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ON THE EFFECTS OF ELECTRICITY UPON MINERALS 

 WHICH ARE PHOSPHORESCENT BY HEAT. 



BY THOS. J. PEARSALL, 



Chemical Assistant in the Laboratory of the Royal Institution. 



D 



(URING some experiments, made to observe the effects 

 of an electrical discharge passed over the variety of fluor 

 spar called chlorophane, which is peculiarly distinguished for 

 its phosphorescence when heated, I remarked certain appear- 

 ances, which are detailed in the following investigation. 



When the electrical discharge is passed over fragments, or 

 the coarse powder of a very fine specimen of chlorophane, a 

 brilliant green light is produced. On repeating the experi- 

 ment many times, I found the phosphorescence re-occurred 

 with each repetition of the discharge, and was even sensibly 

 strengthened by the operation . 



This striking appearance induced me to suppose that even 

 such minerals as had been deprived of the power of phospho- 

 rescing by calcination might have it restored by virtue of 

 electric action, and led me to make the following experiments, 

 which will shew how far this supposition was confirmed. 



A specimen of chlorophane, possessing naturally the pro- 

 perty of phosphorescence in a very high degree, was first 

 subjected to the action of heat. The light emitted was co- 

 loured, first bluish-green, very bright ; then pinkish, blending 

 with pale-whiteness as it became red-hot, when it lost all 

 peculiar light. 



A portion of the same mineral, which had been calcined, 

 and thus deprived of its power of phosphorescence, was then 

 subjected to a single discharge from a small Leyden jar, of 

 about a square foot of coated surface. The substance became 

 luminous during the passage of the electricity, producing a 

 green light. 



On the application of heat to the portion thus electrized, it 

 was found to be phosphorescent, and to emit a green light 

 nearly as strong as a portion of the mineral in its natural state, 

 with which it was compared. This experiment was repeated, 

 and always with constant results, 



