918 Transactions of the American Institute. 



a little tank of ammonio-cupric-sulphate, and is allowed to fall upon a 

 fluorescent body at C, and the light which is emitted by this last 



examined by a spectroscope, D, we see in 

 the case of some substances, such as solu- 

 tions of quinine, aesculine, fustic, stramo- 

 nium and the like, only a continuous 

 spectrum. But in the case of the uranium 

 salts, of thallene and petollucene, either 

 in the solid state or in solution, of bi- 

 chloranthracene, in solution, etc., we find 

 spectra made up of a series of bright 

 - lg ' bands, as a rule, very regularly disposed. 



In the case of the uranium salts these are very remarkable, both 

 for the regularity and diversity of character which they present. 



Plate II shows a number of these, which I have observed and care- 

 fully measured. 



At the time when these observations were made it had been observed 

 by Stokes and Becquerel that a difference existed between the fluo- 

 rescent spectra of two or three uranium salts, but these differences 

 had neither been measured nor in any way accurately described. 

 Yery recently, Becquerel has published in the Comptes Rendus, vol. 

 75, p. 296, an extract from some as yet unpublished memoir, in 

 which the subject is much more fully discussed, but yet in a manner 

 far from perfect, since many of the results announced as general are 

 only true with respect to a few examples, and some of the most 

 remarkable characteristics of certain salts are overlooked. 



A glance at the plate will show how easy it is by this means to dis- 

 tinguish between most of these salts, and how, as in the case of the 

 mixed acetate and double acetate, it is possible to recognize the mixed 

 character of the body and the factors of which it is composed, and 

 this without so much as opening the bottle in which the substance is 

 contained. 



I would draw attention especially to the curious arrangement of 

 bands in the chloride, with the sharp, dark lines running through the 

 centers of the bright bands, and to the narrow bands found in the red 

 portion of the sodio-uranic acetate, and also in many of the other 

 double acetates. 



In addition to their fluorescent spectra these salts show, as a rule, 

 very marked absorption bands, which are indicated on plate I, A in 

 the various spectra by the dark lines above 9 of the scale. 



Though these are shown on the same drawing with the fluorescent 



