Pliny nowhere makes us acquainted with the process by which copper was converted into brass, nor does he seem to have been acquainted with it; but from several facts incidentally mentioned by him, it is obvious that their process was similar to that which is followed at present by modern brass-makers. The copper in grains is mixed with a certain quantity of calamine (cadmia) and charcoal, and exposed for some time to a moderate heat in a covered crucible. The calamine is reduced to the metallic state, and imbibed by the copper grains. When the copper is thus converted into brass, the temperature is raised sufficiently high to melt the whole: it is then poured out and cast into a slab or ingot. The cadmia employed by the ancients in medicine was not calamine, but oxide of zinc, which sublimed during the fusion of brass in an open vessel. It was distinguished by a variety of names, according to the state in which it was obtained: the lighter portion was called _capnitis_. _Botryitis_ was the name of the portion in the interior of the chimney: the name was derived from some resemblance which it was supposed to have to a bunch of grapes. It had two colours, ash and red. The red variety was reckoned best. This red colour it might derive from some copper mixed with it, but more probably from iron; for a small quantity of oxide of iron is sufficient to give oxide of zinc a rather beautiful red colour. The portion collected on the sides of the furnace was called _placitis_: it constituted a crust, and was distinguished by different names, according to its colour; _onychitis_ when it was blue externally, but spotted internally: _ostracitis_, when it was black and dirty-looking. This last variety was considered as an excellent application to wounds. The best cadmia in Pliny’s time was furnished by the furnaces of the Isle of Cyprus: it was used as an external application in ulcers, inflammations, eruptions, &c., so that its use in medicine was pretty much the same as at present. Sulphate and acetate of zinc were unknown to the ancients. No attempt seems to have been made by them to introduce any preparations of zinc as internal medicines. _Pompholyx_ was the name given to oxide of zinc, sublimed by the combustion of the zinc which exists in brass. _Spodos_ seems to have been a mixture of oxides of zinc and copper. There were different varieties of it distinguished by various names.[45] [45] See Plinii Hist. Nat. xxxiv. 13.