[5] See Mr. Powle's account of the Iron Works in the Forest of Dean (1677-8), in the Philosophical Transactions, vol. ii. p. 418, where he says, "After they have pounded their ore, their first work is to calcine it, which is done in kilns, much after the fashion of ordinary lime-kilns, These they fill up to the top with coal and ore, stratum super stratum, until it be full; and so setting fire to the bottom, they let it burn till the coal be wasted, and then renew the kilns with fresh ore and coal, in the same manner as before. This is done without fusion of the metal, and serves to consume the more drossy parts of the ore and to make it friable." The writer then describes the process of smelting the ore mixed with cinder in the furnaces, where, he says, the fuel is "always of charcoal." "Several attempts," he adds, "have been made to introduce the use of sea-coal in these works instead of charcoal, the former being to be had at an easier rate than the latter; but hitherto they have proved ineffectual, the workmen finding by experience that a sea-coal fire, how vehement soever, will not penetrate the most fixed parts of the ore, and so leaves much of the metal unmelted" [6] Phil. Trans. vol. xliv. 305. [7] Reverberatory, so called because the flame or current of heated gases from the fuel is caused to be reverberated or reflected down upon the substance under operation before passing into the chimney. It is curious that Rovenson, in his Treatise of Metallica of 1613, describes a reverberatory furnace in which iron was to be smelted by pit-coal, though it does not appear that he succeeded in perfecting his invention. Dr. Percy, in his excellent work on Metallurgy, thus describes a reverberatory furnace:--"It consists essentially of three parts--a fireplace at one end, a stack or chimney at the other, and a bed between both on which the matter is heated. The fireplace is separated from the bed by a low partition wall called the fire-bridge, and both are covered by an arched roof which rises from the end wall of the fireplace and gradually dips toward the furthest end of the bed connected with the stack. On one or both sides of the bed, or at the end near the stack, may be openings through which the ore spread over the surface of the bed may be stirred about and exposed to the action of the air. The matter is heated in such a furnace by flame, and is kept from contact with the solid fuel. The flame in its course from the fireplace to the stack is reflected downwards or REVERBERATED on the matter beneath, whence the name REVERBERATORY furnace."