22 PHOSPHORESCENCE 



dozen electric discharges passed through non- 

 phosphorescent bodies such as marble, certain 

 varieties of apatite, etc., will give them the pro- 

 perty of becoming luminous by heat. On twenty- 

 one days of exposure to light, these substances 

 rendered artificially phosphorescent lost that pro- 

 perty again. But if kept in a dark room, they 

 retained it. The term "non- phosphorescent 

 bodies," used by Pearsall, is rather exclusive; as 

 phenomena of phosphorescence are so universally 

 spread, that scarcely any substance, if properly 

 experimented with, will prove to be non-phospho- 

 rescent in the strict sense of the word. His ob- 

 servation is, however, exceedingly remarkable. 



Some years ago M. Schonbein showed that 

 metallic arsenic becomes phosphorescent when its 

 temperature is raised to a certain degree.* I 

 imagined that antimony might present the same 

 phenomenon, but found it was not the case. 

 Stibine, or native sulphuret of antimony, I found, 

 however, to be very phosphorescent when heated 

 in a crucible to a dull -red heat. The light pro- 

 duced is white, with a slight tinge of yellow. I 

 have lately observed that copper, native sulphuret 

 of copper, gold and silver are notably phosphores- 

 cent when melted on charcoal before the blow- 



* The metallic arsenic is placed in a small glass globe, and 

 heated with a spirit-lamp. The light is emitted at the same time 

 that the characteristic garlic odour is developed. 



