Fig. 737 represents an ar rangement known as Boetius' furnace. It was the forerunner of the last, and is very similar to it. The chief difference is that air is introduced through a perforated column b, as well as through the air-passages a in the base. The gas and air unite and burn at c. The disadvan tage of the central column is that any glass which may escape from a broken crucible is re_ tained by the column, and can be removed only with great dif ficulty.
Frisbie's Feeder. — Frisbie's patent feeder provides a method of stoking from beneath the fire, and effects a considerable saving in the consumption of fuel. By this principle of feeding from below the fire, the igniting of the fresh coal is a gradual process, and all volatilized coal, combustible gas, and carbonaceous matter pass from below, through the live coals above, and break at once into flame ; thus perfect combus tion, and great intensity of heat, are secured. The heat of the surface of the fire is not abated, nor is cold air admitted into the furnace while supplying fresh fuel, so that a perfectly uniform heat is maintained ; and, as the hottest portion of the fire is constantly at the top, all the heat is utilized, and the grate-bars are preserved from burning and from clinker. The coal is pushed up and outwards equally from the centre of the grate, and the whole fire is stirred and broken up at each fresh supply of fuel, so that no raking is required, and the coal is evenly consumed, leaving little refuse, except fine ashes which drop down through the grate-bars without raking. Figs. 738 and 739 show, in vertical section, the respective positions when feeding and not feeding : A is the opening through the grate ; B, hopper ; C, movable bottom ; D, plunger to feed-hopper ; E, plunger-lever ; F, apron sustaining coal while the hopper is being refilled ; G, rocking-bar, attached to H and K ; H, rocking-shaft; I, hand-lever for working H ; H, lever carrying hopper backwards and forwards ; L, catch ; M, arm supporting hopper and apron ; N, shaft sup porting M.
Siemens' Regenerative Gas Furnace.—The gas-producer is shown in Figs. 740 and 741; the former is a section, and the latter a front elevation, of a pair of gas - producers. The producers are entirely separate from the furnace where the heat is required, and may be made sufficient in number and capa city to supply several furnaces.
The fuel is supplied at inter vals of 2-4 hours, through the charging-boxes A, and descends gradually on the inclined plane B, which is set at an inclination 1 to suit the fuel used. The upper portion of the incline B is made solid, being formed of iron plates covered with fire-bricks ; but the lower portion C is an open grate formed of fiat horizontal steps. The large opening under the lowest flat step is convenient for drawing out ()linkers, which generally collect at that point. The small stoppered holes F at the front, and G at the top, of the producer, are provided to allow the insertion of an iron bar to break up the mass of fuel, and detach clinkers from the side wall. Each producer is capable of converting daily about two tons of fuel into combustible gas, which passes off through the " uptake " H loading to the furnaces. The notion of the gas-producer is ae follows :— The fuel, as it descends, becomes heated, and parts with its volatile constitnents,—namely, the hydrocarbon gases, water, ammonia, and some carbonic acid. There now remains 60-70 per cent. of purely carbonaceous matter to be disposed of, which is accomplished by the action of a current of air slowly entering through the grate C, producing regular combustion immediately upon the grate. The carbonio acid thereby produced, in passing slowly through a layer of incandescent fuel, takes up another equivalent of carbon, and becomes carbonic oxide, which passes off with the other combustible gases to the furnace. Water may be brought to the foot of the grate by the pipe E; this water, absorbing the spare heat of the fire, is converted into steam, which, in its passage through the incandescent fuel, may be decomposed into its elements, after having performed the useful office of disintegrating the clinkers. The total production of combustible gases varies with the admission of air, and since the admission of air depends upon the withdrawal of the gases, the production of gases depends upon the demand for them. A damper D can be inserted in the "uptake," so as to shut off any gas-producer at pleasure.