PENTACHLORIDE OF PHOSPHORUS, PC,.

This compound is produced by allowing phosphorus to burn in excess of dry chlorine gas (which it does spontaneously at ordinary temperatures), or by acting upon the terchloride of phosphorus with chlorine, which gradually converts it into the solid pentachloride. The latter is a snow-white, flocculent substance, which volatilizes below 212° F.; its vapor density is 4.85 at 365° F. (185° C.); it may be fused under pressure, and crystallizes, upon cooling, in transparent prisms. It fumes on exposure to air, and is decomposed by water into phosphoric and hydrochloric acids :

PCI,+5HO=PO,+5HCI.

It forms, with metallic oxides, chloride of the metal and phosphate of the oxide. Pentachloride of phosphorus, like phosphoric acid, is sometimes employed as a dehydrating agent; it has also lately been used for producing chlorine compounds of organic derivation.1

OXYCHLORIDE OF PHOSPHORUS, PC10. Sp. Gr. 1.7.

Pentachloride of phosphorus is gradually converted by aqueous vapor into hydrochloric acid and the above compound :

PCI,+2H0=PC1,0,+2HCl.

This substance is always produced after a time, if pentachloride of phosphorus be preserved in an imperfectly-stoppered bottle.

It is a colorless liquid, very limpid, and of high refracting power. It boils at 230° F. (110° C.), yielding a vapor of the density 5.40; its odor is similar to that of terchloride of phosphorus. It fumes in air, and is decomposed, by contact with water, into hydrochloric and phosphoric acids.

CHLOROSULPHIDE OF PHOSPHORUS, PCIS,.

When dry hydrosulphuric acid is passed over pentachloride of phosphorus, or when the latter is agitated in a vessel filled with the dry gas, a colorless liquid of the above composition is obtained, which boils at 262° F. (128° C.); it is slowly decomposed by water into hydrochloric, hydrosulphuric, and phosphoric acids:

PCI,S,+5HO PO,+3HC1+2HS.

It is converted into sulphophosphoric acid by alkalies, a metallic chloride being simultaneously produced :

PCI,S,+6K0=3KC1+3KO.PO,S.

The sulphophosphates may be crystallized; they correspond to the tribasic phosphates, the formula of sulphophosphate of soda being

3NaO.PO,S,+24110.

This acid may be replaced in its combinations with bases by the weakest acids; when thus liberated, it is at once decomposed into hydrosulphuric and phosphoric acids:

3(HO.PS,O,)+2HO=3(HO.PO,)+2HS.o

PHOSPHORUS and Bromine.

When phosphorus and bromine are brought into contact in a vessel filled with

Compounds of pentachloride of phosphorus with various acids (e. g. sulphuric, phos

phoric, arsenious, and tungstic acids) have been obtained.

2

3 By the action of sulphur on pentachloride of phosphorus, Gladstone has obtained a liquid compound to which he ascribes the formula PSCI.

carbonic acid, they unite instantaneously, with incandescence, the products being a solid or a liquid, according to the proportions used.

Terbromide of Phosphorus (PBr.) may be obtained by adding phosphorus, in very small pieces, to perfectly anhydrous bromine, until the color of the latter disappears perfectly; excess of phosphorus may be separated by distillation.

It is a colorless, very volatile, pungent liquid, which does not solidify at 10°.4 F.(-12° C.); when in contact with air it emits white fumes; and is decomposed by water, with considerable evolution of heat, into hydrobromic and phosphorous acids. It has also the property of dissolving phosphorus.

Pentabromide of Phosphorus (PBr) may be formed by mixing the terbromide with bromine, or by bringing a small excess of the latter in contact with phosphorus. It is a lemon-yellow solid substance, which crystallizes in the rhomboidal form after fusion, and may be obtained in needles by sublimation. It evolves dense fumes in air, and is converted by water into hydrobromic and phosphoric acids. An orybromide of phosphorus, analogous to the oxychloride, of the formula PBr,O,, also exists.

