78 Mr. Pearsall on the Effects of 



An inferior specimen of chlorophane was then heated, when 

 it gave out a strong light of a faint purple colour; but it 

 decrepitated so violently during calcination, that a piece of 

 sufficient size to be electrified alone could not be obtained. 



The splinters were then placed in a glass tube, through 

 which three electrical discharges were passed, producing a deep 

 purple light after each discharge. They were then heated 

 upon platinum, when they evolved phosphoric light of dif- 

 ferent colours, some fragments appearing green, others yellow, 

 the whole finally assuming a deep purple light. These colours 

 were obviously distinct from those of the natural mineral, a 

 portion of which, heated at the same time, shewed only light 

 tints of purple. 



Part of the same calcined specimen, but not electrified, gave 

 no light when heated*. 



Chlorophane, whose phosphorescence had been destroyed by 

 an intense heat, was exposed for two days to the sun's rays 

 without effect ; but a single discharge again restored its phos- 

 phorescence. 



Repeated discharges were made upon the same substance, 

 and it was found that the property was increased by the num- 

 ber and intensity of the discharges, the green light evolved by 

 heat being deeper and of longer duration after three, six, or 

 twelve discharges, than after a single discharge. 



Chlorophane, which had been heated intensely, and had 

 been since exposed, under ordinary circumstances, to daylight 

 for eight months, had not acquired the least phosphorescence ; 

 but it gave a greenish light during the passage of the electri- 

 city, increasing with the strength of the discharge, and was 

 afterwards luminous by heat t- 



A crystal of purple fluor spar, calcined at the same time, 



The mode I adopted was to heat the portions of mineral upon a platinum 

 capsule, covered by a watch-glass. The phosphorescence was thus rapidly pro- 

 duced, and easily governed by the regulated flame of a spirit-lamp. The identical 

 fragments were also readily submitted to repeated examinations ; and I conceive 

 that by using platinum instead of iron, as usually recommended, I guarded 

 against the introduction of matter which might have interfered in the experiments. 

 The calcinations were performed in a crucible at a red heat. 



J- Dr. Brewster exposed specimens to the sun's rays concentrated in the focus 

 of a lens, but without the slightest indication of returning phosphorescence. 

 BaEwsiJSR on the Phosphorescence of Mineral*. Edin, PhU, Journal, i, 387. 



