﻿Lea 
  — 
  Color 
  Relations 
  of 
  Atoms, 
  Ions 
  and 
  Molecules. 
  359 
  

  

  Chromic 
  chloride 
  after 
  sublimation 
  still 
  shows 
  the 
  characteristic 
  

   pale 
  violet 
  color 
  of 
  chromic 
  salts. 
  

  

  These 
  instances 
  might 
  be 
  multiplied 
  bat 
  thej 
  will 
  sufficiently 
  

   show 
  that 
  characteristic 
  color 
  belongs 
  to 
  the 
  atom 
  as 
  well 
  as 
  to 
  

   the 
  ion. 
  

  

  When 
  the 
  atom 
  enters 
  into 
  a 
  molecule 
  such 
  as 
  is 
  produced 
  

   by 
  the 
  union 
  of 
  an 
  elementary 
  kathion 
  with 
  an 
  elementary 
  

   anion, 
  of 
  course 
  that 
  molecule 
  will 
  not 
  give 
  exactly 
  the 
  same 
  

   absorbtion 
  spectrum 
  as 
  the 
  free 
  ion 
  : 
  the 
  vibration 
  of 
  the 
  ion 
  

   is 
  free 
  whereas 
  that 
  of 
  the 
  atom 
  in 
  the 
  molecule 
  is 
  constrained. 
  

   What 
  is 
  contended 
  for 
  is 
  that 
  in 
  the 
  great 
  majority 
  of 
  cases 
  

   the 
  color 
  of 
  the 
  ion 
  and 
  that 
  of 
  the 
  atom 
  are 
  substantially 
  the 
  

   same. 
  Exceptional 
  cases 
  will 
  occur, 
  difficult 
  to 
  explain 
  under 
  

   any 
  theory. 
  Chromous 
  chloride 
  gives 
  a 
  blue 
  solution 
  in 
  water, 
  

   chromous 
  acetate 
  a 
  red 
  one 
  : 
  can 
  therefore 
  the 
  chromous 
  ion 
  be 
  

   both 
  red 
  and 
  blue? 
  

  

  This 
  case 
  is 
  quite 
  the 
  reverse 
  of 
  the 
  results 
  obtained 
  by 
  

   Ostwald 
  in 
  his 
  well-known 
  work 
  done 
  on 
  the 
  permanganates. 
  

  

  The 
  green 
  solution 
  when 
  concentrated 
  of 
  copper 
  chloride 
  

   is 
  a 
  case 
  often 
  cited 
  to 
  show 
  that 
  green 
  molecules 
  may 
  yield 
  

   blue 
  ions. 
  But 
  this 
  maybe 
  explained 
  in 
  quite 
  a 
  different 
  way. 
  

   It 
  is 
  known 
  that 
  many 
  salts 
  exist 
  in 
  strong 
  solutions, 
  as 
  com- 
  

   plex 
  molecules. 
  Hittorf 
  has 
  shown 
  that 
  cadmium 
  iodide 
  in 
  

   strong 
  solution 
  in 
  water 
  exists 
  as 
  (Cd 
  I 
  2 
  ) 
  3 
  . 
  Lenz* 
  gives 
  as 
  a 
  

   formula 
  for 
  the 
  solution 
  of 
  potassium 
  iodide 
  in 
  alcohol 
  

  

  a(Kl), 
  &(KI)„ 
  c(KI) 
  3 
  , 
  etc. 
  

  

  the 
  coefficients 
  a, 
  b, 
  c 
  diminishing 
  rapidly. 
  

  

  It 
  is 
  quite 
  probable 
  that 
  the 
  green 
  color 
  of 
  some 
  copper 
  

   compounds 
  may 
  be 
  due 
  to 
  complex 
  molecules 
  and 
  among 
  them, 
  

   copper 
  chloride. 
  

  

  Criteria 
  of 
  Color. 
  

  

  In 
  making 
  determinations 
  of 
  the 
  colors 
  of 
  ions, 
  and 
  there- 
  

   fore 
  of 
  atoms, 
  I 
  have 
  used 
  the 
  following 
  criteria. 
  

  

  1. 
  When 
  an 
  electrolyte 
  gives 
  a 
  solution 
  in 
  water 
  which 
  is 
  

   colorless 
  when 
  dilute, 
  both 
  the 
  kathion 
  and 
  the 
  anion 
  are 
  color- 
  

   less. 
  Thus 
  for 
  example 
  as 
  lithium 
  bromide 
  gives 
  a 
  colorless 
  

   solution 
  in 
  water 
  it 
  follows 
  that 
  the 
  ions 
  of 
  lithium 
  and 
  bro- 
  

   mine 
  are 
  colorless. 
  It 
  has 
  been 
  already 
  said 
  that 
  no 
  relation 
  

   whatever 
  exists 
  between 
  the 
  color 
  of 
  an 
  atom 
  and 
  that 
  of 
  its 
  

   molecule. 
  So 
  two 
  colorless 
  bromine 
  atoms 
  form 
  the 
  intensely 
  

   colored 
  element 
  bromine. 
  If 
  further 
  proof 
  be 
  required 
  of 
  

   the 
  colorless 
  nature 
  of 
  the 
  bromine 
  atom 
  it 
  is 
  easily 
  obtained 
  

   by 
  considering 
  that 
  the 
  compounds 
  formed 
  by 
  that 
  atom 
  with 
  

  

  * 
  Mem. 
  de 
  l'Ac. 
  Imp. 
  de 
  St. 
  Petersburg, 
  30. 
  

  

  