Metallurgy is an ancient art, and the working of gold, silver and copper dates back to the beginning of history. Being found in a condition of comparative purity, and needing but little refinement, they were, for that reason, the first metals fashioned to meet the wants of man. Iron, somewhat more refractory, appeared later, but it also has an early history, and is mentioned in the Old Testament of the Bible (Genesis iv., 22), in which reference is made to Tubal Cain as an artificer in brass and iron. The iron bedstead of Og, King of Bashan, is another reference. That it was known to the Egyptians and the Greeks at least 1000 B. C., seems reasonably certain. The Assyrians were also acquainted with iron, as is clearly established by the explorations of Mr. Layard, whose contributions to the British Museum of iron articles from the ruins of Ninevah include saws, picks, hammers, and knives of iron, which are believed to be of a date not later than 880 B. C. Iron ore is usually found in the form of an oxide (hematite), and its reduction to the metallic form consists in displacing the oxygen, which is effected by mixing carbon in some form with the ore, and subjecting the mixture to a high heat by means of a blast. The carbon unites with the oxygen and forms carbonic acid gas, which escapes, while the metallic iron fuses and runs out at the bottom of the furnace, and when collected in trough-shaped moulds, is known as pig iron. [Illustration: FIG. 249.--PRIMITIVE IRON FURNACE OF HINDOSTAN.] The first iron furnaces were known as _air bloomeries_, and had no forced draft. The first step of importance in iron making was the forced blast. An early form of blast furnace is shown in Fig. 249, which represents an iron furnace of the Kols, a tribe of iron smelters in Lower Bengal and Orissa. An inclined tray terminates at its lower end in a furnace inclosure. Charcoal in the furnace being well ignited, ore and charcoal resting on the tray are alternately raked into the furnace. The blowers are two boxes, connected to the furnace by bamboo pipes, and provided with skin covers, which are alternately depressed by the feet and raised by cords from the spring poles. Each skin cover has a hole in the middle, which is stopped by the heel of the workman as the weight of the person is thrown upon it, and is left open by the withdrawal of the foot as the cover is raised. The heels of the workman, alternately raised, form alternately acting valves, and the skin cover, when depressed, acts as a bellows. The fused metal sinks to a basin in the bottom of the furnace, and the slag or impurities run off above the level of the basin at the side of the furnace.