﻿530 
  Production 
  of 
  Helium 
  from 
  Primary 
  Radio- 
  El 
  erne 
  ids. 
  

  

  of 
  the 
  total 
  gas, 
  probably, 
  was 
  obtained 
  for 
  the 
  test. 
  The 
  

   experiment 
  was 
  a 
  very 
  perfect 
  one, 
  and 
  D 
  3 
  was 
  seen 
  clearly 
  

   in 
  a 
  fairly 
  strong 
  blue 
  argon 
  spectrum. 
  It 
  was 
  exactly 
  iden- 
  

   tified 
  with 
  reference 
  to 
  the 
  sodium 
  lines 
  and 
  with 
  a 
  comparison 
  

   helium 
  tube, 
  and 
  its 
  quantity 
  was 
  estimated 
  to 
  be 
  about 
  2 
  tenth- 
  

   grams. 
  It 
  corresponded 
  very 
  closely 
  with 
  the 
  calibration 
  

   test 
  C 
  II. 
  This 
  gives 
  for 
  the 
  rate 
  of 
  production 
  of 
  helium 
  

   from 
  thorium 
  about 
  2 
  x 
  10 
  ~ 
  12 
  per 
  year. 
  

  

  Further 
  experiments 
  must 
  now 
  be 
  waited 
  for. 
  Not 
  until 
  

   a 
  consistent 
  series 
  of 
  quantitative 
  tests 
  of 
  this 
  character 
  have 
  

   been 
  carried 
  out, 
  can 
  any 
  reliance 
  be 
  placed 
  upon 
  the 
  results. 
  

  

  Summary. 
  

  

  The 
  present 
  rate 
  of 
  production 
  of 
  helium 
  from 
  uranium 
  and 
  

   thorium 
  indicated 
  by 
  theory 
  is 
  about 
  2 
  x 
  10 
  -12 
  per 
  year 
  as 
  a 
  

   minimum 
  value 
  if 
  it 
  is 
  produced 
  at 
  all, 
  or 
  about 
  4*5 
  X 
  10 
  -12 
  

   per 
  year, 
  calculated 
  by 
  an 
  indirect 
  method 
  on 
  the 
  assumption 
  

   that 
  the 
  a-particle 
  is 
  an 
  atom 
  of 
  helium. 
  The 
  first 
  of 
  these 
  

   values 
  is 
  almost 
  eight 
  times 
  less 
  than 
  the 
  value 
  indicated 
  when 
  

   these 
  experiments 
  were 
  started 
  three 
  years 
  ago. 
  

  

  The 
  minimum 
  quantity 
  of 
  helium 
  detectable 
  by 
  the 
  spectro- 
  

   scope 
  by 
  the 
  special 
  methods 
  employed 
  has 
  been 
  shown 
  to 
  be 
  

   tw 
  r 
  o 
  tenth-grams 
  (10~ 
  10 
  gram), 
  which 
  is 
  somewhat 
  greater 
  

   than 
  was 
  supposed 
  at 
  the 
  commencement 
  of 
  the 
  work. 
  In 
  

   consequence, 
  the 
  question 
  has 
  proved 
  more 
  difficult 
  to 
  settle 
  

   than 
  at 
  first 
  appeared. 
  With 
  the 
  quantities 
  of 
  uranium 
  and 
  

   thorium 
  employed 
  in 
  these 
  experiments, 
  a 
  period 
  of 
  accumu- 
  

   lation 
  of 
  several 
  months 
  is 
  necessary 
  to 
  detect 
  the 
  helium 
  if 
  

   produced 
  at 
  the 
  theoretical 
  rate. 
  

  

  The 
  experimental 
  difficulties 
  in 
  the 
  way 
  of 
  performing 
  

   such 
  tests 
  have 
  now 
  been 
  overcome, 
  but 
  only 
  one 
  positive 
  

   result 
  has 
  so 
  far 
  been 
  obtained. 
  This 
  was 
  with 
  350 
  grams 
  of 
  

   thorium 
  in 
  the 
  form 
  of 
  nitrate. 
  Helium 
  to 
  the 
  extent 
  of 
  

   about 
  two 
  tenth-grams 
  was 
  detected 
  after 
  a 
  period 
  of 
  accu- 
  

   mulation 
  of 
  nearly 
  seven 
  months, 
  which 
  corresponds 
  with 
  a 
  

   rate 
  of 
  helium 
  production 
  of 
  2 
  x 
  10~ 
  12 
  per 
  year. 
  This 
  result 
  

   is 
  of 
  course 
  of 
  no 
  significance 
  until 
  it 
  is 
  confirmed. 
  All 
  the 
  

   other 
  tests 
  so 
  far 
  obtained 
  only 
  indicate 
  that 
  the 
  rate 
  of 
  pro- 
  

   duction 
  of 
  helium 
  from 
  both 
  uranium 
  and 
  thorium 
  is 
  certainly 
  

   below 
  what 
  was 
  first 
  deduced 
  from 
  the 
  imperfect, 
  theory, 
  and 
  

   is 
  certainly 
  not 
  above 
  the 
  rate 
  indicated 
  by 
  the 
  present 
  

   theoretical 
  data. 
  

  

  Since 
  this 
  paper 
  w^as 
  written, 
  by 
  the 
  help 
  of 
  a 
  research 
  

   grant 
  from 
  the 
  Carnegie 
  Trustees, 
  a 
  new 
  series 
  of 
  experiments 
  

   have 
  been 
  successfully 
  started 
  with 
  quantities 
  of 
  materials 
  

   five-fold 
  greater 
  than 
  before 
  attempted. 
  

   Physical 
  Chemistry 
  Laboratory, 
  

   Glasgow 
  University. 
  

  

  