in Inorganic Triple Salts, etc, 419 



seems doubtful, since they have been found to retain 

 potassium, etc., very tenaciously when washed. 6 



It is believed that the instances presented here, where 

 gold, antimony and copper as chlorides, together with 

 iron as bromides and cyanides, when present in two states 

 of valency in triple salts produce exceedingly strong 

 colors, are sufficient to show very conclusively that the 

 new theory in regard to this atomic grouping as a chromo- 

 phore is founded upon facts. 



In regard to the very black salt Cs 4 Ag 2 Au"' 2 Cl 12 , which 

 does not contain a metal in two states of oxidation, the 

 theory must evidently be modified by assuming that 

 atoms of two different metals may sometimes form this 

 chromophore. Possibly it may be essential that the two 

 metals should be closely related, as gold and silver are, 

 as is shown by their positions in Mendeleeff 's table. The 

 salt Cs 4 Cu"Au'" 2 Cl 12 may, perhaps, be regarded in pre- 

 cisely the same way as the one just considered, but its 

 color is not very intense, since it gives a pale powder, and 

 as our chromophore group appears to be a very powerful 

 one, it may be better to consider the color of this cupric 

 salt to be due simply to the ordinary coloring-effects of 

 cupric and auric chlorides. 



It is to be observed that Pollard's salt 7 , (NH 4 ) 6 Ag 2 Au ;i 

 Cl 17 , has a silver-auric grouping in a different ratio, but 

 that in this case the color is very dark red, without 

 opacity. 



The discussion presented here has been given particu- 

 larly in connection with a chromophore grouping in triple 

 salts, but it is not supposed that the effect of this group- 

 ing is necessarily confined to these compounds. No cases 

 of this effect have been thought of in undoubtedly pure 

 double salts, but the black precipitate produced by ammo- 

 nia in solutions of mixed ferrous and ferric salts may be 

 regarded as an effect of the grouping upon a double 

 hydroxide or oxide, unless, indeed, this precipitate con- 

 tains ammonium hydroxide, or some kind of basic salt, 

 as a third constituent. At all events, it appears that the 



6 An extension summary of what is known in regard to the complex cyan- 

 ides of iron, with many references to the literature, is to be found in Beil- 

 steins Handbuch. 



' This Journal, 3, 257, 1922. 



