The Locomotive Of Today

The Boiler : Combustion. 59 is dropped i-ft., it will supply sufficient heat to raise the temperature of i-lb. of water i° F. Similarly, if the quantity of heat abstracted from i-lb. of water in lowering its temper- ature i0 F. were properly applied it would raise a weight oi i-lb. 772-ft. high, or 772-lbs. i-ft. high. In burning, i-lb. of carbon will, if properly consumed, yield 14,500 units of heat, and it has then taken up two atoms ot cxygcii for each atom of itself, and formed carbonic acid ; . if, however, insufficient oxygen is present, it will combine with the oxygen, atom for atom, and form carbonic oxide, and only give up 4,400 units, and thus 10,100 heat units are lost from this cause alone, from which it will be understood how important the necessity for a sufficient air supply is, the oxygen of the air being as much a portion of the fuel burnt as the coal itself. To chemically saturate the carbon contained in one pound of coal 12-1-Ibs. of atmospheric air are required, but under ordinary working conditions this quantity is quite insufficient, and a large production of carbonic oxide and heavy smoke would be the consequence, and it is therefore usual to arrange means by whicli a larger amount can be admitted, from one and a half to twice the above quantity is generally found to be necessary, depending’ upon circumstances; for instance, a much greater quantity of air is required to combine with the more volatile distillates from the coal when it is first put on to the fire, but the supply below the grate can be reduced as the carbon is thoroughly ignited, and more admitted above the fire through the firedoor. It must not, however, be assumed from the foregomg that the quantity of air may be indefinitely increased, as tue evils of'a too large supply are as great as a too small one, foi this excess acts, not by interfering' with the perfect combustion o the carbon, none of which can escape under these altered conditions transformation into carbonic acid, but by lowering- the temperature of the firebox by the mixture of cold air, which, after being raised to a high temperature, is passed out of the chimney, robbing the boiler of heat that should have been employed in raising steam ; from this it will be seen that it is most necessary to regulate the supply of cold air to secure an exact combination of it and the volatile gases of tne coal for perfect combustion. We will now refer to the illustration, Fig. 12, by which the application of the foregoing principles to a. locomotive boiler will be more easily followed. . . The firehole is generally fitted with an air-deflecting- device for directing incoming air downwards on to the fire,.