A plumbago crucible, d, sets upon a perforated plumbago cylinder, e, and is covered to a considerable depth with quartz pebbles from half an inch to an inch in diameter; f f are plugs which may be removed to admit of inspection. The burner is represented in fig. 2, and consists of two chambers of cylindrical cast iron, one for the reception of air and the other for gas. Tubes, varying in number from 6 to 20 or more, pass from the air chamber through the gas chamber, and through the axes of tubes passing from the latter, thus .securing admixture of the combustible gases. A stand, g, fig. 1, supplied with a thumb screw, holds the burner at any desired distance below the crucible. The gas is supplied at the usual pressure, but the air is urged with a bellows or other blowing machine at about 10 times that pressure. In the experiments made by the inventor, the gas and air pipes were of 1/2 in. calibre and 10 in. long, the gas having a half-inch and the air a five-inch water pressure. The quantity of gas used per hour was about 100 cubic feet. Fig. 1 represents the furnace with the gas burner in an erect position, but it is perhaps more frequently used at the top, inverted, as shown in fig. 3, in which an additional perforated clay plate, h, is laid on the top of the upper clay cylinder.

Into the perforation the burner is introduced, and when in action throws its flame down upon the top of the crucible, d, which is now placed upon a foundation of clay plates, k, k, k, raised to the proper height, and of such a size as to leave a vacant space between them and the clay cylinders, which is filled with quartz pebbles, and through which the burned gases pass on their exit, which is now through perforations in the two lower clay plates. The hot gases give up nearly all their heat to the pebbles, and escape at a much lower temperature than would be supposed. The following experiment shows the power of this furnace: A clay crucible, 3 in. in both diameters, was filled with 24 oz. of cast iron, and not covered. The flame being thrown directly upon the iron, it was soon covered with a crust of magnetic oxide. In 20 minutes the crucible was removed, and a hole being broken through the crust, 20 oz. of melted iron was poured out. In the same furnace 16 oz. of copper can be fused in 10 minutes, commencing with the furnace cold, or in 7 minutes after it is hot.

Gore's gas furnace is heated by a burner in which the air and gas are more thoroughly mixed previous to ignition than in Griffin's, but it is generally used in smaller operations.-One of the most important improvements which have been made in the arts is Siemens's regenerating gas furnace, which received the grand prize at the Paris exposition of 1807. The invention is not only important as 'affording an easily managed furnace of great power, but in possessing great economy in regard to fuel. It consists of three essential parts: 1, a gas producer; 2, a regenerator; and 3, a furnace chamber. The gas producer is shown in fig. 4, and is constructed somewhat like a base-burner warming stove, although the action and gaseous products are different because of the different direction of the draught. Bituminous coal is introduced at A, and falls down over an inclined plane, B C, the lower part, C, being a grate for the admission of air. At D there is a stoppered opening, through which an iron bar may be passed to clear the walls of clinkers. At E there is an opening controlled by a valve, and which leads into a flue, F, passing to the regenerator.

The action is as follows:

FIG. 1. Griffin's Gas Furnace.

Fig. 1.-Griffin's Gas Furnace.

Fig. 2. Gas Burner, Griffin's Furnace.

Fig. 2.-Gas Burner, Griffin's Furnace.

Fig. 3. Griffin's Furnace, with Flame inverted.

Fig. 3.-Griffin's Furnace, with Flame inverted.

Fig. 4. Gas Producer, Siemens's Furnace.

Fig. 4.-Gas Producer, Siemens's Furnace.

The coal, being ignited at the grate, is heated to different degrees, a portion being converted into hydrocarbon gases and vapors, in the same manner as in a gas retort. Another portion, answering to the coke, principally combines with the oxygen of the air coming through the grate.and forms carbonic acid, which is therefore a waste product; but a portion of it decomposes steam and furnishes combustible gases, as will presently be explained. But this carbonic acid, having to rise along with the other gases through the in candescent coal above, combines with another equivalent of carbon, forming carbonic oxide, which passes on into the flue with the other combustible gases. But for every cubic foot of carbonic oxide thus pro-duced (the air consisting of about four parts in five of nitrogen by volume), two cubic feet of incombustible nitrogen are also taken up, tending to diminish the heating power. A small stream of water is delivered by the pipe G at the foot of the grate, and there being converted into steam ascends with the draught into the incandescent coal, where it is decomposed, with the generation of hydrogen and carbonic acid gases.

The generation of these gases is at the expense of heat, and therefore the amount of heat which they add in burning is inconsiderable, but the use of the steam serves to regulate the heat in the gas producer. When the heat rises more steam is decomposed, which action diminishes the heat in the gas producer, but increases it in the furnace chamber, where the mixed gases and air are burned. Fig. 5 gives a representation of the regenerators and the furnace chamber. There are two pairs of regenerators to each furnace chamber; one in each pair being for the transmission of air and the other for that of the gases furnished by the gas producer. The regenerators are chambers containing fire bricks, L, built up with open spaces between them to allow of the passage of the gases and air. These fire bricks are for the purpose of absorbing the heat which issues from the furnace chamber, and again yielding it to the gases which pass to the furnace chamber; and this is effected by having two pairs, which are alternately made to deliver currents to and receive them from the furnace chamber, by turning the valve S, in the centre of the figure, one way or the other.

K K is the heating chamber, into the right-hand end of which, as the valve S is now turned, the gases and air are received from the regenerators on the right hand also. The air enters through the openings O O, and the gases from the gas producer through R R. The air, having traversed the openings between the hot fire bricks, passes through N into the entrance of the furnace chamber, where it meets with the gases, heated in the same manner, coming through

Fig. 5. Siemens's Furnace.

Fig. 5.-Siemens's Furnace.

M. The two unite and produce an intense and uniform flame. The heated gases which are the products of the combustion in the furnace chamber pass out at the other end, down the flues M' N' and through the regenerators, yielding their heat to the fire brick in them, and passing into the flue of the tall chimney T. When these regenerators have become sufficiently heated, the valve S is reversed, and the air and gases are received through O' O and R' R, passing up through M' N' into the left-hand •end of the furnace chamber, and out at the other end, through M and N, where before they were received. The flues which pass from the gas producer to the regenerators are not shown in the figures. The gas producers are at a higher level than the regenerators, and therefore a current of gas can be made to flow from the former to the latter by allowing it to cool in the descending portion. The mixture of gases on leaving the producer has a temperature between 300° and 400° F., but on arriving at the descending portion of the flue has lost from 100° to 150°, which increases its density 15 or 20 per cent., so that a current is urged toward the regenerators, which is increased by the expansion produced by the heated fire bricks.

These furnaces are used with great advantage when high and regular heats are required for long periods, and are peculiarly applicable for metallurgic operations, on account of the facility with which, by increasing the amount either of air or of gas in the combustible mixture, an oxidizing or a carbonizing flame may be produced. They are also admirably adapted to glass manufacture, and were at first chiefly employed for that purpose.