﻿Radium 
  Content 
  of 
  Rocks 
  from 
  Suh- 
  Antarctic 
  Islands. 
  813 
  

  

  190-4), 
  and 
  it 
  was 
  exhausted 
  to 
  half 
  an 
  atmosphere 
  by 
  means 
  

   of 
  an 
  oil-pump 
  before 
  any 
  of 
  the 
  collected 
  gases 
  were 
  passed 
  

   in. 
  These 
  gases 
  were 
  allowed 
  to 
  enter 
  very 
  slowl}' 
  through 
  

   CaCl2 
  and 
  H2SO4 
  drying-tubes, 
  and 
  the 
  pressure 
  was 
  then 
  

   brought 
  up 
  to 
  atmospheric 
  by 
  the 
  admission 
  of 
  air, 
  the 
  time 
  

   occupied 
  over 
  this 
  transference 
  through 
  the 
  drying-tubes 
  

   from 
  the 
  stoppage 
  of 
  the 
  boiling 
  to 
  the 
  commencement 
  of 
  

   observations 
  in 
  the 
  electroscope 
  being 
  in 
  every 
  case 
  15 
  

   minutes. 
  Readings 
  of 
  the 
  position 
  of 
  the 
  leaf 
  were 
  taken 
  

   every 
  two 
  minutes 
  for 
  half 
  an 
  hour, 
  and 
  the 
  instrument 
  was 
  

   then 
  re-charged 
  and 
  the 
  leak 
  for 
  the 
  next 
  half 
  hour 
  similarly 
  

   determined. 
  This 
  was 
  sufficient 
  indication 
  that 
  the 
  effect 
  

   was 
  that 
  due 
  to 
  the 
  radium 
  emanation. 
  In 
  some 
  cases, 
  how- 
  

   ever, 
  the 
  gas 
  was 
  studied 
  for 
  three 
  or 
  four 
  hours, 
  but 
  although 
  

   the 
  presence 
  of 
  radium 
  was 
  shown 
  clearly 
  by 
  the 
  increase 
  of 
  

   the 
  rate 
  of 
  leak, 
  yet, 
  owing 
  to 
  the 
  active 
  deposit, 
  so 
  much 
  

   time 
  was 
  lost 
  in 
  bringing 
  the 
  electroscope 
  back 
  to 
  a 
  normal 
  

   condition 
  of 
  natural 
  leak, 
  that 
  it 
  was 
  decided 
  to 
  pump 
  the 
  

   gases 
  out 
  after 
  an 
  hour. 
  

  

  The 
  electroscope 
  was 
  charged 
  to 
  a 
  potential 
  of 
  220 
  volts 
  

   and 
  the 
  movement 
  of 
  the 
  leaf 
  was 
  read 
  by 
  a 
  microscope 
  and 
  

   a 
  micrometer 
  eyepiece, 
  so 
  that 
  the 
  large 
  scale-divisions 
  could 
  

   be 
  subdivided 
  into 
  hundredths. 
  For 
  the 
  means 
  of 
  its 
  stan- 
  

   dardization 
  we 
  are 
  indebted 
  to 
  Professor 
  Rutherford, 
  who 
  

   kindly 
  sent 
  us 
  a 
  solution 
  containing 
  3'14xl0~^ 
  gramme 
  

   of 
  radium. 
  Two 
  separate 
  eighths 
  of 
  this, 
  each 
  containing 
  

   o'925xlO~^'^ 
  gramme 
  of 
  radium, 
  were 
  used 
  as 
  standards. 
  

   Either 
  of 
  these 
  treated 
  in 
  the 
  same 
  way 
  as 
  the 
  rock 
  solutions 
  

   produced 
  an 
  initial 
  leak 
  of 
  61 
  micrometer 
  divisions 
  per 
  

   minute, 
  hence 
  one 
  micrometer 
  division 
  per 
  minute 
  corresponded 
  

   to 
  6*13 
  X 
  10~^^ 
  gramme 
  of 
  radium. 
  

  

  '' 
  Natural 
  " 
  Leak. 
  — 
  The 
  determination 
  of 
  this 
  is 
  an 
  im- 
  

   portant 
  matter 
  in 
  an 
  attempt 
  to 
  evaluate 
  with 
  accuracy 
  the 
  

   amount 
  of 
  radium 
  contained 
  in 
  a 
  rock. 
  In 
  our 
  case 
  the 
  

   electroscope 
  was 
  always 
  charged 
  over 
  night 
  — 
  the 
  insulation 
  

   was 
  sufficiently 
  good 
  for 
  it 
  to 
  retain 
  a 
  considerable 
  portion 
  

   of 
  its 
  charge 
  for 
  forty-eight 
  hours 
  — 
  and 
  the 
  leak 
  found. 
  In 
  

   general 
  it 
  decreased 
  from 
  the 
  time 
  of 
  its 
  initial 
  charging 
  the 
  

   night 
  before 
  to 
  the 
  introduction 
  of 
  the 
  rock 
  gases. 
  From 
  a 
  

   value 
  of 
  1*5 
  micrometer 
  divisions 
  per 
  minute 
  the 
  night 
  before, 
  

   it 
  became 
  about 
  0'8 
  per 
  minute 
  at 
  the 
  time 
  of 
  intro- 
  

   duction 
  of 
  the 
  emanation. 
  AVe 
  consider 
  that 
  this 
  latter 
  

   number 
  cannot 
  be 
  more 
  than 
  '2 
  from 
  the 
  actual 
  value 
  during 
  

   the 
  examination 
  of 
  any 
  of 
  the 
  rocks. 
  Such 
  an 
  error 
  would 
  

   lead 
  to 
  a 
  wrong 
  estimation 
  of 
  the 
  amount 
  of 
  radium 
  in 
  20 
  

   grammes 
  of 
  rock 
  of 
  1'23 
  x 
  10"^-, 
  or 
  an 
  error 
  of 
  0*10 
  x 
  10" 
  ^^ 
  

  

  