BOOK VII.

235

assay ores, we can without great expense add to them a small portion of anysort of flux, but when we smelt them we cannot add a large portion withoutgreat expense. We must, therefore, consider how great the cost is, to avoidincurring a greater expense on smelting an ore than the profit we make out ofthe metals which it yields.

The colour of the fumes which the ore emits after being placed on a hotshovel or an iron plate, indicates what flux is needed in addition to the lead,for the purpose of either assaying or smelting. If the fumes have a purpletint, it is best of all, and the ore does not generally require any flux whatever.If the fumes are blue, there should be added cakes melted out of pyrites orother cupriferous rock ; if yellow, litharge and sulphur should be added; ifred, glass-galls 17 and salt; if green, then cakes melted from cupriferous stones,litharge, and glass-galls ; if the fumes are black, melted salt or iron slag,litharge and white lime rock. If they are white, sulphur and iron which iseaten with rust; if they are white with green patches, iron slag andsand obtained from stones which easily melt; if the middle part of thefumes are yellow and thick, but the outer parts green, the same sand andiron slag. The colour of the fumes not only gives us information as to theproper remedies which should be applied to each ore, but also more or lessindication as to the solidified juices which are mixed with it, and which giveforth such fumes. Generally, blue fumes signify that the ore contains azure ;yellow, orpiment; red, realgar ; green, chrysocolla ; black, black bitumen ;white, tin 18 ; white with green patches, the same mixed with chrysocolla ;the middle part yellow and other parts green show that it contains sulphur.Earth, however, and other things dug up which contain metals, some-times emit similarly coloured fumes.

If the ore contains any stibium, then iron slag is added to it; if pyrites,then are added cakes melted from a cupriferous stone and sand made fromstones which easily melt. If the ore contains iron, then pyrites and sulphurare added ; for just as iron slag is the flux for an ore mixed with sulphur, soon the contrary, to a gold or silver ore containing iron, from which they are

are two precipitates possible, both referred to as feces, —the first, a precipitate of silver chloridefrom clarifying the aqua valens, and the second, the residues left in making the acid bydistillation. It is difficult to believe that silver chloride was the feces referred to in the text,because such a precipitate would be obviously misleading when used as a flux through theaddition of silver to the assays, too expensive, and of no merit for this purpose. Thereforeone is driven to the conclusion that the feces must have been the residues left in the retortswhen nitric acid was prepared. It would have been more in keeping with his usual modeof expression, however, to have referred to this material as a residuus. The materials usedfor making acid varied greatly, so there is no telling what such a feces contained. A listof possibilities is given in note 8, p. 443. In the main, the residue would be undigestedvitriol, alum, saltpetre, salt, etc., together with potassium, iron, and alum sulphates. TheProbierbiichlin (p. 27) also gives this re-agent under the term Toden kopff das ist schlamoder feces auss dem scheydwasset.

17 Recrementum vitri. (Interpretatio Glassgallen). Formerly, when more impurematerials were employed than nowadays, the surface of the mass in the first meltingof glass materials was covered with salts, mostly potassium and sodium sulphates andchlorides which escaped perfect vitrification. This “ slag ” or “ glassgallen ” of Agricolawas also termed sandiver.

18 The whole of this expression is “ candidus, candido.” It is by no means certainthat this is tin, for usually tin is given as plumbum candidum.