TUNGSTEN (W). We/frustum. This clement was discovered by Scheele in 1781, but was not isolated till some few years later. The name indicates" heavy stone," in allusion to the high specific gravity of its Swedish ore.
The chief, if not the only form in which tungsten occurs in nature, is that of tungatic acid ; sometimes free, but snore often combined : it is usually found in company with tin-stone, and till within the last few years has been regarded only as a mineralogical curiosity. Recently, however, tungsten has been combined with iron, and the alloy found to possess the properties of the beet steel.
Tungsten may easily be obtained. from tungstic acid, by reducing with hydrogen or carbon at a high temperature. The most convenient method Is to knead a mixture of tungstio acid and charcoal into a paste with oil, and expose the mass In a carbon crucible to the heat of a blast furnace. It is a steel-gray metal, susceptible of considerable lustre, exceedingly hard and infusible, and of specific gravity 17.0. It does not readily oxidise in the air, and is not magnetio. It is a good conductor of heat and electricity, and by strong oxidising acids is converted into tungstio acid.
The equitalent of tungsten is 92.
Tungsten and oxygen form two definite compounds; binoxide (WO,) and teroxide,ur tungstie acid (WOO A dark indigo-blue coloured oxide has also been described, but it is probably a mixture, or pos sibly a compound of binoxide and teroxide (W,0,= WO„ WO,).
Binoride of tungsten, or tungstous oxide (WO,), is a dark copper coloured, almost black powder, obtained on passing hydrogen over tungatic acid at a low red heat. It has also been formed in lustrous scales. Binoxide of tungsten has a great tendency to absorb oxygen, but forma with soda a compound that is not acted upon by any acid, except hydrofluoric'.
Tungstie a•-id anhydrous acid, or tungstic anhydride, may be procured by decomposing Wolfram (tungstate of iron and manganese Nn(J, 3Fe0, 1V00, with aqua regia, evaporating to dryness, digesting the residue in ammonia, re-crystallising the tungstato of ammonia, drying, and heating to redness. it is a yellow powder, insoluble In water and acids, but soluble in alkalies, and in alkaline carbouatas with effervescence.
Hydrated tungatic acid (HO, WO,) is a yellow precipitate, formed on adding excess of hydrochloric acid to a solution of tungstic anhydride in alkali.
Tanystates.—Those of the alkalies are formed in the manner just indicated, and others may be obtained by double decomposition. Tungstate of soda (NaO, WO, + 2Aq.) possesses the important property of rendering fabrics imintiammable. Muslin soaked in a solution of 20 parts of this salt with 3 of phosphate of soda in 100 parts of water may readily be ironed and otherwise prepared for wear, and is then only charred when brought into contact with fire; It does not itself burn with flame and, therefore, does not propagate its combustion. Tungseate of lead rivals the carbonate as a pigment. A modification of tungstic acid in which two equivalents combine with one of base has been termed metatungstie acid (HO, 'W Tungsten and phosphorus form two compounds. The first is a dark gray powder (1V,P,1 produced when phosphorous vapour is passed over the metal. The second (W,P) occuni in crystalline groups of lustrous prisms, and is obtained on reducing two equivalents of phos phoric acid and one of tuugstic acid in a carbon crucible at a very high temperature.
Tungsten and sulphur form bintlphide (WS,) and tersulphide (WS,). The former Is a bluish-black, crystalline, plumbisgolike powder, which remains undiaaolved when a well fused mixture of equal parts of bitungetate of potash and sulphur is treated with water. The ter sulphide is produced on dissolving tungstic acid IA an alkaline sulphide, and precipitating by an acid : it is slightly :soluble in water, and is a powerful sulphur acid.
Tungsten and chlorine combine In two proportions. On passing the dry gas over the heated metal, both chlorides are formed, the relative 'proportions depending on the amount of chlorine. The bieldoride (%4) Is less volatile than the terehlvride (WOO, Both of them cry& 'rho compounds of tungsten are not poisonous. Their solutions aro not precipitated by sulphide of hydrogen, or sulphide of ammouium. Sulphuric acid and zinc when added to a solution of tungstic acid pro duce a deep blue coloration in the liquid. With borax in the blow pipe flame, the compounds of tungsten yield a yellow bead, becoming blood-red on cooling. The metal is estimated in the state of tungatic anhydride, which contains per cent. of metal.