Thus the physical character and metallic constituents of ores received the first consideration; then the proper treatment to which the ores were to be subjected for the purpose of extracting the metal--which are either mechanical or chemical. The mechanical processes designed to separate the ore from its enclosing rock or other superfluous earthy matter called _gangue_ became known as _ore dressing_ and _ore concentrating_. These included mills with rollers, and stamps operated by gravity, or steam, for breaking up the ore rocks; abrasion apparatus for comminuting the ore by rubbing the pieces of ore under pressure; and smelting, or an equivalent process, for melting the ore and driving off the impurities by heat, etc. The chemical processes are those by which the metal, whatever it may be, is either dissolved or separated from other constituents by either the application to the ore of certain metallic solutions of certain acids, or by the fusion of different ores or metals in substantially the old styles of furnaces; or its precipitation by amalgamating, or by electrolysis--the art of decomposing metals by electricity. In the early decades of the century, by the help of chemistry and physics, the nature of heat, carbon, and oxygen, and the great affinity iron has for oxygen, became better known; and particularly how in the making of iron its behaviour is influenced by the presence of carbon and other foreign constituents; also how necessary to its perfect separation was the proper elimination of the oxygen and carbon. The use of manganese and other highly oxidisable metals for this purpose was discovered. Among the earliest most notable inventions in the century, in the manufacture of iron, was that of Samuel B. Rogers of Glamorganshire, Wales, who invented the iron floor for furnaces with a refractory lining--a great improvement on Cort’s sand floor, which gave too much silicon to the iron; and the _hot air blast_ by Neilson of Glasgow, Scotland, patented in 1828. The latter consisted in the use of heated air as the blast instead of cold air--whereby ignition of the fuel was quickened, intensity of the heat and the expulsion of oxygen and carbon from the iron increased, and the operation shortened and improved in every way. The patent was infringed and assailed, but finally sustained by the highest courts of England. It produced an immense forward stride in the amount and quality of iron manufactured. By the introduction of the hot air blast it became practicable to use the hard anthracite coal as a fuel where such coal abounded; and to use pig iron, scrap iron, and refractory ore and metals with the fuel to produce particular results. Furnaces were enlarged to colossal dimensions, some being a hundred feet high and capable of yielding 80 or 100 tons of metal per day. The forms of furnaces and means for lining and cooling the hearth and adjacent parts have received great attention.