Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/316

 300 IKON is nearly on a level with the tuyeres, and has a groove (cinder notch] cut in it forming a channel through which the cinder continuously flows out when the iron and cinder have risen to a level with the top of the dam since the last tapping ; occasionally the top of the dam is raised to a somewhat higher level than the tuyeres, when it consequently results that the blast is blown in through and not over the liquid cinder. The space between the dam and the top of the tymp arch is rilled up with brickwork, or with clay and sand, &c., with the exception of the cinder channel terminating in the cinder notch ; when the furnace has been tapped and the level of the cinder has sunk below the notch, this cavity is temporarily stopped until the cinder level rises again, to prevent the blast issuing from the hole. In order to prevent wearing away of the dam, water cooling arrangements are sometimes applied analogous to those used for the hot-blast tuyere ( 15); various arrangements of this kind are in use, notably Liirman s. On the Continent the older massive round or square-based class of furnace (of variable dimensions in different localities) is still em ployed to a considerable extent. In some of the smaller-sized fur naces, such as those in use in Sweden and Finland, the heavy external masonry is replaced by a log casing, prevented from heating by a jacket of earth and rock between it and the furnace casing proper. When the furnaces are only in blast at certain seasons (being blown out during the rest of the year), holes for the escape of moisture from the interior brickwork or stonework on relighting are usually provided. The hearth is constructed of a mixture of fireclay and crushed quartz or old used fireclay moulded whilst soft into shape by being rammed in between the outer casing and a wooden internal mould and carefully dried gradually before use. Eachette s furnace (fig. 12), l adopted at Nijne Tagilsk and I. II. FIG. 12. Rachette s Furnace. I. Cross section. II. Longitudinal section. III. Plan at tuyere level. IV. Plan of air courses below the hearth. elsewhere in the Urals, at Mulheim on the Rhino, and in a modified form in certain copper smelting works, differs considerably in shape from the ordinary English form ; the shaft A is an inverted four- sided pyramid, the throat being the widest part of all, about 7 feet wide and 18 long ; towards the hearth D the width diminishes to 275 feet, the total height being about 30 feet. At each end of the oblong hearth is a slaghole and a tapping hole, C, C. The tuyeres B, B arc some dozen in number, arranged in two ranks opposite to one another, each tuyere on one side being midway between the axes of two adjacent tuyeres of the opposite side. In order to keep the walls cool air courses E,E are built under the hearth and others 0,0,0 in the walls of the shaft, all communicating with one another; when the furnace is being blown in these also serve to heat up the walls and dry them, fuel being placed in the lowest and largest air space E and fired. The chief advantages claimed for this form of furnace are that its small height and comparatively slight construc tion render it far less costly to build than more massive furnaces ; that the ascending current of gases must slacken in vertical 1 Taken from Bolley s Handbuch der Chemischcn Technologic vol. ii., part ii., by Dr C. Stolzel. speed as it reaches the wider uppermost portion, and must conse quently be more efficaceous in reducing the ore than in furnaces the shafts of which taper the other way at top, so that the yield of iron relatively to the cubic capacity is larger ; and that when first built it can be blown in much sooner than ordinary furnaces owing tp the air courses. The yield of one of the Ural furnaces, when smelt ing a rich magnetic ore furnishing 67 per cent, of grey pig with charcoal and cold blast, was from three to three and a half times that of the old type of furnace (measured for equal cubic capacity), the consumption of fuel being from 10 to 15 per cent, less (Stolzel). FIG. 13. Feme s Furnace. A peculiar furnace, known as Feme s self-coking furnace, after the name of its inventor, in which raw coal is employed, has been used at the Monkland Iron Works and elsewhere during the last few years. On the top of an ordinary furnace of about 53 feet in height and 7000 cubic feet capacity were erected four chambers or retorts about 20 feet in depth, each having a capacity of 500 cubic feet; external flues, in which a portion of the waste gases wer;e burnt, served to heat these chambers in such a way as to coke the raw coal, the temperature of the flues being about 800 to 900 C. Fig. 13, taken from the Journal Iron