﻿Absorption Spectra and the Solvate Theory of Solution. 731 



apparatus used, reference must be made to the earlier pub- 

 lications * of some of the results of this work. It should be 

 stared that the grating spectroscope alone has been used. 



The work begun by Jones and Uhlerf had to do with 

 three problems. They studied the effect on absorption 

 spectra : of changing the concentration of the solution, of 

 the addition of a dehydrating agent in the form of a second 

 salt, and of the addition of water to non-aqueous solutions 

 uf the salt in question. 



The results of this work were all interpretable in terms of 

 the solvate theory of solution, and in terms of no other 

 generalization; but it could not be said that any direct 

 evidence for the theory was furnished by this earlier work. 



The investigation which followed, however, furnished very 

 direct evidence for the solvate theory. Jones and Anderson X 

 studied the absorption spectra of about 1200 solutions ; 

 including salts of cobalt, nickel, copper, iron, chromium, 

 neodymium, praseod} T mium, and erbium in water and the 

 alcohols as solvents. They varied in some cases the total 

 number of ions in the path of the beam of light ; in other 

 cases the number of ions was kept constant and the number 

 of molecules in the path of the light was varied. This was 

 all accomplished by changing the concentration of the 

 solutions and suitably changing the depth of the solution 

 through which the light passed. By keeping every thing- 

 constant except some one of these factors, and observing the 

 effect on the various lines and bands when a given one of 

 these quantities was varied, it was possible to determine what 

 produced a number of the lines and bands. 



Thus, the ultra-violet absorption of cobalt salts was shown 

 to be due to undissociated molecules or something contained 

 within them, while the green cobalt band was produced by 

 the cobalt atom or something contained within it. 



The absorption spectra of solutions of nickel salts were due 

 chiefly to the nickel atom ; and, similarly, the absorption of 

 copper salts in the red end of the spectrum. 



The A, 3300 band of cobalt disappeared quickly with 

 increase in dilution, even when the total number of molecules 

 in the path of the beam of light was kept constant. It 

 became more intense with rise in temperature. This band, 

 obviously, could not be produced by ions molecules, or atoms, 



* Carnegie Institution of Washington, Publication!* nos. tiO, 110, 130, 

 and 160. Amer. Them. Journ. xxxvii. p. 126 (1007) : xli. pp. 163, 278 

 (1900); xliii. pp. 37,97(1910). 



t Ibid. xxx\ii. p. 126 (1007). Phil. Mag. xix. p. 566 (1010). 



J Carnegie Institution of Washington, Publication no. 110- 



