﻿380 
  

  

  Prof. 
  McLennan 
  and 
  Mr. 
  Kennedy 
  on 
  the 
  

  

  III. 
  Relation 
  between 
  Thickness 
  of 
  Salt 
  Layer 
  and 
  Activity. 
  

  

  Some 
  additional 
  measurements 
  were 
  made 
  to 
  ascertain 
  the 
  

   relation 
  of 
  the 
  activity 
  of 
  a 
  number 
  of 
  the 
  salts 
  to 
  the 
  thick- 
  

   ness 
  of 
  the 
  layer 
  of 
  salt 
  exposed. 
  In 
  making 
  these 
  measure- 
  

   ments 
  the 
  salts 
  were 
  ground 
  to 
  a 
  fine 
  powder 
  and 
  then 
  

   sifted 
  as 
  uniformly 
  as 
  possible 
  on 
  the 
  bottom 
  of 
  a 
  shallow 
  

   tray 
  which 
  had 
  a 
  surface 
  area 
  of 
  22S 
  sq. 
  cms. 
  This 
  tray 
  

   was 
  then 
  placed 
  in 
  the 
  ionizing 
  chamber, 
  and 
  the 
  saturation 
  

   currents 
  measured 
  for 
  each 
  layer 
  as 
  before. 
  

  

  The 
  results 
  obtained 
  with 
  potassium 
  sulphate 
  are 
  recorded 
  

   in 
  Table 
  II., 
  and 
  a 
  curve 
  representing 
  them 
  is 
  shown 
  in 
  

   fig. 
  3. 
  From 
  these 
  it 
  will 
  be 
  seen 
  that 
  the 
  saturation 
  currents 
  

   steadily 
  increased 
  with 
  the 
  thickness 
  of 
  the 
  layer 
  of 
  salt 
  

   exposed 
  until 
  a 
  thickness 
  of 
  2*5 
  cm. 
  was 
  reached, 
  when 
  the 
  

   current 
  assumed 
  a 
  steady 
  value 
  and 
  remained 
  the 
  same 
  for 
  

   greater 
  thicknesses. 
  

  

  Additional 
  observations 
  were 
  made 
  with 
  the 
  halogen 
  salts 
  

   of 
  potassium, 
  and 
  still 
  others 
  with 
  two 
  samples 
  of 
  potassium 
  

   cyanide, 
  one 
  with 
  a 
  sample 
  of 
  potassium 
  hydroxide, 
  and 
  one 
  

   with 
  a 
  second 
  specimen 
  of 
  chloride 
  of 
  potassium. 
  The 
  results 
  

   of 
  these 
  measurements 
  are 
  given 
  in 
  Tables 
  III. 
  and 
  IV., 
  and 
  

   curves 
  representing 
  them 
  in 
  figs. 
  4 
  and 
  5. 
  From 
  all 
  the 
  

   results 
  recorded 
  it 
  will 
  be 
  seen 
  that 
  layers 
  of 
  the 
  different 
  

   salts 
  between 
  2 
  and 
  3 
  mms. 
  were 
  amply 
  sufficient 
  to 
  give 
  the 
  

   maximum 
  saturation 
  currents. 
  

  

  Table 
  II. 
  

  

  Activity 
  of 
  Potassium 
  Sulphate. 
  

  

  Thickness 
  of 
  salt 
  layer 
  

   (mm.). 
  

  

  Activity 
  of 
  salt. 
  

   Saturation 
  current 
  

   (Arbitrary 
  scale). 
  

  

  0-188 
  

  

  32 
  

  

  0-43 
  

  

  61 
  

  

  0-625 
  

  

  86 
  

  

  109 
  

  

  112 
  

  

  1-56 
  

  

  128 
  

  

  2-03 
  

  

  134 
  

  

  2-50 
  

  

  142 
  

  

  3-75 
  

  

  142 
  

  

  5-00 
  

  

  142 
  

  

  