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BOOK X
203
contrary those containing little bitumen are heavy, burn less readily and have only a slight odor of bitumen, for example, the stone from Bina. The latter burn only when placed on live coals and a blast is applied. When the blast is discontinued they cease burning although they can be rekindled again and again. For this reason workmen use this stone for a long time.
Stones that contain a juice useful to painters can be distinguished by their color, for example, those that contain chrysocolla, caeruhum, aerugo, realgar, or orpiment. These stones occur commonly in gold, silver, and copper mines just as stones containing salt, soda, halinitrum, alum, alramentum sutorium, and related juices occur in distinctive de­posits. The latter juices are separated from their mixtures by dissolving them in water; unctuous juices are separated by the heat of fire; and paint­ers separate the juices they wish to use with both fire and water. I shall take up all these things in the, as yet, unwritten book De Re Metallica. Since Nature has not given a new form to the majority of these mixtures the older writers correctly called them "stones."
I shall now take up the other genera, discussing them together with the exception of the sixth genus. As many as eight or more species are in­cluded under a single genus, in fact as many species as there are metals. All contain either an earth or stone and either gold, silver, quicksilver, copper, tin, lead, bismuth, or iron. Since proper names have not been given to these mixtures it is necessary that I give each one the name of the metal it contains and an additional word to distinguish it from the pure metal, either native or the result of smelting. Thus I use the term rude aurum (rude gold1), etc., not because I am unaware that Varro has used the same name for gold that had not been cast and stamped but because I cannot find a similar word that is sufficiently distinctive. Thus rude aurum etc., are species of these four genera.
Since I am not going to take up the four genera separately I shall mention first the features by which species of one genus may be dis­tinguished from those of another. Thus a silver mineral may be of the second genus of mixtures, or the third, fourth, or fifth, as disclosed by smelting either in ovens or furnaces. If only a small amount of slag is obtained we know the mixture contains earth and not stone as well as silver, and therefore belongs to the second genus. If an equal amount of silver and slag are produced it belongs to the third genus; if more silver than slag, to the fourth; and if more slag than silver, to the fifth. Species of the second and fourth genera contain more metal than slag but can be distinguished from one another since the former contains more metal than the latter. If the silver mineral is soft it belongs to the second genus without question but if it is hard it does not necessarily belong to the
1 The literal translation of this term would be "rude" or "native." Since this does not convey the intended meaning, the proper translation would be "mineral" or "ore."