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Solid Bodies. Phosphorescence produced by tearing, splitting, and rubbing.- When boracic acid solidifies after fusion, it splits in cooling, and exhibits along the cracks a light which is visible even in the daytime. (Dumas, Ann. Chim. Phys. 32, 335, also Pogg. 7, 535.) Sulphate of potash fused with cream of tartar and a little common salt, likewise cracks in cooling and emits light. (Schiller, Tascherb. 1791, 54.) Glass-drops almost always emit light when they burst. (Heinrich.) In the cleavage of Russian mica sparks are produced which sometimes start out to the distance of 0:1 inch. (Heinrich.) If two pieces of cloth joined together by a solution of caoutchouc 'in coal-tar be suddenly pulled asunder, or if any cotton fabric be quickly torn, light will be emitted and will be visible in the dark. (Ed. Phil. J. 10, 185.) (No light is developed by the breaking of ropes, silk strings, or wires, or by the splitting of wood.) Cylinders of the following substances, mostly crystalline, emit light when broken, provided the fracture be not clean, but small pieces are thrown off or cracks produced: Fluor-spar, rock-salt, sulphate of potash, rockcrystal, rose quartz, hyalite, topaz, cyanite, adularia, labrador, glassy tremolite, zeolite, yellow blende and sugar, especially Canary sugar and sugar-candy; these substances emit a much brighter light when pounded in a mortar. Bitartrate of potash, Rochelle salt, and glass tubes give out an indistinct light when broken; alum, borax, and Glauber's salt emit done on being broken, but all these substances give out light when pounded in a mortar. (Heinrich.) Tartaric acid becomes luminous when pounded (Morion's J. Chim. Med. 3, 287); so likewise do large masses of beef and mutton suet when bruised by beating. (Bauernfeind, Kestn. Arch. 18, 370.)

Phosphorescence produced by rubbing.—The following substances emit light when rubbed together: Diamonds which become phosphorescent by insulation or beating, chlorate of potash, heavy spar, strontianite, burnt lime, Canton's phosphorus, fluor-spar, many kinds of statuary marble, dolomite, arragonite, anhydrite, Homberg's phosphorus, phosphorite from Estremadura, glass, porcelain, all precious stones and vitreous minerals (the brightest light is emitted by milk quartz and adularia, the faintest by jasper), blende, calomel (comp. Castillo, J. Pharm. 13, 158), corrosive sublimate, sulphate and phosphate of mercury, loaf-sugar, sugarcandy, and resins. (Dessaignes.) – Also: sal-ammoniac, nitre, alum, and blue vitriol (this last only after drying, the pieces being rubbed together while yet warm), borax, rock salt, witherite, double refracting spar, calcspar, many granular limestones, many kinds of alabaster, fuor. spar, apatite, pharmacolite, rock-crystal, quartz, amethyst, agate, chalcedony, hornstone, red and band-jasper, opal, corundum, topaz, adularia, common felspar, labrador, lapis lazuli, tourmalin, pyrope, wetz-schiefer, elastic stone, baked earthenware, calamine, iron pyrites (the last shines by combustion), tinstone, magnetic iron ore, and blood-stone. (Heinrich.) Phosphorescence is likewise exhibited by wet crystals of nitrate of baryta (not by dry ones) when violently thrown one against the other (A. Werner, J. pr. Chem. 14, 249); manna-sugar, and the so-called subresins. (Bonastre, J. Pharm. 10, 191.) According to Mills (Ann. Phil. 23, 235), acetate of lime evaporated' to dryness and heated to 120° C. also emits light when rubbed with a spatula.

No phosphorescence of this kind is exhibited by any of the metals, or by any metallic sulphurets except blende; the hydratos of potash and soda, all salts of ammonia, potash, and soda, except chlorate of potash; gypsum; the heavy metallic oxides; minerals containing heavy metallic oxides in large quantity; all heavy metallic salts except the mercurial salts above mentioned; all vegetable substances except sugar, resin, and certain liquids; all animal substances. (Dessaignes.) Moreover: sulphur, the Bolognian phosphorus, cyanite, steatite, lime, meerschaum, asbestus, teeth, bones, antlers, horns, and amber. (Heinrich.)

