THE GROWTH OF THE STEAM-ENGINE. 



277 



Fig. 41. British Express-Engine. 



by side within the frame, and immediately 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 pounds. The _^ TT lEj 



pulling -power is generally 

 about one-fifth the weight 

 under most favorable con- 

 ditions, and becomes as low 

 as one -tenth on wet rails. 

 The fuel employed is wood 

 in new countries, coke in bi- 

 tuminous coal districts, and 

 anthracite coal in the eastern 

 part of the United States. 

 The general arrangement and the proportions of locomotives differ 

 somewhat in different localities. In Fig. 41, a British express-engine, 

 O is the boiler, N~ the fire-box, Xthe grate, G the smoke-box, and P 

 the chimney. S is a spring, and H a lever safety-valve, T is the 

 whistle, L the throttle or regulator valve, E the steam-cylinder, and 

 TTthe driving-wheel. The force-pump, B C, is driven from the cross- 

 head, I). 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 pounds on standard 

 freight-engines, having several pairs of drivers, to 10,000 pounds on 

 passenger-engines, per axle. The peculiarities of the American type 

 (Figs. 42, 43) 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 

 differences of detail. The cab or house protecting the engine-driver 

 and fireman is an American device, which is gradually coming into 

 use abroad also. The American locomotive (Fig. 43) is distinguished 

 by its flexibility and ease of action even upon 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 stand- 

 ard passenger-engine on the Pennsylvania Railroad is quite similar in 

 form to the Baldwin engine (Fig. 42), and has four driving-wheels 

 (G, IT), 5 feet diameter; steam-cylinders (C, D), seventeen inches 

 diameter and two feet stroke; grate-surface (N) 15^ square feet, and 

 heating-surface 1,058 square feet. It weighs 63,100 pounds, of which 

 39,000 pounds are on the drivers and 24,100 on the truck, L K. The 

 shell of the boiler is 49^ inches diameter and 20 feet 2\ inches long. 



