﻿326 
  Prof. 
  Rutherford 
  and 
  Mr. 
  Richardson 
  : 
  Analysis 
  

  

  aluminium 
  vessel, 
  for 
  under 
  these 
  conditions 
  the 
  7 
  radiation 
  

   excited 
  by 
  j3 
  rays 
  is 
  reduced 
  to 
  a 
  small 
  amount. 
  

  

  The 
  radium 
  D-fE 
  employed 
  was 
  separated 
  from 
  old 
  

   radium 
  preparations 
  by 
  adding 
  a 
  few 
  milligrams 
  of 
  a 
  lead 
  

   salt 
  to 
  the 
  solution 
  and 
  precipitating 
  with 
  hydrogen 
  sulphide*. 
  

   The 
  separation 
  of 
  radium 
  D 
  from 
  radium 
  E 
  was 
  kindly 
  per- 
  

   formed 
  for 
  us 
  by 
  Dr. 
  Russell 
  and 
  Mr. 
  Chadwick. 
  They 
  also 
  

   separated 
  at 
  the 
  same 
  time 
  the 
  radium 
  F 
  (polonium) 
  which 
  

   has 
  been 
  used 
  by 
  them 
  in 
  a 
  study 
  of 
  the 
  7 
  rays 
  emitted 
  by 
  

   that 
  substance. 
  After 
  removal 
  of 
  the 
  radium 
  F 
  by 
  dipping 
  

   a 
  copper 
  plate 
  into 
  the 
  solution 
  of 
  radium 
  D 
  + 
  E 
  + 
  F, 
  the 
  

   radium 
  D 
  and 
  radium 
  E 
  were 
  precipitated 
  together 
  as 
  

   sulphides. 
  The 
  precipitate 
  was 
  dissolved 
  in 
  hydrochloric 
  acid 
  

   and 
  the 
  radium 
  E 
  almost 
  completely 
  removed 
  by 
  dipping 
  a 
  

   nickel 
  plate 
  into 
  the 
  solution. 
  

  

  A 
  small 
  quantity 
  of 
  aluminium 
  chloride 
  was 
  added 
  to 
  the 
  

   radium 
  D 
  solution, 
  and 
  ammonia 
  added. 
  The 
  radium 
  D 
  and 
  

   lead 
  were 
  precipitated 
  while 
  any 
  copper 
  or 
  nickel 
  present 
  was 
  

   dissolved 
  in 
  excess 
  of 
  ammonia. 
  The 
  radium 
  D 
  was 
  filtered 
  off 
  

   and 
  the 
  radiation 
  from 
  it 
  was 
  tested 
  in 
  position 
  on 
  the 
  filter- 
  

   paper. 
  The 
  amount 
  of 
  aluminium 
  and 
  lead 
  mixed 
  with 
  the 
  

   radium 
  D 
  on 
  the 
  filter 
  was 
  not 
  more 
  than 
  a 
  few 
  milligrams, 
  

   and 
  the 
  7 
  radiation 
  excited 
  in 
  this 
  material 
  was 
  negligible 
  

   compared 
  with 
  the 
  primary 
  7 
  radiation. 
  

  

  The 
  radium 
  E 
  which 
  had 
  boen 
  separated 
  on 
  the 
  nickel 
  

   plate 
  was 
  transferred 
  by 
  Dr. 
  Russell 
  and 
  Mr. 
  Chadwick 
  on 
  to 
  

   an 
  aluminium 
  plate 
  by 
  volatilization 
  under 
  definite 
  conditions 
  

   in 
  an 
  electric 
  furnace. 
  As 
  is 
  well 
  known, 
  aluminium 
  can 
  

   only 
  emit 
  a 
  characteristic 
  X 
  radiation 
  of 
  a 
  very 
  easily 
  absorbed 
  

   type, 
  which 
  could 
  not 
  be 
  detected 
  under 
  the 
  experimental 
  

   conditions. 
  On 
  the 
  other 
  hand, 
  the 
  characteristic 
  X 
  radiation 
  

   to 
  be 
  expected 
  from 
  nickel 
  is 
  of 
  the 
  same 
  order 
  of 
  penetrating 
  

   power 
  as 
  the 
  primary 
  7 
  rays 
  from 
  radium 
  D. 
  

  

  The 
  purity 
  of 
  the 
  radioactive 
  substances 
  employed 
  was 
  

   tested 
  by 
  measuring 
  the 
  decay 
  of 
  the 
  /3-ray 
  activity 
  of 
  

   radium 
  E, 
  and 
  the 
  rise 
  of 
  the 
  /3-ray 
  activity 
  of 
  the 
  radium 
  D 
  

   preparation 
  after 
  an 
  initial 
  complete 
  separation 
  of 
  radium 
  E. 
  

   A 
  series 
  of 
  observations 
  showed 
  that 
  radium 
  D 
  was 
  obtained 
  

   almost 
  free 
  from 
  radium 
  E, 
  while 
  the 
  radium 
  E 
  did 
  not 
  

   contain 
  a 
  detectable 
  amount 
  of 
  radium 
  D. 
  

  

  Experimental 
  Method. 
  

  

  The 
  apparatus 
  employed 
  to 
  analyse 
  the 
  7 
  radiation 
  was 
  

   essentially 
  the 
  same 
  in 
  principle 
  as 
  that 
  described 
  in 
  our 
  

  

  * 
  See 
  Boltwood 
  and 
  Rutherford, 
  Phil. 
  Mag. 
  xxii. 
  p. 
  586 
  (1911). 
  

  

  