As a general rule, the same bodies emit light when rubbed with rockcrystal, an etching needle, or a revolving-grindstone; on the latter, phosphorescence is also exhibited by serpentine, zeolite, realgar, sparry iron ore, galena, and Rochelle salt: the friction-light which is generally of a pale yellow colour, is, when produced by the grindstone, of a fiery red. When large grindstones are used, the rise of temperature is inconsiderable (?), for the pieces of fluor-spar which fly off soon cease to shine. (Heinrich.)

Diamonds which do not become luminous by ordinary rubbing emit light when strongly rubbed one against the other, by which small fissures are produced within them. (Dessaignes.)

A peculiar smell is produced when many substances, luminous as well as non-luminous, are rubbed together: on rubbing together pieces of qnartz in the air, a black powder is produced, and a white one if they are rubbed under water. (Dessaigues.)

The emission of light also takes place in vacuo, and under water, provided the latter does not exert a solvent action.

The light is white, yellow, red, or blue, according to the nature of the bodies: its duration is in most cases merely momentary; the diamond, however, shines for a minute when rubbed, and adularia continues luminous for some time and through its whole mass, when flaws have been produced in it by pressure. (Dessaignes.) The intensity of the light in any particular substance is greater, the more it has been previously heated,

- provided the heat has not been raised to redness, in which case the body exhibits no more phosphorescence. A body cooled to a very low temperature, exhibits little or no phosphorescence when pressed. (Dessaignes.)

The following substances become luminous when rubbed with an ordinary quill-feather: Apatite, fluor-spar, rock-crystal, quartz, agate, chalcedony, lapis-lazuli (these five only when newly fractured), síliceous slate, felspar, mica, tremolite, the so-called crystalline sandstone and other varieties, lithomarge and white clay (Heinrich); Canton's and Homberg's phosphorus, dolomite, many kinds of blende, corrosive sublimate, and loaf-sugar (Dessaignes). The diamond alone shines when rubbed with wool or with a brush.' (Dessaignes.)

Sulphate of cinchonin shines with a greenish light when rubbed in a basin at 100°; so likewise does sulphate of quinin, and with greater intensity; both substances become, at the same time, positively electrical. (Callaud, Stratingh.)

All precious stones (excepting diamond), marble, many kinds of blende, and loaf-sngar, become luminous when struck with a wooden or steel hammer. (Dessaignes.)

Phosphorescence from pressure on pulverized bodies. The following substances in the state of powder emit light when struck on the anvil with a hammer, or pressed in the fire-syringe. Arragonite, calcspar, marble limestone, chalk, apatite, alabaster, fluor-spar, amethystine rockcrystal, chalcedony, felspar, mica, chlorit-schiefer, tremolite, and (very faintly) agalmatolite and steatite. These are in fact the bodies which

shine when heated, and the heat which the pressure produces is the cause of the luminosity. (Heinrich.)

When heavy spar, carbonate of baryta, carbonate of strontia, limestone, chalk, dolomite, Canton's and Homberg's phosphorus, and magnesia are heated either to redness or to whiteness and struck as soon as they have ceased to emit light, the luminosity reappears and continues for a longer time. This development of light is perhaps of a different kind. (Dessaigues.)

Liquids. Water, aqueous solution of potash, acetic acid, alcohol, ether, volatile oils, and olive oil become luminous when rapidly compressed in a glass fire-syringe. (Dessaignes.) The same result is obtained with saline solutions. (Heinrich.) The light shows itself most strongly in that part of the liquid which is farthest from the piston, and quickly disappears. The experiment may be several times and uninterruptedly repeated with the same water, the temperature perhaps rising to 5° C. (Heinrich.)

