﻿626* 
  Prof. 
  E. 
  M. 
  Wellisch 
  on 
  the 
  Distribution 
  of 
  the 
  

  

  Radium 
  emanation 
  mixed 
  with 
  air 
  at 
  1 
  atmosphere 
  pressure 
  

   was 
  introduced 
  into 
  one 
  of 
  these 
  vessels, 
  and 
  when 
  a 
  positive 
  

   potential 
  of 
  3000 
  volts 
  was 
  applied 
  to 
  the 
  case 
  it 
  was 
  found 
  

   that 
  about 
  86 
  per 
  cent, 
  of 
  the 
  deposit 
  settled 
  on 
  the 
  cathode. 
  

   In 
  all 
  probability 
  some 
  part 
  of 
  the 
  cathode 
  activity 
  made 
  its 
  

   way 
  to 
  the 
  ebonite 
  insulation, 
  but 
  there 
  did 
  not 
  appear 
  to 
  be 
  

   any 
  gain 
  in 
  the 
  cathode 
  deposit 
  as 
  a 
  result 
  of 
  decreasing 
  the 
  

   cross-section 
  of 
  the 
  containing 
  vessel. 
  

  

  Cathode 
  Deposit 
  in 
  Dry 
  Air 
  at 
  Different 
  Pressures. 
  

  

  4. 
  Throughout 
  the 
  remainder 
  of 
  the 
  experimental 
  investi- 
  

   gation, 
  use 
  was 
  made 
  of 
  the 
  two 
  cylindrical 
  vessels 
  which 
  

   had 
  been 
  employed 
  in 
  the 
  previous 
  research. 
  These 
  vessels 
  

   were 
  identical 
  in 
  construction 
  and 
  the 
  dimensions 
  of 
  each 
  

   were 
  as 
  follows 
  : 
  — 
  

  

  Height 
  (inside) 
  140 
  mm. 
  

  

  Inner 
  diameter 
  58 
  „ 
  

  

  Exposed 
  length 
  of 
  central 
  electrode 
  132 
  „ 
  

  

  Diameter 
  of 
  central 
  electrode 
  . 
  . 
  1'83 
  ,, 
  

  

  The 
  inner 
  electrodes 
  were 
  made 
  longer 
  than 
  those 
  which 
  

   had 
  previously 
  been 
  employed, 
  and 
  care 
  was 
  taken 
  that 
  no 
  

   appreciable 
  part 
  of 
  the 
  active 
  deposit 
  was 
  able 
  to 
  settle 
  on 
  

   the 
  ebonite 
  insulation. 
  During 
  the 
  course 
  of 
  the 
  present 
  

   experiments 
  a 
  fact 
  was 
  noted 
  which 
  had 
  previously 
  escaped 
  

   observation. 
  Discrepancies, 
  in 
  general 
  small, 
  occurred 
  in 
  

   the 
  values 
  for 
  the 
  cathode 
  deposit 
  when 
  the 
  experimental 
  

   conditions 
  appeared 
  to 
  be 
  identical. 
  Repeated 
  attempts 
  to 
  

   ascertain 
  the 
  cause 
  of 
  the 
  discrepancies 
  were 
  for 
  a 
  long 
  time 
  

   unsuccessful, 
  but 
  finally 
  it 
  was 
  ascertained 
  that 
  the 
  incon- 
  

   sistent 
  results 
  arose 
  from 
  the 
  presence 
  of 
  small 
  quantities 
  of 
  

   water 
  vapour 
  in 
  the 
  gas. 
  In 
  the 
  previous 
  research 
  a 
  test 
  

   had 
  purposely 
  been 
  made 
  to 
  find 
  the 
  effect 
  of 
  neglecting 
  to 
  

   dry 
  the 
  gas 
  with 
  which 
  the 
  emanation 
  was 
  mixed 
  ; 
  this 
  test 
  

   appeared 
  to 
  show 
  that 
  the 
  cathode 
  deposit 
  was 
  unaffected 
  by 
  

   omitting 
  this 
  precaution. 
  However, 
  the 
  fallacy 
  of 
  this 
  

   result 
  was 
  shown 
  by 
  more 
  thorough 
  investigation. 
  The 
  

   effect 
  of 
  water 
  vapour 
  is 
  to 
  diminish 
  the 
  cathode 
  deposit, 
  and 
  

   is 
  especially 
  marked 
  when 
  the 
  gas 
  pressure 
  is 
  high 
  and 
  the 
  

   applied 
  potential 
  fairly 
  small 
  ; 
  in 
  these 
  circumstances 
  an 
  

   amount 
  of 
  water 
  vapour 
  which 
  was 
  not 
  sufficient 
  to 
  produce 
  

   any 
  perceptible 
  increase 
  in 
  the 
  recombination 
  of 
  the 
  ions 
  

   present 
  in 
  the 
  gas 
  might 
  easily 
  diminish 
  the 
  cathode 
  deposit 
  

   by 
  30 
  to 
  50 
  per 
  cent. 
  Further 
  illustrations 
  of 
  this 
  effect 
  

   are 
  given 
  later, 
  but 
  in 
  future 
  experiments 
  extreme 
  care 
  was 
  

  

  