It is found in actual working practice that material which does not contain a certain proportion of silica does not work well in the blast-roasting or sintering processes, the resulting product being found to be more irregular in composition and more difficult to operate in the sintering plant. It would therefore appear that a certain class of fine concentrate higher in silica and lower in iron and sulphur contents, which is not quite so suitable for ordinary roasting (owing to the necessity for external heating, due to lower fuel values) is eminently suited for blast roasting or sintering processes, yielding lump products very suitable for subsequent blast-furnace treatment. The reverberatory furnace thus deals most successfully with fine table concentrates high in iron and sulphur, moderately low in silica; roasted, with its required flux, to the necessary extent, and then charged whilst still red hot into the furnaces. To relieve the reverberatories of the greater bulk of the blast-furnace flue-dust, which it treats with more difficulty, fine concentrates, as such, require to be kept out of the blast-furnace charge, either by subjecting the more siliceous material to a preparatory sintering process, or by reserving the highly pyritic variety for roasting and subsequent reverberatory treatment. References. Peters, E. D., “Principles of Copper Smelting.” Offerhaus, C., “Modern Reverberatory Smelting of Copper Ores.” _Eng. and Min. Journ._, June 13, 1908, pp. 1189–1193; June 20, 1908, pp. 1234–1236. Ricketts, L. D., “Experiments in Reverberatory Practice at Cananea, Mexico,” and discussion, _Trans. Inst. Min. and Met._, vol. xix., 1909–10, pp. 147–185. Ricketts, L. D., “Developments of Cananea Practice.” _Engineering and Mining Journal_, Oct. 7th, 1911, p. 693. LECTURE VI. BLAST-FURNACE PRACTICE. Functions of the Furnace — As Melting Agent—Reduction Smelting — Oxidation in the Furnace — The Pyritic Principle — Features of Modern Practice: Water-Jacketing, Increase in Furnace Size, External Settling — Constructional Details of the Furnace. =The Functions of the Blast Furnace.=—The functions of the blast furnace may be considered from three points of view:— =1. As a Melting Agent.= =2. As a Reducing Medium.= =3. As an Oxidising Medium.= In modern copper smelting practice, the blast furnace is under ordinary circumstances never employed in the capacity of a reducing medium, but is used for a variety of work in which its operations range from those of a melting furnace to those more particularly of an oxidising medium, as its oxidising functions are becoming developed to a gradually increasing extent.