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CHAP. 22. (10.)—CADMIA.

The ores of copper furnish a number of resources1 that are employed in medicine; indeed, all kinds of ulcers are healed thereby with great rapidity. Of these, however, the most useful is cadmia.2 This substance is formed artificially, beyond a doubt, in the furnaces, also, where they smelt silver, but it is whiter and not so heavy, and by no means to be compared with that from copper. There are several kinds of it. For, as the mineral itself, from which it is prepared artificially, so necessary in fusing copper ore, and so useful in medicine, has the name of "cadmia,"3 so also is it found in the smelting-furnaces, where it receives other names, according to the way in which it is formed. By the action of the flame and the blast, the more attenuated parts of the metal are separated, and become attached, in proportion to their lightness, to the arched top and sides of the furnace. These flakes are the thinnest near the exterior opening of the furnace, where the flame finds a vent, the substance being called "capnitis;"4 from its burnt appearance and its extreme lightness it resembles white ashes. The best is that which is found in the interior, hanging from the arches of the chimney, and from its form and position named "botryitis."5 It is heavier than the first-mentioned kind, but lighter than those which follow. It is of two different colours: the least valuable is ash-coloured, the better kind being red, friable, and extremely useful as a remedy for affections of the eyes.

A third kind of cadmia is that found on the sides of the furnace, and which, in consequence of its weight, could not reach the arched vaults of the chimney. This species is called "placitis,"6 in reference to its solid appearance, it presenting a plane surface more like a solid crust than pumice, and mottled within. Its great use is, for the cure of itch-scab, and for making wounds cicatrize. Of this last there are two varieties, the "onychitis," which is almost entirely blue on the exterior, and spotted like an onyx within; and the "ostracitis,"7 which is quite black and more dirty than the others, but particularly useful for healing wounds. All the species of cadmia are of the best quality from the furnaces of Cyprus. When used in medicine it is heated a second time upon a fire of pure charcoal, and when duly incinerated, is quenched in Aminean8 wine, if required for making plasters, but in vinegar, if wanted for the cure of itch-scab. Some persons first pound it, and then burn it in earthen pots; which done, they wash it in mortars and then dry it.

Nymphodorus9 recommends that the most heavy and dense pieces of mineral cadmia that can be procured, should be burnt upon hot coals and quenched in Chian wine; after which, it must be pounded and then sifted through a linen cloth. It is then pulverized in a mortar and macerated in rain water, the sediment being again pounded until it is reduced to the consistency of ceruse, and presents no grittiness to the teeth. Iollas10 recommends the same process; except that he selects the purest specimens of native cadmia.

1 Most of these preparations are in reality highly dangerous. Oxides, however, or salts of copper, have been employed internally with success, acting by alvine evacuation and by vomiting. The Crocus Veneris of the old chemists was an oxide of copper. It is still used by the peasants of Silesia, Ajasson says.

2 It is obvious that the "cadmia" here described must be an essentially different substance from the "cadmia" mentioned in the second Chapter of this Book, that being a natural production, possibly calamine or hydrosilicate or carbonate of zinc; while the "cadmia" of this Chapter is a furnace-calamine, a product of the fusion of the ore of copper, or zinc.—B. It is evident, too, that copper ores, impregnated with zinc or calamine, also passed under this name. See Beckmann, Hist. Inv. Vol. II. pp. 33–35, Bohn's Edition, where this subject is discussed at considerable length: also the treatise by Delafosse, in Lemaire's Edition of Pliny.

3 The metal known to us as "cadmium" was discovered by Professor Stromeyer in 1818: it is either associated in its ores with zinc, or forms a native sulphuret.

4 "Smoky residue." None of these substances formed in smelting are preserved for medicinal purposes at the present day. Tutty is an impure oxide of zinc.

5 "Cluster residue." From its resemblance to a bunch of grapes.

6 "Caked residue."

7 "Shell-formed residue."

8 See B. xiv. c. 16.

9 See end of B. iii.

10 See end of B. xii.

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