﻿360 
  Lea 
  — 
  Color 
  Relations 
  of 
  Atoms, 
  Ions 
  and 
  Molecules. 
  

  

  all 
  the 
  alkaline 
  and 
  earthy 
  metals 
  are 
  colorless 
  even 
  when 
  not 
  

   dissociated. 
  As 
  potassium 
  iodide 
  forms 
  a 
  colorless 
  solution 
  in 
  

   water 
  it 
  follows 
  that 
  the 
  atoms 
  of 
  both 
  potassium 
  and 
  iodine 
  

   are 
  colorless. 
  Sodium 
  monosulphide 
  gives 
  a 
  colorless 
  solution 
  

   in 
  water, 
  therefore 
  the 
  atoms 
  of 
  sodium 
  and 
  of 
  sulphur 
  are 
  

   colorless. 
  But 
  the 
  polysulphides 
  are 
  yellow 
  in 
  solution 
  : 
  it 
  fol- 
  

   lows 
  therefore 
  that 
  in 
  them 
  a 
  certain 
  portion 
  of 
  the 
  sulphur 
  

   may 
  exist 
  in 
  a 
  molecular 
  condition. 
  

  

  2. 
  If 
  an 
  electrolyte 
  gives 
  a 
  colored 
  dilute 
  solution 
  in 
  water 
  

   it 
  is 
  necessary 
  first 
  to 
  consider 
  the 
  constitution 
  of 
  the 
  anion. 
  

   If 
  this 
  is 
  a 
  single 
  atom, 
  then 
  the 
  color 
  of 
  the 
  solution 
  belongs 
  

   entirely 
  to 
  the 
  kathion. 
  For 
  it 
  is 
  a 
  very 
  remarkable 
  fact 
  that 
  

   all 
  elementary 
  anions 
  are 
  colorless. 
  This 
  is 
  all 
  the 
  more 
  curious 
  

   that 
  the 
  endless 
  number 
  or 
  organic 
  coloring 
  matters 
  are 
  built 
  

   up 
  chiefly 
  of 
  these 
  colorless 
  anions 
  and 
  of 
  colorless 
  hydrogen. 
  

  

  This 
  criterion 
  enables 
  us 
  to 
  judge 
  as 
  to 
  a 
  large 
  number 
  of 
  

   atoms. 
  As 
  oxides, 
  fluorides, 
  chlorides 
  bromides, 
  etc, 
  all 
  have 
  

   colorless 
  anions, 
  whatever 
  color 
  is 
  shown 
  by 
  their 
  dilute 
  solu- 
  

   tions 
  must 
  be 
  due 
  to 
  the 
  kathion 
  s. 
  

  

  3. 
  Even 
  if 
  the 
  anion 
  is 
  composite, 
  information 
  can 
  often 
  be 
  

   gained. 
  Many 
  composite 
  anions 
  are 
  colorless, 
  for 
  example 
  So 
  4 
  . 
  

   So 
  that 
  when 
  sulphates 
  give 
  solutions 
  that 
  are 
  colored 
  when 
  

   dilute 
  the 
  color 
  must 
  be 
  due 
  to 
  the 
  kathion. 
  

  

  The 
  same 
  is 
  the 
  case 
  with 
  nitrates, 
  phosphates, 
  carbonates, 
  

   etc. 
  In 
  these 
  cases 
  and 
  in 
  many 
  others, 
  knowing 
  the 
  anion 
  to 
  

   be 
  colorless 
  we 
  are 
  certain 
  that 
  the 
  kathion 
  must 
  contribute 
  

   any 
  color 
  that 
  is 
  present. 
  

  

  These 
  criteria 
  will 
  afford 
  the 
  means 
  of 
  deciding 
  upon 
  the 
  

   color 
  of 
  the 
  entire 
  series 
  of 
  elementary 
  atoms. 
  

  

  Classification. 
  

  

  In 
  the 
  preceding 
  sections 
  proof 
  has 
  been 
  offered 
  that 
  the 
  

   colors 
  of 
  the 
  atoms 
  are 
  substantially 
  the 
  same 
  as 
  those 
  of 
  the 
  

   corresponding 
  ions. 
  Especially 
  the 
  fact 
  that 
  a 
  solution 
  of 
  cop- 
  

   per 
  sulphate 
  by 
  a 
  dilution 
  which 
  doubles 
  the 
  number 
  of 
  its 
  

   dissociated 
  ions 
  scarcely 
  shows 
  the 
  slightest 
  change 
  of 
  total 
  

   absorption 
  is 
  strong, 
  one 
  might 
  say, 
  final. 
  

  

  But 
  as 
  respects 
  classification 
  which 
  will 
  form 
  the 
  chief 
  sub- 
  

   ject 
  of 
  the 
  present 
  paper 
  it 
  is 
  absolutely 
  unimportant 
  whether 
  

   these 
  views 
  be 
  accepted 
  or 
  not. 
  We 
  may 
  classify 
  the 
  elements 
  

   according 
  to 
  the 
  color 
  and 
  want 
  of 
  color 
  of 
  their 
  ions 
  or 
  quite 
  

  

  