﻿^50 
  Mr. 
  F. 
  Soddy 
  07i 
  the 
  

  

  The 
  factor 
  used 
  to 
  calculate 
  the 
  quantity 
  of 
  radinm 
  from 
  

   the 
  quantity 
  of 
  uranium 
  is 
  3*4 
  x 
  10~^, 
  instead 
  of 
  3*8 
  x 
  10"'^, 
  

   as 
  previously 
  used. 
  It 
  will 
  be 
  seen 
  that 
  the 
  standards 
  differ 
  

   among 
  themselves 
  in 
  content 
  of 
  radium 
  in 
  the 
  ratio 
  of 
  over 
  

   40 
  to 
  1, 
  but 
  the 
  constant 
  of 
  the 
  instrument 
  as 
  determined 
  

   by 
  the 
  individual 
  standards 
  does 
  not 
  vary 
  from 
  the 
  main 
  

   value 
  more 
  than 
  two 
  per 
  cent. 
  It 
  must 
  be 
  mentioned 
  that 
  

   the 
  value 
  for 
  standards 
  lY. 
  is 
  not 
  comparable 
  with 
  the 
  others. 
  

   The 
  quantity 
  of 
  radium 
  was 
  too 
  high 
  to 
  permit 
  of 
  the 
  charge 
  

   on 
  the 
  leaf 
  being 
  maintained 
  as 
  it 
  leaked 
  away, 
  so 
  the 
  leaf 
  

   was 
  kept 
  permanently 
  connected 
  through 
  the 
  charging 
  rod 
  

   to 
  the 
  negative 
  pole 
  of 
  the 
  250 
  volts 
  mains. 
  Under 
  these 
  

   conditions 
  the 
  charging-rod 
  as 
  well 
  as 
  the 
  leaf-system 
  would 
  

   attract 
  the 
  active 
  deposit, 
  and 
  the 
  part 
  deposited 
  near 
  the 
  

   cork 
  in 
  the 
  neck 
  of 
  the 
  flask 
  would 
  not 
  contribute 
  its 
  full 
  

   effect. 
  For 
  this 
  reason 
  the 
  constant, 
  as 
  is 
  to 
  be 
  expected, 
  is 
  

   too 
  high, 
  and 
  the 
  value 
  has 
  been 
  omitted 
  in 
  calculating 
  the 
  

   mean. 
  The 
  latter 
  is 
  5*78, 
  that 
  is 
  5'78x 
  10~^^ 
  g. 
  of 
  radium 
  

   produces 
  a 
  leak 
  of 
  1 
  division 
  a 
  minute. 
  The 
  two 
  old 
  standards 
  

   gave 
  a 
  mean 
  value 
  of 
  7"3 
  for 
  the 
  constant, 
  the 
  leaf 
  not 
  being 
  

   kept 
  charged 
  during 
  the 
  three-hours 
  interval. 
  This 
  difference 
  

   is 
  not 
  much, 
  if 
  any, 
  greater 
  than 
  can 
  be 
  accounted 
  for 
  by 
  

   the 
  effect 
  of 
  keeping 
  the 
  leaf 
  charged. 
  

  

  IV. 
  Results. 
  

  

  The 
  results 
  are 
  shown 
  in 
  Table 
  II. 
  for 
  the 
  three 
  uranium 
  

   preparations 
  described 
  under 
  Experiments 
  I., 
  II., 
  and 
  IV". 
  

   (II. 
  pp. 
  285-289 
  and 
  290). 
  The 
  later 
  tests 
  in 
  each 
  prepara- 
  

   tion 
  have 
  been 
  performed 
  with 
  the 
  electroscope 
  in 
  its 
  existing 
  

   -condition, 
  for 
  which 
  the 
  constant 
  has 
  been 
  accurately 
  deter- 
  

   mined 
  as 
  described. 
  The 
  first 
  tests 
  were 
  done 
  with 
  another 
  

   leaf- 
  system, 
  which 
  was 
  destroyed 
  after 
  one 
  test 
  owing 
  to 
  

   nitric 
  oxide 
  having 
  been 
  present 
  in 
  the 
  gases 
  boiled 
  out 
  of 
  

   the 
  solution. 
  The 
  factor 
  necessary 
  to 
  reduce 
  the 
  readings 
  

   with 
  this 
  system 
  to 
  the 
  same 
  value 
  as 
  those 
  with 
  the 
  present 
  

   system 
  was 
  found 
  to 
  be 
  0*96. 
  In 
  the 
  initial 
  test 
  shown 
  both 
  

   for 
  Experiments 
  I. 
  and 
  II., 
  to 
  which 
  not 
  much 
  weight 
  can 
  

   be 
  attached, 
  the 
  charging-rod 
  was 
  left 
  after 
  charging 
  close 
  

   to 
  the 
  system 
  as 
  in 
  all 
  previous 
  measurements, 
  whereas 
  the 
  

   present 
  practice 
  is 
  to 
  turn 
  it 
  as 
  far 
  as 
  possible 
  away, 
  which 
  

   was 
  found 
  to 
  increase 
  the 
  sensitiveness 
  1*15 
  times. 
  The 
  

   three 
  tests 
  indicated 
  by 
  a 
  "^ 
  in 
  the 
  last 
  column 
  of 
  the 
  table 
  

   were 
  done 
  by 
  the 
  mercury-pump 
  before 
  the 
  solutions 
  had 
  

   been 
  transferred 
  to 
  the 
  sealed 
  flasks 
  they 
  are 
  now 
  kept 
  in. 
  

   The 
  table 
  shows 
  that 
  in 
  all 
  three 
  preparations 
  the 
  quantity 
  

  

  