AFTER INSOLATION. 13 



submitted to many and varied experiments. It is 

 best obtained by the calcination of pulverized 

 sulphate of baryta, made into a firm paste with 

 common gum. It should be preserved in a bottle 

 which closes hermetically with a glass stopper. 



When such a bottle and its contents are ex- 

 posed to the rays of the sun, or even to daylight, 

 for a certain time, and then taken into a dark 

 room, the sulphuret of barium is seen to be beau- 

 tifully phosphorescent, or to shine like common 

 phosphorus, and the phenomenon will sometimes 

 last a whole hour. The most intense cold does not 

 affect this phosphorescence, and it manifests itself 

 precisely in the same manner whether the sulphuret 

 be placed in vacuo or in the air. 



When nitrate of lime is melted for ten minutes 

 in a crucible, it leaves a residue which manifests, 

 to a less extent, the same phosphorescent property. 

 This residue, which is nothing more than pure 

 lime, or a mixture of lime and nitrite of lime, was 

 known for some time as f ' Baudouin's phosphorus" 

 A like phenomenon is observed with calcined 

 shells. 



Sulphuret of calcium possesses the same phos- 

 phorescent qualities as the sulphuret of barium 

 alluded to above ; hence the former is sometimes 

 known as " Canton's phosphorus. 33 Canton pre- 

 pared it by heating a mixture of three parts of 

 sifted calcined oyster- shells, with one part of sul- 



