Prep. Made by heating the carbonate of zinc in a loosely covered crucible exposed to a dull red heat; the carbonic acid is driven off, and the oxide of zinc remains.

Prop. & Comp. A white powder, without odour or taste, becoming pale yellow by heat, insoluble in water, but soluble in hydrochloric and other acids, and forming white dilute sulphuric acid a solution which gives a white precipitate with hydrosulphuret of ammonia. Oxide of zinc dissolves, without effervescence, in diluted nitric acid; the solution is not affected by chloride of barium or nitrate of silver, and gives a white precipitate with carbonate of ammonia, which dissolves entirely without colour in excess of the reagent; the three latter reactions indicating the absence of sulphates, chlorides, alumina, iron, or other metallic impurities. In composition it is a protoxide (Zn O).

Off. Prep. Unguentum Zinci Oxidi. Ointment of oxide of Zinc. (Oxide of zinc, eighty grains; simple ointment, one ounce. Mix them together.)

Therapeutics. A tonic, especially to the nervous system; also somewhat astringent: locally applied, a slight astringentand desicant. Used chiefly in chorea, hysteria, and epilepsy; and externally, to excoriated surfaces and slight ulcerations.

Dose. 1 gr. to 10 gr., or more in pill or powder.

Adulteration. Chalk, carbonate of magnesia; detected by effervescing, and the special tests of these bodies. Starch has sometimes been used to adulterate this oxide.

Calamina Praeparata. Prepared Calamine. (Not officinal.) An oxide of zinc, prepared from calamine, the native carbonate of zinc, by heat and elutriation.

Prop. & Comp. A greyish powder, almost entirely soluble in dilute sulphuric acid, with scarcely any effervescence; and the precipitate thrown down by ammonia or potash is redissolved by excess of these reagents.

Ceratum Calaminae. Cerate of Calamine; Turner's Cerate, contained in London Pharmacopoeia, 1851. (Prepared calamine, wax, of each, seven ounces and a half; olive oil, one pint. Mix the oil with the melted wax, then remove them from the fire, and when they first begin to thicken add the calamine, and stir constantly until they cool.)

Therapeutics. Only used externally as a desiccant; it possesses no advantages over the pure oxide of zinc.

Adulteration. As found in shops, it often contains little or none of the oxide of zinc; but consists of sulphate of baryta, coloured, an impurity detected by its weight and insolubility.