PHOSPHORUS AND IODINE.

These two substances unite with energy at ordinary temperatures, the phosphorus bursting into flame if air have access. The phosphorus appears to unite with iodine in several proportions; 1 of the former to 24 of the latter forms a black mass, fusing at 104°.8 F. (46° C.); 1 to 16 forms a dark gray crystalline substance, fusing at 84°.2 F. (29° C.); and 1 to 8 an orange-yellow mass, fusing at 212° F. (100° C.); all three are decomposed by water, yielding hydriodic acid; and in addition, the first yields phosphoric acid, the second phosphorous acid, and the third phosphorous acid and phosphorus.

PHOSPHORUS and Nitrogen.

Ammoniacal gas is absorbed by both the chlorides of phosphorus.

The terchloride of phosphorus yields a white solid which is sparingly soluble in water, and has the composition PC,.5NH,. When this compound is heated in a current of carbonic acid, it is resolved into hydrogen, ammonia, phosphorus, and phosphide of nitrogen, Ñ,P. This last is a white amorphous powder, insoluble in all menstrua; it is infusible and does not volatilize at a red heat if air be excluded, but is slowly oxidized when heated in air; when heated in hydrogen it yields ammonia. It is but slowly affected by powerful oxidizing agents.

Gerhardt states that this compound contains hydrogen, and assigns to it the formula PN,H, with the name phospham.

When the pentachloride of phosphorus is saturated with ammoniacal gas, chloride of ammonium is produced, together with a white insoluble substance, of the formula N,P.2HO, to which the names phosphamide and hydrated phosphide of nitrogen have been given. When boiled with water, especially in presence of acids and alkalies, it yields phosphoric acid and ammonia.

When heated out of contact with air, it evolves ammonia, and leaves a gray insoluble residue, which fuses, but is not decomposed when further heated; its formula, according to Gerhardt, is PNO,

When the mass obtained by the action of moist ammonia upon pentachloride of phosphorus is distilled with water, a white substance passes over, which crystallizes in regular prisms; it fuses below 212° F., and may be distilled unchanged; it is insoluble in water and acids, but dissolves easily in alcohol and ether, and appears to possess great stability.

This body has been named the chlorophosphide of nitrogen; its formula is N.P.CI,.

PHOSPHORUS Aand Sulphur.—These elements combine in a number of different proportions; if phosphorus and sulphur be very gently heated together,

they unite with disengagement of much heat, and frequently with explosion. The safest method of causing them to combine is by fusing the phosphorus in a flask under water, and then introducing gradually, small fragments of sulphur. Compounds of a pale yellow color are thus produced, which have been shown by Berzelius to consist of a series of sulphides of phosphorus, analogous to the oxides of that element, as is seen by the following comparison :

They are prepared by fusing together the two elements, in the proper proportions, in the manner described. They are insoluble in water, alcohol, and ether; of the first two there are red modifications. They combine with alkaline sulphides, and give rise to the production of sulphur-salts, analogous to the corresponding salts of the oxides of phosphorus.

PHOSPHORUS AND SELENIUM appear likewise to be miscible in all proportions, at a temperature approaching the fusing point of phosphorus.

No formulæ have yet been assigned to the selenides of phosphorus.

METALLIC PHOSPHIDES.-The affinity of phosphorus for metals is not so powerful as that of sulphur; nevertheless, it unites with the greater number, producing phosphides. These may be obtained by direct union of the metal and phosphorus at elevated temperatures, or by heating the phosphates with charcoal:

3MO.PO,+C,=8CO+M ̧P.

They may also be formed by heating metallic oxides with phosphorus, or by bringing gaseous phosphuretted hydrogen in contact with salts of the metals. They are solid, opaque, and frequently possess metallic lustre. Many of them part with their phosphorus at high temperatures, the corresponding phosphates being sometimes produced at the same time, if air be allowed access. They are converted, by nitric and hypochlorous acids, into phosphates. The alkaline phosphides are decomposed by water, phosphuretted hydrogen being evolved, and hypophosphite of the metallic oxide produced.

