﻿Active 
  Deposit 
  of 
  Actinium 
  in 
  Electric 
  Fields. 
  389 
  

  

  appears 
  that 
  the 
  deposit 
  atoms 
  acquire 
  their 
  positive 
  charge 
  

   during 
  their 
  creation, 
  and 
  are 
  then 
  subjected 
  to 
  recombination 
  

   like 
  positive 
  ions. 
  The 
  evidence 
  is 
  unfavourable 
  to 
  the 
  view 
  

   that 
  initial 
  recombination 
  occurs, 
  for 
  if 
  such 
  occurred 
  one- 
  

   would 
  expect 
  the 
  curve 
  to 
  cut 
  the 
  axis 
  of 
  ordinates 
  above 
  the- 
  

   origin, 
  when 
  extrapolated. 
  The 
  curve 
  showing 
  the 
  relation 
  

   between 
  the 
  cathode 
  activity 
  and 
  voltage 
  must 
  continually 
  

   rise 
  for, 
  whatever 
  the 
  voltage 
  may 
  be, 
  a 
  finite 
  though 
  small 
  

   time 
  must 
  elapse 
  before 
  the 
  deposit 
  atoms 
  reach 
  the 
  

   boundary. 
  

  

  The 
  atoms 
  of 
  actinium 
  A 
  produced 
  at 
  a 
  distance 
  r 
  from 
  

   the 
  axis 
  of 
  the 
  tube 
  rapidly 
  decay, 
  and 
  only 
  a 
  small 
  fraction 
  

   (*—**»■), 
  if 
  charged, 
  reach 
  the 
  wire. 
  The 
  total 
  amount 
  carried 
  

   to 
  the 
  cathode 
  as 
  actinium 
  A 
  is 
  therefore 
  

  

  where 
  T 
  is 
  the 
  mean 
  time 
  of 
  passage. 
  

  

  When 
  V 
  is 
  very 
  great 
  this 
  expression 
  reduces 
  to 
  irp 
  (b 
  2 
  — 
  a 
  2 
  ) 
  ,. 
  

   i. 
  e. 
  the 
  whole 
  of 
  the 
  active 
  matter 
  carrying 
  a 
  positive 
  charge 
  

   is 
  carried 
  there. 
  Under 
  these 
  circumstances 
  the 
  number 
  

   of 
  deposit 
  atoms 
  recombining 
  is 
  negligible. 
  Hence 
  the 
  

   expression 
  gives 
  the 
  cathode 
  activity 
  for 
  large 
  values 
  of 
  V. 
  

   For 
  small 
  values 
  of 
  V 
  the 
  expression 
  becomes 
  

  

  2irpYK 
  

  

  which 
  vanishes 
  with 
  V, 
  as 
  one 
  would 
  expect. 
  The 
  relation 
  

   between 
  the 
  anode 
  activity 
  and 
  the 
  percentage 
  of 
  actinium 
  A 
  

   reaching 
  the 
  wire 
  can 
  be 
  derived 
  from 
  the 
  table. 
  Until 
  at 
  

   least 
  75 
  per 
  cent, 
  of 
  the 
  deposit 
  arrives 
  as 
  actinium 
  B, 
  the 
  loss 
  

   of 
  charge 
  is 
  proportional 
  to 
  the 
  time 
  taken 
  to 
  get 
  on 
  the 
  wire. 
  

   This 
  might 
  have 
  been 
  expected, 
  for 
  whatever 
  be 
  the 
  law 
  of 
  

   recombination 
  of 
  the 
  charges 
  with 
  time, 
  it 
  must 
  for 
  small 
  

   values 
  of 
  the 
  time 
  be 
  linear, 
  as 
  can 
  easily 
  be 
  shown 
  by 
  

   expansion. 
  When 
  the 
  voltages 
  employed 
  are 
  such 
  that 
  the 
  

  

  