In

salt, phosphate of soda, sulphate of magnesia, nitre, sugar, and honey. (Hulme.) According to Hulme, a luminous fish diminishes in brightness when placed in a vacuum; according to Dessaignes, it ceases to shine in vacuo, but regains its luminosity when the air is re-admitted. nitrogen, hydrogen, carbonic acid, and sulphuretted hydrogen gas, the fish continues to shine for a short time only. (Dessaignes, Hulme.) In boiled water or sea-water, it soon ceases to shine when the air is kept from it; but if air-bubbles make their appearance, the phosphorescence re-appears, and continues for a time proportionate to the quantity of air present. In ordinary fat oil, the fish continues to shine for 24 hours: but if the oil has been boiled, the light ceases as soon as the fish is put into it. (Dessaignes.)

The fish, when left to itself, continues phosphorescent for some days until fetid putrefaction ensues, and then the light disappears.

2. Phosphorescence of Putrefying Plants.

The complete decay of the various parts of a plant is also when the temperature is moderate, and moisture and a small quantity of air are present at times accompanied by a peculiar decomposition, resulting in the development of a substance which, like phosphorus, burns at ordinary temperatures, producing light and a small quantity of heat. Nevertheless, this substance cannot be phosphorus (especially in wood which does not contain that element), but must rather be considered as a peculiar, and easily combustible compound of carbon, hydrogen, and oxygen, resulting from the decomposition of the original proximate constituents of the plant.

The phosphorescence is chiefly conspicuous in wood, as well in that of the root, as in that of the stem and branches. The phosphorescence has been observed in the wood of Quercus Robur; Fagus Castanea and sylvatica; Betula alba and Alnus; Corylus Avellana; Pinus Abies, Strobus, picea and sylvestris; Juglans regia; and some species of willow.

The decomposition of the wood must take place in a situation where but a moderate quantity of moisture is present, and the air is almost excluded, in which case, the wood will remain white; when there is much moisture and free access of air, it is reduced to a brown pulverulent mass which is not luminous. Phosphorescent wood is often but little decomposed, and retains a great deal of its hardness. (Heinrich.) John (Schw. 14, 415) saw light emitted by splinters of wood from a newly felled pine. Old wooden pipes often exhibit phosphorescence when taken out of the ground. When roots, which have been dead for some years, are taken out of the earth and kept in a moderately damp place, they often become phosphorescent after a few days. (Heinrich.)-According to Dessaignes, the phosphorescence ceases when the temperature falls to +6°C (42.8° Fah.); according to Heinrich, it shows itself even at 0° C. fainter indeed, but more durable, continuing for more than fifteen days. By boiling water it is irrecoverably destroyed. Wood heated in the air to the boiling point of water recovers its luminosity by immersion in cold water. (Heinrich.) Wood loses its phosphorescent properties by drying; wood which when exposed to the air ceases to emit light after two or three days, remains luminous for fourteen days when wrapped up in moist blotting-paper (Heinrich). In a vessel containing quick-lime it soon ceases to shine (Dessaignes); but by moderately wetting it, the phosphorescence may to a certain extent be restored.

Wood does not shine for a longer time or with greater intensity in oxyen gas than in common air (Heinrich, Dessaignes); according to Böckman and Gärtner, it does not shine more brightly but longer; according to Spallanzani, it shines with greater brightness. According to Dessaignes, the phosphorescence is brighter, but of shorter duration in compressed air. The same observer found that the phosphorescence gradually died away in a vacuum. Heinrich could not produce any decrease of luminosity by rarefying the air. In nitrogen, hydrogen, and phosphuretted hydrogen gas, the wood remains luminous for only a few hours, and then, according to Spallanzani, recovers its luminosity on the re-admission of common air; in fluoride of silicon, chlorine, ammonia, hydrochloric acid, carbonic acid, and sulphuretted hydrogen gas, its phosphorescence ceases in a few minutes, and cannot be wholly restored by contact of air. (Böckmann, Gärtner, Heinrich.)—In unboiled water, fat oil, and mercury, the phosphorescence ceases after an interval varying from 6 to 24 hours; sooner in alcohol, ether, boiled oil, lime-water, solution of sulphuret of potassium, dilute acids, and saline solutions; instantly in sulphuric acid. Saturated solutions of sal-ammoniac, nitre, and common salt, produce at first an increase of luminosity. (Gärtner, Heinrich, Dessaignes.)

