SALTS OF COBALT. 37 



tion of cobalt bromide to which a large amount of calcium bromide is added 

 is similar but not identical with that of a solution of the chloride of cobalt 

 to which a large amount of calcium chloride had been added. The work 

 of Jones and Uhler (" Hydrates in Aqueous Solution") indicates that the 

 absorption of cobalt chloride when "dehydrated" with calcium chloride, 

 aluminium chloride, or calcium bromide, is the same, but that this differs 

 somewhat from the absorption of very concentrated solutions of cobalt 

 chloride alone. In the latter case only three of the five bands were seen, 

 and these were located nearer the red end of the spectrum; but the "dis- 

 placement" was different for different bands, amounting to 170 A.U. for 

 the least refrangible, and 115 A.U. for the most refrangible. 



The entire absence of this red absorption in solutions of moderate 

 concentration shows at once that it can not be accounted for by the simple 

 theory of dissociation, according to which there should be present only 

 ions and molecules. The fact that the absorption does appear in very 

 concentrated solutions naturally suggests that it may be due to aggre- 

 gates of molecules, but this view is not tenable, since the absorption in- 

 creases with rise in temperature. The most reasonable explanation, and 

 the one that best fits the facts, is that it is due to some relatively simple 

 hydrate of the molecule. The conditions which favor the formation of a 

 "simple" hydrate are high temperature, or great concentration, or the 

 addition of large amounts of some dehydrating agent to a moderately 

 concentrated solution, and in all of these cases the absorption in the red 

 appears. That this explanation is the correct one is also made probable 

 by the work of Russell on the absorption of the various dry salts of cobalt. 

 The anhydrous salts all show absorption in the red, as do also the simple 

 hydrates; while hydrates containing 6 molecules of water exert no absorp- 

 tion in this region of the spectrum. 



In non-aqueous solvents only the chloride and bromide have been 

 studied. The chloride, which in aqueous solutions showed an absorption 

 band near X 3300, has in the alcoholic solutions two bands, one at X 3100 

 and the other at X 3600. These bands behave very much like the X 3300 

 band in the aqueous solution, disappearing quite rapidly with dilution. 

 They are most likely due to some relatively simple solvate. A study of 

 the change of absorption with temperature will undoubtedly throw some 

 light on this point. 



The green band is present in all the non-aqueous solutions studied, 

 although its intensity in the acetone solutions is so small that very deep 

 layers of solution were necessary in order to see even a trace of it. This 

 is exactly what we should expect if the view is held that the cobalt atom, 

 no matter with what it is associated, absorbs green light to some extent. 

 The intensity of the band diminishes as we pass from solutions in methyl 

 alcohol to those in ethyl alcohol and acetone, but so do the concentrations; 

 hence, as in aqueous solutions, the intensity of the band may be said to 

 be roughly proportional to the concentration. 



In the red the absorption is much more intense in the non-aqueous 

 than in aqueous solutions, the intensity for equal concentrations increas- 

 ing very rapidly as we pass from methyl alcohol to ethyl alcohol to acetone. 



