Iron being introduced, and its valuable applications known, it became necessary, in those countries that do not afford rich ores, to discover a method by which the poorer might be reduced. This could only be effected by giving such a degree of heat, as would render the earthy matter capable of melting, at a less expense of metal. To increase the mass of fuel, by increasing the depth of the cavity, and actually forming it of walls, thus enabling it to contain a greater quantity, would be obvious means of attaining this end. The ore must be added in smaller proportions, and, being longer in contact with the heated charcoal, would become carbureted; the carbon must therefore be finally burned away, before malleable iron could be attained. A rude but efficient process of this sort, is described by Gmelin as in use among the Tartars; an analogous method, whose use has been superseded by iron imported from Europe, was found among the nations of Guinea; and Mungo Park saw a more perfect application of the same principle at Camalia, on the Gambia. Furnaces of similar character, but more skilfully constructed, are still used in some parts of Germany, and are called _stuckoffen_. As a carburet, or actual cast-iron, must be formed in these processes, and, as the separation of carbon at the bottom of a deep cylinder, and where the metal would probably be covered by a vitreous liquid, is difficult, the iron might sometimes resist the efforts made to render it malleable, and run from the furnace in a liquid form. It might therefore have readily occurred, that it would be less costly to finish the process in a forge. The _stuckoffen_ were therefore converted into _flossoffen_, or melting furnaces, whence the liquid carburet was withdrawn, and afterwards converted into bar iron. Such was probably the cause that led to the original discovery of cast iron, a discovery that cannot be traced further back than the end of the fifteenth century. The uses of cast iron for purposes to which wrought iron is inapplicable, and the readiness with which it is fashioned, by pouring it into moulds, led to the increase of the size of the _flossoffen_, and in the power of the blowing apparatus, which has caused the introduction of the blast furnace. This forms the basis of the methods by which iron in all its forms is chiefly prepared at the present day, and is hence worthy of particular consideration. The difference between the blast furnace proper, and the ancient fires from which it gradually took its rise, consists wholly in its superior height, and in the greater power of the blowing machines, by which its combustion is supplied with air.