﻿the 
  Actinium 
  and 
  Thorium 
  Emanations. 
  

  

  127 
  

  

  It 
  is 
  difficult 
  to 
  fix 
  the 
  exact 
  points 
  at 
  which 
  the 
  curves 
  in 
  

   fig. 
  2 
  attain 
  maximum 
  values. 
  However, 
  the 
  temperature 
  at 
  

   which 
  a 
  fixed 
  amount 
  of 
  emanation 
  escapes 
  at 
  different 
  pres- 
  

   sures 
  can 
  be 
  found 
  with 
  more 
  accuracy 
  by 
  reducing 
  these 
  

   curves 
  to 
  the 
  same 
  scale, 
  as 
  shown 
  in 
  fig. 
  3. 
  The 
  tempe- 
  

   ratures 
  for 
  5 
  per 
  cent, 
  and 
  95 
  per 
  cent, 
  of 
  emanation 
  remaining 
  

   uncondansed 
  can 
  be 
  seen 
  from 
  the 
  second 
  and 
  last 
  columns 
  of 
  

   the 
  table 
  (p. 
  129). 
  These 
  are 
  the 
  inside 
  limits 
  of 
  tempe- 
  

   ratures 
  of 
  initial 
  and 
  of 
  complete 
  condensation. 
  

  

  Experiment 
  with 
  Thorium 
  Emanation. 
  

   Since 
  the 
  thorium 
  emanation 
  had 
  been 
  investigated 
  by 
  

   Rutherford 
  and 
  Soddy, 
  its 
  determination 
  was 
  made 
  only 
  

   under 
  the 
  same 
  conditions 
  as 
  actinium 
  emanation 
  ; 
  so 
  that 
  

   we 
  can 
  compare 
  the 
  behaviour 
  of 
  both 
  more 
  closely. 
  The 
  

   emanation 
  was 
  left 
  for 
  17 
  seconds 
  in 
  the 
  spiral, 
  and 
  the 
  same 
  

   glass 
  tubes 
  were 
  inserted 
  between 
  A 
  and 
  C 
  l5 
  to 
  vary 
  the 
  

   pressure. 
  The 
  fall 
  of 
  the 
  gold-leaf 
  was, 
  in 
  this 
  case, 
  mea- 
  

   sured 
  for 
  60 
  seconds. 
  The 
  activity 
  due 
  to 
  the 
  active 
  deposit 
  

  

  Fig-. 
  4. 
  (Thorium 
  Emanation.) 
  

  

  a 
  

  

  H 
  4 
  

  

  a 
  2 
  

  

  o 
  

  

  3 
  

  

  / 
  y 
  ^^„ 
  ^^ 
  — 
  •— 
  — 
  ^T 
  

  

  / 
  / 
  — 
  &■ 
  e 
  ■" 
  »2 
  

  

  / 
  / 
  S* 
  &_--—*■ 
  a 
  — 
  — 
  8 
  •———'* 
  I 
  

  

  <! 
  -ISO 
  -155 
  -150 
  -145 
  -140 
  -135 
  -130 
  -125 
  -120 
  -IIS 
  

  

  -105 
  -100 
  -95 
  

  

  Temperature. 
  

  

  of 
  thorium 
  was 
  negligible. 
  Consecutive 
  readings 
  as 
  tempe- 
  

   rature 
  rose 
  could 
  not 
  be 
  taken 
  so 
  rapidly 
  as 
  in 
  the 
  previous 
  

   experiments. 
  An 
  interval 
  of 
  6 
  or 
  7 
  minutes 
  was 
  therefore 
  

   allowed 
  between 
  two 
  readings 
  (corresponding 
  to 
  7° 
  or 
  8° 
  C. 
  

   rise 
  in 
  temperature 
  of 
  the 
  spiral). 
  The 
  amount 
  of 
  thorium 
  

   emanation 
  in 
  A 
  had 
  then 
  reached 
  about 
  99 
  per 
  cent, 
  of 
  its 
  

   equilibrium 
  value. 
  Fig. 
  4 
  shows 
  the 
  direct 
  results 
  and 
  

  

  