The phosphorescence of wood in air or oxygen gas is attended with consumption of oxygen and production of carbonic acid without perceptible diminution of volume. (Dessaignes.) Air pumped out of decaying wood contains a little oxygen with a great deal of carbonic acid gas. (Dessaignes.) Hence may be explained the fact that wood continues to emit light, even in media which contain no oxygen, provided they do not exert a destructive action on the phosphorescent matter.

Potatoes kept in a cellar till they began to germinate, were, in one instance, observed to emit light on being cut open. (J. Phys. 33, 225; also Gren. J. d. Phys. 2, 420.)-Kortum (Voigt, n. Nag. 2. 67) frequently observed phosphorescence in valerian roots while yet tolerably fresh.Fresh tormentilla roots gathered in August have been seen to emit light, particularly on those parts where the last year's nodosities were situated. (Berl. Jahrb. 1, 174.)-Likewise gourds, mushrooms, and turf are said to be sometimes phosphorescent.

Göbel (Schw. 40, 257) allowed some raspberry juice mixed with sugar to ferment in a cask, into the bung-hole of which was inserted a glass tube 1 inch wide and 3 feet long, filled with the same juice, so that the carbonic acid gas developed by the fermentation was compelled to escape through the tube. The bubbles of gas which thus ascended continued to exhibit phosphorescence for more than an hour. The light of the bubbles was strongest just as they passed from the cask into the tube, diminished in intensity as they ascended, and disappeared completely when they came in contact with the air. When the gas was collected by means of a gas-delivery tube adapted to the tube above mentioned, it was no longer phosphorescent, had no smell, and exhibited with ammonia the reaction of pure carbonic acid. (Göbel and Schweigger suggest that the development of light in this experiment may be due to electricity: but it is possible that the carbonic acid gas may have been mixed with a very small quantity of a volatile and combustible organic matter produced by the fermentation, and that this substance may have been burnt with development of light, by combining with the oxygen of the air probably held in solution by the juice of the tube, before the bubbles reached the top of the tube.)

B. Development of Light unaccompanied by any alteration in the Ponderable Matter of Bodies.

a. Development of Light after exposure to Light.

A great number of bodies have the property of shining in the dark when they have previously been exposed to light: such bodies are said to exhibit phosphorescence by Insolation or Irradiation. The cause of this phenomenon is probably that the bodies, by being exposed to light, absorb a portion of it unaltered into their substance by adhesion, and subsequently give it out in a dark place,-because there the effort of the light to diffuse itself uniformly through the space devoid of light overcomes its adhesion to the ponderable matter.

Phosphori by Irradiation, Light-absorbers, Light-magnets, are transparent or opaque, colourless or slightly coloured, but never black substances.

The best phosphori by Irradiation are the following: Diamond (some diamonds however have no phosphorescence.) (Heinrich.)

Bonnonian Phosphorus. (1.) A paste made of gum tragacanth and powdered heavy spar free from iron and dried, is placed in layers between small coals in a wind-furnace (or in a crucible,- Wach) ignited for an hour, and transferred while yet warm into well stopped glass vessels. (John.) 3 or 4 per cent of magnesia mixed with the powdered heavy spar improves the phosphorescence considerably. (Wach.) (2.) Osann passes hydrogen gas over sulphate of baryta heated to redness in a tube. (3.) Daguerre fills a marrow-bone, as thick as can be procured, freed from fat and dried, with heavy spar pounded in a non-metallic mortar-lutes it-incloses it in a tube of iron-plate or cast-iron-surrounds and covers it completely with fire-clay-exposes the whole to a red heat in the furnace for at least three hours, then removes the clay from the bone (which should be white after cooling,-a grey colour would show that it had not been heated long enough), breaks it up on paper-and preserves the white or pale yellow phosphorus thus obtained. If it be heated once or twice more in a fresh bone, its phosphorescent properties will be greatly inereased. The sulphate of baryta used must be perfectly free from iron and other heavy metals.

