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  XXIII. 
  Experiments 
  with 
  the 
  Radium 
  Emanation. 
  (1) 
  Tlie 
  

   Volume 
  of 
  the 
  Emanation. 
  By 
  E. 
  Rutherford, 
  F.R.S., 
  

  

  Professor 
  of 
  Physics 
  , 
  University 
  of 
  Manchester 
  * 
  '. 
  

  

  fT^HE 
  amount 
  o£ 
  radium 
  emanation 
  to 
  be 
  obtained 
  from 
  

   JL 
  one 
  gram 
  of 
  radium 
  in 
  equilibrium 
  is 
  a 
  definite 
  quantity, 
  

   and 
  is 
  equal 
  to 
  q/\ 
  where 
  q 
  is 
  the 
  rate 
  of 
  production 
  of 
  

   emanation 
  per 
  second 
  and 
  \ 
  is 
  the 
  radioactive 
  constant 
  of 
  the 
  

   emanation. 
  Taking 
  the 
  half 
  period 
  of 
  the 
  emanation 
  as 
  

   3* 
  75 
  days, 
  the 
  value 
  of 
  A, 
  is 
  1/468000. 
  I 
  have 
  on 
  different 
  

   occasions 
  t 
  calculated 
  the 
  volume 
  of 
  the 
  emanation 
  (at 
  normal 
  

   pressure 
  and 
  temperature) 
  to 
  be 
  expected 
  from 
  one 
  gram 
  of 
  

   radium 
  from 
  the 
  radioactive 
  data 
  at 
  our 
  disposal. 
  As 
  the 
  

   simplest 
  and 
  most 
  probable 
  assumption, 
  it 
  is 
  supposed 
  that 
  

   one 
  atom 
  of 
  radium 
  in 
  breaking 
  up 
  emits 
  one 
  u 
  particle 
  and 
  

   then 
  becomes 
  an 
  atom 
  of 
  the 
  emanation. 
  On 
  the 
  assumption 
  

   that 
  each 
  a 
  particle 
  carries 
  the 
  ordinary 
  ionic 
  charge 
  e 
  of 
  

   3*4xl0~ 
  10 
  electrostatic 
  unit, 
  it 
  was 
  calculated 
  that 
  the 
  

   volume 
  of 
  the 
  emanation 
  from 
  one 
  gram 
  of 
  radium 
  should 
  be 
  

   0*8 
  cubic 
  millimetre. 
  Later 
  work 
  { 
  indicated 
  the 
  probability 
  

   that 
  the 
  « 
  particle 
  carried 
  the 
  charge 
  2e. 
  This 
  reduces 
  the 
  

   calculated 
  volume 
  of 
  the 
  emanation 
  to 
  one-half 
  of 
  the 
  above 
  

   value. 
  Recently, 
  in 
  conjunction 
  with 
  Dr. 
  Geiger, 
  the 
  num- 
  

   ber 
  of 
  a 
  particles 
  expelled 
  per 
  second 
  from 
  one 
  gram 
  of 
  

   radium 
  has 
  been 
  accurately 
  determined, 
  and 
  also 
  the 
  charge 
  

   carried 
  by 
  each 
  a 
  particle. 
  From 
  these 
  data, 
  w 
  r 
  e 
  have 
  calcu- 
  

   lated 
  that 
  the 
  volume 
  of 
  the 
  emanation 
  is 
  0"57 
  cubic 
  mm.— 
  a 
  

   value 
  about 
  intermediate 
  between 
  the 
  other 
  two 
  values 
  §. 
  

  

  The 
  first 
  experiments 
  to 
  measure 
  directly 
  the 
  volume 
  of 
  the 
  

   emanation 
  were 
  made 
  by 
  Ramsay 
  and 
  Soddy 
  || 
  . 
  The 
  

   emanation 
  after 
  suitable 
  treatment 
  was 
  condensed 
  in 
  a 
  glass 
  

   tube 
  surrounded 
  by 
  liquid 
  air. 
  The 
  residual 
  gases 
  were 
  

   pumped 
  off, 
  and 
  the 
  emanation 
  after 
  volatilization 
  was 
  forced 
  

   by 
  raising 
  the 
  mercury 
  into 
  a 
  capillary 
  tube 
  where 
  its 
  volume 
  

   was 
  measured. 
  From 
  the 
  volume 
  of 
  the 
  collected 
  gas 
  

   observed 
  after 
  two 
  days, 
  they 
  concluded 
  that 
  the 
  volume 
  of 
  

   the 
  emanation 
  was 
  about 
  1*2 
  cubic 
  mm. 
  Later 
  a 
  number 
  of 
  

   systematic 
  observations 
  of 
  the 
  volume 
  of 
  the 
  emanation 
  by 
  a 
  

   similar 
  method 
  have 
  been 
  made 
  by 
  Ramsay 
  and 
  Cameron 
  ^[. 
  

  

  * 
  Communicated 
  by 
  the 
  Author, 
  having 
  been 
  read 
  before 
  the 
  Academy 
  

   of 
  Sciences 
  of 
  Vienna, 
  July 
  2, 
  1908. 
  

  

  t 
  ' 
  Radioactivity/ 
  2nd 
  edition, 
  p. 
  288. 
  

  

  X 
  Rutherford, 
  Phil. 
  Mag. 
  Oct.' 
  1906. 
  

  

  § 
  An 
  account 
  of 
  this 
  work 
  was 
  given 
  to 
  the 
  Royal 
  Society, 
  June 
  18, 
  

   1908. 
  

  

  || 
  Proc. 
  Roy. 
  Soc. 
  lxxiii. 
  p. 
  346 
  (1904). 
  

   1f 
  Journ. 
  Chem. 
  Soc. 
  p. 
  1266 
  (1907). 
  

  

  