Vide Arbutus. WINTERA. Vide Drymis. ZINCUM. Zinc.

Syn. Zinc (F.), Zink (G.), Zinco (I.), Spiagter (Russian), Tootanagum ( Tarn.), Sungbusrie (Duk.).

Zinc is a semi-ductile metal procured in great abundance in Britain, particularly in Derbyshire; and in most of the mining countries of Europe. It occurs in

A. The metallic state i. combined with sulphur and iron.

Sp. 1. Blende. Var. a. Yellow blende.

b. Brown blende.

c. Black blende.

B. Oxidized.

ii. combined with silica.

iii. acidified by carbonic acid.

1. Bed Zinc ore.

2. Electric calamine.

3. Common calamine. Var. a. crystallized.

b. compact.

c. earthy.

As the fourth species of these ores is an article of the Materia Medica, we shall describe its characters and properties before we notice those of metallic zinc.

1. Common Calamine.

Officinal. Calamina. Carbonas Zinci impura, Lond. Carbonas Zinci impurus, Edin. Dub. Calamine. Impure Carbonate of Zinc.

1 Very little tannin is present, as it scarcely affects a solution of gelatine.

2 Medical Memoirs, p. 152.

3 Description, etc. of Cutaneous Diseases, i. p. 139.

Syn. Pierre Calaminare (F.), Galmey (S.), Kalmei (Belg.), Gallmeja (Swed.), Pietra Calaminare (I.), Calamina (S), Piedra Calaminar (Port.), Madal tootum (Tarn.).

This ore of zinc is found abundantly in Derbyshire, Somersetshire, Cumberland, and Flintshire, occurring in veins in secondary limestone, generally accompanied by galena, calcareous spar, quartz, and other ores of zinc. In the Harz1 the three varieties are indiscriminately used; and consist, according to an analysis by Mr. Smithson2, of the following components : var. a. 65.2 oxide of zinc, 34.8 carbonic acid; var. b. 64.8 oxide of zinc, 35.2 carbonic acid; var. c. 71.4 oxide of zinc, 13.5 carbonic acid, 15.1 water, - in 100 parts of each variety. They are, however, generally calcined in a moderate heat, by which part of their carbonic acid is dissipated, before they are brought to the shops.

Qualities.-Calamine is usually in the form of greyish yellow, or reddish yellow, friable lumps, without lustre, opaque, and breaking with an irregular, earthy fracture. The specific gravity of the first two varieties is 4.334; that of the last 3.584. Before the blowpipe, calamine becomes yellow; and when exposed to its utmost heat, is sublimed. It dissolves in sulphuric acid with effervescence, but does not gelatinise. It is not used as a remedy till after it is prepared; and then only as an external application.

Officinal preparation.- Calamina preparata, L. E. D.

2. Metallic Zinc Officinal. Zincum, Lond. Edin. Dub. Zinc.

Although the method of extracting zinc from its ores had been long known and practised in India and China, yet it was not known in Europe till about 1721, when Henke pointed out a method of extracting it from its ores. Von Swab first obtained it by distillation in 1742. The Greeks certainly were not acquainted with zinc, although they employed cad-mia, which contained zinc, in the manufacture of brass. At present it is well understood, and conducted in the following manner:-The sulphuret or blende, which is the ore usually employed, is first broken to pieces, and the galena and pyrites separated by hand; and is then roasted in a reverberatory furnace, by which the carbonic acid and part of the sulphur are driven off. The roasted ore being washed, to separate the metallic particles from the lighter parts, is now ground in a mill with one eighth of its weight of charcoal; and put into large earthen jars placed in a circular furnace, and through l The annual produce is 115 tons. 2 Phil. Trans. 1303, 17.

the bottom of each of which passes an iron tube, which goes through the floor of the furnace into a vessel of water placed beneath. The cover of each jar is firmly and accurately luted on, so that the reduced zinc, as it is elevated by the strong heat of the furnace, not finding a vent to escape by the top, descends through the iron tube into the water, and is there condensed in small metallic drops, which are afterwards melted and cast into ingots, in which state it is brought to market1, under the name of Speltre.

Qualities.-Zinc, when rubbed between the fingers, emits a very perceptible odour, and has a peculiar taste. Its colour is brilliant, white with a shade of blue, and its fracture shining and lamellated; hard, yet staining the fingers black when rubbed upon them. Its specific gravity varies from 6.861 to 7.1. In any temperature between 212° to 400°, it is very malleable and ductile; but at a higher temperature it can be pulverised in a mortar. It may be drawn into wire, but its ductility is not great. Exposed to a white heat, in close vessels, it distils over unchanged. Its equivalent is 32.3. Zinc melts at 773° 2 of Fahrenheit; if in contact with air, it is rapidly oxidised; and, at the temperature of ignition, 941° Fah., burns with a white dazzling flame, and is volatilised in the state of a flocculent, white oxide. It is oxidised and soluble in all the acids; and decomposes water when aided by a small portion of sulphuric or of hydrochloric acid : the hydrogen set free holds in solution a small quantity of metallic zinc.

It is used only for pharmaceutical purposes.

Officinal preparations.-Zinci Oxydum, L. E. D. Zinci Sulphas, L. E. D.

3. Impure Oxide of Zinc.

Officinal. Oxidum Zinci Impurum, Edin. Impure Oxide of Zinc. Syn. Tutie (F.), Tutia(C), Tuzia (I.), Atutia (S.).

This substance is supposed to be an artificial compound of the sublimed oxide of zinc that collects in the chimneys of the furnaces in which the ores of this metal are roasted, mixed with clay and water, and baked.

Qualities. - Tutty is inodorous and insipid, of a brownish colour on the outside, moderately hard and ponderous, and breaks with a smooth fracture. The internal colour is yellowish; and the pieces sometimes contain small globules of zinc. The oxide it contains consists of 85 zinc, 15 oxygen, in 100 parts; or 1 equivalent of zinc = 32.3 + 1 of oxygen

1 The principal works are near Bristol, and at Swansea.

2 Daniell.

= 8, making the equivalent = 40.3. It is not employed as a remedy until it is levigated and prepared.

Officinal preparations.- Oxidum Zinci impurum preparatum, E. Unguentum Oxidi Zinci impuri, E. D. Unguentum Zinci, L.