﻿Rays 
  and 
  Product 
  of 
  Uranium 
  X. 
  861 
  

  

  covered 
  Qi^'2 
  (a-rays 
  therefore 
  39). 
  As 
  the 
  subsequent 
  

   history 
  of 
  the 
  preparations 
  showed, 
  a 
  large 
  proportion 
  of 
  the 
  

   radiation 
  reckoned 
  as 
  "a-" 
  in 
  air 
  is 
  due 
  to 
  the 
  slight 
  

   absorption 
  of 
  the 
  /3-rajs 
  in 
  the 
  mica, 
  whereas 
  in 
  hydrogen 
  

   this 
  absorption 
  is 
  nearly 
  negligible. 
  So 
  that 
  in 
  air, 
  even 
  if 
  

   the 
  theoretical 
  growth 
  of 
  a-radiation 
  occurred, 
  it 
  would 
  

   probably 
  be 
  largely, 
  if 
  not 
  entirely, 
  masked 
  by 
  the 
  diminution 
  

   in 
  the 
  difference 
  between 
  the 
  two 
  leaks, 
  covered 
  and 
  un- 
  

   covered, 
  due 
  to 
  the 
  diminution 
  in 
  the 
  absorption 
  of 
  the 
  /3-rays 
  

   as 
  these 
  decayed. 
  In 
  hydrogen 
  the 
  effect 
  is 
  still 
  present 
  to 
  a 
  

   slight 
  extent 
  but 
  not 
  enough 
  to 
  prevent 
  the 
  observation 
  of 
  

   the 
  growth 
  of 
  a-rays, 
  if 
  it 
  occurred 
  at 
  the 
  theoretical 
  rate. 
  

   Subsequent 
  work 
  has 
  thrown 
  doubt 
  on 
  the 
  earlier 
  measure- 
  

   ments 
  in 
  air, 
  and 
  on 
  the 
  conclusion 
  drawn 
  from 
  them 
  in 
  the 
  

   second 
  communication 
  to 
  ' 
  Nature,' 
  that 
  in 
  one 
  preparation 
  a 
  

   rapid 
  growth 
  of 
  a-rays 
  occurred 
  which 
  reached 
  a 
  maximum 
  

   in 
  2'5 
  days 
  from 
  the 
  start. 
  This 
  observation 
  has 
  not 
  been 
  

   repeated 
  either 
  in 
  air 
  or 
  in 
  hydrogen 
  with 
  more 
  perfect 
  

   methods. 
  This 
  is 
  not 
  itself 
  conclusive 
  against 
  it, 
  for 
  it 
  has 
  

   been 
  impossible 
  to 
  prepare 
  two 
  sets 
  of 
  uranium 
  X 
  preparations 
  

   in 
  the 
  same 
  wav. 
  The 
  chemical 
  methods, 
  of 
  separation 
  from 
  

   uranium 
  and 
  of 
  concentration 
  from 
  unidentified 
  impurities, 
  

   employed 
  have 
  varied 
  widely, 
  being 
  dictated 
  by 
  circumstances 
  

   from 
  moment 
  to 
  moment 
  during 
  the 
  process, 
  o\\ing 
  to 
  the 
  

   perpetually 
  changing 
  character 
  and 
  amount 
  of 
  impurities 
  

   and 
  the 
  totally 
  different 
  chemical 
  behaviour 
  of 
  the 
  uranium 
  

   X 
  accordingly. 
  In 
  fact 
  the 
  methods 
  adopted 
  in 
  the 
  last 
  

   separation 
  were 
  often 
  the 
  converse 
  of 
  those 
  formerly 
  most 
  

   relied 
  upon, 
  the 
  uranium 
  - 
  free, 
  uranium 
  X- 
  containing 
  

   substances 
  being 
  dissolved 
  in 
  excess 
  of 
  ammonium 
  carbonate 
  

   and 
  fractionally 
  precipitated 
  by 
  boiling. 
  Sometimes 
  the 
  

   uranium 
  X 
  came 
  down 
  in 
  the 
  last 
  minute 
  fraction 
  almost 
  

   entirely, 
  and 
  in 
  other 
  cases 
  in 
  one 
  of 
  the 
  middle 
  fractions. 
  

   This 
  new 
  method 
  proved 
  an 
  extremely 
  vahiable 
  one 
  in 
  the 
  

   last 
  separation. 
  Unfortunately 
  it 
  was 
  not 
  discovered 
  before 
  

   the 
  whole 
  of 
  the 
  uranium 
  X 
  had 
  been 
  first 
  separated 
  by 
  the 
  

   tedious 
  barium 
  sulphate 
  process. 
  

  

  The 
  earlier 
  observations 
  and 
  the 
  conclusion 
  referred 
  to 
  

   may 
  be 
  rejected 
  at 
  least 
  for 
  the 
  present. 
  The 
  difficultly 
  

   deviable 
  rays 
  behave 
  in 
  an 
  anomalous 
  manner 
  which 
  was 
  at 
  

   fir>t 
  not 
  suspected, 
  in 
  that 
  they 
  do 
  not 
  seem 
  to 
  be 
  a 
  constant 
  

   quantity. 
  In 
  the 
  case 
  of 
  the 
  most 
  recent 
  preparation, 
  which, 
  

   as 
  already 
  explained, 
  differed 
  in 
  the 
  manner 
  of 
  its 
  separation 
  

   from 
  the 
  earlier 
  ones, 
  two 
  successive 
  measurements 
  of 
  the 
  

   difficultly 
  deviable 
  radiation 
  from 
  the 
  covered 
  preparation 
  m 
  

   air. 
  the 
  first 
  immediately 
  after 
  preparation, 
  and 
  the 
  second 
  

  

  