Page:The American Cyclopædia (1879) Volume XIII.djvu/478

462 PHOSPHORESCENCE phorescence in living organisms are seen in animals, as the glowworm and the firefly, and in the myriads of marine radiates, polyps, and I infusoria, which cause the magnificent displays ! of phosphorescence that are often seen at sea by night, especially within the tropics and in the temperate zones during the summer. Vari- I ous causes have been assigned for the phenom- ena of animal phosphorescence, and the causes no doubt vary with different animals. In many it is produced at a particular period of life, and in the firefly and glowworm it is regarded as being produced by an act of the will. M. Jousset has found that the liquid which exudes from the crushed eggs of the glowworm is phosphorescent, and remains so till it dries. In marine animals, according to the observa- tions of several naturalists, a subtile luminous matter is thrown off as a secretion produced by glands having this special function, and some assert that it contains epithelial cells in a state of fatty degeneration, the decomposing fat being the cause of the phosphorescence. The light is increased by exposure to pure oxy- gen gas. MM. Quoy and Gaimard, during a voyage in the tropics, having placed two ani- malcules in a glass of water, the whole mass of the liquid immediately became luminous. The phosphorescence of decaying fish and other animal matter, and of wood (fox fi.re), is due to a peculiar species of slow combustion by which vibrations are excited capable of trans- mitting luminous rays. 2. Many solids become phosphorescent when thrown upon a heated surface, and when heated in any manner be- tween 550 and 750 F. Such are the dia- mond, especially the yellow variety, certain specimens of fluor spar, oyster shells, paper, Indian meal, and numerous well dried organic substances. The light is entirely different from that of incandescence, and is generally of a blue or violet hue, instead of the dull red of incipient incandescence. When phospho- rescence is produced by insolation or exposure to the rays of the sun or any intense source of light, the effect is generally greatly increased by raising the temperature of the substance at the same time. 3. Phosphorescence from me- chanical action is observed when certain bodies are struck with a hammer or subjected to fric- tion, or are broken or violently torn asunder. In many instances the effect is only coexistent with the cause ; in other cases it remains for a considerable time. Adularia, a variety of or- thoclase feldspar, if split by being struck with a hammer, emits at each stroke a light which often lasts for several minutes, and if ground in a mortar it will have the appearance in the dark of being all on fire. Quartz, fluor spar, rock salt, and sugar, when broken or pounded in the dark, exhibit phosphorescence. Light is sometimes emitted by bodies undergoing a state of change, especially when passing from an amorphous to a crystalline state, or during the act of crystallization from solution, and is probably closely allied to the phosphores- cence of mechanical action, which latter is also often accompanied by electrical effects. 4. If a powerful electric discharge is passed through a lump of sugar, it will shine for several sec- onds afterward with a beautiful violet light. Many other non-conducting substances may be affected in a similar manner, but the effect never occurs with a good conductor, such as | any metal. Bodies may lose the power of be- coming phosphorescent by heat or by insola- j tion, but it may be restored by the repeated passage of electric charges through them. M. Alvergniat produces phosphorescence by the action of electricity on chloride or bromide of silicon, in the following manner : A vacuum is made with a mercurial air pump in a glass tube, when the liquid chloride or bromide of silicon is introduced, which fills the space with vapor ; the exhaustion is then continued until the pressure is reduced to 12 or 15 millimetres, when the tube is closed by a blowpipe flame. If it be now rubbed with a piece of silk, a bright glimmer will follow the movement of the rubber. The chloride produces a rose- colored light, and the bromide a greenish yel- low. A similar phenomenon has often been observed in barometer tubes. 5. Phosphores- cence by insolation, or exposure to the light of the sun, has been carefully investigated by A. E. Becquerel. Insolation produces phos- phorescence most readily in those substances which are bad conductors of heat. It was first discovered in 1604 in sulphide of barium, but M. Becquerel has found that it may be ex- cited in many other substances, the sulphides of calcium and strontium being those which exhibit it in the highest degree. When well prepared they will remain luminous in the dark for several hours after exposure to the sun's rays. This phosphorescence takes place in vacuo as well as in air or oxygen, and there- fore the cause must be attributed to molecular action produced by the rays of light. Other phosphors which are excited by insolation are the diamond, particularly the yellow kind, most specimens of fluor spar, aragonite, calcareous concretions, chalk, apatite, heavy spar, fused nitrate of calcium (Baudoin's phosphorus), dried chloride of calcium, and a number of dried organic substances, as paper, silk, and cane, and also amber and milk sugar. Can- ton's phosphorus, prepared by heating sulphur with calcined oyster shells, will after exposure to the sun's rays emit a yellow light sufficient to show the time by a watch ; even the light of an argand lamp will cause it to become phos- phorescent. The Bolognese phosphorus, which is made by uniting heavy spar with gum traga- canth, gives out after insolation a bright light of more than a day's duration. It was found by M. Becquerel that the different rays of the solar spectrum had not the same power to ren- der the substance phosphorescent. The great- est effect is produced by the violet rays, or even a little beyond, the phosphorescent light emitted by the substance being developed by