PHOSPHORESCENCE SPECTRA. 



SOLID SOLUTIONS AND SEMI-FLUIDS. 



47 



The uranyl salts differ from nearly all if not all phosphorescent sub- 

 stances hitherto studied. We do not have, as in the phosphorescent 

 sulphides, the preparations of Waggoner, the ruby, etc., to deal with a 

 trace of active material in solid solution, but with compounds that are 

 in themselves brilliantly phosphorescent. If the peculiar character of 

 the curve of decay is due to that fact it might be expected that uranium 



URANYL SULPHATE 

 URANYL POTASSIUM SULPHATE 



' 



URANYL AMMONIUM SULPHATE 



FIG. 37 



FIG. 38. 



glass, in which the active material is considered to be in a state of solid 

 solution, would have a law of decay corresponding to the prevailing 

 type for such solutions, i. e., with the first process as indicated by the 

 curve for /- 1 / 2 , and time, represented by a line of steeper slope than the 

 line for the second process. A piece of uranium glass gave, however, 

 a decay curve similar to those of the uranyl salts (see fig. 37). Another 



