PHYSICS. 341 



A New Form of Urantl Nitrate. 



Dr. F. E. E. Germann, in a study based upon work of Dr. Howes^ 

 on the fluorescence of frozen solutions, has isolated a new hydrate of 

 uranyl nitrate having 24 molecules of water of crystallization. The 

 crystalhne form of this substance, which melts at —35° C.=t, and the 

 relations of its spectrum to the hydrates with 1, 2, 3, and 6 molecules,^ 

 are under examination. Dr. Germann's method, which involves the 

 determination of the curves of cooUng of solutions of various degrees of 

 concentration, will be extended to other uranyl compounds. 



The Structure of Broad Fluorescence Bands. 



The fluorescence spectrum of the uranyl salts, as has been repeatedly 

 demonstrated in the course of our investigations, is a complex of equi- 

 distant components. This structure has been shown to be common to 

 all the compounds thus far studied and has been considered as perhaps 

 peculiar to them. Whether a similar structure exists in the case of 

 other fluorescence spectra is difficult to determine, especially because 

 in the usual broad-banded type the merging of the components is 

 almost complete and no method of resolution has as yet been discovered. 

 Evidence of complexity, however, has been found from time to time. 

 A study of existing data on the fluorescence of commercial anthracene, 

 using the measurements made by Miss McDowell, who photographed 

 the visible and ultra-violet bands, shows that this spectrum is made 

 up of two partially overlapping complexes, one due to the fluorescence 

 of chrysogen, ha\'ing a constant frequency interval of about 131, and 

 the other due to anthracene with an interval of about 121. 



Dr. Howes, who has recently completed a discussion of McLennan's 

 data on the ultra-violet fluorescence of iodine vapor,^ finds that all the 

 bands of this complicated spectrum may be arranged, like the bands of 

 the uranyl spectra, in series having constant frequency intervals ; also 

 that there is a strikingly symmetrical grouping of the bands around 

 certain mercury lines which were employed as sources of excitation. 



An analysis of very careful and detailed spectrophotometric measure- 

 ments of the broad bands of the phosphorescence sulphides has revealed 

 a similar structure in these spectra.'* They are found to consist of 

 components forming one or more series of constant frequency, as in the 

 uranyl spectra, but so closely overlapping as to give the appearance of 

 a single homogeneous band. It is proposed to extend such observa- 

 tions to other fluorescent materials in order to determine whether this 

 is the general underlying character of luminescent radiation. 



'Howes: Physical Review (2), vi, p. 192 (1915). 



^Nichols and Merritt: Physical Review (2), x, p. 113 (1917). 



^J. C. McLennan: Proceedings Royal Society, lxxxviii, p. 281, and xci, p. 23. 



^Nichols: Proceedings of Amer. Phil. Society, lvi, p. 268 (1917). 



