﻿Radium 
  Emanation 
  in 
  the 
  Atmosphere. 
  585 
  

  

  and 
  others 
  have 
  detected 
  radium 
  and 
  measured 
  its 
  amount 
  in 
  

   rocks, 
  waters, 
  &c, 
  so 
  that 
  there 
  are 
  many 
  agencies 
  by 
  which 
  

   radium 
  emanation 
  can 
  be 
  supplied 
  to 
  the 
  atmosphere. 
  It 
  is 
  

   of 
  importance 
  to 
  find 
  the 
  amount 
  of 
  radium 
  emanation 
  in 
  the 
  

   atmosphere 
  in 
  order 
  to 
  calculate 
  how 
  far 
  the 
  natural 
  ioni- 
  

   zation 
  of 
  the 
  air 
  is 
  due 
  to 
  changes 
  going 
  on 
  in 
  the 
  air 
  and 
  

   how 
  far 
  due 
  to 
  radiation 
  from 
  the 
  earth 
  or 
  from 
  sources 
  

   exterior 
  to 
  the 
  earth 
  and 
  its 
  atmosphere, 
  and 
  also 
  to 
  find 
  how 
  

   the 
  amount 
  of 
  emanation 
  in 
  the 
  atmosphere 
  varies 
  with 
  

   weather 
  conditions. 
  

  

  This 
  paper 
  contains 
  an 
  account 
  of 
  an 
  attempt 
  made 
  by 
  two 
  

   methods 
  to 
  measure 
  the 
  amount 
  of 
  radium 
  emanation 
  in 
  the 
  

   portion 
  of 
  the 
  atmosphere 
  near 
  the 
  earth. 
  The 
  amount 
  of 
  

   emanation 
  in 
  a 
  given 
  volume 
  of 
  air 
  is 
  expressed 
  in 
  terms 
  

   of 
  the 
  mass 
  of 
  radium 
  which 
  would 
  be 
  sufficient 
  to 
  keep 
  up 
  

   the 
  supply 
  of 
  emanation, 
  the 
  radium 
  and 
  its 
  emanation 
  

   being 
  supposed 
  to 
  be 
  in 
  radioactive 
  equilibrium. 
  This 
  neces- 
  

   sitated 
  the 
  use 
  of 
  a 
  known 
  quantity 
  of 
  radium 
  ; 
  and 
  Professor 
  

   Rutherford 
  was 
  good 
  enough 
  to 
  give 
  me 
  a 
  solution 
  of 
  radium 
  

   bromide 
  containing 
  3*14 
  x 
  10~ 
  9 
  gram 
  of 
  radium*. 
  In 
  essence, 
  

   the 
  principle 
  of 
  the 
  experiment 
  is 
  first 
  to 
  measure, 
  by 
  some 
  

   meaus 
  or 
  other, 
  the 
  emanation 
  in 
  a 
  known 
  volume 
  of 
  air, 
  

   and 
  then 
  to 
  measure 
  by 
  the 
  same 
  means 
  the 
  emanation 
  given 
  

   off 
  from 
  the 
  solution 
  in 
  a 
  known 
  time. 
  A 
  direct 
  comparison 
  

   of 
  the 
  two 
  figures 
  enables 
  one 
  to 
  calculate 
  the 
  amount 
  of 
  

   radium 
  which 
  is 
  capable 
  of 
  supplying 
  the 
  emanation 
  in 
  a 
  

   known 
  volume 
  of 
  air, 
  the 
  assumption 
  being 
  made 
  that 
  the 
  

   emanation 
  in 
  the 
  air 
  is 
  in 
  radioactive 
  equilibrium 
  with 
  the 
  

   radium 
  that 
  gives 
  rise 
  to 
  it. 
  

  

  Two 
  methods 
  of 
  experiment 
  were 
  tried 
  : 
  — 
  

  

  (1) 
  Absorption 
  by 
  Charcoal, 
  

  

  (2) 
  Condensation 
  by 
  Liquid 
  Air; 
  

  

  and 
  an 
  electrical 
  method 
  of 
  testing 
  was 
  used 
  throughout, 
  the 
  

   amount 
  of 
  emanation 
  being 
  expressed 
  in 
  terms 
  of 
  the 
  in- 
  

   creased 
  electrical 
  conductivity 
  it 
  imparted 
  to 
  a 
  known 
  volume 
  

   of 
  air. 
  

  

  Method 
  (1) 
  will 
  be 
  described 
  first. 
  

  

  (1) 
  The 
  Charcoal 
  Method. 
  

  

  In 
  a 
  letter 
  to 
  'Nature' 
  in 
  Oct. 
  1906, 
  Prof. 
  "Rutherford 
  

   announced 
  that 
  he 
  had 
  found 
  that 
  when 
  a 
  stream 
  of 
  air 
  con- 
  

   taining 
  radium 
  emanation 
  was 
  slowly 
  passed 
  at 
  ordinary 
  tem- 
  

   peratures 
  through 
  charcoal 
  made 
  from 
  the 
  shells 
  of 
  coconuts, 
  

  

  * 
  The 
  solution 
  was 
  acidified 
  with 
  hydrochloric 
  acid. 
  This 
  prevents 
  

   partial 
  precipitation 
  of 
  the 
  radium 
  by 
  the 
  carbonic 
  acid 
  of 
  the 
  air 
  which 
  

   is 
  bubbled 
  through 
  the 
  solution. 
  

  

  