﻿580 
  Prof. 
  J. 
  Joly 
  on 
  the 
  

  

  after 
  being 
  brought 
  into 
  solution 
  by 
  50 
  cc. 
  of 
  HCl 
  and 
  

   diluted 
  with 
  water, 
  was 
  tested 
  for 
  thorium. 
  The 
  filtrate 
  

   was 
  separately 
  tested. 
  The 
  total 
  quantity 
  of 
  thorium 
  found 
  

   was 
  139*5 
  X 
  10~^ 
  gram. 
  Of 
  this 
  the 
  alkaline 
  solution 
  held 
  

   just 
  one-twelfth 
  part. 
  Deducting 
  the 
  natural 
  thorium 
  — 
  

   52 
  X 
  10"^ 
  gram 
  — 
  a 
  balance 
  of 
  87'5 
  X 
  10~^ 
  gram 
  remains. 
  But 
  

   1*2 
  milligram 
  of 
  thorianite 
  should 
  contain 
  83*7x10"^ 
  gram 
  

   of 
  thorium, 
  according 
  to 
  Dunstan''s 
  analysis. 
  The 
  discrepancy 
  

   is 
  within 
  the 
  limits 
  of 
  error 
  attending 
  the 
  weighing 
  out 
  of 
  the 
  

   thorianite. 
  A 
  second 
  experiment 
  of 
  the 
  same 
  character 
  on 
  the 
  

   same 
  pumice 
  was 
  made, 
  in 
  which 
  1 
  milligram 
  of 
  thorianite 
  

   was 
  taken. 
  The 
  filtration 
  was 
  effected 
  while 
  the 
  solution 
  was 
  

   hot. 
  The 
  thorium 
  found 
  was 
  117*5 
  x 
  10~^ 
  gram, 
  all 
  of 
  

   which 
  was 
  in 
  the 
  acid 
  solution. 
  Deducting, 
  as 
  before, 
  the 
  

   natural 
  thorium, 
  a 
  balance 
  of 
  65*5 
  X 
  10~^ 
  gram 
  remains 
  to 
  

   account 
  for 
  the 
  inserted 
  thorium 
  — 
  which 
  was, 
  on 
  Dunstan's 
  

   analysis, 
  69*8 
  X 
  10"^ 
  gram. 
  The 
  discrepancy 
  is 
  again 
  within 
  

   the 
  errors 
  of 
  the 
  weighing. 
  

  

  These 
  experiments 
  were 
  made 
  with 
  the 
  double 
  object 
  of 
  

   testing 
  the 
  method 
  of 
  determination 
  and 
  of 
  finding 
  whether 
  

   ThX 
  was 
  removed 
  in 
  the 
  filtrate; 
  which 
  from 
  the 
  well 
  

   known 
  experiment 
  of 
  Rutherford 
  and 
  Soddy 
  might, 
  perhaps, 
  

   have 
  been 
  expected. 
  In 
  a 
  few 
  cases 
  out 
  of 
  many 
  I 
  have 
  

   found 
  some 
  radioactivity 
  in 
  the 
  alkaline 
  solution, 
  and 
  I 
  

   have 
  not 
  generally 
  been 
  able 
  to 
  connect 
  its 
  appearance 
  with 
  

   the 
  temperature 
  at 
  which 
  filtration 
  is 
  effected. 
  The 
  radio- 
  

   activity 
  observed 
  occasionally 
  in 
  the 
  alkaline 
  solution 
  seems 
  

   generally 
  to 
  diminish 
  in 
  a 
  few 
  days 
  but 
  never 
  quite 
  to 
  

   disappear. 
  A 
  little 
  both 
  of 
  thorium 
  and 
  of 
  thorium 
  X 
  are 
  

   possibly 
  separated 
  in 
  such 
  cases. 
  The 
  testing 
  of 
  both 
  

   solutions 
  is, 
  therefore, 
  desirable, 
  especially 
  if 
  freshly 
  made 
  

   up 
  solutions 
  are 
  being 
  dealt 
  with. 
  In 
  dealing 
  with 
  old 
  

   solutions 
  the 
  error, 
  if 
  this 
  is 
  not 
  done, 
  will 
  generally 
  be 
  

   small. 
  A 
  good 
  plan 
  is 
  to 
  mix 
  both 
  solutions 
  together 
  after 
  

   the 
  residue 
  has 
  been 
  brought 
  into 
  solution. 
  The 
  alkaline 
  

   solution 
  should, 
  in 
  this 
  case, 
  be 
  first 
  acidified. 
  In 
  certain 
  

   basic 
  rock-solutions 
  this 
  procedure 
  is, 
  however, 
  not 
  admissible; 
  

   a 
  precipitate 
  forming. 
  

  

  In 
  the 
  thorium 
  experiments 
  carried 
  out 
  in 
  connexion 
  with 
  

   the 
  lavas, 
  the 
  velocity 
  of 
  air-current 
  from 
  the 
  flask 
  to 
  the 
  

   electroscope 
  was 
  about 
  two 
  cubic 
  centimetres 
  per 
  second. 
  

   With 
  this 
  current 
  the 
  sensibility 
  of 
  the 
  electroscope 
  was 
  

   1*55 
  X 
  10~^ 
  gram 
  thorium 
  per 
  scale- 
  division 
  per 
  hour. 
  This 
  

   velocity 
  of 
  air- 
  draft 
  is 
  sufficiently 
  slow 
  to 
  secure 
  the 
  results 
  

   against 
  error 
  from 
  the 
  passage 
  of 
  the 
  short-lived 
  emanation 
  

   of 
  actinium. 
  

  

  