1895.] Phosphorescence and Photographic Action. 667 



the use of glass to be abandoned when necessary. As a general 

 rule it may be stated that the great majority of substances ex- 

 hibiting feeble phosphorescence at ordinary temperature, become 

 markedly more active at these very low temperatures. Thus gelatin, 

 celluloid, paraffine, ivory, horn, and india-rubber become distinctly 

 luminous, with a bluish or greenish phosphorescence, after cooling 

 to — 180° and being stimulated by the electric light. Hydroquinone 

 was more luminous than the isomeric resorcinol or pyrocatechol, and 

 in the same way pyrogallol was faint compared with phloroglucol. 

 All alkaloids forming fluorescent solutions become phosphorescent 

 at low temperatures. The hydrocarbons, alcohols, acids and ethers 

 of the fatty series are all more or less active, and glycerin, sulphuric 

 and nitric acids are all very bright, so also are concentrated hydro- 

 chloric acid and strong ammonia solution. Coloured salts generally 

 show little activity, but a large number of colourless salts are very 

 luminous. Water when pure is only feebly phosphorescent, but 

 remarkably so when impure. Acetic acid and acetamide appeared 

 fairly equal in luminosity ; hippuric acid was very fine, as were most 

 substances containing a ketone group. Lithium platinocyanide 

 changed from white to red on cooling, and was excelled in phos- 

 phorescing power by yellow ammonium platinocyanide, which was 

 exceedingly bright. 



Definite organic substances possessing exceptional powers of phos- 

 phorescence when stimulated at — 180° C, are acetophenone, benzo- 

 phenone, asparagin, hippuric acid, phthalic anhydride, urea, creatine, 

 urethane, succinimide, triphenyl methane, diphenyl, salicylic acid, 

 glycogen, aldehyde-ammonia, &c. It will require long and laborious 

 experiments, however, to measure the relative brightness of the phos- 

 phorescence of bodies belonging to definite series. 



Eemarkable results were obtained with an egg-shell and a feather 

 respectively. The egg shone brilliantly as a globe of blue light, and 

 the feather was equally brilliant, its outline showing clearly in the 

 darkened room. Other organic substances giving good results were 

 cotton-wool, paper, leather, linen, tortoiseshell, and sponge, all phos- 

 phorescing brightly, as did also a white flower, a cultivated species 

 of Dianthus. Coloured glasses and papers as a rule exhibit no phos- 

 phorescence, and when the alcohols are coloured by the addition of a 

 trace of iodine, the luminous effect is destroyed. Milk was shown to 

 be highly phosphorescent and much brighter than water. The 

 white of egg has greater phosphorescing power than the yolk, white 

 substances generally being superior in this resjDect to coloured ones. 

 On cooling a layer of white of egg on the outside of a test tube to 

 — 190°, and then exposing it to a flash of the electric arc, the brilliancy 

 of the phosphorescent light is very striking. The chloro-, bromo-, 

 iodo-, sulpho-, and nitro-compounds, as a rule, show nothing, or are but 

 faintly luminous. Amongst basic bodies nicotine is more luminous 

 than quinoline or pyridine. Metals also phosphoresce, but in this 

 case the action is due to some organic film deposited from the air, 



