Electricity on Minerals. 81 



In these, as well as in the preceding experiments, portions of 

 the same calcined mineral, but not electrified, were heated at 

 the same time ; but in no instance did the non-electrified sub- 

 stance evolve light. 



In this table, it will be observed that Nos. 1, 2, and 3, did 

 not possess light in their natural state, but light was imparted 

 to them by electricity. 



No. 4 possessed alight of a faint colour, which became whiter 

 as it was heated, but its conferred light ended in purple. 



Those numbered from 5 to 10 had light restored to them, 

 which differed, however, in colour from their previous natural 

 phosphorescence. 



11 and 12 had light given to them. 



No. 13 had light restored to it. 



I now proceed to some remarks on colour given to fluor 

 spar by electricity. In some experiments with the white 

 fluors which had a yellowish tinge, it was observed that, after 

 the powder was electrified, or when six or seven discharges 

 had been made through a piece of the mineral, that a difference 

 was perceptible between the electrified and the natural mineral, 

 the electrified substance having a bluish tint, whilst the other 

 was white. The phosphorescence was also stronger, where the 

 tint thus given was most obvious. 



As the colour had been most decidedly given by electricity 

 to some portions of a crystallized mass of dark compact purple 

 fluor, which had been rendered colourless by heat, some white 

 pieces were selected and broken ; one portion had twelve dis- 

 charges passed over and through it, which produced a light blue 

 colour, very decided upon the edges and angles of the laminae, 

 especially toward the exterior. Both fragments were then 

 heated ; that which had been electrified gave a pale blue light 

 of short duration, and, when cold, had lost its blue tint; the 

 other portion evolved no light. 



The fact, also, was well shewn by confining the electrical 

 effects to one extremity of a colourless portion ; a perceptible 

 tint was caused by a few discharges. 



Some splinters and fragments were placed in a small heap, 

 inside a glass tube, open at both ends, and between the two ends 

 of the wires of the discharger, which were about an inch apart, 



VOL. I. OCT. 1830. G 



