Page:De re metallica (1912).djvu/317

 BOOK VIII. 273 in a short strake, at the head of which stands the washer, who draws the water upward with a wooden hoe. The water running down again, carries all the light particles into a trough placed underneath. I shall deal more fully with this method of washing a little later. Ore is burned for two reasons ; either that from being hard, it may become soft and more easily broken and more readily crushed with a hammer or stamps, and then can be smelted ; or that the fatty things, that is to say, sulphur, bitumen, orpiment, or realgar 3 may be consumed. Sulphur is frequently found in metallic ores, and, generally speaking, is more harmful to the metals, except gold, than are the other things. It is most harmful of all to iron, and less to tin than to bismuth, lead, silver, or copper. Since very rarely gold is found in which there is not some silver, even gold ores containing sulphur ought to be roasted before they are smelted, because, in a very vigorous furnace fire, sulphur resolves metal into ashes and makes slag of it. Bitumen acts in the same way, in fact sometimes it consumes silver, which we may see in bituminous cadmia*. I now come to the methods of roasting, and first of all to that one which is common to all ores. The earth is dug out to the required extent, and thus is made a quadrangular area of fair size, open at the front, and above this, firewood is laid close together, and on it other wood is laid trans- versely, likewise close together, for which reason our countrymen call this pile of wood a crate ; this is repeated until the pile attains a height of one or two cubits. Then there is placed upon it a quantity of ore that has been broken into small pieces with a hammer ; first the largest of these pieces, next those of medium size, and lastly the smallest, and thus is built up a gently sloping cone. To prevent it from becoming scattered, fine sand of the indicates that it was his term for the complex copper-zinc-arsenic-cobalt minerals found in the well-known, highly bituminous, copper schists at Mannsfeld. The later Mineralogists, Wallerius (Miner alogia, Stockholm, 1747), Valmont De Bomare (Mineralogie, Paris, 1762), and others assume Agricola's cadmia biiuminosa to be " black arsenic " or " arsenic noir," but we see no reason for this assumption. Agricola's statement (De Nat. Foss., p. 369) is .. . . the schistose stone dug up at the foot of the Melibocus Mountains, or as they are now called the Harz (Hercynium), near Eisleben, Mannsfeld, and near Hettstedt, is similar to spinos (a bituminous substance described by Theophrastus), if not identical with it. This is black, bituminous, and cupriferous, and when first extracted from the mine it is thrown out into an open space and heaped up in a mound. Then the lower part of the mound is surrounded by faggots, on to which are likewise thrown stones of the same kind. Then the faggots are kindled and the fire soon spreads to the stones placed upon them ; by these the fire is communicated to the next, which thus spreads to the whole heap. This easy reception of fire is a characteristic which bitumen possesses in common with sulphur. Yet the small, pure and black bituminous ore is distinguished from the stones as follows : when they burn they emit the kind of odour which is usually given off by burning bituminous coal, and besides, if while they are burning a small shower of rain should fall, they burn more brightly and soften more quickly. Indeed, when the wind carries the fumes so that they descend into nearby standing waters, there can be seen floating in it something like a bituminous liquid, either black, or brown, or purple, which is sufficient to indicate that those stones were bituminous. And that genus of stones has been recently found in the Harz in layers, having occasionally gold-coloured specks of pyrites adhering to them, representing various flat sea-fish or pike or perch or birds, and poultry cocks, and sometimes salamanders."
 * 0rpiment and realgar are the red and yellow arsenical sulphides. (See note on p. in).
 * Cadmia biiuminosa. The description of this substance by Agricola, given below,