URANIUM SALTS. 



119 



Phosphorescent bands. 



The bands of the nitrate and acetate come at about the same place in 

 the spectrum, whereas the chloride and sulphate bands are farther towards 

 the red. H. Becquerel ' finds that at low temperatures the phosphorescent 

 uranyl bands become quite sharp in the same way that absorption bands 

 do. For uranyl nitrate he gives the following table: 



Further work has recently been published by J. Becquerel and Onnes. 2 

 At the temperature of solid hydrogen the intensity of emission is not dimin- 

 ished and the bands which existed at liquid-air temperatures undergo 

 further subdivision. Lowering the temperature shifts the emission bands 

 towards the violet. For instance, for the double sulphate of uranyl and 

 potassium: 



The displacement of the phosphorescent bands caused by lowering 

 the temperature from 20 to 14 is very small, and it is quite possible that 

 as the temperature is lowered the bands approach asymptotically a limiting 



Compt. rend., 144, 459-462 (1907). 



2 Conimun. Phys. Lab., Univ. Leyden, N 06. 110, 111. 



