BOOK VII. 235 



assay ores, we can without great expense add to them a small portion of any 

 sort of flux, but when we smelt them we cannot add a large portion without 

 great expense. We must, therefore, consider how great the cost is, to avoid 

 incurring a greater expense on smelting an ore than the profit we make out of 

 the metals which it yields. 



The colour of the fumes which the ore emits after being placed on a hot 

 shovel 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 purple 

 tint, 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 or 

 other cupriferous rock ; if yellow, litharge and sulphur should be added ; if 

 red, glass-galls^' 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 is 

 eaten with rust ; if they are white with green patches, iron slag and 

 sand obtained from stones which easily melt ; if the middle part of the 

 fumes are yellow and thick, but the outer parts green, the same sand and 

 iron slag. The colour of the fumes not only gives us information as to the 

 proper remedies which should be apphed to each ore, but also more or less 

 indication as to the solidified juices which are mixed with it, and which give 

 forth such fumes. Generally, blue fumes signify that the ore contains azure ; 

 3'ellow, orpiment ; red, realgar ; green, chrysocoUa ; black, black bitumen ; 

 white, tin^* ; white with green patches, the same mixed with chrysocoUa ; 

 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 from 

 stones which easily melt. If the ore contains iron, then pyrites and sulphur 

 are added ; for just as iron slag is the flux for an ore mixed with sulphur, so 

 on 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 chloride 

 from clarifying the aqua valens, and the second, the residues left in making the acid by 

 distillation. 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 the 

 addition of silver to the assays, too expensive, and oi no merit for this purpose. Therefore 

 one is driven to the conclusion that the feces must have been the residues left in the retorts 

 when nitric acid was prepared. It would have been more in keeping with his usual mode 

 of expression, however, to have referred to this material as a residuus. The materials used 

 for making acid varied greatly, so there is no telling what such a feces contained. A list 

 of possibilities is given in note 8, p. 443. In the main, the residue would be undigested 

 vitriol, alum, saltpetre, salt, etc., together with potassium, iron, and alum sulphates. The 

 Probierbuchlin (p. 27) also gives this re-agent under the term Toden kopff das ist schlam 

 oder feces auss dem scheydwasser. 



''■'' Recremenium vitri. {Interpreiatio Glassgallen). Formerly, when more impure 

 materials were employed than nowadays, the surface of the mass in the first melting 

 of glass materials was covered with salts, mostly potassium and sodium sulphates and 

 chlorides which escaped perfect vitrification. This " slag " or " glassgallen " of Agricola 

 was also termed sandiver. 



i^The whole of this expression is " candidus, candido." It is by no means certain 

 that this is tin, for usually tin is given as plumbum candidum. 



