28 PHOSPHOEESCENCE 



friction of mercury in the vacuum of the baro- 

 meter tube produces a phosphorescent light. 



When oxygen gas or air are compressed sud- 

 denly in a piston, heat alone is produced. The 

 light seen in this experiment is owing to the com- 

 bustion of some of the oil of the piston, as proved 

 by Thenard. "When the piston is imbibed with 

 water, no light is perceived ; and M. Saissy, of 

 Lyons, has proved that oxygen alone, by its com- 

 burent power, is the cause of this light. 



If chlorate of potash, fluor-spar, feldspar, sugar, 

 etc. be struck in the dark, or ground down in a 

 mortar, they present very vivid phosphoric radia- 

 tions. With crystallized substances which are 

 cleavable, i. e. easily divided into thin laminae, this 

 phosphorescence is very remarkable ; with sugar, 

 for instance, each fissure produced by the shock of 

 the pestle gives birth to a streak of light which 

 lasts for an instant, and when a certain quantity 

 of any of these substances is ground down rapidly 

 in a mortar, the whole mass appears as if on fire. 

 This beautiful phenomenon is exceedingly striking 

 when transparent feldspar is experimented upon. 

 It has lately been discovered that dry hypophos- 

 phites of lime, soda, etc., become phosphorescent 

 when shaken or stirred in the dark. (Note. 

 These salts are apt to explode violently when 

 evaporated to dryness at too high a temperature. 

 Tuson, in ' Chemical News/ August, 1860.) 



