﻿516 
  Mr. 
  F. 
  Soddy 
  on 
  the 
  Production 
  of 
  

  

  certainly 
  be 
  greater 
  than 
  1*2 
  X 
  10~ 
  10 
  , 
  but 
  to 
  an, 
  at 
  present, 
  

   indeterminate 
  extent. 
  This 
  direct 
  value 
  therefore 
  may 
  be 
  

   unsound, 
  and 
  the 
  error 
  affects 
  also 
  the 
  derived 
  calculations 
  

   for 
  thorium. 
  As 
  about 
  to 
  be 
  shown, 
  the 
  increase 
  from 
  this 
  

   cause 
  is 
  not, 
  unfortunately, 
  likely 
  to 
  be 
  very 
  great. 
  

  

  There 
  is 
  also 
  an 
  indirect 
  method 
  of 
  calculating 
  the 
  rate 
  of 
  

   production 
  of 
  helium 
  by 
  a 
  comparison 
  of 
  the 
  a-rays, 
  for 
  

   which 
  Boltwood 
  has 
  just 
  recently 
  supplied 
  much 
  more 
  

   complete 
  data 
  than 
  were 
  before 
  available. 
  It 
  leads 
  to 
  a 
  

   greater 
  value 
  than 
  the 
  direct 
  method, 
  which 
  we 
  have 
  seen 
  

   is 
  likely 
  to 
  give 
  too 
  low 
  a 
  value, 
  and 
  is 
  perhaps 
  to 
  be 
  

   preferred. 
  Boltwood 
  deduces 
  from 
  his 
  most 
  recent 
  deter- 
  

   mination 
  of 
  the 
  proportionate 
  a-radiation 
  contributed 
  by 
  

   each 
  of 
  the 
  radioactive 
  bodies 
  in 
  uranium 
  minerals 
  (Am. 
  

   Journ. 
  Sci., 
  April 
  1908, 
  p. 
  296) 
  that 
  the 
  a-activity 
  of 
  radium 
  

   (free 
  from 
  all 
  products) 
  is 
  1,300,000 
  times 
  that 
  of 
  uranium. 
  

   As 
  the 
  range 
  of 
  the 
  a-particle 
  is 
  the 
  same 
  in 
  each 
  case, 
  the 
  

   rate 
  of 
  disintegration 
  of 
  uranium 
  bv 
  this 
  method 
  comes 
  out 
  

   at 
  3*48 
  X 
  10- 
  4 
  -=-l'3 
  x 
  10 
  6 
  = 
  2-7 
  x 
  lO" 
  10 
  . 
  This 
  is 
  225 
  times 
  

   the 
  " 
  direct 
  value," 
  and 
  gives 
  for 
  the 
  rate 
  of 
  production 
  of 
  

   helium 
  from 
  uranium 
  and 
  thorium 
  4*5 
  x 
  10~~ 
  12 
  (year) 
  -1 
  . 
  

   For 
  pitchblende, 
  containing 
  equilibrium 
  amounts 
  of 
  all 
  

   products, 
  Boltwood 
  (he. 
  cit.) 
  finds 
  the 
  a-activity 
  to 
  be 
  about 
  

   4*7 
  times 
  that 
  contributed 
  by 
  the 
  uranium. 
  As 
  some 
  of 
  this 
  

   activity 
  is 
  due 
  to 
  a-rays 
  of 
  much 
  higher 
  velocity 
  than 
  those 
  

   of 
  uranium, 
  one 
  can 
  deduce 
  in 
  this 
  method 
  of 
  calculation 
  that 
  

   for 
  pitchblende 
  the 
  rate 
  of 
  production 
  of 
  helium 
  should 
  be 
  

   about 
  four 
  times 
  that 
  of 
  the 
  uranium 
  it 
  contains. 
  Whereas, 
  

   of 
  course, 
  on 
  the 
  simple 
  disintegration 
  theory, 
  which 
  re- 
  

   cognizes 
  in 
  pitchblende 
  the 
  existence 
  of 
  seven, 
  and 
  indicates 
  

   eight, 
  a-ray 
  or 
  helium-producing 
  changes, 
  only 
  one 
  of 
  which 
  

   is 
  contributed 
  by 
  uranium, 
  it 
  is 
  to 
  be 
  expected 
  that 
  pitch- 
  

   blende 
  would 
  produce 
  helium 
  at 
  eight 
  times 
  the 
  rate 
  of 
  the 
  

   uranium 
  present, 
  which 
  is 
  twice 
  the 
  preceding 
  value. 
  Bolt- 
  

   wood 
  himself 
  points 
  out 
  that 
  the 
  discrepancy 
  could 
  be 
  

   partially 
  accounted 
  for 
  on 
  the 
  assumption 
  that 
  uranium 
  

   suffers 
  two 
  a-ray 
  changes, 
  which 
  is, 
  according 
  to 
  the 
  pre- 
  

   ceding 
  view, 
  that 
  the 
  uranium 
  atom 
  gives 
  two 
  helium 
  atoms. 
  

   Certainly 
  his 
  results 
  are 
  most 
  suggestive. 
  The 
  a-radiation 
  

   from 
  the 
  radium 
  series 
  is 
  in 
  good 
  agreement 
  with 
  the 
  

   view 
  that 
  a 
  single 
  a-particle 
  is 
  expelled 
  by 
  radium 
  and 
  by 
  

   each 
  of 
  its 
  successive 
  a-ray 
  products, 
  the 
  a-radiation 
  from 
  

   uranium 
  is 
  slightly 
  more 
  than 
  would 
  be 
  the 
  case 
  if 
  it 
  expelled 
  

   two 
  a-particles, 
  while 
  the 
  whole 
  of 
  the 
  a-ray-changes 
  of 
  the 
  

   actinium 
  series 
  together 
  only 
  constitute 
  about 
  one-half 
  the 
  

   effect 
  of 
  a 
  single 
  a-ray 
  change 
  in 
  the 
  radium 
  series. 
  As 
  

  

  