2 ESSAY I. 



hardly any of its weight, and that it appeared in every 

 respect like fluor mineral which had not been burnt, only 

 that it : (1) neither showed any signs of decrepitation nor 

 phosphorescence on being heated anew; (2) that it was 

 more friable than before ; and (3) .that the green sort had 

 become reddish, and the white had lost its transparency. 



SECTION III. 



I put a piece of fluor heated to phosphorescence into cold 

 water. It immediately lost a great part of its light, retain- 

 ing, however, some glimmering for very near an hour. The 

 same thing happened when it was put into acids, instead of 

 water ; but the solution of fluor in acids, though made by 

 boiling, showed no kind of phosphorescence. A piece of 

 fluor in its luminous state, suspended by means of a brass 

 wire in the vacuum of an air-pump, continued to emit light 

 for about an hour, but it was faint during the last half- 

 hour. 



SECTION IV. 



The following experiments were made in order to find 

 whether the property of becoming phosphoric could be 

 restored to the fluor after it had been once lost. 



Fluor mineral that had been thoroughly heated was 

 stratified with powder of charcoal in a crucible, which, after 

 being well closed, was kept hot for two hours. It was then 

 taken out of the fire, cooled and heated again, but no light 

 appeared. Burnt fluor was exposed to the sunshine for a 

 whole day, and afterwards heated, with as little success. I 

 therefore conclude that its phosphorescence does not depend 

 upon a subtile inflammable matter. 





