COLOR-PHOTOGRAPHS OF THE PHOSPHORESCENCE 

 OF CERTAIN METALLIC SULPHIDES. 



By EDWARD L. NICHOLS. ^ 

 (Read April 14, igi6.) 



Among the most beautiful and interesting of phosphorescent sub- 

 stances are the sulphides prepared and described several years ago 

 by Professors Lenard and Klatt/ of Heidelberg. These substances 

 which consist of the sulphide of barium, calcium or strontium, with 

 a small admixture of some metallic salt — usually of copper, bismuth 

 or lead — are prepared by heating with a flux such as sodium sul- 

 phate, sodium borate or lithium phosphate. After exposure to day- 

 light or to violet or ultra-violet rays they glow for a considerable 

 time with characteristic colors which depend upon the particular 

 mixture used. 



Variations in the brightness of phosphorescence with the time 

 find convenient indication by means of the curve of decay and the 

 effects of temperature, etc., on the intensity are likewise capable of 

 graphic or analytical expression. These relationships have already 

 been extensively studied by the authors just cited and others and in 

 a paper read before the American Philosophical Society in April, 

 1910, I presented the results of such an investigation. The subtle and 

 fleeting changes of color which occur as the phosphorescence dies 

 away or when the substance is heated or cooled or when we compare 

 sulphides varying in composition, do not lend themselves to such 

 methods of expression. The efifects must be seen to be appreciated 

 and it seemed of interest to try to record some of the phenomena by 

 means of color photographs. 



Now the glow of even the brightest of these phosphorescent sub- 

 stances is in reality of very low intensity and color-plates such as the 

 Lumiere plates used in the experiments to be described are relatively 



1 Lenard and Klatt, Annalcn dcr Pltysik, 15 (1904), also Lenard, ibid., 

 31, p. 641 (1910). 



494 



