﻿Radioactivity 
  of 
  Potassium 
  and 
  other 
  Alkali 
  Metals. 
  389 
  

  

  The 
  saturation 
  currents 
  were 
  not 
  reduced 
  to 
  half 
  value 
  until 
  

   the 
  columns 
  of 
  air 
  traversed 
  amounted 
  to 
  between 
  12 
  and 
  

   15 
  cms., 
  and 
  even 
  with 
  the 
  salts 
  at 
  a 
  distance 
  of 
  40 
  cms. 
  

   from 
  the 
  chamber 
  the 
  ionizing 
  currents 
  were 
  still 
  approxi- 
  

   mately 
  15 
  per 
  cent, 
  of 
  their 
  highest 
  values. 
  

  

  From 
  the 
  form 
  of 
  the 
  curves 
  it 
  is 
  evident 
  that 
  the 
  radiations 
  

   from 
  the 
  different 
  potassium 
  salts 
  were 
  not 
  identical 
  in 
  their 
  

   composition. 
  The 
  absorption 
  curves 
  for 
  the 
  sulphate 
  and 
  the 
  

   chloride 
  were 
  very 
  similar, 
  but 
  that 
  for 
  the 
  cyanide 
  was 
  

   markedly 
  different, 
  and 
  indicated 
  by 
  its 
  shape 
  that 
  the 
  rays 
  

   from 
  this 
  salt, 
  besides 
  being 
  heterogeneous 
  in 
  character, 
  

   contained 
  a 
  predominating 
  proportion 
  of 
  the 
  more 
  penetrating 
  

   types.^ 
  

  

  It 
  is 
  of 
  interest 
  to 
  note, 
  too, 
  that 
  the 
  absorption 
  curves 
  in 
  

   fig. 
  6 
  show 
  no 
  irregularities 
  in 
  their 
  initial 
  portions, 
  such 
  as 
  

   one 
  would 
  have 
  expected 
  if 
  the 
  radiations 
  had 
  consisted, 
  

   amongst 
  others, 
  of 
  a 
  type 
  possessing 
  the 
  characteristics 
  of 
  

   the 
  a 
  radiations 
  from 
  the 
  known 
  radioactive 
  elements. 
  

  

  These 
  results, 
  it 
  will 
  be 
  seen, 
  are 
  in 
  accordance 
  with 
  

   Campbell 
  and 
  Wood's 
  observations, 
  and 
  confirm 
  the 
  con- 
  

   clusions 
  reached 
  by 
  them 
  that 
  the 
  radioactivity 
  exhibited 
  by 
  

   the 
  potassium 
  salts 
  possesses 
  the 
  characteristics 
  of 
  either 
  a 
  ft 
  or 
  

   an 
  easily 
  absorbed 
  7 
  radiation, 
  rather 
  than 
  those 
  of 
  an 
  a 
  type. 
  

  

  In 
  a 
  second 
  series 
  of 
  measurements 
  on 
  the 
  absorption 
  of 
  

   the 
  potassium 
  rays, 
  the 
  tray 
  was 
  filled 
  with 
  a 
  quantity 
  of 
  

   potassium 
  sulphate 
  and 
  then 
  placed 
  in 
  the 
  ionizing 
  chamber, 
  

   resting 
  on 
  the 
  bottom. 
  The 
  salt 
  was 
  covered 
  successively 
  

   with 
  an 
  increasing 
  number 
  of 
  sheets 
  of 
  tinfoil, 
  and 
  the 
  

   saturation 
  current 
  measured 
  for 
  each 
  set 
  of 
  the 
  absorbing- 
  

   sheets. 
  The 
  foil 
  used 
  was 
  0'0089 
  mm. 
  in 
  thickness. 
  The 
  

   values 
  of 
  the 
  currents 
  corresponding 
  to 
  the 
  different 
  thick- 
  

   nesses 
  of 
  tinfoil 
  are 
  given 
  in 
  Table 
  IX., 
  and 
  the 
  manner 
  in 
  

  

  Table 
  IX. 
  

  

  Thickness 
  of 
  tinfoil, 
  

   (cm.) 
  

  

  Saturation 
  current 
  

   (Arbitrary 
  scale). 
  

  

  0-00000 
  

  

  188 
  

  

  •00089 
  

  

  163 
  

  

  •00178 
  

  

  149 
  

  

  •00446 
  

  

  106 
  

  

  01157 
  

  

  50 
  

  

  •01607 
  

  

  31 
  

  

  •02839 
  

  

  10 
  

  

  