PHOSPHORESCENCE SPECTRA. 



49 



sufficient to be detected. Another sample so prepared as to reduce the 

 amount of water to a minimum did, however, exhibit phosphorescence 

 of measurable duration. This preparation, so slow was its rate of 

 flow, might be regarded as a plastic solid rather than a viscous liquid. 

 A bead of microcosmic salt, colored in the usual manner with uranium 

 oxide, was comparable in its phosphorescence with canary glass. 



URAMYL AMMONIUM SULPHATE 



I'* 



50 



40 



30 



20 



10 



.001 



.002 



.003 



SEC. 



FIG. 40. 



It appears that the persistence of luminescence is due to the con- 

 sistency of the substance and disappears as the fluidity increases ; also 

 that the peculiar type of decay here described is common, not only to 

 the crystalline uranyl salts in general, but also to the gelatinous forms, 

 as in this double salt, and to substances in which uranium appears in 

 solid solution, as in the case of the canary glass. 



THE THIRD PROCESS. 



E. Becquerel, 1 in the course of his great pioneer work on phosphores- 

 cence, made a number of observations on the uranyl salts and on 



1 E. Becquerel, Annales de Chimie et de Physique (3), LXII, p. 1. 1861. 



