276 



NICHOLS— EFFECTS OF TEMPERATURE 



[April 22, 



case of the zinc sulphide, for example, the longest duration observed 

 was at — 40° but there is evidently another maximum at some 

 temperature above that of the room and still another at or below 

 the temperature of liquid air. The curve for Ba Bi K shows a 

 very pronounced and remarkable maximum at — 132°, above and 

 below which temperature the duration of phosphorescence falls off 

 with great rapidity. Between — 40° and — 80° the duration is so 

 short that measurements can scarcely be made with this apparatus. 

 In the case of the third compound in question (barium sulphide with 



.Soo^ 



Fig. 10. Fig. ii. 



Fluorescence of solid anthracene. 



copper and lithium as the active metals), see Fig. 9, the duration of 

 phosphorescence falls off as the temperature diminishes until at 

 about — 60° it is difficult to observe the existence of any phos- 

 phorescence whatever. The fleeting glow at these temperatures ap- 

 pears of a different color from that observed either at higher or 

 lower temperatures. As the temperature of liquid air is approached 

 the duration increases again until it becomes measurable. It reaches 

 a maximum at about — 160° after which it begins once more to 

 decrease. 



