192	DE NATURA FOSSILIUM
	The best material of the fourth genus has a purplish color while the poorest quality is gray or blackish. The second genus is black, the others reddish. When moistened diphryges changes to the color of copper or becomes blue. All genera have a copper taste. They have mixed properties. Some is moderately acrid and astringent and hence is used as a cure for recurrent ulcers. At one time burnt ocher was sold for reddish diphryges according to Dioscorides but this fraud can be detected readily by taste since ocher never has a copper taste. Diphryges takes up cadmia in furnaces by settling, according to Galen. This latter is the portion of the metallic material that pours out from the furnace, as long as the ore is being smelted, through the force of the flame and blast. Although cadmia is produced in furnaces in which gold, silver, and lead ores are smelted the best is produced in copper furnaces from pyrite and native zinc ores. That produced from other kinds of copper ores is never abundant and is not as good as that from pyrite ore that contains some lead and silver. There are four species of cadmia but many more names. When the dense part of the charge is poured from the furnace the cadmia congeals in a mass on the walls after diphryges. If an abundance of material is smelted the crust is thicker than when a small amount is smelted. Crusts of this material form whenever ore is melted in a furnace. When the crusts are thick the furnaces have to be cleaned more often than when they are thin. When these masses resembled crusts the Greeks called them χλακϊτκ, when banded fwvins, and when veined, similar to onyx and hence variable in color, όνυχϊτι,ς. When broken cadmia is found to have alternate white and gray layers while the surface is usually blue, especially that found in furnaces in which metals have not been refined for some time. In the lower portions of these same furnaces another genera of cadmia is obtained from dense material that is earthy and hard. It is called όστρακΐτις since it has the appearance of sea-shells. It is more ten-aceous, usually black, and found more often in furnaces in which cuprifer­ous pyrite is not smelted. All of these genera are of the dense portions. When a charge is poured a lighter portion is carried upward because of its lightness and settles on the higher parts of the furnace where it congeals in similar forms. These surfaces have the appearance of grapes and for that reason are called βοτρυϊης. Although it is dense, the lighter material is fragile and the heavier even more so. The color is similar to spodos. When broken it is found to be gray inside and usually greenish from cop­per staining. Botryites has even more tenuous portions than the other genera already mentioned. A part of the tenuous portion rests on the iron rods in the top of the furnace and when congealed into a solid mass pro­duces the cadmia botryites. Material coming from Alexandria is similar to this and since it is curved everyone recognizes that it has been removed from a rod. The very finest material produced, because of its lightness, is carried to the higher parts of a furnace with the smoke and hence is called KCLKvlris. It is found, as Pliny writes, in the openings of the furnace where