﻿Lea 
  — 
  Color 
  Relations 
  of 
  Atoms, 
  Ions 
  and 
  Molecules. 
  373 
  

  

  From 
  this 
  we 
  pass 
  to 
  the 
  next 
  colorless 
  group 
  of 
  nine 
  ele- 
  

   ments 
  commencing 
  with 
  cadmium 
  and 
  ending 
  with 
  lanthanum. 
  

   Approaching 
  the 
  next 
  colored 
  group 
  we 
  as 
  before 
  find 
  a 
  tran- 
  

   sitional 
  element, 
  in 
  this 
  case 
  but 
  one. 
  At 
  least 
  but 
  one 
  is 
  now 
  

   known, 
  but 
  as 
  we 
  have 
  now 
  come 
  to 
  the 
  region 
  of 
  little 
  known 
  

   metals 
  of 
  the 
  rare 
  earths 
  it 
  is 
  possible 
  that 
  some 
  one 
  of 
  those 
  

   not 
  yet 
  thoroughly 
  known 
  may 
  take 
  its 
  place 
  alongside 
  of 
  

   cerium 
  and 
  thus 
  bring 
  this 
  approach 
  into 
  complete 
  symmetry 
  

   with 
  all 
  the 
  others. 
  

  

  Cerium 
  connects 
  itself 
  with 
  the 
  colorless 
  group 
  immediately 
  

   preceding 
  by 
  having 
  colorless 
  ions 
  and 
  with 
  the 
  colored 
  group 
  

   immediately 
  following 
  by 
  its 
  colored 
  ions. 
  

  

  The 
  colored 
  group 
  thus 
  reached, 
  composed 
  of 
  metals 
  having 
  

   colored 
  ions 
  only, 
  consists 
  of 
  didymium, 
  samarium 
  and 
  erbium. 
  

   Then 
  follow 
  the 
  transitionals 
  tantalum 
  (?) 
  and 
  tungsten. 
  

  

  Next, 
  a 
  series 
  having 
  ions 
  colored 
  at 
  all 
  valencies, 
  namely 
  

   osmium, 
  iridium, 
  platinum 
  and 
  gold. 
  With 
  gold 
  the 
  regular 
  

   series 
  terminates. 
  

  

  There 
  follows 
  what 
  may 
  be 
  called 
  the 
  most 
  curious 
  part 
  of 
  

   the 
  entire 
  range 
  of 
  elements. 
  This 
  is 
  found 
  in 
  the 
  little 
  group 
  

   of 
  six 
  at 
  the 
  extreme 
  end. 
  In 
  the 
  principal 
  series 
  the 
  colored 
  

   groups 
  are 
  always 
  immediately 
  preceded 
  and 
  introduced 
  by 
  

   transitional 
  elements, 
  that 
  is 
  elements 
  having 
  both 
  colorless 
  

   and 
  colored 
  ions. 
  The 
  usual 
  number 
  of 
  these 
  transitionals 
  is 
  

   two. 
  In 
  the 
  small 
  final 
  group 
  the 
  first 
  two 
  colored 
  elements 
  

   act 
  as 
  transitionals 
  to 
  the 
  third. 
  The 
  first 
  of 
  the 
  colored 
  

   metals 
  is 
  thallium, 
  this 
  metal 
  is 
  allied 
  to 
  the 
  alkalies 
  by 
  its 
  

   thallious 
  salts 
  which 
  are 
  colorless 
  ; 
  it 
  is 
  also 
  closely 
  related 
  to 
  

   the 
  heavy 
  metals, 
  lead 
  and 
  mercury 
  which 
  are 
  on 
  each 
  side 
  of 
  

   it. 
  Even 
  thallic 
  sulphate 
  and 
  nitrate 
  are 
  colorless 
  salts 
  decom- 
  

   posed 
  by 
  water. 
  But 
  the 
  thallic 
  haloids 
  form 
  colored 
  crystals 
  

   and 
  colored 
  solutions 
  and 
  thus 
  correspond 
  perfectly 
  to 
  colored 
  

   ions. 
  Therefore 
  thallium 
  whilst 
  chiefly 
  related 
  to 
  the 
  colorless 
  

   elements 
  on 
  each 
  side 
  of 
  it 
  has 
  nevertheless 
  made 
  a 
  well- 
  

   marked 
  step 
  towards 
  color 
  by 
  its 
  single 
  pair 
  of 
  colored 
  ions. 
  

  

  The 
  next 
  colored 
  metal, 
  bismuth, 
  has 
  advanced 
  much 
  fur- 
  

   ther 
  towards 
  color, 
  for 
  of 
  its 
  four 
  valencies 
  all 
  but 
  one 
  have 
  

   colored 
  ions. 
  It 
  still 
  retains 
  its 
  relation 
  however 
  with 
  the 
  

   colorless 
  elements 
  on 
  each 
  side 
  of 
  it, 
  lead 
  and 
  thorium, 
  by 
  its 
  

   one 
  pair 
  of 
  colorless 
  ions 
  corresponding 
  to 
  bismuth 
  trioxide. 
  

  

  Finally 
  we 
  have 
  the 
  last 
  of 
  all 
  the 
  metals, 
  uranium, 
  with 
  

   colored 
  ions 
  at 
  all 
  valencies. 
  Standing 
  alone 
  it 
  occupies 
  as 
  it 
  

   were 
  the 
  position 
  of 
  a 
  group 
  to 
  which 
  its 
  transitionals, 
  thallium 
  

   and 
  bismuth, 
  lead 
  up, 
  and 
  with 
  it 
  the 
  series 
  of 
  the 
  elements 
  

   closes. 
  

  

  