﻿248 
  ANNUAL 
  EEPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1929 
  

  

  earths 
  found 
  a 
  natural 
  and 
  essential 
  place. 
  It 
  was 
  moreover 
  shown 
  

   that 
  for 
  no 
  a 
  priori 
  reason 
  could 
  uranium 
  be 
  regarded 
  as 
  the 
  final 
  

   element 
  of 
  the 
  table, 
  but 
  that 
  a 
  continuation 
  of 
  the 
  scheme 
  of 
  electron 
  

   grouping 
  allowed 
  a 
  theoretical 
  conclusion 
  with 
  an 
  element 
  of 
  atomic 
  

   number 
  118. 
  The 
  whole 
  work 
  was 
  supported 
  by, 
  and 
  coordinated 
  

   with 
  the 
  extensive 
  and 
  weighty 
  evidence 
  of 
  spectroscopic 
  research. 
  

   The 
  application 
  of 
  Bohr's 
  quantum 
  orbit 
  development 
  scheme 
  made 
  

   it 
  clear 
  that 
  the 
  element 
  of 
  atomic 
  number 
  72 
  could 
  not 
  be 
  a 
  rare 
  

   earth 
  metal 
  celtium 
  as 
  was 
  originally 
  supposed, 
  but 
  must 
  be 
  an 
  

   undiscovered 
  higher 
  analogue 
  of 
  zirconium 
  and 
  titanium, 
  likely 
  to 
  

   exist 
  in 
  ores 
  of 
  these 
  metals, 
  while 
  on 
  the 
  chemical 
  side 
  this 
  was 
  sup- 
  

   ported 
  by 
  the 
  fact 
  that 
  discordant 
  values 
  of 
  the 
  atomic 
  weight 
  of 
  

   titanium 
  pointed 
  to 
  the 
  presence 
  of 
  minute 
  traces 
  of 
  an 
  undiscovered 
  

   analogue. 
  This 
  view 
  was 
  soon 
  brilliantly 
  and 
  completely 
  confirmed 
  

   by 
  the 
  discovery 
  of 
  hafnium 
  by 
  Coster 
  and 
  Hevesy 
  in 
  zirconium 
  

   minerals 
  in 
  1923. 
  The 
  lines 
  in 
  the 
  X-ray 
  spectrum 
  of 
  the 
  new 
  element 
  

   were 
  found 
  to 
  be 
  well 
  defined; 
  the 
  amount 
  of 
  metal 
  present 
  was 
  quite 
  

   appreciable 
  and 
  easily 
  separated 
  from 
  the 
  rare 
  earths, 
  all 
  in 
  agreement 
  

   with 
  theoretical 
  considerations. 
  

  

  Special 
  interest 
  has 
  always 
  been 
  attached 
  to 
  the 
  fact 
  that 
  the 
  

   periodic 
  table 
  had 
  indicated 
  an 
  undiscovered 
  halogen 
  and 
  an 
  alkali 
  

   metal. 
  Moseley's 
  scheme 
  confirmed 
  gaps 
  for 
  atomic 
  numbers 
  85 
  and 
  

   87 
  corresponding 
  respectively 
  to 
  these 
  elements, 
  and 
  it 
  was 
  somewhat 
  

   surprising 
  that 
  elements 
  of 
  two 
  such 
  well-defined 
  and 
  distinctive 
  

   groups 
  should 
  have 
  so 
  long 
  eluded 
  discovery. 
  Among 
  elements 
  of 
  

   this 
  region, 
  however, 
  a 
  further 
  factor 
  demanded 
  attention, 
  that 
  of 
  radio- 
  

   activity. 
  Under 
  what 
  conditions 
  might 
  these 
  two 
  elements 
  be 
  reason- 
  

   ably 
  expected 
  to 
  exist? 
  According 
  to 
  their 
  place 
  in 
  the 
  table 
  and 
  also 
  

   from 
  their 
  atomic 
  numbers, 
  they 
  occupied 
  alternate 
  positions 
  among 
  

   the 
  most 
  characteristically 
  radioactive 
  elements. 
  Moreover 
  potassium 
  

   and 
  rubidium 
  had 
  long 
  been 
  known 
  to 
  exhibit 
  a 
  faint 
  radioactivity, 
  

   although 
  extensive 
  work 
  on 
  them 
  had 
  failed 
  to 
  reveal 
  the 
  presence 
  of 
  

   any 
  higher 
  analogues 
  to 
  explain 
  this 
  phenomenon. 
  Suggestions 
  were 
  

   forthcoming 
  in 
  connection 
  therewith; 
  Loring 
  proposed 
  the 
  view 
  that 
  

   elements 
  of 
  low 
  atomic 
  number 
  may 
  be 
  regarded 
  as 
  having 
  absorbed 
  

   corpuscular 
  radiation, 
  and 
  an 
  intermediate 
  stage 
  in 
  which 
  an 
  element 
  

   absorbs 
  radiation 
  and 
  emits 
  it 
  radio 
  actively 
  suggests 
  itself 
  to 
  account 
  

   for 
  the 
  observed 
  radioactivity 
  of 
  potassium 
  and 
  rubidium, 
  without 
  the 
  

   apparent 
  accumulation 
  of 
  any 
  radioactive 
  product. 
  On 
  the 
  other 
  

   hand, 
  Hahn 
  discussed 
  the 
  possibihty 
  of 
  85 
  and 
  87 
  occurring 
  in 
  the 
  

   subsidiary 
  disintegration 
  series 
  of 
  one 
  of 
  the 
  radioactive 
  elements; 
  

   but 
  Uttle 
  evidence 
  can 
  be 
  advanced 
  in 
  support 
  of 
  such 
  a 
  view. 
  He 
  

   and 
  also 
  Hevesy 
  independently 
  tried 
  to 
  detect 
  87 
  by 
  a 
  study 
  of 
  the 
  

   disintegration 
  of 
  mesothorium-2, 
  but 
  in 
  neither 
  case 
  was 
  any 
  con- 
  

   clusive 
  result 
  obtained. 
  

  

  