GENERAL DISCUSSION OF RESULTS. 139 



pounds of the salt and solvent. The reason for this conclusion is that in mix- 

 tures of two solvents, each set of solvent bands appears; the intensity of any 

 solvent band being a function of the relative amounts of the solvents present. 

 That these compounds or solvates have a definite composition seems to 

 be indicated by the fact that for most of the neodymium, uranyl, and 

 uranous salts there appears only a single set of "solvent" bands for each 

 solvent; and in mixtures of these solvents in most cases but two sets of 

 bands are necessary to explain the results. The persistence of solvent 

 bands varies quite widely for the different solvents, and appears to be great- 

 est for water and glycerol and less for the alcohols. This persistence of 

 any one solvent band seems to be the same for quite widely different 

 salts. There are, however, some cases where it may be possible that inter- 

 mediate solvates are formed. Neodymium chloride dissolved in mixtures 

 of water and glycerol seems to indicate that the "water" band X 4274 

 gradually shifts to the "glycerol " bands. 



Probably no salts show more characteristic bands than some of the ura- 

 nous salts in the various solvents: water, the alcohols, acetone, and glycerol. It 

 seems probable that the absorbers are the same for the corresponding 

 bands of any two "solvent" spectra. An important fact indicating this 

 is given by Becquerel, who found the Zeeman effect to be the same 

 when different solvents of the same salt were used. It is generally conceded 

 that at higher temperatures solvates are broken up. At present, work is 

 being done on solutions containing mixtures of two solvents in such pro- 

 portion as to give both sets of solvent bands. As the critical temperature 

 of one solvent is approached, according to the foregoing theory, the bands 

 of that particular solvent should disappear. In many cases the two sets 

 of solvent bands differ not only in wave-lengths but also in intensity, 

 and in the number of components. Of all the bands of the neodymium 

 absorption spectra, the "water" band X 4274 is one of the strongest, and 

 one that is freest from neighboring bands. Yet, in different solvents this 

 band may become a doublet, a triplet, or may even apparently break up 

 into a whole series of bands. It is quite certain that when the mechanism 

 of these changes is known, our knowledge of chemical compounds will be 

 increased very greatly, and it is very important that gradual changes of sol- 

 vent or salt may be made at low temperatures where the bands are much 

 sharper, and work is now in progress on this problem. 



In some cases it is possible to break up the absorption bands by 

 chemical methods into very fine bands. A very striking example is the 

 case of uranyl and uranous salts in acetone solutions. The uranyl salt in 

 acetone gives six bands in the region k 5000 that are characteristic of 

 acetone solutions. By the addition of hydrochloric acid to an acetone 

 solution the uranyl bands are broken into fine components. Several of 

 the uranyl bands become triplets and some doublets. But the most marked 

 example is the addition of hydrochloric acid to an acetone solution of 

 uranous chloride. Several very broad uranous bands are broken up into 

 a number of very fine and quite intense bands. 



One very interesting result has come to light from the examination of 

 the effect of free nitric acid on the absorption spectra of uranyl nitrate; 



