TRANSACTIONS OF THE SECTIONS. 69 



On the Fluorescence and Phosphorescence of Diamonds. 

 By J. H. Gladstone, Ph.D., F.R.S., F.C.S. 



While examining the remarkable chromatic properties of Prof. Way's mercurio- 

 clcctric light, the author observed, that of four diamonds on a ring, two were beauti- 

 fully fluorescent, one slightly so, and the remaining one perfectly unaffected in that 

 manner. Some other diamonds were found to exhibit the same phenomenon in this 

 light, though the majority did not. The fluorescence resembled that of bisulphate of 

 quinine, and was produced by the same rays, so that the interposition of a solution of 

 quinine stopped the power of the light to produce this effect. The same two diamonds 

 were found to be fluorescent by the lightning flash. On exposing the ring to the 

 sun and bringing it into a dark place, it was ascertained that the two most fluorescent 

 diamonds were very phosphorescent, and the slightly fluorescent one slightly phos- 

 phorescent, while the fourth exhibited neither phenomenon. On examining the long 

 paper of M. Becquerel on phosphorescent substances, published just previously in 

 the * Annales de Chimie et de Physique ', it was found that he had obtained somewhat 

 similar results ; the diamond, however, is a difficulty for M. Becquerel, as it forms 

 an exception to the rule that " the fluorescence produced is always of the same shade 

 as the phosphorescence." In like manner with the ring in question, while the fluor- 

 escence is blue, the phosphorescent tint is a greenish white, scarcely resolved by the 

 prism, but by the action of absorbent media appearing to be between D and E of the 

 solar spectrum. No blue was observable, even the moment after exposure to the 

 sunshine. 



Red or yellow glass interposed between the sun and the diamonds prevented the 

 phosphorescence, while blue glass, similarly interposed, gave rise to a brilliant display, 

 suggesting the idea that the less refrangible rays of the spectrum are positively anta- 

 gonistic to this power ; yet the diamonds become phosphorescent when exposed to 

 the light of a candle. On one occasion, when exposed to the sun's rays through 

 cobalt blue glass, they shone visibly when removed merely into dim daylight. On 

 another occasion, after simple exposure to the sun, they were observed to emit light 

 for an hour and a quarter. 



If this phosphorescence be the continuous result of some molecular change wrought 

 on the diamond by light, it would appear probable that the effect would go on increa- 

 sing with the amount of exposure, at any rate, up to some saturation point. This is 

 no doubt true to a certain extent ; but in endeavouring to reach this point, the author 

 found that a long exposure to sunshine diminishes the phosphorescent power of the 

 diamonds. This did not seem to be due to differences in the atmosphere or tempe- 

 rature, or to any diminution of the power of the eye to perceive the phosphorescent 

 light, but to be a property inherent in the stone itself. The effect is a very marked 

 one; and what is specially remarkable, is that the diamond which has thus almost 

 lost the power of phosphorescing is fouwd the next day as sensitive as ever. 



On Photographs of Fluorescent Substances. 

 By J. H. Gladstone, Ph.D., F.R.S., F.C.S. 



It is well known, on the one hand, that the chemical action of light resides mainly 

 in the most refrangible rays, and, on the other hand, that these rays are altered in 

 their refrangibility and effect on the visual organs by fluorescent substances. It 

 occurred to the author that such substances would probably exert little photographic 

 action. Hence he had made two drawings on sheets of white paper, one in an acid 

 salt of quinine, the other in a very pale solution of chlorophyll, and had taken photo- 

 graphs of them. Although the drawing in quinine was quite undistinguishable from 

 the white paper, and the chlorophyll drawing nearly so, when they were viewed in 

 the camera for adjusting the focus, they were strongly marked on the photographic 

 image by the little chemical action that had been exerted by them. The sheets of 

 paper, and the drawings developed on the glass plates, were exhibited, showing that 

 what theory had suggested as probable was true in fact. 



On a New Form of Instantaneous Generator of Illuminating Gas by means 

 of Superheated Aqueous Vapour and any Hydrocarburet whatever. By 

 MM. Isoard and Son. 

 The apparatus in question for transforming aqueous vapour into illuminating gas, 



