﻿304 
  Prof. 
  E. 
  Rutherford 
  : 
  Experiments 
  

  

  obtained, 
  the 
  liquid 
  air 
  was 
  removed, 
  the 
  stopcock 
  B 
  

   closed, 
  and 
  the 
  emanation 
  after 
  volatilization 
  was 
  allowed 
  

   to 
  expand 
  into 
  the 
  tube 
  E. 
  Since 
  the 
  volume 
  of 
  the 
  

   U-tube 
  was 
  small 
  compared 
  with 
  the 
  tube 
  E, 
  the 
  greater 
  

   part 
  of 
  the 
  emanation 
  after 
  volatilization 
  expands 
  into 
  the 
  

   tube 
  E. 
  The 
  experiments 
  were 
  made 
  in 
  a 
  darkened 
  room 
  ; 
  

   so 
  that 
  the 
  moment 
  of 
  almost 
  complete 
  volatilization 
  of 
  the 
  

   emanation 
  could 
  be 
  observed 
  by 
  the 
  sudden 
  phosphorescence 
  

   of 
  the 
  tube 
  E 
  due 
  to 
  the 
  entrance 
  of 
  the 
  emanation. 
  The 
  stop- 
  

   cock 
  A 
  was 
  then 
  closed 
  and 
  the 
  emanation 
  forced 
  into 
  the 
  

   capillary, 
  where 
  its 
  volume 
  was 
  measured 
  at 
  regular 
  intervals. 
  

  

  Activity 
  measurements. 
  

  

  In 
  this 
  type 
  of 
  experiment, 
  it 
  is 
  of 
  importance 
  to 
  determine 
  

   accurately 
  the 
  amount 
  of 
  emanation 
  in 
  the 
  capillary 
  where 
  

   the 
  volume 
  is 
  measured. 
  This 
  was 
  done 
  by 
  comparison 
  of 
  

   the 
  7 
  ray 
  activity 
  due 
  to 
  the 
  emanation 
  in 
  the 
  capillary 
  with 
  

   that 
  due 
  to 
  a 
  standard 
  sample 
  of 
  radium 
  bromide 
  which 
  gave 
  

   a 
  heating 
  effect 
  of 
  110 
  gram-calories 
  per 
  gram 
  per 
  hour. 
  

   When 
  the 
  emanation 
  had 
  been 
  forced 
  into 
  the 
  capillary, 
  the 
  

   residual 
  emanation 
  in 
  the 
  U-tube 
  and 
  connexions 
  was 
  completely 
  

   pumped 
  out 
  and 
  all 
  sources 
  of 
  7 
  rays 
  removed 
  to 
  a 
  distance. 
  

   A 
  small 
  closed 
  lead 
  electroscope 
  was 
  placed 
  at 
  a 
  distance 
  of 
  

   76 
  cms. 
  from 
  the 
  emanation 
  in 
  the 
  capillary, 
  and 
  the 
  rate 
  of 
  

   discharge 
  observed 
  about 
  three 
  hours 
  after 
  the 
  introduction 
  

   of 
  the 
  emanation. 
  The 
  7 
  ray 
  activity 
  compared 
  with 
  a 
  

   standard 
  is 
  then 
  a 
  measure 
  of 
  the 
  amount 
  of 
  emanation 
  

   expressed 
  in 
  terms 
  of 
  the 
  equilibrium 
  quantity 
  present 
  in 
  one 
  

   milligram 
  of 
  pure 
  radium. 
  Measurements 
  were 
  made 
  daily 
  

   of 
  the 
  7 
  ray 
  activity 
  of 
  the 
  emanation. 
  Experiment 
  showed 
  

   that 
  the 
  highly 
  concentrated 
  emanation 
  compressed 
  into 
  a 
  

   small 
  volume 
  had 
  the 
  usual 
  rate 
  of 
  decay, 
  viz. 
  half 
  period 
  in 
  

   3' 
  75 
  deys. 
  Measurements 
  of 
  this 
  character 
  are 
  essential 
  if 
  

   any 
  accuracy 
  is 
  required. 
  It 
  is 
  not 
  sufficient 
  to 
  assume 
  that 
  

   all 
  the 
  emanation 
  formed 
  in 
  a 
  certain 
  interval 
  of 
  days 
  is 
  

   pumped 
  off 
  from 
  the 
  radium 
  solution. 
  Moreover 
  a 
  small 
  

   part 
  of 
  the 
  emanation 
  is 
  left 
  behind 
  in 
  every 
  operation 
  of 
  

   transferring 
  the 
  emanation 
  from 
  ODe 
  vessel 
  to 
  another. 
  It 
  

   may 
  be 
  mentioned 
  that 
  in 
  most 
  of 
  the 
  experiments 
  the 
  amount 
  

   of 
  emanation 
  whose 
  volume 
  and 
  activity 
  were 
  measured 
  was 
  

   equivalent 
  to 
  the 
  equilibrium 
  quantity 
  from 
  60 
  to 
  140 
  milli- 
  

   grams 
  of 
  radium. 
  Usually 
  the 
  amount 
  of 
  emanation 
  pumped 
  

   off 
  during 
  the 
  experiment 
  corresponded 
  to 
  20 
  or 
  30 
  milli- 
  

   grams 
  of 
  radium. 
  

  

  