296 JONES AND ANDERSON— ABSORPTION SPECTRA OF [April 15 



centration, and the two are nearly identical, throughout, excepting 

 for the fact that the absorbing power of the bromide appears to be 

 somewhat greater than that of the chloride. 



2. Solutions of the salts in non-aqueous solvents give spectra 

 which are not only different for different salts, but the spectrum 

 of any one salt is different in the different solvents. An apparent 

 exception is the spectrum of neodymium or praseodymium chloride 

 in methyl and ethyl alcohols, which are almost exactly alike. 



3. When a salt like neodymium chloride is dissolved in mixtures 

 of water and one of the non-aqueous solvents, and the relative 

 amounts of the two solvents in the mixture is varied, no marked 

 change in the spectrum is observed when the amount of water is 

 changed from 100 per cent, to about 15 or 20 per cent. As the 

 amount of water is still further reduced we find that the solution 

 gives a spectrum which consists of a superposition of the spectra 

 belonging to the aqueous and the non-aqueous solutions ; the former 

 decreasing in intensity while the latter increases as the amount of 

 water is decreased. The composition of the mixed solvents, which 

 will show the two spectra with about one-half their normal inten- 

 sity, depends upon the concentration of the salt in solution ; and a 

 constant ratio between the number of molecules of water and those 

 of the dissolved salt were indicated by the experiments, this ratio 

 having the value 10. 



Praseodymium chloride, dissolved in mixtures of water and 

 methyl or ethyl alcohol, shows in general the same kind of change 

 in the spectrum as neodymium chloride ; but in addition there appears 

 in the alcoholic solutions an entirely new band having no analogue 

 in the aqueous solution. In the former this new band in the ultra- 

 violet is by far the most intense in the entire spectrum. It disap- 

 pears entirely on addition of water, having about half its normal 

 intensity for a half normal solution when the water content of the 

 solvent is about 8 per cent. 



These facts seem to us inexplicable on any other hypothesis than 

 the one we have made, namely, that when a salt of one of these 

 elements is dissolved in any solvent, both the molecules of the salt 

 and the ions formed from these become sohated, that is, they com- 

 bine with a certain number of molecules of the solvent. While in 



