TUNGSTIC acid. In the year 1781; Scheele and Bergman, in investigating the nature of tungsten by the Swedes, discovered that it is composed of lime combined with a peculiar acid. Their discovery was afterwards confirmed by several chemists, who detected the same acid in the mineral called wolfram. This acid always exists in combination with lime and iron. It may be obtained by reducing the former to a fine powder, and treating it with nitric or muriatic acids, which unite with the lime; and then by alkalies, which dissolve the acid. The alkaline solution is to be precipitat ed by the nitric or muriatic acid ; the precipitate is to be carefully washed and dried, which is the tungstic acid in the solid state. The tungstic acid thus pre pared, is in the form of a white powder, which has an acid and metallic taste, changes the colour of vegetable blues into red, and has a specific gravity, ac cording to Bergman, equal to 3.6. Heat ed before the blow-pipe, the tungstic acid becomes first yellow, then brown, and at last black; it affords no smoke, and gives no sign of flision. When it is calcined for some time in a crucible, it is deprived of the property of dissolving in water. Exposed to the air it suffers no change. It is soluble in twenty parts of
boiling water, but it is partially separated on cooling. _ This solution has an acid taste, and reddens the tincture of turnsole. Heated with charcoal, it is reduced, but with difficulty, to the metallic state. With sulphur and phosphorus it becomes of a grey colour, but without reduction. The acids do not dissolve the tungstic acid in the form of white powder, but they change completely its properties. The sulphuric acid changes it to a blue, and the nitric and muriatic acids convert it into a tine yellow colour. In this state it has lost its taste and solubility, has be come specifically heavier, and has ac quired the property of forming salts with the same bases, distinctly different from those formed with what was called the white acid. The compounds which it forms with the alkalies, earths, and me tallic oxides, are a species of neutral salts; but the chemical combination is not fully completed to hide the alkaline properties of the former. In forming these corn pounds, it is the only property in which it agrees with the acids. The compounds are denominated tungstates.