_Lead_ was well known to the Egyptians. In Pliny’s time it was mainly procured from Spain and from Britain (Derbyshire). Leaden pipes were used by the Romans for the conveyance of water, and sheet lead was employed by them for roofing purposes. The Romans were also aware of alloys of lead and tin. _Argentarium_ was composed of equal parts of lead and tin; _tertiarium_, used as a solder, consisted of two parts of lead and one part of tin. _Iron_, although now the most important of the common metals, was not in general use until long after the discovery of gold, silver, and copper. This was probably due to the fact that, although its ores are relatively abundant and widely distributed, its extraction as a metal demanded greater skill and more appliances than were possessed by the earlier races. Metallic iron was, however, well known to the Egyptians, who employed it in the manufacture of swords, knives, axes, and stone-chisels, both as malleable iron and as steel. Steel was also known to the Chinese as far back as 2220 B.C., and they were acquainted with the methods of tempering it. The good quality of Chinese steel caused it to be highly prized by Western nations. The earliest people to smelt iron are supposed to have been the Chalybes, a nation inhabiting the neighbourhood of the Black Sea; it is from them that the ancient name for steel—_chalybs_—is derived, and also our word “chalybeate.” _Mercury_ has long been known, but there is no evidence that the ancient Egyptians were aware of its existence, or it would probably have been mentioned by Herodotus. It was familiar to Aristotle, and its mode of manufacture from cinnabar is described by Theophrastus (320 B.C.), who terms it “liquid silver.” Processes of amalgamation were known to Pliny, who notes the readiness with which mercury dissolves gold. Pliny appears to distinguish the native metal found in Spain, which he terms _argentum vivum_ (quicksilver), from that obtained by sublimation or distillation from cinnabar, which he calls _hydrargyrum_, from which we get the chemical symbol for mercury Hg. A considerable number of metallic compounds were known to the ancients, and were employed by them as medicines and as pigments. The oxides of copper, known as _flos æris_, and _scoria æris_, obtained by heating copper bars to redness and exposing them to air, were used as escharotics. Verdigris, or _ærugo_, was made by the same methods as now. Blue vitriol, or _chalcantum_, is described by Pliny, who says that the blue transparent crystals are formed on strings suspended in its solution.