﻿Distribution 
  of 
  Thorium 
  in 
  the 
  Earth's 
  Surface. 
  141 
  

  

  exist 
  to 
  retain 
  the 
  short-lived 
  emanation, 
  was 
  investigated 
  by 
  

   adding 
  to 
  such 
  rock-sohitions 
  known 
  quantities 
  of 
  thorium. 
  

   Thus 
  ihe 
  rock 
  solution 
  referred 
  to 
  in 
  the 
  above 
  table 
  is 
  that 
  

   of 
  St. 
  Gothard, 
  No. 
  162 
  South, 
  which 
  had 
  yielded 
  very 
  little 
  

   emanation, 
  as 
  may 
  be 
  seen 
  by 
  reference 
  to 
  the 
  table 
  of 
  results 
  

   on 
  the 
  St. 
  Gothard 
  rocks 
  given 
  further 
  on. 
  Again, 
  the 
  

   following 
  experiments 
  on 
  rock 
  solutions 
  (prepared 
  from 
  

   20 
  grams 
  of 
  rock) 
  may 
  be 
  cited. 
  One 
  half 
  a 
  cubic 
  centimetre 
  

   of 
  standard 
  solution 
  was 
  used 
  in 
  the 
  case 
  of 
  each. 
  

  

  Gain 
  in 
  Scale- 
  

   Divisions 
  per 
  hour. 
  

  

  Basalt, 
  800 
  ccs. 
  (acid), 
  before 
  addition 
  of 
  sol. 
  A 
  8 
  

  

  Same, 
  after 
  „ 
  „ 
  23 
  

  

  G-ranite, 
  1400 
  ccs. 
  (acid), 
  before 
  addition 
  of 
  sol. 
  A... 
  9*5 
  

  

  Same, 
  after 
  „ 
  „ 
  23"5 
  

  

  It 
  will 
  be 
  seen 
  that 
  the 
  basalt 
  solution 
  shows 
  the 
  normal 
  

   increased 
  rate 
  of 
  discharge 
  for 
  the 
  added 
  thorium, 
  that 
  is 
  

   at 
  the 
  rate 
  of 
  30 
  scale-divisions 
  for 
  one 
  c.c. 
  The 
  granite 
  

   gives 
  the 
  increased 
  rate 
  of 
  discharge 
  as 
  28 
  divisions 
  for 
  

   1 
  c.c. 
  The 
  basalt 
  solution 
  was 
  not 
  limpid 
  ; 
  the 
  granite 
  

   solution 
  was 
  muddy 
  and 
  very 
  bulky. 
  

  

  In 
  preparing 
  test 
  solutions, 
  a 
  small 
  quantity 
  of 
  acid 
  should 
  

   be 
  added 
  to 
  the 
  water 
  before 
  the 
  addition 
  of 
  the 
  standard 
  

   solution. 
  I 
  have 
  found 
  that 
  in 
  neutral 
  solutions 
  there 
  is 
  

   sometimes 
  a 
  partial 
  loss 
  of 
  emanating 
  power 
  which 
  may 
  

   increase 
  on 
  successive 
  experiments. 
  This 
  has 
  not 
  been 
  

   noticed 
  on 
  acid 
  solutions. 
  Successive 
  tests 
  applied 
  to 
  rock 
  

   solutions 
  reveal 
  rather 
  a 
  small 
  increase 
  of 
  emanating 
  power 
  

   than 
  otherwise. 
  

  

  The 
  determinations 
  given 
  in 
  my 
  last 
  paper 
  were, 
  as 
  then 
  

   stated, 
  based 
  on 
  the 
  emanating 
  power 
  of 
  commercial 
  thorium 
  

   nitrate, 
  and 
  I 
  drew 
  attention 
  to 
  the 
  fact 
  that 
  the 
  calibration 
  

   of 
  the 
  electroscope 
  by 
  a 
  thorium 
  mineral 
  in 
  radioactive 
  

   equilibrium 
  must 
  probably 
  have 
  the 
  effect 
  of 
  lowering 
  the 
  

   deduced 
  results. 
  As 
  stated 
  above, 
  the 
  constant 
  of 
  the 
  electro- 
  

   scope 
  referred 
  to 
  thorianite 
  is 
  2"2 
  x 
  10~^, 
  whereas 
  that 
  based 
  

   on 
  commercial 
  thorium 
  nitrate 
  was 
  2'S 
  x 
  10 
  ~^. 
  Some 
  struc- 
  

   tural 
  changes 
  in 
  the 
  apparatus 
  do 
  not, 
  however, 
  permit 
  the 
  

   former 
  results 
  to 
  be 
  revised 
  exactly 
  according 
  to 
  the 
  above 
  

   figures 
  ; 
  but 
  a 
  direct 
  comparison 
  of 
  the 
  standard 
  nitrate 
  solu- 
  

   tion 
  with 
  the 
  standard 
  thorianite 
  solution 
  B 
  has 
  shown 
  that 
  

   the 
  emanating 
  powers 
  are 
  closely 
  in 
  the 
  proportion 
  of 
  2 
  to 
  3. 
  

   The 
  reduction, 
  by 
  one 
  third, 
  of 
  the 
  values 
  formerly 
  given, 
  

   will 
  bring 
  these 
  results 
  into 
  close 
  agreement 
  with 
  the 
  

   thorianite 
  standard 
  of 
  emanating 
  power. 
  The 
  revised 
  

   readings 
  are 
  given 
  below 
  with 
  some 
  few 
  additional 
  determi- 
  

   nations. 
  The 
  result 
  on 
  the 
  Moffat 
  Dale 
  shale 
  has 
  been 
  

  

  