Page:EB1911 - Volume 27.djvu/395

Rh metatungstic acids. Two sodium salts, viz. Na2HPW12O40·nH2O and Na3·PW12O40·nH2O, are obtained by heating sodium hydrogen phosphate with a tungstate. The most important silicotungstic acids are silicodecitungstic acid H8W10SiO36·3H2O, tungstosilicic acid, H8W12SiO42·20H2O, and silicoduodecitungstic or silicotungstic acid, H8W12SiO42·29H2O. On boiling gelatinous silica with ammonium polytungstate and evaporating with the occasional addition of ammonia, ammonium silicodecitungstate is obtained as short rhombic prisms. On adding silver nitrate and decomposing the precipitated silver salt with hydrochloric acid, a solution is obtained which on evaporation in a vacuum gives the free acid as a glass mass. If this be dissolved in water and the solution concentrated some silicic acid separates and the filtrate deposits triclinic prisms of tungstosilicic acid. Silicotungstic acid is obtained as quadratic pyramids from its mercurous salt which is prepared from mercurous nitrate and the salt formed on boiling gelatinous silicic acid with a polytungstate of an alkali metal.

Pertungstic Acid, HWO4.&mdash;The sodium salt, NaWO4·H2O, is obtained by evaporating in a vacuum the product of boiling a solution of sodium paratungstate with hydro en peroxide. lts solution liberates chlorine from hydrochloric acid and iodine from potassium iodide.

Halogen Compounds.&mdash;Although the trioxide is soluble in hydrofluoric acid, evaporation of the solution leads to the recovery of the oxide unchanged. A double salt of the oxyfiuoride, viz. 2KF·WO2F2·H2O, is obtained as crystalline scales by dissolving normal potassium tungstate in hydrofluoric acid and adding (potassium hydroxide till a permanent precipitate is just forme . Other oxyfluorides are known. The hexafluoride, WF6, is a very active gaseous compound, which attacks lass and metals, obtained from tungsten hexachloride and hydrofluoric acid (Ruff and Eisner, Ber., 1905, 38, p. 742). Oxyfluorides of the formulae WOF4 and WO2F2 are also known. Tungsten forms four chlorides, viz. WCl2, WCl4, WCl5, WCl6. The dichloride, WCl2, is an amorphous grey powder obtained by reducing the hexachloride at a high temperature in hydrogen, or, better, by heating the tetrachloride in a current of carbon dioxide. It changes on exposure to air and dissolves slightly in water to give a brown solution, the insoluble portion gradually being converted into an oxide with evolution of hydrogen. The tetrachloride, WCl4, is obtained by partial reduction of the higher chlorides with hydrogen; a mixture of the penta- and hexa-chloride is distilled in a stream of hydrogen or carbon dioxide, and the pentachloride which volatilizes returned to the flask several times. This gives the tetrachloride as a greyishbrown crystalline powder. It is very hygroscopic and with cold water gives the oxide and hydrochloric acid. On heating it gives the di- and penta-chlorides. At a high temperature hydrogen reduces it to the metal partly in the form of a black pyrophoric powder. The pentachloride, WCl5, is obtained as a product in the preparation of the tetrachloride. It forms black lustrous crystals, or when quickly condensed, a dark green crystalline powder. It melts at 248° and boils at 275.6°; the vapour density corresponds to the above formula. It is more hygroscopic than the tetrachloride; and when treated with much water the bulk is at once decomposed into the blue oxide and hydrochloric acid, but an olive-green solution is also produced. The hexachloride, WCl6, is obtained by heating the metal in a current of dry chlorine in the absence of oxygen or moisture, otherwise some oxychloride is formed; a sublimate of dark violet crystals appear at first, but as the hexachloride increases in quantity it collects as a very dark red liquid. When perfectly pure, the hexachloride is stable even in moist air, but the presence of an oxychloride brings about energetic decomposition; similarly water has no action on the pure compound, but a trace of the oxychloride occasions sudden decomposition into a greenish oxide and hydrochloric acid. It melts at 275°, and boils at 346.7° (759.5 mm.). Vapour density determinations indicate that dissociation occurs when the vapour is heated above the boiling point.

Several oxychlorides are known. The monoxychloride, WOCl4, is obtained as red acicular crystals by heating the oxide or dioxychloride in a current of the vapour of the hexachloride, or from the trioxide and phosphorus pentachloride. It melts at 210.4° and boils at 227.5 forming a red vapour. Moist air brings about the immediate formation of a yellowish crust of tungstic acid. The dioxychloride, WO2Cl2, is obtained as a light lemon-yellow sublimate on passing chlorine over the brown oxide. It is unaffected by moist air or cold water, and even when boiled with water the decomposition is incomplete. Tungsten combines directly with bromine to give, when the bromine is in excess, the penta- and not a hexabromide. This substance forms crystals resembling iodine, which melt at 276° and boil at 333°. It slowly evolves bromine on standing, and is at once decomposed by water into the blue oxide and hydrobromic acid. The dibromide, WBr2, is a non-volatile bluish black powder obtained by reducing the pentabromide with hydrogen. By passing bromine vapour over red-hot tungsten dioxide a mixture of WO2Br2 and WOBr4 is obtained, from which the latter can be removed by gently heating when it volatilizes. The dioxybromide forms light red crystals or a yellow powder; it volatilizes at a red heat, and is not acted upon by water. The monoxybromide forms brownish-black needles, which melt at 277° and boil at 327.5°; it is decomposed by water. The di-iodide is obtained as green metallic scales on passing iodine over red-hot tungsten.

