278 Pearsall on the Communication of 



of chemical investigation, I maybe allowed to give some expe- 

 riments, which present this subject in a new point of view. 



The fluors are those used in the former experiments upon 

 phosphorescence ; they were all rendered white by heat. 



Green fluor from Cornwall, after calcination, was colourless, 

 nearly transparent, and in very small splinters, which obtained 

 a pink tint after thirty-two discharges of a large jar. 



Crystal of No. 2, in the first Table, appeared naturally pale 

 green by transmitted light, but blue by reflected light ; heated 

 to redness, it became colourless and opalescent : forty dis- 

 charges caused blue tints upon the edges. 



Large lemon-coloured crystal of fluor was opaque white 

 after calcination ; thirty-six discharges produced decided blue 

 and lilac colours. 



Cumberland cubic fluor (No. 5.) was purple by reflected 

 light ; the white opaque calcined fragments were rendered 

 decidedly pink by thirty-six discharges. 



No. 6. The purple cubic fluor from Berealston, Cumber- 

 land, when viewed by transmitted light, showed bands of blue 

 and violet ; by calcination a difference in structure was evi- 

 dent, by the alternating opaque planes : fifty discharges gave a 

 faint blue to some portions only. 



Dark purple fluor became white by calcination, and received 

 a bluish tint by twenty-four discharges. 



Twelve discharges rendered No. 8 bluish ; sixty electrical 

 explosions upon the calcined fluor caused it to appear blue. 



No. 9 was opalescent by calcination ; it acquired a faint 

 pink tint by twenty-four discharges of electricity. 



These various tints preclude the idea of fallacy, from the 

 deposition of foreign matter by the electrical discharges : in 

 one experiment, when nearly one hundred discharges had 

 been made over fragments, and metal was deposited in the 

 track of the discharge, it still preserved its metallic lustre. 

 Hence there appears every reason to conclude, that the colour 

 induced is the effect of structure alone. 



These tints so produced were not permanent; some portions 

 in the light lost all colour in a few days ; other portions, kept in 

 darkness, showed these external tints after two months. 



The pink tints are strongest upon the edges, and soften 

 upon the planes. 



