BOOK IX.

396

the cadmia ; this sweeping is done twice a year. The soot mixed withpompholyx and the cadmia, being chipped off, is thrown down througha long chute made of four boards joined in the shape of a rectangle,that they should not fly away. They fall on to the floor, and are sprinkledwith salt water, and are again smelted with ore and litharge, and becomean emolument to the proprietors. Such chambers, which catch the metallicsubstances that rise with the fumes, are profitable for all metalliferousores; but especially for the minute metallic particles collected by washingcrushed ores and rock, because these usually fly out with the fire of thefurnaces.

I have explained the four general methods of smelting ores ; now Iwill state how the ores of each metal are smelted, or how the metal is obtainedfrom the ore. I will begin with gold. Its sand, the concentrates fromwashing, or the gold dust collected in any other manner, should very oftennot be smelted, but should be mixed with quicksilver and washed with tepidwater, so that all the impurities may be eliminated. This method I ex-plained in Book VII. Or they are placed in the aqua which separatesgold from silver, for this also separates its impurities. In this method wesee the gold sink in the glass ampulla, and after all the aqua has been drainedfrom the particles, it frequently remains as a gold-coloured residue at thebottom ; this powder, when it has been moistened with oil made fromargol 27 , is then dried and placed in a crucible, where it is melted with boraxor with saltpetre and salt; or the same very fine dust is thrown into moltensilver, which absorbs it, and from this it is again parted by aqua valens 28 .

It is necessary to smelt gold ore either outside the blast furnace in acrucible, or inside the blast furnace ; in the former case a small charge of oreis used, in the latter a large charge of it. Rudis gold, of whatever colourit is, is crushed with a libra each of sulphur and salt, a third of a libra of copper,

“ stuff flies up with the smoke to the upper chamber, and adheres to the walls of the roof.“ The substance which is thus formed has at first the appearance of bubbles 'on water, after-“ ward increasing in size, it looks like skeins of wool. The heaviest parts settle in the bottom,“ while some fall over and around the furnaces, and some lie on the floor of the building." This latter part is considered inferior, as it contains a lot of earth and becomes full of dirt.”

Pliny (xxxiv, 33) appears somewhat confused as to the difference between thetwo species : “ That which is called pompholyx and spodos is found in the copper-smelting“ furnaces, the difference between them being that pompholyx is separated by washing, while“ spodos is not washed. Some have called that which is white and very light pompholyx, and“it is the soot of copper and cadmia ; whereas spodos is darker and heavier. It is scraped“ from the walls of the furnace, and is mixed with particles of metal, and sometimes with“charcoal.” (xxxiv, 34.) “The Cyprian spodos is the best. It is formed by fusing“ cadmia with copper ore. This being the lightest part of the metal, it flies up in the fumes“ from the furnace, and adheres to the roof, being distinguished from the soot by its whiteness.“ That which is less white is immature from the furnace, and it is this which some call ‘ pom-“ pholyx.’ ” Agricola (De Naiura Fossilium, p. 350) traverses much the same ground as theauthors previously quoted, and especially recommends the pompholyx produced when makingbrass by melting alternate layers of copper and calamine ( cadmia fossilis).

Z7 Oleo, ex fece vini sicca confecto. This oil, made from argol, is probably thesame substance mentioned a few lines further on as “ wine,” distilled by heating argol in aretort. Still further on, salt made from argol is mentioned. It must be borne in mind that thisargol was crude tartrates from wine vats, and probably contained a good deal of organicmatter. Heating argol sufficiently would form potash, but that the distillation product couldbe anything effective it is difficult to see.

28 Aqua valens. No doubt mainly nitric acid, the preparation of which is explainedat length in Book X, p. 439).