Strontian Phosphorus may be prepared in a similar manner (1) from cœlestin (John): its luminosity may be greatly increased by the addition of 3 or 4 per cent. of magnesia to the powdered cœlestin.

Canton's Posphorus. (1.) Canton exposes a mixture of 3 parts of sifted and calcined oyster-shells and 1 part of flowers of sulphur to a strong fire for an hour. (2.) Grotthuss places oyster-shells-which have been previously cleaned and ignited by themselves for half an hour-in alternate layers with pounded sulphur in a crucible, the inner surfaces of the shells being turned downwards, and heats the crucible in a windfurnace for at least an hour. The oyster-shells must be previously well burnt so as to remove all dark spots, and their inner surfaces must be cleaned from adhering ashes with a soft brush which will not injure them. The phosphorus is more luminous when the burnt oyster-shells are heated with sulphur in their entire state than when they are pounded. Moderate ignition for half an hour in contact with sulphur is generally quite sufficient: more powerful and longer-sustained ignition produces a phosphorus which is but faintly luminous. Pure lime heated with sul

VOL. I.

phur yields a much weaker phosphorus than that produced from oystershells, because the latter contain a little magnesia. (Wach.) (3.) Dessaignes ignites gypsum mixed with flour.

Osann's Phosphori.-a. Antimonial Phosphorus: Formed by placing cleaned and ignited oyster-shells in alternate layers with finely pounded sulphuret of antimony in a well covered crucible, and heating the mixture for an hour after cooling, the white pieces are to be picked out, the yellow and black ones thrown away.-b. Realgar Phosphorus: The same mode of preparation, but using realgar instead of sulphuret of antimony.— c. Arsenical Phosphorus: A paste formed of neutral arseniate of baryta and gum tragacanth is dried and iguited for half an hour between coals or on an earthenware support: it has a greyish yellow colour.-d. Burnt oyster-shells treated as in a with orpiment instead of sulphuret of antimony, or-e. with mosaic gold, or-f. with cinnabar, or-g. with a mixture of sulphur and zinc-blende, or-h. with arsenious acid. Of all these phosphorescent compounds, the most luminous are a, b, and c.

Wach's Phosphori: a. Burnt oyster-shells thinly sprinkled with solution of artificial tersulphuret of arsenic, covered after drying with pounded sulphur, and ignited in a covered crucible, produce an excellent phosphorus.-b. Three parts of burnt oyster-shells disposed in alternate layers with 1 part of a mixture of 10 parts of flowers of sulphur and 1 part of oxide of antimony, and moderately heated in a covered crucible.-c. Similarly with oxide of zinc.-d. With oxide of cadmium.-e. With peroxide of tin. f. A solution of arseniate of ammonia is dropped upon calcined oyster-shells, which are then sprinkled with sulphur and ignited.-Similarly with chloride of antimony--h. With sulphate of zinc.--. With sulphate of cadmium.-k. With proto-chloride of tin.--. Good phosphori are likewise obtained by igniting hyposulphite or sulphite of baryta, strontia, or lime, particularly hyposulphite of lime mixed with 3 or 4 per cent. of magnesia.

Lastly, among good phosphori may be enumerated: Homberg's Phosphorus (chloride of calcium, which Homberg formed by melting 1 part of sal-ammoniac with 2 parts of slaked lime); Baldwin's Phosphorus (nitrate of lime fused till the nitric acid begins to decompose); many kinds of fluor-spar, as the chlorophane of Nertschinsk (Grotthuss), and a variety of fluor-spar from Dauuria (Schw. 49, 259); strontianite; arragonite; calcspar; marble; stalactites; chalk, and slightly-burnt oyster-shells.

Less powerfully luminous, according to Heinrich, are: Crystallized boracic acid, sal-ammoniac, sulphate of potash, nitre, crystallized carbonate, borate, and sulphate of soda: rock-salt, witherite, radiating heavy spar from Bologna, marienglas, fibrous gypsum, alabaster, artificial sulphate of lime, (common fluor-spar-Grotthuss), crystallized sulphate of magnesia, crystallized alum, arsenious acid, pharmacolite, freshly prepared flowers of zinc, sulphate of mercury, tartar, benzoic acid, loaf-sugar, sugar of milk, bleached wax, white paper (especially when it has been heated almost to burning: yellow and red paper are nearly as phosphorescent as white, dark blue paper is not at all so-(Grotthuss); egg-shells, corals, snails, pearls, bones, teeth, ivory, leather, and skins of men and animals.

