On Phosphorescence. 7 



snlphnric acid. Small pieces of causlic barytes as dry a3 

 it was possible lo procure them, emit no light when thrown 

 into this acid, and are not at first dissolved in it. When 

 moistened by the breath simply, they give out light at the 

 moment of touching the acid, and are converted into sul- 

 phate of barytes. When too much moistened they again 

 become dull. Lime and stronlian exhibit the same phte- 

 nomena. According to this remark as to the quantity of 

 •water necessary to phosphorescence, the autlior made sul- 

 phates and muriates of soda and of potash and fluate of 

 lime, deprived of ail phosphorescence, because they con- 

 tained no water, by using alcoholic solutions, instead of 

 aqueous solutions, in the ordinary operations of precipita- 

 tions or double decompositions which give birlli lo tliese 

 salts. It is to be remarked, that the salts which have lost 

 by calcination their phosphorescence, with the water which 

 they contained, take up part of it again after bavin??; under- 

 gone igneous fusion. It is the same with glass and metallic 

 scales become dull by calcination, which shine once more 

 on the warm supporter after having been fused. 



The examination which the autlior afterwards enters into 

 of the relations between electricity and phosphorescence by 

 elevation of temperature, presents facts of great interest. 

 An)ong' the metallic powders, those of z'nc and antimony 

 are the most phosphorescent, and those of gold and silver 

 are least so. All of them, when prepared m damp weather 

 with all the precauiions most proper forniaking them shine, 

 are inphosphoreseent, as well as the metallic oxides. In 

 dry weather the contrary is the case. Antimony even in 

 very dry weather loses us jibosphoreseenec, if it be pounded 

 and stronidy rubbeil against a metallic mortar. In an in- 

 sulated vessel, it acquires a high degree of ph.o'iphorcscent 

 properties. Glass pounded in dry weather is more luminous 

 than when the operation has been performed in a damp 

 atmosphere. It loses almost all its phosphorescence when 

 pouiulcd in wet linen; but it does not lose it, like antimony, 

 when the operation is performed in a metallic mortar, be- 

 cause there is no transmission of the electrical fluid. It is 

 not the ease with adular spar, the powder of which does 

 not retain a fine phosphorescence unless it has been pre- 

 pared in an insulating mortar. In all cases where a vessel 

 of this nature has been employed, the author took care to 

 use one with an insulating pest'e. in the last place, glass 

 rendered dull by calcination resumes all its phospl-.orc- 

 sccnee si lu-n exposed on an insulating supporter bctwceii 

 the two balls of an electrical excilator, after it has received 

 A 4 four 



