176 DISCUSSION OF EVIDENCE. 



of the existence of "solvent bands" in the absorption spectra of neo- 

 dymium and praseodymium salts in water and the alcohols. The 

 question arose, was this a phenomenon peculiar to these salts, or does 

 the solvent play a general role in the absorption of light by solutions? 



Jones and Strong attempted to answer this question by studying a 

 large number of salts in a large number of solvents. They worked 

 especially with salts of neodymium and uranium, because these sub- 

 stances had sharp absorption lines and bands whose positions could 

 easily be determined with reasonable accuracy. Work was done not 

 only with uranyl salts, but with uranous. A convenient method was 

 found for reducing uranyl salts to the uranous condition, and uranous 

 salts were found to have very sharp absorption lines. 



Uranyl chloride was studied in the following solvents : water, methyl, 

 ethyl, propyl, isopropyl, butyl, and isobutyl alcohols, glycerol, ether, 

 methyl ester, and formamide. A comparison of the wave-lengths of 

 the absorption lines and bands in these different solvents brought out 

 the fact that the wave-lengths of some of the lines and bands differed 

 considerably in the different solvents. The results here showed that 

 the solvent unquestionably has much to do with the absorbing power 

 of the solution, "solvent bands" appearing very frequently. The 

 wave-lengths of a few of the different lines and bands of uranyl chloride 

 in the above-named solvents have been tabulated, 1 and the table is 

 here reproduced. It shows at a glance the different wave-lengths of 

 the several lines and bands compared. 



TABLE 51. Wave-lengths of uranyl chloride absorption lines. 



In water XX 4025, 4170, 4315, 4460, 4560, 4740, and 4920 



In methyl alcohol XX 4090, 4220, 4345, 4465, 4590, 4760, and 4930 



In ethyl alcohol XX 4100, 4250, 4400, 4580, 4750, and 4900 



In propyl alcohol XX 4100, 4230, 4400, 4580, 4750, and 4910 



In isopropyl alcohol... XX 4 100, 4250, 4360, 4560, 4750 



In butyl alcohol XX 4100, 4240 4390, 4560, 4750, and 4970 



In isobutyl alcohol XX 4400, 4560, 4720, and 4900 



In ether XX 4040, 4160, 4300, 4444, and 4630 



In methyl ester XX 4030, 4160, 4280, 4440, 4620, 4790, and 4920 



In glycerol XX 4025, 4140, 4260, 4400, 4540, 4720, and 5050 



In formamide XX 4450, 4650 and 4840 



The absorption spectra of uranyl nitrate in mixtures of water and 

 methyl alcohol were studied. The absorption in water was much less 

 than in pure methyl alcohol. The addition of water to the alcoholic 

 solution diminished the absorption. In the mixtures of water and 

 methyl alcohol the absorption bands became very broad. A study 

 of these broadened bands showed that they were the "alcohol" and 

 "water" bands coexisting, and that one set of bands was not simply 

 the other set shifted in position. The importance of this fact has 

 already been referred to in the work of Jones and Anderson. It shows 

 that the "alcohol " bands are fundamentally different from the "water " 



'Journ. Franklin Inst., Dec. 1913, p. 528; also Phil. Mag., May 1912, p. 730. 