CARBON.

Sym. C. Eq. 6. Sp. Gr., as diamond, 3.5 to 3.55 (as graphite, 1.9 to 2.3). § 118. Lavoisier was the first to show that carbonic acid consisted of oxygen and another element, carbon; and that this element existed in the pure state as the diamond. Carbon is also found, nearly pure, in plumbago, or graphite, and in anthracite. In coal it is associated with iron, hydrogen, earthy and alkaline compounds, &c. In most vegetable and animal substances it is the principal constituent; it also occurs in many minerals, in combination with oxygen (as carbonic acid).

The DIAMOND Occurs principally at Golconda, in Borneo, and Brazil. It is found in gravel or sand, or in a kind of conglomerate of fragments of chalcedony, jasper, and quartz. Diamonds are generally found rough, and coated with a crust which renders them but slightly translucent; on removing this, however, they are very brilliant, and generally colorless and transparent, though they also occur black, yellowish or brown, blue, green, and rose-colored. They refract light powerfully. The regular octohedron is the primitive form of the diamond; its most general form, however, is that of the octohedron, of which the planes are replaced by low pyramids of three planes the figure presents twenty-four planes, and is

therefore almost spherical in form. The surfaces of the crystal are seldom flat, having generally become curved, in consequence of the continued attrition to which they have been subjected in the motion of the alluvial materials with which it is associated; in fact, the action of this attrition is so considerable, as frequently to have reduced crystals of the form just described to that of an octohedron with convex faces.1

The diamond is the hardest of all gems, its natural facets being harder than those produced by polishing. The glazier, in choosing the diamond for cutting glass, makes use of an edge of the crystal formed by naturally curved surfaces, since the edges formed by flat planes merely scratch the glass without producing any fissure.

The diamond may be cleaved in the direction of the octohedral plane; it can only be polished by means of its own dust. The diamond may be exposed to a white heat in a closed crucible without undergoing any change. When heated in air, it begins to burn at about the fusing-point of silver. If it be placed between the two charcoal points of a very powerful battery, it becomes so brilliant from incandescence that the eye is dazzled when looking at it; but if viewed through a smoked glass it will be observed to swell up considerably and divide into fragments. When cold, it is no longer transparent, but metallic gray in appearance, and very friable, resembling coke formed from bituminous coal. Fused nitre rapidly oxidizes the diamond, the carbonic acid produced being retained by the potassa in the nitre. Its examination according to this method affords the best proof of its being pure carbon.

GRAPHITE, BLACK-LEAD, OR PLUMBAGO, is another crystalline modification of carbon, very different in appearance and physical properties to the diamond. It is found imbedded, in the form of rounded masses, in strata of limestone, mica-schist, and granite. The most celebrated locality for this mineral is Borrowdale, in Cumberland. The crystalline form, in which it is occasionally found, is the six-sided table; it generally consists, however, of aggregates of small gray metallic scales, perfectly opaque, soft, and unctuous to the touch; it may be easily cut, and produces a lead-gray mark upon paper. It always contains an admixture of manganese and iron (existing apparently as oxides, combined with silicic and titanic acids). Some specimens contain as much as 28 per cent. of these impurities, while in others only traces are found. Graphite, like the diamond, is unalterable by heat. It may be prepared artificially by bringing an excess of charcoal in contact with fused cast-iron; a portion of the carbon dissolves, and separates out again on cooling, in large scales.

§ 119. COAL.-The form in which carbon is found most abundantly in nature is that of coal, in which substance it is associated with other bodies, very variable in their nature.

