DISCUSSION OF EVIDENCE. 173 



Jones and Anderson also did some work on the absorption spectra of 

 cobalt salts in certain non-aqueous solvents. The green band appeared 

 in all of the non-aqueous solutions studied. This is just what would 

 be expected if this band is due to the cobalt atom. The intensity of 

 this band in non-aqueous solvents was found to be proportional to 

 the concentration. 



The red absorption is more intense in the non-aqueous solvents 

 than in water, the intensity increasing from methyl alcohol to ethyl 

 alcohol to acetone. With increase in the dilution the band narrows 

 rapidly in methyl alcohol, more slowly in ethyl alcohol, and remains 

 nearly constant in acetone. All of these facts are in accord with the 

 view that this band is due to simple solvates. We should expect the 

 power to form solvates to be greater for methyl alcohol than for ethyl alco- 

 hol, and greater for ethyl alcohol than for acetone. In ethyl alcohol 

 and acetone at ordinary temperatures most of the solvates are probably 

 simple enough to absorb in the red, while in methyl alcohol this is 

 the case only at elevated temperatures or in concentrated solutions. 



The nickel absorption bands are similar in their behavior to the 

 green band of cobalt. The absorption of nickel salts seems to be 

 largely a function of the nickel atom. The widening of the band 

 X 3960, with concentration and with hydrating agents, indicates that 

 the simplest hydrates have a somewhat different absorption from the 

 more complex. The ultra-violet absorption of copper salts decreases 

 rapidly with dilution, when we keep the product of depth of layer and 

 concentration constant. This would indicate that this absorption is 

 not due to the ions, but must be due in some way to the molecules. 

 The absorption decreases with the dilution, even when the molecules 

 in the path of the light are kept constant. This would indicate that 

 the absorbing power of molecules is affected by the surroundings. 



The increase in the absorption with concentration when the mole- 

 cules are kept constant might be due to the formation of molecular 

 aggregates or might be due to solvates. To decide between these two 

 alternatives we must take into account the effect of rise in tempera- 

 ture on the absorption. Rise in temperature increases the absorption, 

 but rise in temperature breaks down the molecular aggregates. There- 

 fore, this absorption can not be due to aggregates. Solvates become 

 simpler both by rise in temperature and by increase in the concentra- 

 tion of the solution. Both should produce the same effect on the 

 absorption if this absorption is due to simple solvates, and such is the 

 fact. We must therefore conclude that the ultra-violet absorption of 

 copper salts is due to simpler hydrates. 



For equal concentration the ultra-violet absorption of copper salts 

 is least in the aqueous solutions, and increases as we pass from methyl 

 to ethyl alcohol. Further, the change in this absorption with dilution 

 is greatest for the aqueous solutions, and decreases as we pass to methyl 