The following are phosphorescent in a tolerably high degree: Tartaric acid; also seeds, grain flour, starch, crums of bread, gum-arabic, feathers, cheese, yolk of egg, muscular flesh, tendons, isinglass, glue, horn-all well dried; moreover, the alburnum of trees, bleached linen, bleached cottonyarn, and other bleached vegetable fibres.

Moderately phosphorescent are: Ice, oxide of antimony, sulphate of zinc, white lead, iron pyrites, alum-slate, basalt, potter's clay, fuller's earth, bark of trees, amber.

Feebly luminous are: Cœlestin, smalt, magnetic iron ore, red ochre, undried seeds, flour, and starch; also, according to Grotthuss, blue carbonate of copper (Kupfer-lazar), and beryl.

Very feebly and often not at all luminous are: Glass, silica, rockcrystal, amethyst, cornelian, prase, heliotrope, sapphire, corundum, chrysolite, spinell, emerald, topaz, tourmalin, hyacinth, garnet, melanite, leucite, adularia, common felspar, zeolites and other minerals; chloride of zinc, yellow blende, wood, most kinds of resin and gum, silk, and animal substances not well dried.

The following, according to Heinrich, exhibit no phosphorescence: Water and all other liquids, sulphur, graphite, all metals in the free state, baryta, strontia, lime, apatite, red lead, red oxide of mercury, fresh parts of plants, unbleached yarn of hemp and flax, mineral pitch, fossil tar, coal, jet, turf, charcoal. Moreover, according to Dessaignes, all metallic sulphurets except orpiment.

According to Dessaignes, phosphorescence is also exhibited by: Glucina, phosphorite from Estremadura, orpiment, flowers of sulphuret of antimony (spiessglanz-blumen), sulphate and phosphate of lead, protochloride of tin, a mixture of peroxide of tin and oxide of lead, and imperfectly slaked baryta, strontia, and lime.

These bodies will not shine in the dark unless they are first exposed to light even the Bolognian and Canton's phosphorus, which are prepared by ignition, do not shine when left to cool in the dark and not first exposed to light (John): neither do the realgar and antimonial phosphori, even when heated to 100° C. (Osann.). Most of these bodies require to be exposed to the direct rays of the sun. The Cantonian and Bolognian phosphorus, diamond, paper, chlorophane, sulphate of potash and common salt, are rendered luminous by reflected sunlight; the five substances first nained, by strong lamp-light; the Bononian phosphorus, and Osann's phosphori a, b, c, by the light of phosphorus burning in oxygen gas. (Phosphorus burning in oxygen gas under a bell-jar makes Canton's phosphorus but very feebly luminous, because the light passes through the glass-E. Becquerel.) The last three phosphori (not the Bolognian) are also rendered phosphorescent by the light of sulphur burning in oxygen gas, and even by the light of a tallow candle, placed at the distance of a foot; the antimonial phosphorus, likewise by the light of white-hot iron at the distance of a foot; (in the last experiment the phosphorus was placed in a dish surrounded with ice); burnt oyster-shells, by the light of burning alcohol impregnated with common salt; Canton's phosphorus and some diamonds are also rendered luminous by moonlight. The intensity of the emitted light is however always proportional to that of the light by which the phosphorescence has been excited. Bodies may be rendered luminous by irradiation, even when immersed in water. (Heinrich, Dessaignes, Osann.)

Canton's phosphorus, after being exposed to daylight for two seconds, exhibits the greatest luminosity when immersed in water: the light appears to be somewhat fainter when the substance is freely exposed to day-light; fainter again when the light falls upon it through a plate of rock-crystal 7 inches thick; still fainter when it passes through blue glass, and faintest of all when the light reaches the phosphorus after passing through a plate of white glass 3 millimetres thick, or through a