The neck of the flask is furnished with a gas-delivery-tube, the end of which dips under water. When so prepared, phosphoretted hydrogen takes fire spontaneously as the bubbles of it, having ascended through the water, come into contact with the air. This remarkable property is due to the presence in the gas of a small quantity of the liquid phosphide of hydrogen, H ̧P. The vapour of this liquid is spontaneously inflammable, and its combustion sets fire to the HP, which then burns to H2O and PО. Thus, 2 If a little alcohol be added to the contents of the flask, the liquid PH, is retained, and the PH, loses the property of taking fire in contact with the air. It may, however, always be ignited by contact with a burning body. Phosphoretted hydrogen is also formed when phosphorous acid is heated. 4H PO = 3H,PО + PH ̧. 3 Phosphoretted hydrogen is produced in nature when animal matter containing P rots or putrefies. The smell of foul fish is partly due to this gas; and the light which is emitted by such substances is owing to the gradual oxidation of the gas in the air. Ignes fatui, "Will-o'-the-wisp," &c. are supposed to be owing to the same cause. § 266. Phosphoretted hydrogen is a colourless gas, of an offensive smell, like that of stale fish. It consists of 1 vol. of P weighing 62, united with 6 vols. of H, each weighing 1, con tracted to 4 vols.* Its density is therefore 62+6 or 17 (com pared with air 1.17). It is feebly alkaline, and may combine with HI to form the compound PH2HI or PH1I, It is preferable to take the density of P as 62; at lower temperatures the specific gravity of P is lower. PH, may be supposed to consist of 1 vol. of P (=31) with 3 vols. of H (weighing each 1), contracted to 2 vols., being thus like NH.. But, as a rule, the higher a vapour is heated the more nearly does its density approach that which it has in gaseous combination. corresponding to NHI. On account of its similarity to ammonia in composition and properties, it is sometimes called phospham. $267. Carbide of phosphorus is not at present known. Nitride of phosphorus is a body of doubtful composition; it is not known whether it contains hydrogen; it is at present of little interest. Combinations of Phosphorus with Chlorine. Two chlorides of phosphorus are known, PCl, and PCI.. $268. Terchloride of phosphorus, PC1,.-Some dry sand is put into a retort, A (fig. 67), and upon this some pieces of dry phosphorus are laid. Through the cork in the tubulus T, a bent Fig. 67. Р T A R tube, P, passes and opens just above the phosphorus. Through this tube a current of perfectly dry chlorine (§ 181) is passed, while the retort is heated by a lamp. The two elements unite with flame, and the PCl, distils over into R. § 269. Terchloride of phosphorus, PCL,, has a density of 1.45; its boiling-point is 78° C. 1 vol. of P (=62) combines with 6 vols. of Cl (each =35·5), and there is contraction to 4 vols.* 62+6x35.5 4 The density of its vapour is therefore or 68.75 (compared with air 4-74). Thrown into water it at first sinks through, but is soon decomposed into H,PO, and HCl. PCI, 3H,0 H ̧PO, + 3HCI. = * Compare note, p. 174. We have already (§ 263) seen this reaction employed for making HPO. Owing to the mutual decomposition of PCl, and H ̧O, the former fumes in moist air and gives rise to the acids H,PO, and HCl, which irritate the eyes and lungs. § 270. Pentachloride of phosphorus, PC1,, is formed by passing dry chlorine over PCI,; the gas is immediately absorbed and a yellowish-white solid body is produced, which is the pentachloride of phosphorus. If the chlorine be used in excess, the PC1, is got quite pure. § 271. PCI, volatilizes without change at 148° C., and, unless under pressure, it does not previously fuse. Thrown into an excess of water the two bodies decompose one another with great violence, phosphoric and hydrochloric acids being produced, the former of which immediately combines with water. § 272. The density of the vapour of PC1, is derived as follows:— 1 vol. of vapour of P (weighing 62) unites with 10 vols. of Cl (each weighing 35.5), and a condensation to 8 vols. follows. The 62+10 x 35.5 8 density is therefore 3.59). or 52.12 (compared with air § 273. Oxychloride of phosphorus, POCI,.