﻿628 
  Messrs. 
  F. 
  Soddy 
  and 
  A. 
  S. 
  Russell 
  on 
  the 
  

  

  In 
  the 
  third 
  separation 
  careful 
  check 
  was 
  kept 
  of 
  the 
  

   weight 
  and 
  initial 
  activity 
  of 
  each 
  batch 
  of 
  crystals 
  after 
  the 
  

   operation. 
  From 
  the 
  time 
  of 
  accumulation 
  of 
  uranium 
  X 
  in 
  

   the 
  crystals 
  between 
  the 
  second 
  and 
  third 
  separations 
  it 
  was 
  

   deduced 
  that 
  the 
  initial 
  content 
  of 
  uranium 
  X 
  before 
  separa- 
  

   tion 
  was 
  98*5 
  per 
  cent, 
  of 
  the 
  equilibrium 
  quantity. 
  All 
  but 
  

   2S 
  per 
  cent, 
  of 
  the 
  equilibrium 
  quantity 
  of 
  uranium 
  X 
  was 
  

   separated 
  initially, 
  but 
  at 
  the 
  date 
  of 
  the 
  comparison 
  of 
  the 
  

   uranium 
  X 
  with 
  radium 
  this 
  had 
  increased. 
  From 
  a 
  curve 
  

   of 
  the 
  regeneration 
  of 
  uranium 
  X 
  with 
  time^ 
  the 
  initial 
  

   y8-activity 
  of 
  the 
  crystals 
  and 
  their 
  weight, 
  it 
  was 
  deduced 
  

   that 
  on 
  that 
  date 
  44*35 
  per 
  cent, 
  of 
  the 
  equilibrium 
  quantity 
  

   of 
  uranium 
  X 
  was 
  present 
  in 
  the 
  crystals. 
  The 
  amount 
  in 
  

   the 
  preparations 
  was 
  therefore 
  98'5 
  per 
  cent. 
  — 
  44*35 
  per 
  cent., 
  

   or 
  54*15 
  per 
  cent, 
  of 
  the 
  equilibrium 
  quantity 
  of 
  47 
  kilograms 
  

   of 
  uranyl 
  nitrate. 
  This 
  is 
  equal 
  to 
  the 
  uranium 
  X 
  in 
  

   12*13 
  kilograms 
  of 
  metallic 
  uranium 
  in 
  equilibrium. 
  On 
  a 
  

   particular 
  day, 
  8 
  days 
  after 
  the 
  commencement 
  of 
  the 
  last 
  

   recrystallization, 
  and 
  2 
  days 
  after 
  the 
  finish 
  of 
  the 
  separation, 
  

   the 
  7-activity 
  of 
  the 
  preparations 
  was 
  equivalent 
  to 
  the 
  

   7-activity 
  of 
  0*094 
  mg. 
  of 
  radium 
  bromide, 
  measured 
  through 
  

   a 
  thickness 
  of 
  2*52 
  cm. 
  of 
  lead. 
  Xow 
  it 
  will 
  be 
  shown 
  later 
  

   that 
  the 
  absorption 
  coefficient 
  for 
  lead, 
  for 
  a 
  range 
  of 
  from 
  

   1 
  to 
  5 
  cm. 
  of 
  lead, 
  for 
  the 
  radium 
  7-rays 
  is 
  0*495, 
  and 
  for 
  

   the 
  uranium 
  7-rays 
  is 
  0*725 
  (cm.)~^. 
  It 
  is 
  true 
  that 
  for 
  

   thicknesses 
  below 
  1 
  cm. 
  of 
  lead 
  the 
  absorption 
  coefficients 
  of 
  

   the 
  7-rays, 
  both 
  of 
  uranium 
  and 
  radium, 
  appear 
  to 
  be 
  greater 
  

   than 
  those 
  given, 
  but 
  for 
  present 
  purposes 
  no 
  great 
  error 
  is 
  

   likely 
  to 
  be 
  introduced 
  if 
  we 
  calculate 
  the 
  ratio 
  of 
  the 
  initial 
  

   intensities 
  of 
  the 
  7-rays 
  of 
  uranium 
  and 
  radium 
  from 
  the 
  

   observed 
  intensities 
  by 
  means 
  of 
  these 
  coefficients. 
  Thus 
  

   the 
  initial 
  7-activity 
  of 
  the 
  uranium 
  X 
  in 
  equilibrium 
  with 
  

   12*13 
  kilograms 
  of 
  metallic 
  uranium 
  is 
  equal 
  to 
  the 
  initial 
  

   7-activity 
  of 
  0*17 
  mg. 
  of 
  radium 
  bromide, 
  or 
  that 
  from 
  1 
  kilogram 
  

   of 
  uranium 
  is 
  equivalent 
  to 
  *0138 
  mg. 
  

  

  It 
  must 
  be 
  mentioned 
  that 
  the 
  ultimate 
  standard 
  of 
  com- 
  

   parison 
  of 
  radium 
  in 
  this 
  case 
  and 
  throughout 
  was 
  a 
  sealed 
  

   tube 
  containino- 
  6*7 
  mo-, 
  of 
  Giesel's 
  radium 
  bromide. 
  The 
  

   weight 
  was 
  taken 
  with 
  great 
  care 
  before 
  sealing, 
  but 
  it 
  is 
  

   probable, 
  since 
  the 
  compound 
  was 
  fairly 
  old 
  when 
  weighed, 
  

   that 
  decomposition 
  had 
  occurred, 
  and 
  that 
  the 
  weight 
  of 
  

   radium 
  therein 
  was 
  considerably 
  greater 
  than 
  the 
  formula- 
  

   weight. 
  Thus 
  if 
  the 
  conversion 
  into 
  carbonate 
  by 
  the 
  air 
  

   had 
  been 
  complete 
  the 
  percentage 
  of 
  radium 
  in 
  the 
  standard 
  

   would 
  be 
  79, 
  instead 
  of 
  53*5 
  as 
  initially. 
  Taking 
  provisionally 
  

   a 
  mean 
  value 
  of 
  66' 
  6 
  per 
  cent, 
  of 
  radium 
  in 
  the 
  sample 
  the 
  

  

  