B Y CLUA VA GE, ETC. 29 



In 1858, M. Landerer, of Athens, discovered 

 that an organic salt, Valerate of quinine, becomes 

 phosphorescent whilst it is being powdered in a 

 niortar. The light emitted, which is very strong at 

 first, becomes feeble as the pulverization proceeds, 

 and ceases altogether when the crystals are reduced 

 to powder. When the crystallization of fluoride of 

 sodium takes place in a dark room, this salt is 

 seen to twinkle with phosphorescent light. The 

 same is observed when sulphate of soda and sul- 

 phate of potash crystallize together. Waechter 

 has observed that chlorate of baryta crystallizes 

 from its solution in long rhombic prisms with pro- 

 duction of light. 



A most interesting production of light was ob- 

 served and published ( ( Journ. des Sc. Physiques 

 et Chimiques/ de M. de Fontenelle), by Professor 

 Pontus, in 1833, who showed that a vivid spark 

 is produced when water is made to freeze rapidly. 

 A small glass globe, terminating in a short tube, 

 is filled with water, the whole is covered with a 

 sponge or cotton-wool imbibed with ether, and 

 placed in an air-pump. As soon as the experi- 

 menter begins to produce a vacuum, the ether 

 evaporates, and the sponge or cotton-wool dries, 

 the temperature of the water descends rapidly. 

 But some instants before congelation takes place, 

 a brilliant spark, perfectly visible in the daytime, 

 is suddenly shot out of the little tube that termi- 



