﻿the 
  Actinium 
  and 
  Thorium 
  Emanations. 
  131 
  

  

  actinium 
  emanation. 
  He 
  placed 
  half 
  a 
  gramme 
  of 
  an 
  

   actinium 
  salt, 
  of 
  activity 
  of 
  about 
  -4000, 
  in 
  a 
  glass 
  tube. 
  

   This 
  tube 
  was 
  connected 
  through 
  a 
  series 
  of 
  U-tubes 
  to 
  

   another, 
  in 
  which 
  a 
  screen 
  of 
  zinc 
  sulphide 
  was 
  enclosed. 
  

   By 
  exhausting 
  the 
  tubes 
  to 
  a 
  high 
  vacuum, 
  the 
  actinium 
  

   emanation 
  diffused 
  rapidly 
  through 
  them, 
  and 
  the 
  scintil- 
  

   lations 
  on 
  the 
  screen 
  were 
  observed 
  through 
  a 
  microscope. 
  

   The 
  U-tubes 
  were 
  cooled 
  in 
  petroleum 
  ether 
  to 
  — 
  170° 
  C. 
  in 
  

   a 
  Dewar's 
  vessel, 
  and 
  the 
  temperature 
  was 
  allowed 
  to 
  rise 
  

   slowly. 
  A 
  thermo-couple, 
  inserted 
  in 
  the 
  vessel, 
  was 
  used 
  

   to 
  measure 
  the 
  temperature. 
  In 
  this 
  way, 
  he 
  observed 
  that 
  

   the 
  scintillation 
  began 
  at 
  about 
  —143° 
  C, 
  this 
  being 
  the 
  

   mean 
  of 
  four 
  experiments 
  giving 
  values 
  of 
  —149° 
  C, 
  

   -140° 
  C, 
  —143° 
  C, 
  and 
  -140° 
  C. 
  The 
  scintillation 
  

   attained 
  a 
  maximum 
  intensity 
  in 
  the 
  neighbourhood 
  of 
  

   — 
  100° 
  C. 
  These 
  two 
  temperatures 
  of 
  complete 
  and 
  initial 
  

   condensation 
  are 
  not 
  widely 
  different 
  from 
  those 
  found 
  by 
  

   the 
  writer, 
  but 
  the 
  method 
  is 
  merely 
  qualitative 
  in 
  character. 
  

   In 
  the 
  present 
  research 
  a 
  quantitative 
  comparison 
  of 
  the 
  con- 
  

   densation 
  phenomena 
  of 
  the 
  emanation 
  of 
  thorium 
  and 
  

   actinium 
  has 
  been 
  made 
  by 
  the 
  electrical 
  method, 
  under 
  

   varying 
  conditions 
  of 
  pressure 
  and 
  temperature, 
  similar 
  in 
  

   general 
  character 
  to 
  that 
  made 
  by 
  Butherford 
  and 
  Soddy 
  

   for 
  the 
  emanations 
  of 
  thorium 
  and 
  radium. 
  

  

  Summary 
  of 
  Results. 
  

  

  Tbe 
  actinium 
  emanation 
  begins 
  to 
  condense 
  at 
  about 
  

   — 
  120° 
  C, 
  and 
  some 
  of 
  the 
  emanation 
  remains 
  uncondensed 
  

   below 
  that 
  temperature. 
  At 
  about 
  —150° 
  C. 
  it 
  condenses 
  as 
  

   a 
  whole. 
  These, 
  and 
  the 
  intermediate 
  temperatures, 
  at 
  which 
  

   a 
  certain 
  proportion 
  of 
  the 
  emanation 
  condenses, 
  vary 
  with 
  

   -the 
  pressure, 
  but 
  the 
  variation 
  becomes 
  less 
  when 
  the 
  pressure 
  

   increases. 
  Experiments 
  on 
  similar 
  lines 
  with 
  thorium 
  

   emanation 
  show 
  that 
  it 
  condenses 
  at 
  about 
  2° 
  or 
  3° 
  C. 
  higher 
  

   temperature 
  than 
  the 
  actinium 
  emanation, 
  the 
  dependence 
  of 
  

   their 
  condensation-points 
  upon 
  pressure 
  being 
  very 
  similar. 
  

  

  In 
  conclusion 
  I 
  wish 
  to 
  thank 
  Prof. 
  Rutherford 
  for 
  sug- 
  

   gesting 
  the 
  experiment, 
  and 
  for 
  his 
  continual 
  interest 
  and 
  

   advice 
  during 
  the 
  progress 
  of 
  this 
  research. 
  

  

  Physical 
  Laboratory, 
  

   Owens 
  College, 
  Manchester. 
  

  

  K2 
  

  

  