I LOCOMOTIVE. 389 LOCOMOTIVE. tendent of motive i)nver. Lake Shore and Michi- gan Southern Railway, arc of interest. The en- gine selected as an example is a passenger en- gine, weighing about 175.000 pounds, and having three pairs of 80-inch drivers. Some of the small details have not been estimated, and others have been omitted from these figures because of their miscellaneous character; such, for in- stance, as the brasswork about the engine, cab- fittings, the piping, boiler-lagging, boiler-jackets, etc. Exclusive of tlicse the amount of wrought iron in the engine is 10,0.50 pounds; cast iron, 19,550 pounds, of which 11,.350 pounds are in the cylinders and 1700 pounds in the grates; cast steel, 27.000 pounds, of which about 16,000 pounds are in the driving and truck wheels; pressed steel, 10.50 pounds; rolled-steel plates and shapes. 3770 pounds; forged steel, 1 1,270 pounds; tire-steel, 10,500 pounds; malleable iron, 1300 pounds; and wood, 4100 pounds. The boiler weighs 47,850 pounds, and the water in the boiler 22,500 pounds, making a total weight of 167.100 pounds. Cl.ssific.tion". Locomotives are classified according to the number and arrangement of their driving and truck wheels. The various classes and the service for which each is chiefly employed are as follows: American or eight- wheeled locomotive: this type of locomotive has two pairs of driving wheels with a four-wheeled truck in front of them and is employed chiefly in passenger ser'ice. Atlantic loconcotive : this type of locomotive consists of two pairs of drivers, a four-wheeled leading truck and a pair of trailing wheels, and is employed exclusively for high-speed passenger service. Mogul loco- motive: this type of locomotive has three pairs of drivers and a pair of leading wheels, and is used for heavy freight service and to a consider- able extent for passenger senice. Ten-ivhceled locomotive: this type of locomotive has three pairs of drivers and a four-wheeled leading truck, and is employed for heavy and high-speed pas- senger sei"ice. Consolidation : this type of loco- motive' has four pairs of drivers and a pair of leading wheels, and is u.sed exclusively for freight service. Decapod: this type of engine has five pairs of drivers and no truck-wheels, and is used as a pushing engine on heavy grades and for very heavy freight service, ilastodon : this type of engine has four pairs of drivers and a foui-- wheeled leading truck. Switching: for switching purposes engines having either two pairs or three pairs of drivers are used and are known respectively as 'four-wheeled' and 'six- wheeled' switchers. Fornejj : this type of engine has two pairs of drivers placed well forward and a four-wheeled trailing truck, and is used for suburban passenger and elevated railway service. There are several other types of locomotives in limited use, but those named are the standard forms. CoMPOu:xD Locomotives. The compound loco- motive is one in which the steam is admitted to one cylinder called the high-pressure cylinder, where it partially expands in doing its work, and whence it exhausts into the steam-chest of a larger cylinder, called the low-pressure cylinder, where it completes its expansion and finishes its work. The compound principle has been applied to locomotives in three ways: (1) Two-cylin- der compounds, with a cylinder on each side: the steam passes from the high-pressure cylinder on one side through the smoke-box and across the engine to the low-pressure cylinder on the oppo- site side; (2) three-cylinder compounds, with a high-pressure cylinder on each side, the steam from which exhausts into a low-nressure cylinder beneath the smoke-box; (3) four-cylinder com- ])ounds, with a high-pressure and a low-pressure cylinder on each side of the engine, each pair working independently of the other. In the United States four makes of two-cylinder loco- motives are in use; they are named the Rich- mond, Schenectady, Pittsburg, and Brooks, from the names of the works at which they originated. These four makes differ from each other princi- pally in the construction and operation of their intercepting valves. This valve is an ingenious and rather complicated mechanism, whose func- tion it is to admit live steam from the boiler directly into the low-pressure cylinder, and then to cut off that flow of steam when the exhaust of the high-pressure cylinder has raised the pres- sure in the receiver leading to the low-pressure cylinder sufficiently to enable it to deliver steam to the latter. The necessity of being able to deliver live steam into the low-pressure cylinder arises when the crank of the high pressure stops on the dead centre. Intercepting valves are some- times designed to cut off the live steam auto- matically, and sometimes this operation is per- formed from the cab by suitable lever arrange- ments. Three-cylinder locomotives have only been used experimentally 'a the United States, but they have met witn considerable favor in Europe. Four-cylinder compound locomotives are of two forms ; in one, the high-pressure cylinder is set above the low-pressure cylinder, as shown in FlO. 15. CBOeS-SECTION OP CYI.1SDEE8. Fig. 15, and in the other the two cylinders on each side are set end to end, or tandem. The form of four-cylinder compound most used in the United States is that having each pair of cylin- ders arranged as shown in Fig. 15. This draw- ing shows the piston-valve between the two cylin- ders, and by means of the arrows the course of the steam from its entrance to the high- pressure cylinder to its exhaust from the low- pressure cylinder. The general use of compound locomotives is of comparatively recent date, the first locomotive of this type having been built In 1875. The great advantage claimed for the com- pound locomotive is economy of fuel, which is variously stated to be from 10 per cent, to 30 per cent, over single engines.
