The Locomotive Of Today

The Boiler: Firebars, Rocking Grates, Air Jets, &c. 23 sufficient fuel on so small a grate in the limitecl time to produce steam in large enough quantities for the work that a locomotive has to do. The fire-bars are about ^-in. thick on their upper edge, and taper off to f-in. at bottom, being 4 to 4^-in. deep, with thickkning pieces at the ends, and also in the centre in cases where the bars are long, for the purpose of keeping them the required distance apart. They are usually made of cast iron, though wrought iron when used appears to offer some advan- tages, its point of fusion is higher, and it will stand more rough usage, being less easily broken, but it bencis and twists with heat sooner than cast iron does. The bars are usually made about half the length of the grate, thoug'h sometimes they are made long enough to go the entire length of the box. They are carried on bearers of wrought iron, which extend across the bottom of the box, and rest upon brackets fixed either upon the foundation ring or upon the ash-pan, the latter being preferable, as they are more easily removecl. A, Fig. 5, shows such an arrangement of bars. The bearers may be made of cast iron, and provided with distance pieces on their upper side; the bars need not then be thickened at the ends, but placed between these projections, so keeping the necessary air spaces between. This arrangement of bearers and bars is shown at B. The rate of combustion of coal on each sq. ft. or grate ranges from 40 to 120-lbs. per hour. Rocking or movable firebars, actuated by levers worked from the foot-plate are often employed in America on coal burning engines, but their use does not find favor hére, probably because the coal is better and does not clinker so much. Water grates are also used, and consist of tubes passing from front to back of the firebox and connecting the water spaces tog'ether, but not always arranged in one plane,, every fourth one being raised above the others; this arrange- ment of fire-bars has been adopted for very long fireboxes using hard coal. We have only mentioned the commoner forms of fire-grate and bars used, but many moclifications can be met with, including double-bars, transverse, spaced, etc., etc. In a few locomotives holes are provided through the water spaces just above the level of the fire, through which atmospheric air is induced to assist combustion; and in extension of this principle steam jets have also been employed. The ash-pan is of box form about i-ft. deep, fitting under the firebox and made up of iron plates J to yg-in. thick ; it is provided with doors or dampers often at the front end only for