In this system the solid fuel is converted into crude gas; this gas is mixed with a regulated quantity of atmospheric air, and then burnt. The arrangements are essentially the gas-producer, or apparatus for converting the fuel bodily into the gaseous state; then there are the regenerators. These are sunk chambers filled with fire-bricks, piled in such a manner that a current of air or gas, passing through them, is broken into a great number of parts, and is checked at every step by the interposition of an additional surface of fire-brick; four of these chambers are placed below each furnace. The third essential is the heated chamber, or furnace proper. This, the furnace-chamber, communicates at each extremity with two of the regenerative chambers, and, in directing currents of gas and air upward through them, the two gaseous streams meet on entering the heated chamber, where they are ignited. The current descends through the remaining two regenerators, and heats the same in such a manner that the uppermost checkerwork is heated to nearly the temperature of the furnace, whereas the lower portions are heated to a less and less degree, the products of combustion escaping into the chimney comparatively cool. In the course of, say, one hour, the currents are reversed, and the cold air and gas, ascending through the two chambers which have been previously heated, take up the heat there deposited, and enter into combustion at their entrance into the heated chamber, at nearly the temperature at which the products of combustion left the chamber. It is not difficult to conceive that by this arrangement, and with its power of accumulation, any degree of temperature may be obtained in the furnace-chamber, without having recourse to purified gas, or to an intensified draught. Where the temperature of the melting-chamber has certainly exceeded 4,000 degrees of Fahrenheit, the products of combustion escape into the chimney at a temperature of only 240 degrees. The practical result of this regenerative system is stated to be, that a ton of steel requires by the ordinary method about three tons of Durham coke—which, being estimated as coal, will be about four tons—to melt it, whereas, in Siemens's furnace, the melting is effected with twelve hundred-weight of ordinary coal. This economy is produced by reserving the heat, by means of the regenerator, which is ordinarily allowed to escape by the chimney.
Another plan for consuming coal with economy has been recently introduced by Mr. T. R. Crampton, and is now in use at the Royal Arsenal, Woolwich, and at the Bowling Iron Works, in Yorkshire. Instead of converting coal into gas, as in the Siemens process, the coal is reduced by Mr. Crampton to a very fine powder, and then blown into the heated chamber by means of a fan-blast. By this arrangement the perfect combustion of the coal is produced, and a heat of the highest intensity can be obtained. The utilization of this heat, without waste, when it is produced, is an important question still requiring careful attention. There are several other experiments being carried
