338 STEAM CARRIAGE used however only experimentally. George Stephenson in 1814 introduced the locomotive in Great Britain. The steam blast of Hack- worth, the tubular boiler of S6guin, and the link motion of Stephenson constitute the es- sential features of the modern locomotive. (See RAILROAD.) Locomotives have gradually and steadily increased in size and power from the date of their introduction. The Rocket, which first proved conclusively in 1829 the value of steam locomotion, weighed 4J tons. In 1835 Robert Stephenson, who had con- structed it with his father, writing to Robert L. Stevens, said that he was making his en- gines heavier and heavier, and that the en- gine of which he enclosed a sketch weighed nine tons and could draw "100 tons at the rate of 16 m. an hour, on a level." Loco- motives are now built weighing 70 tons, and powerful enough to draw more than 2,000 tons at a speed of 20 m. an hour. The modern lo- comotive consists of a boiler of the form shown in the article STEAM BoiL^t, mounted upon a strong light frame of forged iron, by which it is connected with the wheels. The largest FIG. 4. British Express Engine. engine yet constructed in the United States is said to be one in use on the Philadelphia and Reading railroad, having a weight of about 100,000 Ibs., which is carried on 12 driving wheels. A locomotive has two steam cylin- ders, either side by side within the frame, and immediately 1 beneath the forward end of the boiler, or on each side and exterior to the frame. The engines are non-condensing and of the simplest possible construction. The whole machine is carried upon strong but flexible steel springs. The steam pressure is usually more than 100 Ibs. The pulling power is generally about one fifth the weight under most favorable conditions, and becomes as low as one tenth on wet rails. The fuel employed is wood in new countries, coke in bituminous coal districts, and anthracite coal in the east- ern part of the United States. The general ar- rangement and the proportions of locomotives differ somewhat in different localities. In fig. 4, a British express engine, O is the boiler, K the fire box, Xthe grate, G the smoke box, and ' the chimney. S is a spring and R a lever safety valve, T is the whistle, L the throttle or regulator valve, E the steam cylinder, and W the driving wheel. The force pump, B C T is driven from the cross head, D. The frame is the base of the whole system, and all other parts are firmly secured to it. The boiler is made fast at one end, and provision is made for its expansion when heated. Adhesion is secured by throwing a proper proportion of the weight upon the driving wheel W. This is from about 6,000 Ibs. on standard freight engines, having several pairs of drivers, to 10,- 000 Ibs. on passenger engines, per axle. The peculiarities of the American type are the truck or bogie supporting the forward part of the engine, the system of equalizers, or beams which distribute the weight of the machine equally over the several axles, and minor dif- ferences of detail. The cab or house protect- ing the engine driver and fireman is an Ameri- can device, which is gradually coming into use abroad also. The American locomotive is dis- tinguished by its flexibility and ease of action upon even roughly laid roads. The cost of passenger locomotives of ordinary size is about $12,000 ; heavier engines sometimes cost $20,- 000. The locomotive is usually furnished with a tender, which carries its fuel and water. The standard passenger engine on the Pennsylva- nia railroad has four driving wheels, 5 ft. di- ameter ; steam cylinders, 17 in. diameter and 2 ft. stroke ; grate surface 15| sq. ft., and heat- ing surface 1,058 sq. ft. It weighs 63,100 Ibs., of which 39,000 Ibs. are on the drivers and 24,100 on the truck. The shell of the boiler is 49J in. diameter and 20 ft. 2 in. long. The fire box is of steel, 6 ft. 2 in. long outside, 3 ft. wide, and 5 ft. 4 in. high. The tubes are of iron, 142 in number, 2Jin. diameter, and 11 ft. 7 in. long. The steam dome is 30 in. outside diameter, the smoke stack 14 in. The feed water is supplied by one pump of 2 in. diame- ter and 2 ft. stroke, and by a No. 8 Giffard in- jector. The valves are 16 in. wide by 8 in. long, and have 5 in. travel: The steam ports are 15f| in. wide and 1 in. long, and the exhaust port 15f| by 2 in. The lap of the valve is, outside f in., inside -^ in. The eccentrics have a throw of 4 in. The freight engine has six driving wheels, 54f- in. in diameter. The steam cylinders are 18 in. in diameter, stroke 22 in., rte surface 14.8 sq. ft., heating surface 1,096 It weighs 68,500 Ibs., of which 48,000 are on the^ drivers and 20,500 on the truck. The boiler is nearly of the same dimensions as that of the passenger engine, but the tubes are 2 in. in diameter, 12 ft. 9 T 9 ^ in. long, and 119 in number. The stack is 18 in. in diameter. The pump is 2 in. in diameter, and has a stroke of 22 in. The valve has f in. inside lap, -J s in. outside. The former takes a train of five cars up an average grade of 90 ft. to the mile.. The latter is attached to a train of 11 cars. On a grade of 50 ft. to the mile, the former takes 7 and the latter 17 cars. Tank engines for very heavy work, such as on grades of 320 ft. to the mile, which are found on some of the moun-
