﻿312 
  Experiments 
  with 
  the 
  Radium 
  Emanation. 
  

  

  viz. 
  0*59, 
  0*66, 
  and 
  0*58 
  c.mm., 
  and 
  the 
  calculated 
  volume, 
  

   viz. 
  O'ol 
  c.mm. 
  

  

  We 
  have 
  already 
  seen 
  that 
  it 
  is 
  difficult 
  to 
  offer 
  a 
  satis- 
  

   factory 
  explanation 
  of 
  the 
  initial 
  contraction. 
  Before 
  this 
  

   can 
  be 
  done, 
  a 
  large 
  number 
  of 
  further 
  experiments 
  will 
  be 
  

   required. 
  The 
  work 
  outlined 
  in 
  this 
  paper 
  is 
  merely 
  pre- 
  

   liminary, 
  and 
  it 
  is 
  hoped 
  in 
  a 
  later 
  paper 
  to 
  give 
  the 
  results 
  

   of 
  a 
  more 
  complete 
  examination 
  of 
  the 
  volume 
  of 
  the 
  

   emanation 
  and 
  of 
  the 
  changes 
  it 
  undergoes. 
  

  

  Remarks 
  on 
  the 
  Condensation 
  of 
  the 
  Emanation. 
  

  

  When 
  the 
  emanation 
  was 
  obtained 
  in 
  a 
  nearly 
  pure 
  state, 
  

   it 
  condensed 
  exceedingly 
  rapidly 
  at 
  any 
  point 
  cooled 
  below 
  

   the 
  temperature 
  of 
  condensation 
  ( 
  — 
  150° 
  C). 
  If 
  the 
  emana- 
  

   tion 
  were 
  contained 
  in 
  the 
  U-tube 
  (fig. 
  1), 
  the 
  slow 
  approach 
  

   of 
  the 
  liquid 
  air 
  to 
  the 
  bottom 
  of 
  the 
  tube 
  caused 
  the 
  con- 
  

   densation 
  in 
  some 
  cases 
  to 
  take 
  place 
  over 
  an 
  extremely 
  

   small 
  area, 
  probably 
  at 
  a 
  point 
  where 
  the 
  tube 
  was 
  thinnest. 
  

   A 
  brilliant 
  phosphorescent 
  speck 
  was 
  then 
  observed, 
  and 
  it 
  

   almost 
  appeared 
  as 
  if 
  one 
  could 
  see 
  the 
  liquid 
  emanation 
  in 
  the 
  

   form 
  of 
  a 
  flat 
  globule 
  condensed 
  over 
  an 
  area 
  of 
  less 
  than 
  

   half 
  a 
  square 
  millimetre. 
  This 
  effect 
  was 
  often 
  observed 
  and 
  

   is 
  very 
  striking. 
  After 
  a 
  few 
  minutes 
  the 
  emanation, 
  even 
  

   at 
  the 
  temperature 
  of 
  liquid 
  air, 
  gradually 
  diffuses, 
  and 
  the 
  

   area 
  of 
  distribution 
  becomes 
  much 
  larger. 
  Ramsay 
  has 
  

   observed 
  that 
  the 
  emanation 
  condensed 
  at 
  the 
  temperature 
  

   of 
  liquid 
  air 
  can 
  be 
  partly 
  removed 
  by 
  continual 
  pumping, 
  

   indicating 
  that 
  it 
  has 
  an 
  appreciable 
  vapour-pressure 
  at 
  that 
  

   temperature. 
  This 
  effect, 
  however, 
  becomes 
  far 
  more 
  notice- 
  

   able 
  when 
  using 
  a 
  pentane 
  bath 
  whose 
  temperature 
  is 
  not 
  

   more 
  than 
  10 
  c 
  or 
  20° 
  C. 
  below 
  the 
  temperature 
  of 
  conden- 
  

   sation. 
  Every 
  stroke 
  of 
  the 
  pump 
  then 
  removes 
  a 
  not 
  

   inconsiderable 
  fraction 
  of 
  the 
  total 
  emanation. 
  There 
  is 
  

   another 
  effect 
  observed 
  which 
  is 
  very 
  striking. 
  Suppose 
  

   that 
  the 
  nearly 
  pure 
  emanation 
  contained 
  in 
  the 
  U-tube 
  is 
  

   condensed 
  over 
  a 
  small 
  area 
  by 
  applying 
  the 
  liquid 
  air 
  only 
  

   to 
  the 
  bottom 
  of 
  the 
  U-tube. 
  If 
  the 
  U-tube 
  is 
  then 
  fully 
  

   immersed 
  in 
  liquid 
  air, 
  in 
  the 
  course 
  of 
  about 
  ten 
  minutes 
  it 
  

   will 
  be 
  observed 
  by 
  the 
  phosphorescence 
  that 
  the 
  emanation 
  

   is 
  distributed 
  throughout 
  the 
  tube, 
  even 
  though 
  the 
  U-tube 
  

   is 
  not 
  connected 
  with 
  the 
  pump. 
  In 
  addition, 
  a 
  part 
  of 
  the 
  

   emanation 
  has 
  condensed 
  above 
  the 
  level 
  of 
  the 
  liquid 
  air. 
  

   Such 
  experiments 
  bring 
  out 
  clearly 
  that 
  the 
  emanation 
  has 
  a 
  

   sensible 
  vapour-pressure 
  far 
  below 
  the 
  temperature 
  of 
  con- 
  

   densation. 
  There 
  is 
  continual 
  volatilization 
  of 
  the 
  emanation 
  

   in 
  one 
  part 
  of 
  the 
  tube 
  and 
  condensation 
  in 
  another 
  part. 
  

  

  I 
  desire 
  to 
  thank 
  Mr. 
  T. 
  Royds, 
  M.Sc, 
  who 
  very 
  kindly 
  

   assisted 
  me 
  in 
  many 
  of 
  these 
  experiments. 
  

  

  University, 
  Manchester. 
  

  

  

  