The Locomotive Of Today

The Boiler: Firebrick Arch, Firing. 61 and the construction of this has already been mentionecl when dealing with firedoors. The best form appears to be the plate, bent to shape, and introduced independently of the door, as it can then be more easily removed and replaced than if it forms part of the door itself. A firebrick arch is built up across the front portion of the box, just below the bottom tubes, and reaching over towards the firehole, is inclined at the same angle as the air deflector, and forms an arch across the box, hence its name. It is supported on a row of copper studs or in some cases an angle iron on either side of the box. Its object is to deflect the fire over towards the back of the firebox at the top, and so, by retarding the escape of the more volatile gases contained in the coal, ensure perfect combustion ; it also causes the heat to be more equally diffused over the whole of the inside of the box, and by preventing cold air passing over and striking the tubes reduces leakages there. Firebricks or firelumps are generally employed for building these arches. On many Continental and American engines a water bridge takes the place of the brick work. The damper is opened to the extent fbund necessary for the admission of sufficient air for burning the required quantity of coal, whilst a further supply is admitted at the firehole door to complete the combustion. The latter should be as large as possible having due regard to the working of the eng'ine and the State of the fire. The coal should never be thrown into the firebox in large lumps, but should be broken up to about the size of a man’s fist, and spread evenly over the grate, if anything the sides and corners should have most. Holes are to be avoided as they allow cold air to enter the box, cooling it, and causing leakages. The fire should not be too thick, as then a heavy biast is required to form proper combustion, nor too thin, admitting too much air, and “lifting ’ when the engine is running. The proper thickness, of course, depends upon the quality of the coal and the nature of the work to be done, and is best found by practice, but should not be more than g inches as a rule, and in many cases it may be much thinner. The bars must be kept clear from clinker, as this retards the passage of air through the fuel, and causes the great loss of heating effect mentioned above, when the carbon is only supplied with half its proper quantity of oxygen. A few flint stones thrown on the grate when the fire is thin will assist in the removal of clinker when formed. Care should be taken to have a clear fire before an engine starts on a journey, so that it will not be necessary to introduce