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Air, oxygen, and chlorine are, according to Saissy and Dessaignes, the only gases which emit light in the glass fire-syringe; according to Heinrich, this effect is also produced by hydrogen, nitrogen, nitrous oxide, and carbonic acid gas. (The assertion that hydrogen gives the brightest light and at the same time the greatest heat, excites a suspicion that the gas used in the experiments was mixed with common air.) The luminous appearance is produced with greater certainty when to the lower surface of the piston there is attached a sponge moistened with water,—or still better with solution of alum,-or else some fine threads of glass or asbestus,-on account of the action of the points (Schweigger, Schw. 40, 10). Spongy platinum attached to the piston does not favour the production of light. (Pfaff. Schw. 40, 1.) Tliénard (Ann. Chim. Phys. 44, 181; also Pogg. 19, 442) attributes this light merely to the combustion of the leather of the piston and the grease used to lubricate it, in the compressed gases, inasmuch as this appearance has been observed only in air, oxygen, and chlorine. When the piston is made of brass covered with felt and lubricated with water, no light is seen, unless the felt has not been sufficiently moistened; neither is there any luminous appearance produced when the tube has been carefully cleaned from grease with caustic potash. Since the luminosity of gases shows itself only when the piston fits the tube very closely, and this close adaptation is not easily attained by the use of water,-and moreover, since some of the following experiments appear to confirm the fact of the development of light by the compression of gases,—the matter must for the present be looked upon as undecided. (Gm.)

Detonating bulbs (i. e. glass bulbs hermetically sealed and nearly empty of air) when thrown on the ground, exhibit a faint white light in bursting. (Helwig, Gilb. 51, 112.) – Vapour-bulbs (glass bulbs filled with alcohol, and burst by heating) give no light. (Heinrich.)

Airpump-light. A glass cylinder bound over with a strong bladder and exhausted of air appears, when the bladder breaks by the pressure of the external air, to be filled with a white light which is brighter in proportion as the cylinder was more completely exhausted of air. (Dessaignes, Gilb. 49, 310; Heinrich.) This light is undoubtedly caused by the pressure exerted on the exceedingly rarefied air of the cylinder and the portion which first enters by that which rapidly follows it. Deparcieux observed light on the bursting of a glass bulb closed and full of air under an exhausted receiver.

Airgun-light. When an airgun is discharged, light is sometimes seen at the mouth of the barrel; according to Leyser (Gilb. 8, 340), only when the barrel is of iron, not when it is lined with brass. According to Heinrich, the gun must be fully charged, and even then only the first two or three discharges are accompanied by light, whether the gun be loaded with ball or not. The light is also apparent when the barrel is lined with lead, and most clearly when it is made of glass; it is not produced when the barrel is very wide, unless it be partly divided by a cleft ramrod. Leyser and more particularly Hart (Qu. J. of Sc. 15, 64), assert that light is not produced unless the barrel contains dust, or powdered fluor-spar or sugar is put into it; this would show that the light is produced by friction. According to Schweigger (Schw. 40, 22), the development of light is favoured by holding a crust of quartz-crystals or a coil of wire before the mouth of the barrel.

Light is seeu in the sudden decomposition of peroxide of hydrogen, iodide of nitrogen, chloride of nitrogen, and oxide of chlorine; in these decompositions, gases are suddenly set free which probably produce light by pressing on the surrounding air or the undecomposed portion of the gaseous compound.

d. Luminous appearances accompanying Crystallization. Many salts in crystallizing from their aqueous solutions, and benzoic acid in passing from the state of vapour into the crystalline condition, often exhibit a brilliant, sparkling light,—whilst in other instances, the same substances, under circumstances precisely similar, present no appearance of the kind. This phenomenon probably depends in every case on the passage of the body from the amorphous to the crystalline state, and is precisely analogous to the luminous appearance which accompanies the crystallization of arsenious acid (p. 105), and the phosphorescence of other amorphous bodies when heated (p. 106).

