Referring to the table. Nos. 1. 3, and 5 are the classes most widely used for passenger and freight service on light lines, laid with rails weighing from 50 to 60 lbs. per yd. No. 2. ex press passenger engine, is the type at present in use on the fastest trains between New York and Washington, and represents the most approved practice in high-speed locomotives. No. 4, heavy " Ten-wheel " locomotives, are used for passenger service on the long severe grades of the Baltimore and Ohio Railroad, for heavy fast-freight service on the New York, Lake Erie and Western Railroad, and for both passenger and freight service on other lines. The full-page illustration shows a compound engine of this class on the New York, Lake Erie and Western Railroad. No. 6. "Consolidation" type, has been generally adopted for heavy freight service, and especially for the haulage of coal, iron-ore, and other heavy materials.
having four pairs of driving,-wheels not only is the greater part of the to tal weight utilized for adhesion, but the weight is so distributed as to bring a less load per axle than in either the " Mogul " or "American" types. With driviug-wheels not ex ceeding 50 in. diameter, the length of driving-wheel base is such as to permit passing any ordinary curves, say up to 15°, or 382 ft. radius, with ease. No. 7, heavy Consolidation type, is the development of the ordi nary Consolidation engine to meet the necessity for a powerful locomo tive for and pushing service on mountain lines, inclines, etc. It is the resultant of the adoption of the same loads per axle for Consoli dation engines as have been found practicable with American, Mogul, and Ten-wheel engines, the diameter and spread of driving-wheels remain ing unchanged. In many locations, where pushing-engines are employed, it is practicable to lay heavier rails, and, if necessary, to specially strength en the bridges for such distance as may he required. If, however, the distributed weight of such an engine is greater than the rails or bridges can safely carry, the seine aggregate weight can be divided among five pairs of driving-wheels, making an engine of the Deeapod type, the di mensions of which are given by No. 8. Although a wheel-base of 17 ft. is necessary for the five pairs of driv ing-wheels, the passage of curves is facilitated by allowing extra play be tween the track and the flanges of the rear pair of coupled wheels. The rigid wheel-base is thins virtually re duced to 12 ft. 8 in., and curves of 330 ft. radius may be safely traversed. No. ft is a light switching locomotive. It is of the simplest type possible. the fuel and water being carried on the machine itself, and all the weight, being on the driving-wheels, is util ized for adhesion. It is therefore ex tremely powerful for its aggregate weight. Its short wheel-base permits it to enter with ease the sharpest curves in switches and side-tracks. Such engines are built of all sizes, from 7 X 12 cylinders and 7 tons weight to 17 X 24 cylinders and 35 tons weight, and are extensively em ployed for handling cars at railway termini, on docks, and around fur naces, mills, mines, and other indus trial establiShIllents. For service
where greater tank and fuel Fpnee is necessary than can be provided on the engine itself. a. separate tender carried on four or eight wheels can be used instead of the saddle-tank. Engines for similar service are con structed with three pairs of driving wheels, when the weight of the en gine or of the rails renders it inexpe dient to concentrate it on two pairs.
Such engines are referred to by Nos. 10 and 11 in the table. The heavy switching-engines used by the principal railway lines are usually of this pattern, with eight-wheel tender and wedge-shape or sloping-top tank. This peculiar form of tank is adopted for two reasons, viz., to enable the engine-men to have a better view of the track and cars when backing and coupling. and to enable the trainmen more conveniently to climb over the tender. Switch ing-engines are now generally made of sufficient power to handle as great a weight of train as the freight locomotives can bring in. They must therefore have as much weight on the driving-wheels as the heaviest road-engines. No. 12 is the pattern generally adopted for elevated railroad service in New York, Brooklyn, and other cities; also for light passenger service on short suburban surface-roads. In many of the larger cities, notably Chicago, where heavy suburban service on the surface railways requires special engines of great power, locomotives are employed of the type referred to by No. 13. They are built with four and six wheels coupled, and frequently with cylinders as large as 18 X 24.
general features of the boiler do not differ from those shown in Vol. I of this work. That part of the boiler over the furnace is enlarged by what is termed the wagon-top, for two purposes, viz., to give greater steam-space, and to increase the weight on the driving-wheels. The furnace and outer shell are made of mild steel, the usual requirements a tensile strength of as nearly as possible 55,000 to 65,000 lbs., elongation 30 per cent in section 2 in. long, and phosphorus not exceeding for fire box plates, and .05 for the plates of the outer shell. The tubes are of lap-welded iron, usually No. 13 Binning:lam wire-gauge, but frequently No. 12 or 11, rolled in the tube-plates and beaded over. The ends in the fire-box tube-plate are swaged down to allow for a copper ring or liner, which acts as a gasket or cushion between the tube and the plate. rendering the tubes less liable to leak under variations of temperature. The fire-door opening is formed by flang ing and riveting together the inner and outer sheets. A conspicuous difference between English and American boiler construction is the absence in the latter of angle-irons for join ing the parts: thus, the smoke-box tube-plate is made circular in form, flanged and riveted into the cylindrical waist of the boiler. The usual working steam-pressure is from 135 to 150 lbs. per sq. in., but recently a number of railways have sought greater efficiency and economy by adopting pressures of from 160 to 180 lbs.