﻿Radioactivity 
  of 
  Potassium 
  and 
  other 
  Alkali 
  Metals, 
  

  

  Table 
  X. 
  

   Absorption 
  by 
  Tinfoil. 
  

  

  391 
  

  

  Thickness 
  of 
  

   tin! 
  oil 
  

   (cm.). 
  

  

  I 
  

  

  lo' 
  

  

  X. 
  

  

  0-00089 
  

  

  •867 
  

  

  160 
  

  

  •00178 
  

  

  •793 
  

  

  130 
  

  

  •00446 
  

  

  •563 
  

  

  124 
  

  

  •01157 
  

  

  •265 
  

  

  115 
  

  

  •01607 
  

  

  •165 
  

  

  112 
  

  

  •02839 
  

  

  •053 
  

  

  104 
  

  

  The 
  values 
  obtained 
  by 
  Rutherford* 
  for 
  the 
  constant 
  \ 
  

   when 
  studying 
  the 
  absorption 
  of 
  the 
  /3 
  rays 
  from 
  uranium 
  

   with 
  screens 
  of 
  tinfoil 
  was 
  96 
  ? 
  and 
  later 
  the 
  value 
  found 
  by 
  

   Crowtherf 
  for 
  the 
  same 
  constant 
  under 
  similar 
  circumstances 
  

   was 
  69 
  '3. 
  A 
  comparison 
  of 
  these 
  values 
  and 
  those 
  given 
  in 
  

   Table 
  IX. 
  makes 
  it 
  evident 
  that 
  while 
  the 
  rays 
  emitted 
  by 
  

   the 
  potassium 
  salts 
  were 
  very 
  heterogeneous 
  in 
  character, 
  

   they 
  did 
  not 
  contain 
  any 
  types 
  possessing 
  greater 
  penetrating 
  

   power 
  than 
  the 
  {3 
  rays 
  emitted 
  by 
  uranium 
  salts. 
  This 
  result, 
  

   too, 
  is 
  in 
  keeping 
  with 
  what 
  Campbell 
  and 
  Wood 
  found 
  in 
  

   their 
  investigations 
  on 
  the 
  absorption 
  of 
  these 
  potassium 
  

   rays. 
  

  

  VII. 
  Activity 
  of 
  Potassium 
  Salts 
  and 
  Secondary 
  Radiations. 
  

  

  A 
  set 
  of 
  measurements 
  was 
  made 
  with 
  the 
  object 
  of 
  ascer- 
  

   taining 
  whether 
  the 
  radiation 
  emitted 
  by 
  the 
  potassium 
  salts, 
  

   which 
  from 
  its 
  characteristics 
  evidently 
  consisted 
  of 
  /3 
  rays, 
  

   was 
  due 
  to 
  some 
  property 
  inherent 
  in 
  the 
  salts, 
  or 
  whether 
  

   it 
  was 
  due 
  to 
  a 
  secondary 
  radiation, 
  of 
  exceptionally 
  high 
  

   intensity, 
  excited 
  in 
  the 
  salt 
  by 
  the 
  penetrating 
  radiation 
  

   which 
  is 
  known 
  to 
  exist 
  at 
  the 
  surface 
  of 
  the 
  earth. 
  

  

  A 
  cylinder 
  of 
  lead 
  some 
  60 
  cms. 
  high 
  and 
  25 
  cms. 
  in 
  

   diameter 
  was 
  prepared, 
  and 
  the 
  natural 
  conductivity 
  of 
  the 
  

   air 
  in 
  this 
  cylinder 
  determined. 
  A 
  layer 
  of 
  potassium 
  sul- 
  

   phate 
  was 
  then 
  placed 
  in 
  a 
  tray 
  on 
  the 
  bottom 
  of 
  the 
  cylinder, 
  

   and 
  when 
  the 
  conductivity 
  of 
  the 
  air 
  was 
  again 
  measured 
  it 
  

   was 
  found 
  to 
  be 
  approximately 
  twice 
  as 
  high 
  as 
  it 
  was 
  before 
  

   the 
  salt 
  was 
  introduced. 
  

  

  From 
  this 
  it 
  was 
  evident 
  that 
  the 
  radiation 
  from 
  the 
  salt 
  

  

  * 
  Rutherford, 
  ' 
  Radioactivity,' 
  2nd 
  edition, 
  p. 
  

   t 
  Phil. 
  Mag. 
  Oct. 
  1906, 
  p. 
  379. 
  

  

  is; 
  

  

  