—When PC1, is exposed to moist air under a bell-jar, it is gradually converted into the oxychloride; that is, at first only two equivalents of Cl are extracted and replaced by one of O. If PCI, be heated with the proper quantity of some body which parts with water with some difficulty, the same partial replacement takes place. It may for this purpose be heated with two equivalents of monohydrated oxalic acid (§ 160). 3 PC1, + H2C2O = CO + CO2 + POCI, + 2HC1. 5 2 POCI, boils at 110° C., and, like PC1,, though not with so much violence, is decomposed by H2O into H,PO, and HCl. Combinations of Phosphorus with others of the preceding elements. § 274. The terbromide and pentabromide of phosphorus are similar in their formation and properties to the corresponding chlorine compounds; their formulæ are PBr, and PBr ̧. § 275. There are two iodides of phosphorus, PI, and PI ̧. Both are got by adding I in proper proportion to P dissolved in CS; on cooling they crystallize out as orange-coloured or deepred solids. § 276. Sulphides of phosphorus.-Sulphur and phosphorus, when heated together under water, combine with explosive violence. Several such compounds are known, varying in composition according to the proportions of the elements employed, and so closely resembling one another physically, as to offer great difficulty in their separation. Such compounds may be made with less danger if red phosphorus is used; but a greater heat is then required to make the elements unite. CHAPTER XIV. SILICON OR SILICIUM AND ITS COMPOUNDS WITH THE PRECEDING ELEMENTS. Symbol, Si. Equivalent, 28. (Theoretical) density, 56 (compared with air 3.86). § 277. Silicon, Si, occurs very abundantly in nature, but almost always in the form of oxide of silicon, SiO, (silicic acid), either alone or combined with bases, as Ca, Mg, K, Na, &c. In fact almost all rocks, with the exception of the carboniferous (limestone, dolomite, marble), consist essentially of silicates of the above metals. Silicic acid uncombined with any base constitutes quartz, flint, some kind of sea-sand, &c. In combination with aluminium it forms clay, slate, &c. In combination with alu minium and potassium it forms felspar. Granite consists partly of free silicic acid (or quartz), partly of silicate of aluminium and silicate of potassium (or felspar), and partly of silicate of aluminium and silicate of magnesium (or mica). The metals may vary, being replaced by others; but the silicic acid is an invariable constituent. Silicic acid is also found in plants, especially in the stalks of grasses, reeds, canes, &c., and in the husks of grain. § 278. Silicon, Si, may be obtained artificially by heating silicic acid with potassium; but it is prepared more advantageously by heating a double fluoride of silicon and potassium with sodium. The sodium withdraws the fluorine from the fluoride of silicon, leaving the potassium also in combination with fluorine. The fluorides of potassium and sodium are removed by being dissolved in water. The silicon is thereby left as a brown powder. § 279. Si'.-So prepared, silicon is heavier than water, and is not attacked by nitric or sulphuric acid. When strongly heated in the air, it burns with great brilliance, being oxidized to SiO. It may be fused under NaCl, and is got on cooling as a steelgrey mass harder than glass. Si corresponds to the charcoalor soot-form of carbon. § 280. Si3.-Silicon may be got in a form similar to the graphitic form of carbon, and in a similar manner. On heating in a crucible the above-mentioned fluoride of potassium and silicon with Al, instead of Na, the Al withdraws the Fl, and the reduced Si dissolves in the excess of the melted Al. The latter metal is removed by treating the mixed mass with hot strong HCl, and traces of SiO, by means of HFl (§ 217). Silicon so obtained greatly resembles graphite, and is much less oxidizable than S', the preceding modification of the element. § 281. Sia.-Silicon may be obtained in a third modification— namely, the crystalline one, and corresponding therefore to the diamond or crystalline modification of carbon. This form is got by passing the vapour of tetrachloride of silicon, SiCl, (§ 289), over metallic aluminium heated to a white heat in a porcelain |