274 Pearsall on the Communication of 



and examined after a lapse of fifty days. They still possessed 

 increased phosphorescence : in some the order of tints was 

 still the same; in others a change was observed, and the 

 orange tints evidently prevailed. 



On the Influence of Structure upon Phosphorescent Bodies. 



As the mineral phosphate of lime, called APATITE, possesses 

 naturally an intense degree of phosphorescence, other forms of 

 this chemical compound were experimented with. 



Phosphate of lime was precipitated by alkalies from solution 

 in muriatic acid : it was collected, and allowed to aggregate by 

 carefully drying it ; the temperature was afterwards raised, but 

 there was no appearance of light. It was then calcined : small 

 compact hard lumps and powder were electrified by twenty 

 discharges from two feet of surface, but no phosphorescence 

 was induced. 



Apatite was in like manner dissolved, precipitated, dried, 

 calcined, and electrified, but no phosphorescence was induced. 



Phosphate of lime calculus was electrified and heated, rib 

 light appeared : being calcined to redness, twelve discharges 

 were made ; the fragments when heated evolved differently 

 coloured light; the yellow, green, and orange colours were 

 increased by twenty discharges, the light also being rendered 

 stronger. It is evident that change of texture would result 

 in this case by the destruction of the organic matter diffused 

 through the earthy mass. 



As these bodies might be regarded as identical in chemical 

 respects, their great difference in phosphorescent power is due, 

 in some way, to the mechanical condition of the bodies : cohe- 

 sion, arrangement of particles, texture, and extent of surface, 

 are all circumstances which may influence the result. 



The solidity of fluor spar was destroyed by levigation, but 

 phosphorescence was evident when the powder was heated. 



Crystallized fluor spar (fluoride of calcium) was powdered 

 and dissolved in muriatic acid, from which it was preci- 

 pitated by ammonia, then dried, and calcined at a red heat, 

 without exhibiting light. Electricity also did not confer 

 phosphorescence. 



