﻿[ 
  313 
  ] 
  

  

  XXIV. 
  Spectrum 
  of 
  the 
  Radium 
  Emanation. 
  By 
  Prof. 
  E. 
  

   Rutherford, 
  F.R.S., 
  and 
  T. 
  Royds, 
  M.Se., 
  Beyer 
  Fellow, 
  

  

  University 
  of 
  Manchester 
  *. 
  

  

  [Plates 
  X. 
  & 
  XI.] 
  

  

  THE 
  first 
  determination 
  of 
  the 
  spectrum 
  of 
  the 
  radium 
  

   emanation 
  was 
  made 
  in 
  1904 
  by 
  Ramsay 
  and 
  Collie 
  f, 
  

   who 
  obtained 
  visual 
  observations 
  of 
  the 
  wave-lengths 
  of 
  eleven 
  

   lines. 
  They 
  stated 
  that 
  the 
  emanation 
  was 
  a 
  bright 
  line 
  

   spectrum 
  similar 
  in 
  general 
  character 
  to 
  that 
  observed 
  for 
  

   other 
  monatomic 
  gases. 
  Since 
  that 
  time, 
  no 
  further 
  informa- 
  

   tion 
  on 
  this 
  important 
  subject 
  has 
  been 
  forthcoming. 
  In 
  a 
  

   previous 
  paper 
  %■> 
  on 
  e 
  of 
  us 
  has 
  given 
  an 
  account 
  of 
  methods 
  

   employed 
  in 
  purification 
  of 
  the 
  emanation 
  and 
  determination 
  

   of 
  its 
  volume. 
  In 
  order 
  to 
  test 
  the 
  purity 
  of 
  the 
  emanation, 
  

   an 
  electrodeless 
  discharge 
  was 
  passed 
  in 
  the 
  capillary 
  tube 
  in 
  

   which 
  the 
  volume 
  of 
  the 
  emanation 
  was 
  measured, 
  and 
  visual 
  

   observations 
  of 
  the 
  wave-lengths 
  of 
  the 
  main 
  lines 
  were 
  made 
  

   by 
  means 
  of 
  a 
  direct 
  reading 
  Hilger 
  spectroscope. 
  We 
  have 
  

   observed 
  the 
  spectrum 
  of 
  the 
  radium 
  emanation 
  in 
  this 
  way 
  

   on 
  four 
  different 
  occasions 
  during 
  the 
  past 
  two 
  months. 
  It 
  

   was 
  evident 
  that 
  a 
  number 
  of 
  new 
  lines 
  were 
  present, 
  which 
  

   were 
  not 
  recorded 
  in 
  the 
  initial 
  observations 
  of 
  Ramsay 
  and 
  

   Collie. 
  As 
  soon 
  as 
  the 
  measurements 
  of 
  the 
  volume 
  had 
  been 
  

   completed, 
  arrangements 
  were 
  made 
  to 
  photograph 
  the 
  

   emanation 
  spectrum 
  in 
  order 
  to 
  determine 
  the 
  wave-lengths 
  

   of 
  the 
  lines 
  with 
  more 
  accuracy 
  than 
  is 
  possible 
  with 
  visual 
  

   observations. 
  For 
  this 
  purpose, 
  a 
  quantity 
  of 
  radium 
  

   emanation 
  was 
  purified 
  as 
  completely 
  as 
  possible 
  by 
  the 
  

   methods 
  outlined 
  in 
  the 
  last 
  paper. 
  The 
  emanation 
  was 
  first 
  

   condensed 
  in 
  a 
  U-tube 
  surrounded 
  by 
  liquid 
  air, 
  and 
  the 
  

   uncondensed 
  gases 
  completely 
  pumped 
  off. 
  The 
  emanation 
  

   was 
  then 
  left 
  for 
  three 
  hours 
  in 
  contact 
  with 
  a 
  tube 
  coated 
  

   with 
  caustic 
  potash 
  to 
  remove 
  the 
  last 
  traces 
  of 
  carbon 
  dioxide. 
  

   Finally, 
  the 
  U-tube 
  was 
  surrounded 
  by 
  a 
  pentane 
  bath 
  cooled 
  

   down 
  by 
  liquid 
  air, 
  and 
  the 
  uncondensed 
  gases 
  pumped 
  off 
  

   at 
  a 
  temperature 
  above 
  that 
  of 
  liquid 
  air. 
  In 
  order 
  to 
  obtain 
  

   the 
  spectrum, 
  a 
  small 
  vacuum 
  tube 
  of 
  capacity 
  about 
  

  

  * 
  Communicated 
  by 
  the 
  Authors. 
  A 
  preliminary 
  account 
  of 
  this 
  work 
  

   was 
  published 
  as 
  a 
  letter 
  in 
  ' 
  Nature,' 
  July 
  8, 
  1908. 
  

   t 
  Proc. 
  Roy. 
  Soc. 
  lxxiii. 
  p. 
  470 
  (1904). 
  

   \ 
  See 
  Rutherford, 
  " 
  Volume 
  of 
  Emanation," 
  Phil. 
  Mag. 
  Aug. 
  1908. 
  

  

  Phil. 
  Mag. 
  S. 
  6. 
  Vol. 
  16. 
  No. 
  92. 
  Aug. 
  1908. 
  " 
  Y 
  

  

  