90 A STUDY OF THE ABSORPTION SPECTRA. 



more diffuse for the chloride. Practically only the a, b, and c bands appear 

 with any strength. 



Of these, a and b are the stronger. They appear of about the same 

 intensity and are about 80 Angstrom units wide. For the bromide a is 

 considerably weaker than 6. The sulphate and nitrate, on the other hand, 

 show practically all of the uranyl bands, the bands being the strong -st in 

 the sulphate solution. In this salt solution the b and c bands are si c to 

 ten times as strong as the a band. In the nitrate this difference is not so 

 marked, and the bands appear somewhat finer than in the case of any 

 other salt. The acetate shows the greatest absorption of the salts men- 

 tioned above. Here, the a, b, and c bands are very faint. About half a 

 dozen very faint bands appear together. 



For the normal solution the ultra-violet and blue-violet bands merge 

 together and end at X 4550. For the 0.75 normal solution the blue-violet 

 band is limited by regions of absorption beyond the limits XX 4500 and 

 3900, for the 0.5 normal solution, XX 4470 and 3950, and for the 0.33 normal 

 solution, XX 4400 and 4050, the center of the band thus being at / 4200. 

 Collecting the results of their measurements of the center of this blue- 

 violet band we have: 



Uranyl chloride A 4200 



Uranyl nitrate X 4150 



Uranyl bromide X 4250 



Uranyl acetate X 4200 



Uranyl sulphate X 4180 



Therefore, for all these salts the blue-violet bands appear at th r > same 

 position. 



The band also widens with increase in concentration quite uniformly. 

 The edges of the ultra-violet band are: 0.75 normal X 3700, 0.5 normal 

 X 3670, 0.33 normal X 3650, 0.25 normal X 3630, 0.16 normal X 3600, and 

 0.125 normal X 3570. 



The positions of three of the uranyl bands (a, b, and c) were measured. 

 On account of the extreme faintness of c the result for this band is not very 

 accurate: a, 4920; 6, 4740; c, 4560; d, 4460; e, 4315; /, 4170; y, 4025. 



In addition to the bands already given, uranyl chloride has several 

 remarkabfy fine bands in the green. These bands are not more than 5 aig- 

 strom units wide and were first seen on spectrograms made on the W ratten 

 and Wainwright red-sensitive films. They appear only for aqueous solu- 

 tions of uranyl chloride. The addition of calcium or aluminium chloride 

 causes them to disappear. They do not appear in the alcoholic solutions. 

 Uranyl sulphate shows the same bands at about the same position as the 

 chloride but much weaker too weak to be separated. The wave-1 -ngths 

 are as follows: XX 5185, 5200, 6000, 6020, 6040, and 6070. 



So far as the writers know, this is the first time that these bands have 

 been noticed in aqueous solutions. Uranyl salts give a spectrum of mis- 

 sion through phosphorescence, and this spectrum appears to be a continua- 

 tion of the absorption spectra to longer wave-lengths. Becqu'r 1 ' has 



1 Mem Acad. Sci., 40 (1872). 



