232

BOOK VII.

been kindled, this kind of ore is roasted in an enclosed pot, which is stoppedup with lute. A less valuable ore is even burned on a hearth, being placedupon the charcoal; for we do not make a great expenditure upon metals, ifthey are not worth it. However, I will go into fuller details as to all thesemethods of preparing ore, both a little later, and in the following Book.

For the present, I have decided to explain those things which miningpeople usually call fluxes 6 because they are added to ores, not only forassaying, but also for smelting. Great power is discovered in all these fluxes,but we do not see the same effects produced in every case ; and some are of avery complicated nature. For when they have been mixed with the oreand are melted in either the assay or the smelting furnace, some of them,because they melt easily, to some extent melt the ore ; others, because theyeither make the ore very hot or penetrate into it, greatly assist the fire inseparating the impurities from the metals, and they also mix the fused partwith the lead, or they partly protect from the fire the ore whose metal contentswould be either consumed in the fire, or carried up with the fumes and fly outof the furnace ; some fluxes absorb the metals. To the first order be-longs lead, whether it be reduced to little granules or resolved into ash byfire, or red-lead 7 , or ochre made from lead 8 , or litharge, or hearth-lead, or

6 Additamenta, —“ Additions.” Hence the play on words.

We have adopted “ flux ” because the old English equivalent for all these materialswas “ flux,” although in modern nomenclature the term is generally restricted to thosesubstances which, by chemical combination in the furnace, lower the melting point of someof the charge. The " additions ” of Agricola, therefore, include reducing, oxidizing,sulphurizing, desulphurizing, and collecting agents as well as fluxes. A critical examina-tion of the fluxes mentioned in the next four pages gives point to the Author’s assertion that“ some are of a very complicated nature.” However, anyone of experience with home-taught assayers has come in contact with equally extraordinary combinations. The fourorders of “ additions ” enumerated are quite impossible to reconcile from a modern metal-lurgical point of view.

7 Minium secundarium. {Inierpretatio, — menning. PbgOq). Agricola derived his Latinterm from Pliny. There is great confusion in the ancient writers on the use of the wordminium, for prior to the Middle Ages it was usually applied to vermilion derived fromcinnabar. Vermilion was much adulterated with red-lead, even in Roman times, and finallyin later centuries the name came to be appropriated to the lead product. Theophrastus(103) mentions a substitute for vermilion, but, in spite of commentators, there is noevidence that it was red-lead. The first to describe the manufacture of real red-lead wasapparently Vitruvius (vn, 12), who calls it sandaraca (this name was usually applied to redarsenical sulphide), and says : “ White-lead is heated in a furnace and by the force of the“ fire becomes red lead. This invention was the result of observation in the case of an“ accidental fire, and by the process a much better material is obtained than from the mines.”He describes minium as the product from cinnabar. Dioscorides (v, 63), after discussingwhite-lead, says it may be burned until it becomes the colour of sandaracha, and is calledsandyx. He also states (v, 69) that those are deceived who consider cinnabar to be thesame as minium, for minium is made in Spain out of stone mixed with silver sands. There-fore he is not in agreement with Vitruvius and Pliny on the use of the term. Pliny(xxxin, 40) says : “ These barren stones (apparently lead ores barren of silver) may be“ recognised by their colour ; it is only in the furnace that they turn red. After being“ roasted it is pulverized and is minium secundarium. It is known to few and is very“ inferior to the natural kind made from those sands we have mentioned {cinnabar). It is“ with this that the genuine minium is adulterated in the works of the Company.” Thisproprietary company who held a monopoly of the Spanish quicksilver mines, “ had many“ methods of adulterating it {minium)— a source of great plunder to the Company.”Pliny also describes the making of red lead from white.

s Ochra plumbaria, {Inierpretatio,—pleigeel; modern German,— Bleigelb). The Germanterm indicates that this “ Lead Ochre,” a form of PbO, is what in the English trade isknown as massicot, or masticot. This material can be a partial product from almost anycupellation where oxidation takes place below the melting point of the oxide. It mayhave been known to the Ancients among the various species into which they divided