﻿Active 
  Deposit 
  of 
  Radium 
  in 
  an 
  Electric 
  Field. 
  633 
  

  

  through 
  the 
  vapour 
  during 
  the 
  activation, 
  due 
  mainly 
  to 
  the 
  

   fact 
  that 
  the 
  ether 
  being 
  near 
  the 
  point 
  of 
  condensation 
  was 
  

   partly 
  conducting 
  ; 
  this 
  conduction 
  current 
  may 
  have 
  been 
  

   responsible 
  for 
  the 
  increased 
  amount 
  of 
  the 
  cathode 
  deposit 
  

   at 
  the 
  highest 
  pressure. 
  Apart 
  from 
  this 
  it 
  appears 
  that 
  for 
  

   ether 
  vapour 
  the 
  limiting 
  value 
  of 
  the 
  cathode 
  activity 
  is 
  

   approximately 
  10 
  per 
  cent. 
  

  

  Summary 
  and 
  Discussion 
  of 
  Results. 
  

  

  8. 
  When 
  the 
  emanation 
  is 
  mixed 
  with 
  any 
  gas 
  there 
  

   appears 
  to 
  be 
  a 
  definite 
  limit 
  to 
  the 
  fraction 
  of 
  the 
  active 
  

   deposit 
  which 
  settles 
  on 
  the 
  cathode. 
  This 
  limit 
  is 
  inde- 
  

   pendent 
  of 
  the 
  pressure 
  of 
  the 
  gas 
  provided 
  it 
  is 
  high 
  enough 
  

   to 
  prevent 
  the 
  deposit 
  particles 
  from 
  recoiling 
  on 
  to 
  the 
  

   walls 
  of 
  the 
  vessel 
  ; 
  it 
  is 
  in 
  general 
  dependent 
  on 
  the 
  nature 
  

   of 
  the 
  gas. 
  This 
  limiting 
  value 
  is 
  in 
  general 
  obtained 
  only 
  

   with 
  large 
  potentials; 
  with 
  smaller 
  potentials 
  the 
  fraction 
  of 
  

   the 
  cathode 
  deposit 
  is 
  decreased 
  as 
  a 
  result 
  of 
  columnar 
  re- 
  

   combination 
  of 
  the 
  positively 
  charged 
  particles 
  with 
  negative 
  

   ions 
  ; 
  and 
  with 
  very 
  small 
  potentials 
  the 
  charged 
  particles 
  

   recombine 
  with 
  negative 
  ions 
  in 
  the 
  volume 
  of 
  the 
  gas. 
  Small 
  

   traces 
  of 
  water 
  vapour 
  have 
  a 
  considerable 
  effect 
  in 
  diminish- 
  

   ing 
  the 
  number 
  of 
  positively 
  charged 
  particles 
  : 
  the 
  water 
  

   vapour 
  appears 
  to 
  be 
  effective 
  in 
  bringing 
  about 
  increased 
  

   recombination 
  both 
  volume 
  and 
  columnar 
  between 
  the 
  charged 
  

   particles 
  and 
  the 
  negative 
  ions. 
  

  

  It 
  has 
  been 
  shown 
  in 
  Section 
  5 
  that 
  even 
  in 
  air 
  which 
  has 
  

   been 
  thoroughly 
  dried 
  the 
  recombination 
  between 
  the 
  charged 
  

   deposit 
  particles 
  and 
  the 
  negative 
  ions 
  is 
  greater 
  than 
  the 
  

   recombination 
  between 
  the 
  positive 
  and 
  negative 
  ions. 
  This 
  

   result, 
  which 
  is 
  in 
  all 
  probability 
  to 
  be 
  ascribed 
  to 
  the 
  larger 
  

   size 
  and 
  mass 
  of 
  the 
  deposit 
  particles, 
  is 
  not 
  in 
  accord 
  with 
  

   the 
  experimental 
  result 
  of 
  H. 
  W. 
  Schmidt*, 
  who 
  came 
  to 
  

   the 
  conclusion 
  that 
  as 
  far 
  as 
  recombination 
  and 
  mobility 
  are 
  

   concerned 
  the 
  active 
  particles 
  behave 
  as 
  positive 
  ions. 
  

  

  The 
  process 
  which 
  accompanies 
  the 
  deposit 
  of 
  the 
  active 
  

   particles 
  on 
  the 
  cathode 
  appears 
  to 
  be 
  most 
  suitably 
  explained 
  

   in 
  the 
  following 
  manner. 
  At 
  the 
  moment 
  of 
  expulsion 
  of 
  

   the 
  a-particle 
  from 
  the 
  atom 
  of 
  emanation 
  the 
  residual 
  part 
  

   recoils 
  into 
  the 
  gas; 
  in 
  air 
  at 
  a 
  pressure 
  of 
  1 
  atmosphere 
  the 
  

   range 
  of 
  this 
  recoil 
  atom 
  has 
  been 
  shown 
  to 
  be 
  about 
  -fa 
  mm. 
  

   As 
  it 
  moves 
  through 
  the 
  gas 
  the 
  recoil 
  atom 
  produces 
  a 
  large 
  

   number 
  of 
  ions, 
  and 
  in 
  the 
  act 
  of 
  ionization 
  it 
  is 
  possible 
  

   that 
  the 
  recoil 
  atom 
  may 
  lose 
  its 
  positive 
  charge. 
  On 
  the 
  

   other 
  hand, 
  recoil 
  atoms 
  which 
  at 
  any 
  time 
  are 
  uncharged 
  

   * 
  H. 
  W. 
  Schmidt, 
  Phys. 
  Zeit. 
  ix. 
  p. 
  184 
  (1908). 
  

  

  