﻿[ 
  377 
  ] 
  

  

  XXXI. 
  On 
  the 
  Radioactivity 
  of 
  Potassium 
  and 
  other 
  Alkali 
  

   Metals. 
  By 
  Prof. 
  J. 
  C. 
  McLennan 
  and 
  Mr. 
  W. 
  T. 
  

   Kennedy*. 
  

  

  I. 
  Introduction. 
  

  

  IX 
  the 
  course 
  o£ 
  some 
  experiments 
  made 
  by 
  them 
  on 
  the 
  

   radioactivity 
  of 
  a 
  series 
  o£ 
  salts 
  which 
  had 
  hitherto 
  been 
  

   considered 
  inactive, 
  Messrs. 
  Campbell 
  and 
  Wood 
  (Proc. 
  Camb. 
  

   Phil. 
  Soc. 
  vol. 
  xiv. 
  pt. 
  1, 
  p. 
  15, 
  1P07) 
  found 
  that 
  potassium 
  

   salts 
  exhibited 
  a 
  radioactivity 
  greater 
  than 
  that 
  of 
  any 
  other 
  

   substance 
  previously 
  examined 
  which 
  did 
  not 
  contain 
  any 
  of 
  

   the 
  so-called 
  radioactive 
  elements. 
  

  

  In 
  seeking 
  for 
  the 
  source 
  of 
  this 
  activity 
  these 
  experimenters 
  

   found 
  it 
  impossible 
  to 
  separate 
  out 
  any 
  active 
  impurity 
  from 
  

   the 
  salts 
  examined, 
  and 
  they 
  were 
  led 
  by 
  the 
  results 
  of 
  their 
  

   investigation, 
  which 
  included 
  measurements 
  on 
  the 
  activities 
  

   of 
  a 
  limited 
  number 
  of 
  compounds 
  of 
  potassium, 
  to 
  conclude 
  

   that 
  the 
  activity 
  originated 
  with 
  the 
  potassium 
  itself 
  and 
  

   was 
  an 
  atomic 
  property 
  of 
  that 
  metal. 
  

  

  In 
  a 
  later 
  paper 
  (Proc. 
  Camb. 
  Phil. 
  Soc. 
  vol. 
  xiv. 
  pt. 
  2, 
  

   1907) 
  Campbell 
  described 
  some 
  additional 
  experiments 
  

   dealing 
  with 
  the 
  character 
  of 
  the 
  radiation 
  emitted 
  by 
  the 
  

   potassium 
  salts, 
  and 
  in 
  concluding 
  expressed 
  the 
  opinion 
  that 
  

   the 
  radiation 
  consisted 
  of 
  /3 
  rays 
  possessing 
  an 
  average 
  

   velocity 
  less 
  than 
  that 
  of 
  the 
  /3 
  rays 
  of 
  uranium. 
  

  

  In 
  a 
  recent 
  note 
  by 
  one 
  of 
  us 
  (' 
  Xature/ 
  May 
  14th, 
  and 
  

   Phys. 
  Zeit. 
  Aug. 
  1st) 
  an 
  account 
  is 
  given 
  of 
  some 
  expe- 
  

   riments 
  Avhich 
  involved 
  a 
  minute 
  examination 
  of 
  the 
  radio- 
  

   activity 
  of 
  a 
  large 
  number 
  of 
  potassium 
  and 
  other 
  salts. 
  In 
  

   this 
  note 
  it 
  was 
  stated 
  that 
  while 
  the 
  results 
  of 
  this 
  exami- 
  

   nation 
  confirmed 
  the 
  discovery 
  made 
  by 
  Campbell 
  and 
  Wood, 
  

   that 
  potassium 
  salts 
  generally 
  possess 
  an 
  exceptionally 
  high 
  

   activity, 
  and 
  emit 
  a 
  radiation 
  possessing 
  considerable 
  pene- 
  

   trating 
  power, 
  they 
  did 
  not 
  support 
  the 
  conclusion 
  that 
  the 
  

   activity 
  of 
  these 
  salts 
  was 
  connected 
  with 
  a 
  normal 
  atomic 
  

   property 
  of 
  potassium 
  and 
  that 
  it 
  was 
  always 
  directly 
  pro- 
  

   portional 
  to 
  the 
  amount 
  of 
  that 
  metal 
  present 
  in 
  the 
  salt. 
  

  

  The 
  salts 
  used 
  in 
  this 
  examination 
  were 
  those 
  ordinarily 
  sold 
  

   as 
  chemically 
  pure, 
  and 
  in 
  drawing 
  the 
  conclusion 
  just 
  re- 
  

   ferred 
  to 
  it 
  was 
  assumed 
  that 
  the 
  salts 
  were, 
  as 
  they 
  purported 
  

   to 
  be, 
  of 
  a 
  high 
  grade 
  of 
  purity. 
  It 
  has 
  been 
  found, 
  however, 
  

   since 
  the 
  publication 
  of 
  this 
  note 
  that 
  the 
  assumption 
  was 
  by 
  

  

  * 
  Communicated 
  by 
  the 
  Authors. 
  

  

  