Mine Haulage.—Up to a very recent period, the coal cut by the various machines already described has been hauled from the side head ings or rooms to the shaft bottoms almost ex clusively by mules, but they are being rapidly supplanted by improved systems of steam haul age in the anthracite coal regions, and electric haulage in the bituminous drift mines adopted to meet the demands of various conditions which necessitate haulage systems of greater speed and power than that afforded by the use of mules.
The solution of the problem of mine haul age, constantly increasing in complexity by the longer haulage consequent on the extension of the mines, and the demand for a larger output, requires the consideration of several important factors, such as the grades of the haulage roads, the height of the veins of coal and the expense of the installation and maintenance of the vari ous forms of haulage machinery. Electricity as applied to mine haulage appears to satisfy these conditions better than any other form of power, and the development and extensive use of the electric mine locomotive is the natural result of the best efforts in this direction.
These locomotives are made in a great variety of forms and are equipped with single or double multipolar motors. They range in weight from 2% to 15 tons, and are operated either by the more familiar overhead trolley wire, or the later third-rail systems. The latter consists of a stationary third rail of heavy iron bars running between the two track rails which are used as the return conductor. The bars of the third rail are perforated at regular intervals throughout their entire length, and are made into a continuous rail by means of fish plates. The locomotive consists of a substantial steel frame mounted on suitable track wheels. This
frame also carries two steel sprocket or traction wheels, which are driven by the electric motors of the machine, by means of suitable gearing. These sprocket wheels engage the third rail through the perforations therein, and serve the double purpose of driving the locomotive along, and taking up the current from the third rail to feed the electric motor. The third rail is en closed in an insulating wood casing, and is usually laid about five inches off the centre of the regular track, thus allowing sufficient room for the animals to work without interrupting the operation of the mine while the plant is being installed. The chief advantage of the system appears to be its positive working; the practicability of using light rails on heavy grades; and the minimum consumption of power in moving the dead weight of locomo fives of comparatively light tonnage. The loco motives used at the present time in operating the 'Morgan° electric third rail haulage systems range from 6,000 to 10,000 pounds in weight, and range in capacity from 75 to 150 horse power. The smaller machines are equipped with single motors and the larger with double motors, wound for either 250 or 500 volts, as may be desired.
These locomotives as well as those operating the trolley systems are capable of hauling trains of 40 to 50 cars each, or about double the number of cars usually comprising a cable train. These cars are made in a great variety of forms to adapt them for different kinds of service, and have either steel or wooden bodies. They are arranged to open at the side, or with a 'drop-gate' having °wings* which prevent the coal from spilling out at the ends of the gate when lowered. This gate also serves as an extension platform from which the coal may be conveniently shoveled.