  

   thermostat. 
  At 
  15°, 
  and 
  at 
  35° 
  and 
  above, 
  the 
  thermostat 
  was 
  

   regulated 
  to 
  that 
  temperature 
  which 
  would 
  give 
  the 
  desired 
  

   temperature 
  in 
  the 
  beaker. 
  Even 
  this 
  was 
  not 
  sufficient 
  in 
  

   cases 
  where 
  the 
  difference 
  in 
  temperature 
  was 
  large, 
  since 
  the 
  

   difference 
  was 
  then 
  found 
  to 
  increase 
  with 
  decrease 
  in 
  the 
  sur- 
  

   face 
  of 
  contact 
  between 
  the 
  beaker 
  and 
  the 
  reaction 
  liquid, 
  

   that 
  is, 
  with 
  the 
  depth 
  of 
  the 
  liquid 
  in 
  the 
  beaker, 
  which 
  

   decreased 
  about 
  one-fourth 
  during 
  the 
  course 
  of 
  the 
  experi- 
  

   ment. 
  In 
  such 
  cases 
  the 
  temperature 
  of 
  the 
  thermostat 
  was 
  

   gradually 
  varied 
  as 
  the 
  volume 
  of 
  the 
  liquid 
  diminished. 
  

   Thus, 
  to 
  maintain 
  the 
  temperature 
  of 
  the 
  liquid 
  in 
  the 
  beaker 
  

   at 
  65° 
  it 
  was 
  found 
  necessary 
  to 
  set 
  the 
  thermostat 
  to 
  67*7° 
  

   at 
  the 
  start 
  and 
  gradually 
  raise 
  its 
  temperature 
  during 
  the 
  

   experiment 
  to 
  68*2° 
  at 
  the 
  end. 
  By 
  careful 
  use 
  of 
  this 
  ex- 
  

   pedient 
  the 
  temperature, 
  even 
  at 
  65°, 
  where 
  the 
  error 
  was 
  

   largest, 
  was 
  maintained 
  for 
  the 
  most 
  part 
  within 
  0*2° 
  of 
  the 
  

   correct 
  value, 
  greater 
  variations 
  occurring 
  but 
  rarely, 
  and 
  then 
  

   only 
  for 
  very 
  brief 
  periods. 
  

  

  For 
  the 
  experiments 
  at 
  0° 
  the 
  thermostat 
  was 
  kept 
  at 
  that 
  

   temperature 
  by 
  the 
  frequent 
  addition 
  of 
  liberal 
  quantities 
  of 
  

   fine 
  snow. 
  The 
  temperature 
  in 
  the 
  beaker, 
  directly 
  measured, 
  

   was 
  always 
  between 
  one 
  and 
  two-tenths 
  of 
  a 
  degree 
  higher, 
  

   averaging 
  + 
  0*15°. 
  

  

  The 
  rate 
  of 
  the 
  reaction 
  follows 
  the 
  equation 
  

  

  jr 
  = 
  2-3-^-log-^- 
  (I) 
  

  

  The 
  reaction 
  velocities 
  were 
  calculated 
  by 
  substituting 
  the 
  

   observed 
  values 
  of 
  c 
  in 
  this 
  equation, 
  At 
  being 
  the 
  duration 
  of 
  

   a 
  single 
  reaction 
  period, 
  i. 
  e. 
  the 
  time 
  interval 
  between 
  the 
  

   removal 
  of 
  two 
  consecutive 
  samples 
  of 
  the 
  solution. 
  These 
  in- 
  

   tervals 
  were 
  generally 
  ten 
  minutes 
  in 
  length, 
  but 
  somewhat 
  

   shorter 
  reaction 
  periods 
  were 
  employed 
  at 
  the 
  highest 
  tempera- 
  

   tures, 
  and 
  longer 
  periods 
  at 
  the 
  lowest. 
  The 
  velocity 
  con- 
  

   stants 
  so 
  obtained 
  were 
  first 
  corrected, 
  as 
  described 
  below, 
  for 
  

   variations 
  in 
  the 
  rate 
  of 
  stirring. 
  So 
  corrected 
  they 
  represented 
  

   the 
  apparent 
  rate 
  of 
  the 
  reaction, 
  but 
  not 
  in 
  general 
  its 
  true 
  

   velocity, 
  since 
  in 
  many 
  cases 
  a 
  further 
  correction 
  was 
  needed 
  

   to 
  compensate 
  for 
  the 
  effect 
  of 
  evaporation 
  from 
  the 
  solution. 
  

   Corrections 
  for 
  Variations 
  in 
  the 
  Rate 
  of 
  Stirring. 
  — 
  The 
  

   average 
  rate 
  of 
  stirring 
  during 
  each 
  reaction 
  period 
  was 
  deter- 
  

   mined 
  and 
  a 
  correction, 
  based 
  on 
  the 
  assumption 
  that 
  the 
  

   reaction 
  velocity 
  varies 
  as 
  the 
  4/5 
  power 
  of 
  the 
  rate 
  of 
  stir- 
  

   ring,* 
  was 
  afterward 
  calculated 
  and 
  applied 
  to 
  the 
  observed 
  

  

  *An 
  empirical 
  relation 
  shown 
  in 
  a 
  previous 
  paper 
  (this 
  Journal 
  (4), 
  xxix, 
  

   251, 
  1910) 
  to 
  be 
  approximately 
  true 
  for 
  an 
  apparatus 
  of 
  this 
  type 
  and 
  

   dimensions. 
  

  

  