PROPERTIES OF TUNGSTATES.

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the acid, and let the remaining yellow powder, after being washedin distilled -water, be digested in liquid ammonia till it is renderedconsiderably whiter. This ammoniacal solution is then pouredoff, and the residual undecomposed part of the tungstate is oncemore treated with nitric acid as before. The acid being again se-parated it is again digested with liquid ammonia, and so on alter-nately till it is totally decomposed.

The ammoniacal solution is then decomposed by the addition ofnitric acid; the tungstic acid becomes precipitated in the formof a white powder, which, after being washed, dried, and exposedto heat, assumes a yellow colour.

Rationale. ..On adding nitric acid to the ammoniacal solu-tion, nitrate of ammonia is formed, and the tungstic acid be-comes separated, but this last is not perfectly free from ammonia,it is therefore necessary- to heat it, or to wash it in diluted ni-tric acid, by which means the adhering ammonia is either vola-tilized or neutralized, which then may be washed away bymeans of distilled water.

The tungstic acid may also be obtained from the mineral calledwolfram, in which it is combined with iron and manganese, andfrequently with silex, in die state of a yellow oxid, as directedbefore, p. 16.

PROPERTIES OP TUNGSTATES.

These salts are very little known. Most of them, when dis-solved in water, are decomposed by all the acids : these combi-nations occasion a precipitate, which is a triple compound,varying according to die acid employed.

METHODS OF OBTAINING TUNGSTATES.

Tungstate of potash, soda, or ammonia, may be formed bydissolving tungstic acid in the alcaline solutions. Tungstate ofmagnesia is obtained by boiling tungstic acid with carbonate ofmagnesia.

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