Tungsten disulphide, WS2, is obtained as soft black acicular crystals by the action of sulphur, sulphuretted hydrogen or carbon bisulphlde on tungsten. The trisulphide, WS3, is obtained by dissolving the trioxide in ammonium sulphide or by passing sulphuretted hydrogen into a solution of a tungstate and precipitating by an acid in both cases. When dry it is a black mass which yields a liver-coloured powder. It is sparingly soluble in cold water, but is easily dissolved by potassium carbonate or ammonia. By dissolving it in a hydro sulphide a sulphotungstate is produced; these salts can also be obtained by passing sulphuretted hydrogen into a solution of a tungstate.

A nitride, W2N3, is obtained as a black powder by acting with ammonia on the oxytetrachloride or hexachloride; it is insoluble in sodium hydroxide, nitric and dilute sulphuric acids; strong sulphuric acid, however, gives ammonia and tungstic acids. Ammonia does not react with tungsten or the dioxide, but with trioxide at a red heat a substance of the formula W5H6N3O5 is obtained, which is insoluble in acids and alkalis and on ignition decomposes, evolving nitrogen, hydrogen and ammonia. Phosphorus combines directly with the metal to form W3P4; another phosphide, W2P, results on igniting a mixture of phosphorus pentoxide and tungsten trioxide.

The atomic weight has been determined by many investigators; the chief methods employed being the analysis and synthesis of the trioxide and the analysis of the hexachloride. The former was employed by Pennington and Smith and Desi (Zeit. anorg. Chem., 1895, 8, pp. 198, 205) who obtained the value 183.42.

TUNGUSES, a widespread Asiatic people, forming a main branch of the Mongol division of the Mongol-Tatar family. They are the Tung-hu of the Chinese, probably a corrupt form of tonki or donki, that is, “ men ” or “ people.” The Russian form Tungus, wrongly supposed to mean “ lake people,” appears to occur first in the Dutch writer Massa (1612); but the race has been known to the Russians ever since they reached the Yenisei. The Tungus domain, covering many hundred thousand square miles in central and east Siberia and in the Amur basin, stretches from the Yenisei eastwards to the Pacific, where it occupies most of the seaboard between Korea and Kamchatka. It also reaches the Arctic Ocean at two points, in the Nisovaya tundra, West of the Khatanga River, and in a comparatively small enclosure in the Yana basin over against the Lyakhov (New Siberia) Archipelago. But the Tunguses proper are chiefly centred in the region watered by the three large eastern tributaries of the Yenisei, which from them take their names of the Upper, Middle or Stony, and Lower Tunguska. Here the Tunguses are known to the Samoyedes by the name of Aiya or “ younger brothers,” implying a comparatively recent; immigration (confirmed by other indications) from the Amur basin, which appears to be the original home both of the Tunguses and of the closely allied Manchus. The Amur is still mainly a Tungus river almost from its source to its mouth: the Oroches (Orochus), Daurians, Birars, Golds, Manegrs, Sanagirs, Ngatkons, Nigidals, and some other aboriginal tribes scattered along the main stream and its affluents&mdash;the Shilka, Sungari and Usuri&mdash;are all of Tungus stock and speech. On the Pacific the chief subdivisions of the race are the Lamuts, or “ sea people,” grouped in small isolated hunting communities round the west coast of the Sea of Okhotsk, and farther south the Tazi between the Amur delta and Korea, The whole race, exclusive of Manchus, numbers probably little more than 50,000, of whom some 10,000 are in the Amur basin, the rest in Siberia. The Tungus type is essentially Mongolic, being characterized by broad flat features, small nose, wide mouth, thin lips, small black and somewhat oblique eyes, black lank hair, dark olive or bronze complexion, low stature, averaging not more than 5 ft. 4 in.; they are distinguished from other Mongolic peoples by the square shape of the skull and the slim, wiry, well-proportioned figure. This description applies more especially to the Tunguska tribes, who may be regarded as typical Tunguses, and who, unlike most other Mongols, betray no tendency to obesity. They are classed by the Russians, according to their various pursuits, as Reindeer, Horse, Cattle, Dog, Steppe and Forest Tunguses. A few have become settled agriculturists; but the great bulk of the race are still essentially forest hunters, using the reindeer both as mounts and as pack animals. Nearly all lead nomad lives in pursuit of fur-bearing animals, whose skins they supply to Russian and Yakut traders in exchange for provisions, clothing and other necessaries