﻿602 
  

  

  Mr. 
  J. 
  Satterlv 
  on 
  the 
  Amount 
  of 
  

  

  II. 
  The 
  Condensation 
  Method. 
  

   Another 
  method 
  of 
  measuring 
  the 
  emanation 
  now 
  suggested 
  

   itself 
  to 
  me, 
  viz. 
  that 
  of 
  freezing 
  or 
  rather 
  condensing 
  the 
  

  

  Ffc. 
  4. 
  

  

  t 
  viz. 
  mat 
  or 
  treezmg 
  or 
  

   emanation 
  out 
  of 
  the 
  air 
  by 
  the 
  help 
  of 
  liquid 
  

   air. 
  At 
  normal 
  pressures 
  liquid 
  air 
  boils 
  at 
  

   about 
  - 
  182° 
  C. 
  Rutherford 
  and 
  Soddy 
  * 
  found 
  

   that 
  radium 
  emanation 
  condensed 
  at 
  a 
  tem- 
  

   perature 
  of 
  about 
  — 
  150° 
  C. 
  They 
  also 
  found 
  

   that 
  with 
  a 
  flow 
  of 
  2 
  cc. 
  per 
  sec. 
  through 
  their 
  

   tube 
  (which 
  meant 
  a 
  velocity 
  along 
  the 
  tube 
  of 
  

   50 
  cms. 
  per 
  sec.) 
  there 
  was 
  no 
  escape 
  of 
  ema- 
  

   nation 
  at 
  — 
  154° 
  C. 
  (they 
  could 
  read 
  to 
  ^ 
  part). 
  

   At 
  — 
  152° 
  C. 
  one-half 
  per 
  cent, 
  came 
  off 
  and 
  at 
  

   -150° 
  0, 
  50 
  per 
  cent, 
  came 
  off. 
  No 
  doubt 
  all 
  

   would 
  come 
  off 
  if 
  given 
  a 
  time 
  long 
  enough. 
  

   They 
  concluded 
  that 
  the 
  condensed 
  emanation 
  

   exerts 
  a 
  true 
  vapour-press 
  Lire 
  and 
  commences 
  

   to 
  volatilise 
  slowly 
  2° 
  0. 
  below 
  its 
  volatilising 
  

   point. 
  

  

  From 
  these 
  results 
  it 
  seemed 
  that 
  if 
  I 
  could 
  

   pass 
  air 
  through 
  a 
  long 
  tube 
  immersed 
  in 
  liquid 
  

   air 
  so 
  that 
  the 
  air 
  was 
  a 
  long 
  time 
  in 
  the 
  

   neighbourhood 
  of 
  metal 
  surfaces 
  at 
  —182° 
  C. 
  

   I 
  had 
  a 
  very 
  good 
  chance 
  of 
  condensing 
  out 
  all 
  

   the 
  emanation. 
  

  

  My 
  first 
  thought 
  was 
  to 
  imitate 
  Rutherford 
  D 
  

   and 
  Soddy 
  and 
  use 
  a 
  long 
  spiral 
  of 
  fine-bored 
  ^ 
  

   copper 
  tubing. 
  If 
  air 
  passed 
  through 
  a 
  spiral 
  

   of 
  tubing 
  of 
  1 
  mm. 
  bore 
  at 
  the 
  rate 
  lof 
  half 
  

   a 
  litre 
  per 
  minute 
  (my 
  usual 
  current), 
  the 
  

   velocity 
  of 
  the 
  air 
  would 
  be 
  1000 
  cms. 
  per 
  

   second, 
  and 
  even 
  if 
  I 
  used 
  500 
  cms. 
  of 
  such 
  

   tube 
  the 
  air 
  would 
  take 
  only 
  half 
  a 
  second 
  

   to 
  pass 
  through 
  the 
  spiral. 
  This 
  was 
  not 
  

   thought 
  long 
  enough. 
  The 
  next 
  plan 
  was 
  to 
  

   put 
  a 
  large 
  number 
  of 
  fine 
  tubes 
  in 
  parallel 
  

   so 
  that 
  the 
  apparatus 
  could 
  be 
  made 
  more 
  com- 
  

   pact, 
  the 
  magnitude 
  of 
  the 
  current 
  increased, 
  

   and 
  also 
  the 
  length 
  of 
  time 
  during 
  which 
  the 
  

   air 
  was 
  subjected 
  to 
  the 
  action 
  of 
  the 
  liquid 
  air 
  

   increased. 
  The 
  form 
  finally 
  adopted 
  is 
  shown 
  

   in 
  the 
  figure 
  (fig. 
  4). 
  The 
  apparatus 
  is 
  made 
  

   of 
  brass. 
  Although 
  brass 
  is 
  heavy 
  and 
  the 
  

   apparatus 
  therefore 
  has 
  a 
  large 
  capacity 
  for 
  heat, 
  yet 
  it 
  was 
  

   * 
  Phil. 
  Mag. 
  May 
  1903. 
  

  

  