﻿Active 
  Deposit 
  of 
  Actinium 
  in 
  Electric 
  Fields. 
  399 
  

  

  that 
  observations 
  on 
  various 
  occasions 
  gave 
  different 
  relative 
  

   values 
  to 
  the 
  anode 
  and 
  cathode 
  activities 
  under 
  these 
  cir- 
  

   cumstances. 
  This 
  is 
  no 
  more 
  than 
  might 
  have 
  been 
  expected, 
  

   since 
  there 
  is 
  no 
  reason 
  why 
  the 
  amount 
  of 
  dust, 
  and 
  

   especially 
  dust 
  negatively 
  electrified, 
  should 
  be 
  constant 
  

   over 
  long 
  periods 
  o£ 
  time. 
  

  

  It 
  still 
  remains 
  to 
  be 
  proved 
  that 
  the 
  dust 
  and 
  nuclei 
  

   actually 
  carried 
  a 
  negative 
  charge. 
  No 
  direct 
  evidence 
  was 
  

   obtained. 
  Pollock* 
  has 
  shown 
  that 
  the 
  majority 
  of 
  the 
  

   large 
  ions 
  found 
  in 
  the 
  atmosphere 
  at 
  Sydney 
  carry 
  negative 
  

   charges. 
  These 
  slowly 
  moving 
  ions 
  would 
  collect 
  active 
  

   deposit, 
  and 
  therefore 
  act 
  in 
  the 
  above 
  manner. 
  Rudgef 
  

   has 
  recently 
  shown, 
  in 
  his 
  work 
  on 
  the 
  electrification 
  asso- 
  

   ciated 
  with 
  dust 
  clouds, 
  that 
  in 
  England 
  atmospheric 
  dust 
  

   is 
  usually 
  negatively 
  electrified. 
  This 
  was 
  confirmed 
  to 
  

   some 
  extent, 
  by 
  taking 
  samples 
  of 
  dust 
  from 
  shelves, 
  &c, 
  in 
  

   the 
  laboratory 
  that 
  had 
  not 
  been 
  disturbed 
  for 
  some 
  time. 
  

   This 
  was 
  tested 
  by 
  Rudge's 
  method. 
  Many 
  samples 
  showed 
  

   little 
  or 
  no 
  electrification 
  when 
  blown 
  into 
  a 
  cloud, 
  but 
  some 
  

   samples, 
  consisting 
  of 
  very 
  fine 
  material 
  collected 
  from 
  the 
  

   more 
  inaccessible 
  places, 
  exhibited 
  a 
  fairly 
  strong 
  negative 
  

   electrification. 
  

  

  If 
  the 
  supply 
  of 
  negatively 
  charged 
  dust 
  is 
  sufficiently 
  

   great, 
  it 
  may 
  happen 
  that 
  most 
  or 
  all 
  of 
  the 
  active 
  deposit 
  

   is 
  eventually 
  collected 
  by 
  the 
  dust. 
  Under 
  these 
  conditions, 
  

   the 
  variation 
  of 
  anode 
  and 
  cathode 
  activity 
  with 
  time 
  would 
  

   be 
  such 
  that 
  it 
  would 
  appear 
  as 
  if 
  the 
  active 
  deposit 
  originally 
  

   possessed 
  a 
  positive 
  charge, 
  and 
  on 
  recombination 
  reversed 
  

   its 
  electrification. 
  This 
  particular 
  case 
  is 
  strikingly 
  shown 
  

   in 
  fig. 
  11 
  J. 
  If 
  we 
  add 
  together 
  the 
  anode 
  and 
  cathode 
  

   activity, 
  we 
  obtain 
  a 
  curve 
  which 
  will 
  represent 
  the 
  amount 
  

   of 
  activity 
  present 
  in 
  the 
  chamber 
  at 
  any 
  time, 
  provided 
  

   that 
  the 
  amount 
  of 
  active 
  deposit 
  carrving 
  no 
  charge, 
  which 
  

   collects 
  on 
  the 
  electrodes 
  by 
  diffusion, 
  is 
  negligible. 
  This 
  

   curve 
  was 
  found 
  to 
  be 
  roughly 
  exponential 
  and 
  represents 
  

   the 
  rate 
  at 
  which 
  the 
  active 
  matter, 
  as 
  a 
  whole, 
  is 
  carried 
  to 
  

   the 
  walls 
  of 
  the 
  vessel 
  by 
  diffusion. 
  If 
  we 
  correct 
  the 
  

   observed 
  values 
  by 
  means 
  of 
  this 
  curve 
  for 
  diffusion, 
  we 
  

  

  * 
  Pollock, 
  Le 
  Radium, 
  vi. 
  p. 
  129 
  (1909). 
  

  

  t 
  Rudge, 
  Phil. 
  Mag. 
  xxv. 
  p. 
  481 
  (1913). 
  

  

  % 
  I 
  am 
  indebted 
  to 
  Miss 
  Doris 
  Bailey, 
  B.Sc, 
  for 
  the 
  curves 
  in 
  fig. 
  11. 
  

   Under 
  the 
  direction 
  of 
  Professor 
  Rutherford 
  she 
  performed 
  most 
  of 
  the 
  

   preliminary 
  work 
  on 
  actinium 
  B 
  during 
  the 
  session 
  1911-1912 
  and 
  

   generously 
  placed 
  her 
  results 
  at 
  my 
  disposal. 
  

  

  2 
  E 
  2 
  

  

  