Pickel observed sparkling appearances in all parts of a vessel in which sulphate of potash was crystallizing; this continued for an hour. Schönwald saw sparks emitted during the evaporation and crystallization of a solution of i part of common salt and 2 parts of sulphate of potash, and found that the resulting crystals were luminous when rubbed. Schiller dissolved in hot water a mixture of sulphate of potash, cream of tartar, and a small quantity of common salt which had been fused at a high temperature, and filtered the solution; during the crystallization flashes of light continued to dart through the liquid for several hours, and the crystals still shone when they were removed with a spatula several days after. According to Giobert, sulphate of potash does not emit light in crystallizing, when it contains sulphate of magnesia mixed with it; the light is first seen when the liquid becomes moderately concentrated and begins to crystallize by cooling; during slow evaporation no light is emitted. The larger the surface of the vessel, the brighter is the light; it seems also to be strengthened by previous exposure of the liquid to the sun. The crystals shine with the greatest brightness after the liquid has been poured off; but they cease to shine when dried upou blotting-paper.-Crystals which had separated from a solution of sulphate

of cobalt and potash at 12° C. emitted sparks for half an hour after the liquid had been poured off. (Herrmann.) A solution of several ponnds of sulphate of potash crystallizing at + 20° C. emitted light for two hours ; pieces of the crystalline crust even continued to shine when taken into the hand and their light grew stronger when they were rubbed. When a glass rod was moved over the crystalline crust at the bottom of the liquid, its track was marked by a luminous line. When the same saline mass was redissolved by heating the supernatant liquid and again crystallized by cooling, it was no longer phosphorescent. (Berzelius and Wöhler.) On evaporating a solution of bisulphate of potash in a porcelain basin, the crystals of neutral sulphate of potash which formed, emitted a strong light for half an hour and continued to shine even when taken out of the liquid; the latter also exhibited a sparkling light, especially when stirred. (Pleischl.)—A solution of acid sulphate of potash, neutralized with carbonate of potash, filtered, evaporated to the crystallizing point and divided among a number of wooden and stone-ware crystallizing vessels, exhibited towards evening on the surfaces of all the vessels a succession of sparks, the emission of which continued with a peculiar noise for several hours, but ceased when the liquid had become quite cold; the mother liquid exhibited no more light when further evaporated. (Sager, Br. Arch. 36, 274.)

Crystallized neutral sulphate of potash dissolved in water and brought to the crystallizing point by evaporation never emits light: neither does fused sulphate of potash similarly treated,—for in cooling from a state of fusion it acquires a crystalline structure. But sulphate of potash fused with sulphate of soda in the proportion of equal atoms in the proportion of 11 parts : 9 parts) yields, on cooling, an amorphous, fissured, crumbling mass of vitreous fracture, a saturated solution of which in boiling water prepared inmediately after cooling, then filtered hot and slowly cooled, emits light. The formation of every crystal is accompanied by a bright spark. For the first few hours, the crystals continue to shine when taken out of the liquid and rubbed, but not so strongly as during their formation. They have the form of sulphate of potash, but contain about one atom of dry sulphate of soda mixed with every 2 atoms of sulphate of potash. When redissolved in water, they emit no light on crystallizing. If the mass is dissolved in water not quite boiling, and the solution slowly evaporated to dryness, no light is emitted, and the two salts crystallize separately. If the melted mass is exposed to the air for 24 hours before it is dissolved in water, but few luminous crystals are seen; and if it has been left undissolved for several days, in which case it appears to become crystalline and separate into its two component salts, none at all. A fused mixture of 3 atoms of sulphate of potash and 2 atoms of sulphate of soda similarly treated yields less light. When crystallized sulphate of potash and crystallized sulphate of soda are boiled together in water, a very faint light is sometimes observed during the subsequent crystallization: : a portion of amorphous double salt appears therefore to be produced by the boiling.–A surer method of producing light, and of con. siderable brilliancy, is to fuse together 2 parts of sulphate of potash with 1 part of common salt, and treat the fused mass as above. The crystals obtained are the above mentioned compound of sulphate of potash and sulphate of soda, free from common salt. A strong light is also obtained by treating in a similar manner a mixture of 8 parts of sulphate of potash with 3 parts of dry carbonate of soda. (If the fused mass be

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