# Encyclopædia Britannica, Ninth Edition/Tungsten

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TUNGSTEN (Germ. wolfram, or, antiquated, scheel), one of the metallic elements of chemistry. The mineral tungsten (meaning in Swedish "heavy stone") used to be taken for a tin ore until this was disproved by Cronsted. Scheele showed in 1781 that it is a compound of lime with a peculiar acid, the metallic nature of which was recognized in the same year by Bergmann. It occurs only as a component of a number of relatively rare minerals, the most important of which are wolfram or wolframite, (Fe, Mn)O.WO$_3$, and scheelite (tungsten), CaOWO$_3$ (see Mineralogy). The metal is prepared from the pure oxide WO$_3$ by reduction with hydrogen in a platinum tube at a high temperature. It forms resplendent tin-white or grey plates, or a dull black powder similar to hydrogen-reduced iron. Sp. gr. = 19·129, water of 4° C. = 1 (Roscoe). It is more difficult to fuse than even Manganese (q.v.). It is unalterable in ordinary air; oxygen and even chlorine act upon it only at a high temperature. Hydrochloric and sulphuric acid do not attack it. Nitric acid attacks it slowly, aqua regia readily, with formation of the trioxide WO$_3$. Impure tungsten is now being prepared industrially for the production of a peculiar kind of steel (see Iron vol. xiii. p. 352).
Chlorides.—Tungsten forms four chlorides,—WCl$_2$ WC1$_4$, WC1$_5$, WCl$_6$. The highest, WCl$_6$, is obtained by heating the pure powdery metal in a current of absolutely pure chlorine. In the presence of moisture or air oxy-chlorides are produced. It sublimes off as a dark red liquid, freezing into crystals. These fuse at 275° C. and re-solidify at 270°; the liquid boils at 346°·7. The sp. gr. of the vapour is in accordance with the formula at 350°; at higher temperatures it dissociates into WC1$_5$ and free C1$_2$ (Roscoe). When the vapour of WC1$_6$ is passed over heated trioxide, the two bodies unite, W0$_3$ with 2WC1$_6$ into 3WOC1$_4$, forming magnificent red needles, which fuse at 210°·4 and boil at 227°·5 C. (Wöhler). Both compounds, WCl$_6$ and WOC1$_4$, are decomposed by water, the oxy-chloride more readily, with formation of hydrochloric acid and trioxide. For other chlorides and oxy-chlorides, see the ordinary hand-books of chemistry.
The binoxide, WO$_2$, is obtained when the trioxide is reduced by hydrogen at a dull red heat. This oxide is very prone to pass into trioxide or tungstate. An interesting and beautiful class of compounds of WO$_3$, WO$_2$, and bases are known as tungsten bronzes. The first of these was discovered by Wöhler. Normal tungstate of soda, Na$_2$OWO$_3$, is fused, and trioxide added to it as long as it dissolves. The product is then heated in hydrogen as long as water goes away, and the substance thus reduced is exhausted successively with water, hydrochloric acid, caustic potash ley, and again with water. A residue of the composition Na$_2$O.W$_2$O$_6$ + WO$_2$ remains in the shape of magnificent gold-like lustrous cubes, of specific gravity 6·617, which conduct electricity like a metal. Only hydrofluoric acid dissolves this soda-tungsten bronze. There are a number of other tungsten bronzes, all distinguished by metallic lustre and magnificent purple, red, yellow, or blue colours.
Analysis.—Oxides of tungsten dissolve in fused microcosmic salt, Na$_2$OP$_2$O$_5$; the bead becomes blue in the reducing flame, in the presence of iron blood-red, and in the oxidizing flame colourless. When heated on charcoal with (not too much) carbonate of soda or cyanide of potassium in the reducing flame, they yield a grey heavy powder of metal, obtainable by elutriation. The process fails in the presence of too much alkali. Insoluble tungstates (e.g., the ordinary tungsten minerals) are disintegrable by fusion with alkaline carbonate; the fuse, when treated with water, yields a solution of alkaline tungstate. This solution, when mixed with excess of hydrochloric acid, gives a white precipitate of hydrated trioxide, which on boiling becomes yellow by partial dehydration. The yellow unignited precipitate is soluble in aqueous ammonia. If tungstate of alkali solutions are mixed with hydrochloric acid and then treated with metallic zinc, they become blue through the formation of a compound of WO$_3$ and WO$_2$ or rather the respective chloride; this reaction gains in definiteness through the presence of phosphoric acid.(w. d.)