O/i Phosphorescence. 5 



to possess this property if it has prcvioLisly undergone a 

 stronger heat: but it preserves that of becoming Uuiiinou.s 

 on a body still holler. The same substanee subjected se- 

 veral times successively to a temperature of 300° gave a 

 fine light which lasted at the lirst projection 30", at the 

 second 13", and at the third lo'''. Fii'tcen other successive 

 projections gave a light of the same duration and intensity 

 as the fourth. Vitreous bodies lose their phosphoric pro- 

 perties with great difficulty : for this purpose they must he 

 calcined strongly for half an hour, or even an hour, while 

 all the metallic bodies, their phosphorescent oxides, and 

 all the metallic salts, lose it on the first projection in au 

 iron spoon slightly heated. Lime, barytes, strrmtian, mag- 

 nesia, alumine, and silex, cannot lose iheir phosphoric pro- 

 perly, whatever may be the degree of heat to which they 

 are subjected. These earths heated at first to 100" or 123" 

 do not omit any light on a support heated to 250°, whereas 

 they shine well if thrown upon it cold. The carbonates of 

 lime, barytes, and stronlian, lose their phosphorescence upon 

 a moderate calcination, and resume it afterwards if we cal- 

 cine them to whiteness for half an hour, which seems to 

 arise from their then passing partly to the state of caustic 

 alkaline earths. All the earthy or alkaline salts lose their 

 phosphorescence upon calcination : those which are solu- 

 ble resume it in proportion to their solubility, when ihey 

 remain exposed to the air, particularly if humid. The in- 

 soluble salts, in the same way as quartz, adular, glass, &c. 

 lose it entirely. The vegetable and animal substances lose 

 it in the same way, but only when reduced to the state of 

 charcoal. 



The author, after having explained these facts, passes to 

 some general considerations. He has ascertained that the 

 most phosphorescent bodies are those, in the composition 

 o{ which some of their elements have passed from the 

 gaseous or licjuld to ilie solid state. He remarks that the 

 light of phosphorescence is, like every other, decomposable 

 by the help of a prism into rays of various colours. It is 

 of itself coloured generally in blue in all the phosphore- 

 scent bodies which do not contain metallic oxides, and be- 

 oomes so in bodies which contain them, — like the powder of 

 calcined bones, the light of which is yellow, the phosphate 

 of lime of Estrcmadura, and the green fluatc of lime, which 

 present a green light, when we free them from the oxides 

 which ihey contain, by dissolving ihcm in the muriatic acid 

 and precipitating them with ammonia. 



The phosphorescence of mineral substances undergoes no 

 A 3 Yariatiou 



