﻿950 
  Messrs. 
  Marsden 
  and 
  Wood 
  on 
  the 
  Determination 
  of 
  

  

  The 
  source 
  of 
  actinium 
  was 
  placed 
  in 
  a 
  side 
  tube 
  A 
  1? 
  A 
  2 
  

   being 
  a 
  similar 
  dummy 
  tube. 
  The 
  ends 
  were 
  closed 
  air- 
  

   tight 
  by 
  plates 
  B 
  : 
  and 
  B 
  2 
  Hastened 
  on 
  with 
  hard 
  wax. 
  

   Exhaustion 
  was 
  carried 
  out 
  through 
  side 
  tubes 
  Ci 
  and 
  C 
  2 
  , 
  

   which 
  for 
  1 
  cm. 
  length 
  nearest 
  the 
  apparatus 
  had 
  a 
  bore 
  of 
  

   about 
  05 
  sq. 
  mm. 
  By 
  means 
  of 
  a 
  mercury 
  pump 
  the 
  

   pressure 
  was 
  reduced 
  to 
  -below 
  1 
  mm. 
  Hg, 
  and 
  the 
  stopcock 
  

   S 
  closed. 
  Dewar 
  flasks 
  containing 
  liquid 
  air 
  were 
  then 
  

   placed 
  round 
  the 
  charcoal 
  bulb 
  and 
  U-tube, 
  so 
  as 
  to 
  reduce 
  

   the 
  pressure 
  well 
  below 
  1/1000 
  mm. 
  and 
  ensure 
  the 
  mean 
  

   free 
  path 
  of 
  the 
  molecules 
  being 
  large 
  compared 
  with 
  the 
  

   size 
  of 
  the 
  vessel. 
  In 
  this 
  way 
  the 
  effusion 
  of 
  the 
  emana- 
  

   tion 
  is 
  not 
  influenced 
  by 
  the 
  presence 
  of 
  the 
  air 
  molecules. 
  

   The 
  charcoal 
  U-tube 
  was 
  used 
  to 
  prevent 
  any 
  vapour 
  from 
  

   the 
  grease 
  of 
  the 
  stopcock 
  entering 
  the 
  chambers. 
  

  

  The 
  apparatus 
  was 
  kept 
  evacuated 
  for 
  three 
  hours 
  so 
  that 
  

   the 
  active 
  deposit 
  attained 
  practical 
  equilibrium. 
  The 
  plates 
  

   Bj 
  and 
  B 
  2 
  were 
  then 
  quickly 
  taken 
  off, 
  and 
  loose 
  brass 
  plates 
  

   which 
  fitted 
  closely 
  and 
  covered 
  the 
  bases 
  of 
  the 
  two 
  

   chambers 
  were 
  removed 
  for 
  activity 
  measurements. 
  These 
  

   measurements 
  were 
  made 
  in 
  an 
  ordinary 
  a-ray 
  electroscope. 
  

   As 
  the 
  apparatus 
  was 
  made 
  as 
  nearly 
  symmetrical 
  as 
  possible, 
  

   the 
  ratio 
  of 
  the 
  activities 
  gives 
  the 
  ratio 
  of 
  Nj/Nj 
  in 
  equation 
  

   (2), 
  i. 
  e. 
  the 
  ratio 
  of 
  the 
  numbers 
  of 
  emanation 
  atoms 
  present 
  

   per 
  c.cm. 
  in 
  the 
  steady 
  state. 
  

  

  The 
  following 
  are 
  the 
  data 
  for 
  a 
  set 
  of 
  experiments, 
  nos. 
  4, 
  

   5, 
  and 
  6 
  being 
  made 
  with 
  the 
  bulb 
  containing 
  actinium 
  and 
  

   the 
  dummy 
  bulb 
  interchanged, 
  so 
  as 
  to 
  eliminate 
  any 
  slight 
  

   dissymmetry. 
  

  

  A= 
  -01022 
  sq. 
  cm. 
  V 
  1= 
  = 
  V 
  2 
  = 
  270 
  c.cs. 
  

  

  X=0'178 
  = 
  19°C. 
  = 
  292° 
  absolute. 
  

  

  Ratio 
  of 
  Activities. 
  

  

  (1) 
  2-16 
  (4) 
  2-19 
  

  

  (2) 
  2-13 
  (5) 
  2-12 
  

  

  (3.) 
  2-18 
  (6) 
  2-18 
  

  

  Mean 
  = 
  2*16. 
  

  

  /. 
  M= 
  [3636>5 
  (2-16-1) 
  ^^ 
  J 
  x292 
  = 
  eqn. 
  (2) 
  

  

  = 
  236. 
  

   Further 
  experiments 
  were 
  made 
  with 
  a 
  hole 
  of 
  only 
  

  

  

  