for this traffic they usually have smaller drivers than for passenger work.

Q. For heavier freight service, where greater tractive power is desired than can be had with only two driver pairs, what arrangement is made?

A. More drivers are added, as in (1) the Mogul (Fig. 8), in which there are three pairs of drivers and a pony or two-wheel truck; (2) the consolidation, in which there are four pairs of drivers and a two-wheel truck (Fig. 9); (3) the ten-wheeler, in which there are three pairs of drivers and a four-wheel truck (Fig. 10); (4) the twelvewheeler, in which there are four pairs of drivers and a four-wheel truck; and (5) the decapod, in which there are five pairs of drivers and a two-wheel truck (Fig. 11.) Q. For what class of service is the Mogul or 2-6-0 type adapted?

A. For freight service on comparatively level roads; or on heavy rails, where a large load per axle is permissible, and even for comparatively fast freight service.

Q. What proportion of the total weight of the Mogul is on the drivers?

A. Averaging 80 to 85 per cent.

Q. What about its boiler capacity?

A. There may be provided sufficient for moderate speeds; and wide grates may be used because of the usually chosen small drivers.

Q. How is depth of throat sheet secured?

A. By sloping the fire-box down at the front end between the second and the third pair of drivers.

Q. What class of engine is best adapted for fast freight?

A. The ten-wheeler is coming into great favor for this purpose; having six wheels coupled and a four-wheeled truck, as shown in Fig. 10, page 17.

Q. For what other class of traffic is the "ten-wheel" or 4-6-0 type adapted?

A. For heavy and fast passenger service; requiring a

tractive power that six wheels alone can give without overloading the fish plates and does not require too much steam. Having great hauling capacity in proportion to

Fig. 8. Mogul Freight Engine with Tender.

the total weight, it is a good type for passenger service, not calling for sustained high speed. It is also good for freight trains of moderate weight and high speed, having more speed than the 2-8-0 or Consolidation type.

IL

Fig. 9. Consolidation Engine for Heavy Freight.

Q. With what sized drivers is it best adapted as an "all-around" engine for passenger and fast freight service?

A. About 63 to 69 inches.

Q. What is the limitation of this type in passenger service?

A. The driver diameter, as where the drivers are over 73 inches the fire-box may not be extended laterally over the rear drivers.

Q. How may the throat sheet be given sufficient depth with this type, where the drivers are, say, 69 inches in diameter?

A. By sloping the mud ring downward toward the front end of the engine, between the second and third driver pairs.

Q. For what class of fuel is it a favorite?

A. Anthracite.

Q. What complaint is sometimes made of "tenwheelers"?

A. That they are easily derailed.

Q. Is this complaint justified?

A. Only this far, that the fault is as much that of the track as of the engine. Where the rigid wheel base is long, the track must have easier curves, or a wider gage on curves, or the train must go more slowly around curves than where the rigid wheel base is short. Either the track must be made to conform to the new conditions of long rigid wheel base, or the speed must be reduced

on curves.

Q. For heavy freight what seem to be the best adapted types of engine in America?

A. (1) The consolidation, having eight wheels coupled and a pony truck in front as shown in Fig. 9, and (2) the decapod, having ten wheels coupled and a pony truck, as shown in Fig. 11.

Q. For what service is the consolidation or 2-8-0 type especially suited?

A. For freight service requiring high starting power, as it has a large proportion of the weight on the driving wheels, and permits, by reason of large cylinders and comparatively large drivers, starting heavy trains and working steep grades. Where desired, the fire-box may be extended laterally over the rear drivers.

Q. What proportion of the total weight may be on the drivers?

A. From 85 per cent to even as high as 90; although this latter is rare.

Q. How may the front fire-box end be given sufficient depth?

A. By sloping it downward toward the front of the engine, ending between the third and fourth driver pairs, below their tops.

Q. What is the difference, as regards the wheel-base and weight distribution, between the Mogul and the tenwheeler?

A. In the Mogul the front drivers are nearly as far from the main or middle driver as the back drivers are; in the ten-wheeler, Fig. 10, by reason of the back-wheels,

TI

Fig. 10. Ten-wheeler for Fast Freight.

which are in the rear of the cylinders, the front drivers are quite close to the middle pair, and thus get proportionately less weight.

Q. What is the advantage of increasing the number of drivers?

A. It enables adding to the engine weight, which gives traction, without putting so much load on any one pair of drivers as to wear the rail unnecessarily or to be injurious to rail-joints.

Q. Is the Mogul engine ever used for passenger service?

A. Yes, but it is usually restricted to freight work.

Q. What is the general make-up of switching engines? A. They usually have two or three driver pairs, short wheel-base and no truck, if for switching only, and seldom have tenders, the fuel and water being carried on the engine; if they do, the tenders have instead of two trucks, only two wheel pairs. Such an engine with three pairs of drivers may be seen in Fig. 16.

Fig. 11. "Decapod" for Heavy Freight.

Q. What class of engines is desirable for both switching and local service?

A. There are several types. One has two pairs of drivers coupled, and a back tank, with a four-wheeled

Fig. 12. Engine for Switching and Local Service, with Back Tank. (Forney Type.)

truck under it; this being the Forney type. (Fig. 12.) Another has two pairs of wheels coupled, and a pony truck in front, with a four-wheel tender, as in Fig. 15. A third is of the Forney type, that is, with a back tank supported on its own wheels borne by the engine-frame; but there is only one pair of such wheels, as shown in