﻿306 
  Prof. 
  E. 
  Rutherford 
  : 
  Experiments 
  

  

  has 
  gone, 
  the 
  essential 
  conditions 
  for 
  the 
  purification 
  of 
  the 
  

   emanation 
  depend 
  upon 
  the 
  pumping 
  off 
  the 
  residual 
  gases 
  at 
  

   a 
  temperature 
  below 
  the 
  temperature 
  of 
  volatilization 
  of 
  the 
  

   emanation 
  and 
  considerably 
  above 
  the 
  temperature 
  of 
  liquid 
  

   air 
  ; 
  and 
  the 
  long 
  exposure 
  of 
  the 
  emanation 
  to 
  caustic 
  potash. 
  

   By 
  the 
  former 
  method 
  practically 
  all 
  the 
  known 
  inactive 
  

   gases 
  would 
  be 
  pumped 
  off. 
  I 
  think 
  the 
  high 
  value 
  of 
  the 
  

   volume 
  of 
  the 
  emanation 
  obtained 
  by 
  Ramsay 
  and 
  Cameron 
  

   must 
  be 
  ascribed 
  to 
  the 
  presence 
  of 
  other 
  gases 
  besides 
  the 
  

   emanation, 
  which 
  are 
  condensed 
  at 
  the 
  temperature 
  of 
  

   liquid 
  air. 
  

  

  Changes 
  in 
  Volume. 
  

  

  Ramsay 
  and 
  Cameron 
  (loc. 
  cit.) 
  have 
  given 
  a 
  number 
  of 
  ex- 
  

   amples 
  of 
  the 
  changes 
  in 
  volume 
  observed 
  in 
  their 
  experiments 
  

   to 
  measure 
  the 
  volume 
  of 
  the 
  emanation. 
  The 
  volume 
  of 
  the 
  

   gas 
  in 
  the 
  capillary 
  usually 
  diminished 
  with 
  time 
  rapidly 
  

   during 
  the 
  first 
  two 
  hours 
  to 
  about 
  half 
  value 
  and 
  then 
  more 
  

   slowly. 
  I 
  have 
  observed 
  very 
  similar 
  effects 
  in 
  my 
  experi- 
  

   ments, 
  using 
  impure 
  emanation. 
  In 
  some 
  cases 
  the 
  volume 
  

   diminished 
  in 
  the 
  course 
  of 
  several 
  hours 
  to 
  less 
  than 
  half 
  

   value, 
  but 
  after 
  this 
  preliminary 
  decrease 
  little 
  change 
  was 
  

   observed 
  in 
  the 
  volume 
  over 
  the 
  further 
  interval 
  of 
  a 
  week. 
  

   In 
  other 
  experiments, 
  the 
  volume 
  increased 
  instead 
  of 
  

   diminishing 
  in 
  the 
  course 
  of 
  a 
  few 
  hours, 
  sometimes 
  

   increasing 
  to 
  twice 
  the 
  initial 
  volume, 
  followed 
  later 
  by 
  a 
  

   slow 
  decrease 
  with 
  time. 
  The 
  expansion 
  or 
  contraction 
  of 
  

   the 
  volume 
  has 
  in 
  many 
  cases 
  no 
  direct 
  connexion 
  with 
  the 
  

   volume 
  changes 
  of 
  the 
  emanation 
  itself, 
  for 
  the 
  true 
  volume 
  

   of 
  the 
  emanation 
  present 
  was 
  in 
  some 
  experiments 
  certainly 
  

   not 
  more 
  than 
  20 
  per 
  cent, 
  of 
  the 
  total 
  *. 
  It 
  is 
  difficult 
  to 
  

   explain 
  these 
  expansions 
  and 
  contractions 
  except 
  on 
  the 
  suppo- 
  

   sition 
  that 
  the 
  gases 
  mixed 
  with 
  the 
  emanation 
  either 
  combine 
  

   or 
  dissociate 
  under 
  the 
  influence 
  of 
  the 
  powerful 
  radiation 
  from 
  

   the 
  emanation. 
  Until 
  experiments 
  are 
  made 
  with 
  some 
  known 
  

   gas 
  or 
  gases 
  added 
  to 
  pure 
  emanation, 
  we 
  can 
  only 
  speculate 
  

   upon 
  the 
  nature 
  of 
  the 
  gases 
  present 
  and 
  the 
  combinations 
  or 
  

   dissociations 
  which 
  are 
  effected. 
  There 
  is 
  another 
  possibility 
  

   which 
  may 
  prove 
  to 
  be 
  an 
  important 
  factor 
  in 
  the 
  volume 
  

   changes, 
  especially 
  with 
  nearly 
  pure 
  emanation. 
  It 
  is 
  believed 
  

   that 
  the 
  positive 
  and 
  negative 
  ions 
  produced 
  in 
  a 
  gas 
  at 
  

  

  * 
  Ramsay 
  and 
  Cameron 
  explained 
  the 
  decrease 
  of 
  volume 
  observed 
  in 
  

   their 
  experiments 
  on 
  the 
  assumption 
  that 
  the 
  emanation 
  changed 
  from 
  a 
  

   monatomic 
  to 
  a 
  diatomic 
  gas. 
  Since 
  the 
  volume 
  in 
  these 
  experiments 
  

   certainly 
  contained 
  less 
  than 
  20 
  per 
  cent, 
  of 
  emanation, 
  the 
  explanation 
  is 
  

   inadmissible. 
  

  

  