SALTS OF C( PER. 



57 





In general, the absorption spectrum >f copper salts in the region of 

 the spectrum investigated is much simpl than that of cobalt salts, inas- 

 much as it presents only two or at most t ee absorption bands. Of these, 

 only the one at A 4730 in acetone solution lies wholly in the spectral region 

 studied; the band in the ultra-violet is hat might be termed one-sided, 

 no region of transparency on its more i rangible side having ever been 

 found. The band in the red is, however, rictly a band, a region of trans- 

 parency existing in the infra-red. The I mvior of this band throughout 

 strongly suggests the green band of cobalt alts in solution, while the ultra- 

 violet absorption is somewhat different rom anything we have found 

 thus far, resembling more nearly the ab rption of iron salts, to be dis- 

 cussed in the next chapter. 



Since the absorption in the ultra-viole lecreases rapidly with dilution, 

 when the product of concentration and >;pth of layer is kept constant, 

 it seems reasonable to suppose that the c< per ion has little or nothing to 

 do with it, and hence that it must be ascrnd to the molecules; but as the 

 absorption decreases with dilution, even w.;n molecules are kept constant, 

 without, however, entirely disappearing (; was the case with some cobalt 

 bands), we must conclude that the absoi'ng power of a molecule is in- 

 fluenced considerably by its immediate siroundings. As usual, there are 

 at least two possible ways of explaining he increase in the absorption 

 with concentration, when molecules are k t constant. One is to assume 

 the formation of aggregates of molecules, ad that the absorbing power of 

 the molecule is increased thereby; the oth- is to assume the existence of 

 solvates, and that the absorbing power of a lolecule decreases with increase 

 in the complexity of the solvate. To detle between these two possible 

 explanations we need only take into accoui the change in the absorption 

 produced by a rise in the temperature of 1 solution. This change is the 

 same qualitatively as that produced by ncreasing the concentration. 

 Molecular aggregates are broken down by ;e in temperature, and hence, 

 by the assumption made above as to the feet of aggregates on absorp- 

 tion, this should decrease the absorption in.-ad of increasing it. We must 

 conclude, therefore, that the change in th absorption is not due to the 

 formation of aggregates. 



Solvates are made simpler both by in^ca --H'nn nnd 1>\ 



rise in temperature; and, accordingly, frou 

 regarding the effect of complexity of solval 

 should produce similar differences in the 

 accordance with observed facts. We coi 

 violet absorption of solutions of copper 

 cules of the dissolved salt, and that t 1 

 is decro^ ^f -^y of 



. 

 uding 



for 



jr B, the 

 the depths 



j made to the light 



decreases somewhat with 

 g to 140 A.U., and in B 



59 



