﻿Distribution 
  of 
  Thorium 
  in 
  the 
  Eartlis 
  Surface. 
  147 
  

  

  to 
  the 
  method 
  used 
  by 
  Strutt 
  in 
  his 
  investigations 
  on 
  the 
  

   amount 
  oE 
  radium 
  contained 
  in 
  rocks. 
  

  

  It 
  remained 
  to 
  be 
  seen 
  whether 
  part 
  of 
  the 
  activity 
  could 
  

   not 
  be 
  due 
  to 
  actinium. 
  Although 
  the 
  presence 
  of 
  traces 
  of 
  

   actinium 
  cannot 
  be 
  excluded 
  in 
  an 
  absolute 
  way 
  for 
  the 
  

   moment 
  (careful 
  tests 
  are 
  being 
  carried 
  out 
  presently 
  in 
  

   order 
  to 
  settle 
  definitely 
  the 
  question), 
  it 
  is 
  certain 
  that 
  the 
  

   greatest 
  part 
  of 
  the 
  activity 
  shown 
  by 
  my 
  hydroxides 
  is 
  due 
  

   to 
  thorium. 
  In 
  fact, 
  by 
  using 
  a 
  very 
  sensitive 
  electroscope 
  

   built 
  for 
  researches 
  on 
  the 
  ionization 
  in 
  closed 
  vessels, 
  I 
  

   succ3eded 
  in 
  obtaining 
  quite 
  distinct 
  phenomena 
  of 
  excited 
  

   activity 
  from 
  the 
  hydroxides, 
  the 
  rate 
  of 
  decay 
  being 
  that 
  of 
  

   thorium-excited 
  activity, 
  without 
  any 
  sign 
  of 
  an 
  initial 
  rapid 
  

   fall 
  which 
  could 
  be 
  attributed 
  to 
  the 
  presence 
  of 
  actinium. 
  

  

  After 
  the 
  activity 
  of 
  the 
  hydroxides 
  had 
  been 
  determined, 
  

   a 
  given 
  amount 
  of 
  thorium 
  hydroxide 
  in 
  radioactive 
  equi- 
  

   librium 
  was 
  added 
  to 
  them, 
  and 
  the 
  activity 
  newly 
  determined. 
  

   In 
  this 
  way 
  the 
  amount 
  of 
  thorium 
  hydroxide 
  necessary 
  to 
  

   produce 
  the 
  activity 
  originally 
  shown 
  by 
  the 
  hydroxides 
  could 
  

   be 
  calculated, 
  and 
  therefore 
  also 
  the 
  amount 
  of 
  thorium 
  that 
  

   must 
  be 
  present 
  in 
  each 
  sample 
  of 
  rock. 
  

  

  The 
  results 
  so 
  far 
  obtained, 
  to 
  which 
  has 
  been 
  added 
  the 
  

   one 
  obtained 
  in 
  a 
  quite 
  different 
  way 
  for 
  the 
  soil 
  of 
  Rome, 
  are 
  

   the 
  following 
  : 
  — 
  

  

  Vegetal 
  earth 
  (Rome) 
  1*45 
  x 
  10~^ 
  gr. 
  p. 
  gr. 
  

  

  Syenite 
  (La 
  Balma, 
  Biella) 
  8*28 
  x 
  10-^ 
  

  

  Syenite 
  (Bagni,Biella) 
  ()-30xl0-^ 
  

  

  Granite 
  (Baveno, 
  Lake 
  Major). 
  . 
  . 
  3*14 
  x 
  10"^ 
  „ 
  

  

  Granite 
  (Voges, 
  France) 
  2-07x 
  10"^ 
  „ 
  

  

  Finally, 
  in 
  a 
  quite 
  recent 
  paper 
  {Rendic, 
  R. 
  Accad, 
  d. 
  

   Lincei, 
  xviii. 
  1st 
  sem. 
  p. 
  289, 
  1909), 
  although, 
  of 
  course, 
  the 
  

   small 
  number 
  of 
  specimens 
  of 
  rocks 
  examined 
  by 
  me 
  does 
  

   not 
  allow 
  us 
  to 
  draw 
  any 
  definitive 
  conclusions, 
  1 
  have 
  cal- 
  

   culated 
  the 
  average 
  production 
  of 
  heat 
  due 
  to 
  the 
  products 
  

   of 
  the 
  thorium 
  family 
  contained 
  in 
  the 
  rocks 
  examined 
  by 
  

   me, 
  finding 
  that 
  it 
  is 
  about 
  twice 
  the 
  average 
  production 
  of 
  

   heat 
  due 
  to 
  the 
  products 
  of 
  the 
  uranium-radium 
  family 
  con- 
  

   tained 
  in 
  the 
  igneous 
  rocks 
  examined 
  by 
  Strutt. 
  Further, 
  

   as 
  it 
  is 
  easy 
  to 
  calculate, 
  the 
  average 
  amount 
  of 
  y 
  rays 
  

   emitted 
  by 
  the 
  products 
  of 
  the 
  thorium 
  fiimily 
  contained 
  in 
  

   the 
  specimens 
  tested 
  by 
  me 
  is 
  over 
  six 
  times 
  greater 
  than 
  the 
  

   average 
  amount 
  of 
  y 
  ravs 
  emitted 
  by 
  the 
  uranium-radium 
  

   "^ 
  L2 
  

  

  