BOOK VIII.
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UESTIONS of assaying were explained in the last Book, and I have now come to a greater task, that is, to the description of how we extract the metals. First of all I will explain the method of preparing the ore[1]; for since Nature usually creates metals in an impure state, mixed with earth, stones, and solidified juices, it is necessary to separate most of these impurities from the ores as far as can be, before they are smelted, and therefore I will now describe the methods by which the ores are sorted, broken with hammers, burnt, crushed with stamps, ground into powder, sifted, washed, roasted, and calcined[2].
1 As would be expected, practically all the technical terms used by Agricola in this chapter are adaptations. The Latin terms, canalis, area, lacus, vasa, cribrum, and fossa, have had to be pressed into service for many different devices, largely by extemporised combinations. Where the devices described have become obsolete, we have adopted the nomenclature of the old works on Cornish methods. The following examples may be of interest:—
Simple buddle = Canalis simplex Short strake = Area curta
Divided buddle = Canalis tabellis distinctus Canvas strake = Area linteis extensis contecta
Ordinary strake = Canalis devexus Limp = Radius.
The strake (or streke) when applied to alluvial tin, would have been termed a "tye" in some parts of Cornwall, and the "short strake" a "gounce." In the case of the stamp mill, inasmuch as almost every mechanical part has its counterpart in a modern mill, we have considered the reader will have less difficulty if the modern designations are used instead of the old Cornish. The following are the essential terms in modern, old Cornish, and Latin:
Stamp . . Stamper Stamp-stem . . Lifter Shoes Mortar-box . . Box Cam-shaft . . Barrell . . Stamp-heads . . Capita Denies Pili denies Laminae foraminum plenat Lacus Cribrum anguslum . Pilum Cams . . Caps .Pilum Tappets ..Tongues Screens . . Crate . . Capsa Settling pit . . Catchers . .Axis Jigging sieve . .Dilleugher
2 Agricola uses four Latin verbs in connection with heat operations at temperatures under the melting point: Calefacio, uro, torreo, and cremo. The first he always uses in the sense of "to warm" or "to heat," but the last three he uses indiscriminately in much the same way as the English verbs burn, roast, and calcine are used; but in general he uses the Latin verbs in the order given to indicate degrees of heat. We have used the English verbs in their technical sense as indicated by the context.
It is very difficult to say when roasting began as a distinct and separate metallurgical step in sulphide ore treatment. The Greeks and Romans worked both lead and copper sulphides (see note on p. 391, and note on p. 403), but neither in the remains of old works nor in their literature is there anything from which satisfactory details of such a step can be obtained. The Ancients, of course, understood lime-burning, and calcined several salts to purify them or to render them more caustic. Practically the only specific mention is by Pliny regarding lead ores (see p. 391). Even the statement of Theophilus (1050-1100, a.d.), may refer simply to rendering ore more fragile, for he says (p. 305) in regard to copper ore: "This stone dug up in abundance is placed upon a pile and burned (comburitur) after the manner of lime. Nor does it change colour, but loses its hardness and can be broken up, and afterward it is smelted." The Probierbüchlein casually mentions roasting prior to assaying, and Biringuccio (iii, 2) mentions incidentally that "dry and ill-disposed ores before everything must be roasted in an open oven so that the air can get in." He gives no further information; and therefore this account of Agricola's becomes practically the first. Apparently roasting, as a preliminary to the treatment of copper sulphides, did not come into use in England until some time later than Agricola, for in Col. Grant Francis' "Smelting of Copper in the Swansea District" (London, 1881, p. 29), a report is set of the "Doeinges of Jochim Ganse"—an imported German—at the "Mynes by Keswicke in Cumberland, a.d., 1581," wherein the delinquencies of the then current practice are described: "Thei never coulde, nether yet can make (copper) under xxii. tymes passinge thro the fire, and xxii. weekes doeing thereof ane sometyme more. But now the nature of these ix. hurtfull humors abovesaid being discovered and opened by Jochim's way of doeing, we can, by his order of workeinge, so correct theim, that parte of theim beinge by nature hurtfull to the
