﻿518 
  Mr. 
  F. 
  Soddy 
  on 
  the 
  Production 
  of 
  

  

  and 
  helium 
  but 
  no 
  radium, 
  as 
  conclusive 
  evidence 
  that 
  helium 
  

   is 
  a 
  disintegration 
  product 
  of 
  thorium. 
  He 
  finds 
  from 
  a 
  

   recent 
  examination 
  of 
  a 
  large 
  number 
  of 
  rare, 
  and 
  repre- 
  

   sentative 
  common 
  minerals, 
  that 
  helium 
  in 
  detectable 
  

   quantity 
  is 
  present 
  in 
  all. 
  In 
  every 
  case 
  but 
  one 
  it 
  can 
  be 
  

   accounted 
  for 
  by 
  the 
  presence 
  of 
  the 
  uranium-radium 
  series 
  

   and 
  of 
  thorium. 
  The 
  exception 
  is 
  Beryl, 
  which 
  contains 
  

   noticeable 
  amounts 
  of 
  helium 
  and 
  is 
  scarcely 
  radioactive. 
  

   The 
  existence 
  of 
  even 
  this 
  one 
  exception 
  would 
  appear 
  to 
  

   weaken 
  somewhat 
  the 
  argument 
  he 
  draws 
  from 
  the 
  presence 
  

   of 
  helium 
  in 
  fluor, 
  and 
  shows 
  the 
  necessity 
  for 
  caution 
  in 
  

   drawing 
  conclusions 
  by 
  the 
  indirect 
  method. 
  

  

  Sufficient 
  has 
  been 
  said 
  to 
  show 
  the 
  deep 
  importance 
  of 
  

   obtaining 
  if 
  possible 
  a 
  direct 
  experimental 
  determination 
  of 
  

   the 
  rate 
  of 
  production 
  of 
  helium 
  from 
  the 
  primary 
  radio- 
  

   elements 
  and 
  from 
  the 
  radioactive 
  minerals. 
  There 
  is 
  little 
  

   doubt 
  that 
  such 
  results, 
  if 
  they 
  can 
  be 
  obtained, 
  would 
  

   prove 
  invaluable 
  in 
  settling 
  some 
  of 
  the 
  outstanding 
  problems 
  

   in 
  radioactivity 
  which 
  radioactive 
  methods 
  from 
  their 
  nature 
  

   are 
  unable 
  unaided 
  to 
  solve. 
  

  

  Method 
  of 
  Work, 
  and 
  Early 
  Experiments. 
  

  

  The 
  process 
  recently 
  described 
  (Soddy, 
  Proc. 
  Roy. 
  Soc. 
  

   1907, 
  78 
  A, 
  p. 
  429) 
  for 
  the 
  detection 
  and 
  measurement 
  of 
  

   infinitesimal 
  quantities 
  of 
  helium 
  has 
  been 
  exclusively 
  used. 
  

   It 
  depends 
  on 
  the 
  use 
  of 
  calcium 
  heated 
  to 
  its 
  volatilisation 
  

   point 
  in 
  a 
  specially 
  constructed 
  vacuum 
  electric 
  furnace. 
  

   All 
  known 
  gases 
  but 
  those 
  of 
  the 
  argon 
  family 
  are 
  perectly 
  

   absorbed. 
  The 
  completeness 
  of 
  the 
  absorption 
  under 
  proper 
  

   conditions 
  is 
  such 
  that 
  the 
  residual 
  gas 
  compressed 
  several 
  

   thousand 
  times 
  (by 
  filling 
  the 
  absorption 
  vessel 
  after 
  cooling 
  

   with 
  mercury) 
  into 
  the 
  smallest 
  possible 
  spectrum-tube 
  

   hardly 
  suffices 
  to 
  conduct 
  the 
  discharge, 
  and, 
  in 
  the 
  absence 
  

   of 
  argon 
  gases, 
  the 
  spectrum-tube 
  remains 
  on 
  the 
  verge 
  of 
  

   non-conductance. 
  The 
  sensitiveness 
  of 
  the 
  method 
  as 
  a 
  test 
  

   for 
  the 
  presence 
  of 
  helium 
  is 
  increased 
  many 
  thousand 
  times 
  

   by 
  filling 
  the 
  apparatus 
  with 
  mercury, 
  although 
  the 
  labour 
  

   of 
  the 
  investigations 
  entailed 
  in 
  the 
  continual 
  cutting 
  down 
  

   and 
  building 
  up 
  of 
  the 
  complex 
  apparatus 
  is 
  of 
  course 
  very 
  

   great. 
  The 
  general 
  method 
  throughout 
  has 
  been 
  to 
  store 
  the 
  

   substances 
  under 
  examination 
  in 
  solution 
  in 
  glass 
  flasks 
  

   placed 
  on 
  water-baths. 
  The 
  air 
  is 
  first 
  as 
  completely 
  as 
  

   possible 
  removed 
  by 
  boiling 
  the 
  solutions 
  and 
  pumping 
  with 
  

   a 
  mercury-pump 
  through 
  a 
  U-tube 
  placed 
  in 
  a 
  freezing- 
  

   mixture. 
  A 
  new 
  mercury-pump 
  filled 
  with 
  new 
  mercury, 
  

   provided 
  with 
  two 
  large 
  drying- 
  tubes, 
  containing 
  sulphuric 
  

  

  