Microscopic examination of the various kinds of coal leaves no doubt that they are of vegetable origin; even the most massive coals exhibit some evidence of vegetable structure, and in others of inferior order, the complete forms of various portions of plants are frequently found compressed between the layers, more or less perfectly transformed into coal. These observations, added to the results of careful researches on the subject, render it evident that coal has been produced by the combined action of heat and pressure upon vegetable matter; in short, that it consists of the vegetation of former ages, which has been buried beneath waters, and subsequently become gradually transformed into coal by the effect of heat, generated by the action of moisture, assisted by the pressure of deposits of mud, sand, or clay, which had gradually displaced the water. This process of subterraneous combustion appears, indeed, to have been analogous to that ob

1 Diamond in the amorphous state, of a brownish-black color, has been found in Brazil, and also in some parts of Switzerland.

served when vegetable matter, such as hay, flax, &c., is closely packed in a moist state, when it is found gradually to undergo a species of fermentation, or slow combustion, evolving inflammable vapors, and becoming ultimately carbonized.

All vegetable matter, if exposed in a moist state to very considerable pressure, the escape of the gaseous matter being thus, to a great extent, prevented, would become converted into bitumen, lignite, brown coal, or even perfect coal, according to the intensity and duration of the action. Gaseous compounds, rich in carbon, evolved by the first action of heat, would, under these circumstances, be robbed of a portion of that constituent as the temperature increased, or even suffer entire decomposition with deposition of carbon (see § 129).

In laying bare or removing deposits of coal, quantities of inflammable gas, known as fire-damp (carburetted hydrogen), are continually found pent up in fissures, or gradually escaping from the pores of the coal, in which it has remained for ages compressed. The inflammable gas frequently found escaping from morasses and stagnant pools, to which the name marsh-gas has been given, evidently results from the same species of fermentation, or partial combustion of vegetable matter inclosed under water in the slime and mud; the resulting gaseous products (carburetted hydrogen, carbonic acid, &c., making their escape to the surface of the water, since the pressure exerted upon them is insufficient to retain them. After a time, the mass covering the surface of the earth in such localities is found to consist of imperfectly-charred vegetable matter, to which the name peat, or turf, is given, and which evidently represents the coal in its first stage of formation.

Upon examining the different kinds of coal, they are found to vary considerably in composition and appearance, according to the temperature to which they have been exposed, and the period of their formation.

The more perfect the conversion of vegetable matter into mineral charcoal has been, the smaller is the proportion of elements (hydrogen and oxygen) found in the coal, which originally existed as, or are easily convertible into, volatile compounds.

The brown-coal, or lignite, represents the earliest stage of the process of carbonization, and is the coal of most recent formation. It has a brown, earthy, and sometimes fibrous and woody appearance; large masses of it are found retaining the original form of the trunks of trees, and others containing very perfect forms of leaves, &c. This coal contains from 57 to 70 per cent. of carbon, from 6 to 8 per cent. of hydrogen, and from 14 to 37 per cent. of oxygen, besides nitrogen, and earthy and alkaline salts. Some varieties (particularly alum-shale), contain a large quantity of alumina, and are employed extensively for the manufacture of alum.

The black-coal, or pit-coal, is in a far more advanced state of carbonization than the lignites, but still contains a considerable amount of bituminous matter. Under this head are classed many varieties of coal. The most bituminous of these is the cannel coal; it is dense, black, devoid of lustre, exhibiting a conchoidal fracture, and capable of receiving a high polish. When held in the flame of a candle, it easily ignites, burning with a steady, bright flame. This coal has of late come into very extensive use for the manufacture of illuminating gas, of which it yields a better quality than other species of coal. The other varieties of pit coal also possess a laminated structure, and more or less brilliancy; the principal kinds have received the names, pitch-coal, cubical coal, splint coal,

A species of cannel-coal (the bog-head coal) found at Bathgate, in Scotland, has lately received extensive application. When submitted to distillation, it yields a large quantity of oily matter, which is very valuable as a lubricating agent, and from which a peculiar crystalline solid, termed paraffine, may be separated. This latter has been proposed as an illuminating material.