This view will assist in showing the relation of the parts, especially the coal screen above the conveyor trough and the slidable connection of the conveyor trough on the tender. The whole stoker being attached to the locomotive proper, the necessary flexibility between locomotive and tender is provided for by swivel connection at forward end of the conveyor trough at the point where it is attached to the elevator hopper, and the fore-and-aft movement incident to the usually loose coupling connection between locomotive and tender is provided for by simply having the conveyor through slide upon the bracket placed below the trough, as can be readily observed in this photograph.

This photograph of the general side view of the stoker will give you a better idea of the driving means for operating the conveyor screw through sprocket connections on back of hopper, which are in turn operated by the endless elevator chain of buckets as they pass the main sprocket in lower left-hand part of elevator hopper, and also the elbows, tubes, and distributers which are placed on and through the backhead of the locomotive.

The following is a photograph of a pen-and-ink sketch of a large Mikado locomotive equipped with the Street stoker, and will serve to give a better conception of the general arrangement of the openings above coal screen and the availability of the ordinary fire door and the usual space in cab for locomotive engineer and fireman. This view also shows a sliding door provided in roof of cab for inspection of stoker motor.

Photograph of phantom view of Street locomotive stoker.

As I mentioned earlier in the paper, this stoker is particularly representative of that method of firing by which the coal is put into the firebox above the level of the fuel bed and dropped upon the surface of the fire continually, while the locomotive is being operated, and distributed over the entire grate area at the rate of combustion. Other stokers have been designed to partially carry out this methodthe Hanna stoker, for instance, while putting coal into the firebox continually, does not spread it over the entire grate area at the rate of combustion, as it will have been observed that the movable mechanical directive means which assist the jets in the Hanna stoker

in distributing the coal have the effect of putting coal to the different parts of the firebox in excess of the rate of combustion and then moving the directed stream of coal toward other parts of the firebox to permit the coal, just delivered, to be consumed in the meantime.

The routine of the process of firing a locomotive with the Street Istoker is about as follows: The coal is assisted in passing down through the slide opening just in front of the main body of coal in the locomotive tender by the movement of the tender screen, this screen, by the way, being operated through a travel of three or four inches fore and aft by mechanical means and connections in the main elevator hopper. This movement of the screen materially assists a stream of coal being regularly delivered to the conveyor trough just below the opening, where it is carried forward and dropped into the main elevator hopper.

The endless chain of buckets, each bucket lifting about one pound of coal, then takes up the coal and carries it to the main discharge pipe in upper section of elevator casing, where it is again screened, divided, and directed toward the firing elbows. The coal drops by gravity to these elbows and is forced into the firebox by steam jets which are controlled by the blast-controlling device operated by main driving shaft of the elevating mechanism. The cams on this blast device are within the control of the fireman, so that the interval and duration of the jets may be adjusted to meet the conditions of operation. The jets are intermittent in action, but the coal is admitted to the firebox continually and is, in effect, scattered over the entire grate area all of the time while the stoker is in operation.

During the slight interval between the operation of the jets the coal is carried into the firebox from the firing elbows by the draft of air which enters the firebox at the stoker openings and is carried partially over the grate area, and, as the jets start, the coal is still further driven forward and, as the pressure of the jet increases, the wave of coal is projected farther and farther toward the throat sheet. As the pressure begins to die down the main wave of coal is then spread, with less force, toward the back part of the grate area.

The motor which operates the stoker has a variable speed governor-variable speed in the sense that it can be set to run at different rates of speed as may be required to drive the conveying, elevating, and stoking mechanisms at speeds suitable for supplying coal in proportion to the amount required for any given output of the locomotive.

The several constant speeds of the stoker motor make it possible for the fireman to set the stoker to run at the different rates for any interval of time that the locomotive may be operated with any particular setting of the reverse lever and throttle. The highest speed of the stoker motor represents the delivery of the proper amount of coal to fire the locomotive to its maximum capacity, and at the lower speeds at which the motor can be set the delivery of the coal will be in amounts proportioned properly to operate the locomotive at several different rates of output. The relation between the delivery of the coal by the conveyor and its elevation by the buckets of the elevator is arranged for in the initial application of the stoker to any particular locomotive.

If a delivery of coal is required of less quantity than the delivery at the slowest speed of the motor, the amount can be further reduced by partly closing, with the sliding plate, the opening over the tender screen or by disconnecting the stoker motor from the stoking mechanism through means of the friction clutch which is introduced between the motor and the stoker for the purpose of readily stopping and starting the stoker when desired.

Means are also provided to permit the fireman to control the supply of coal delivered to each of the three elbows. The increase and decrease of the supply to the center elbow are adjusted by turning larger or smaller screen openings to register with the discharge opening for the middle distributer, so that in this way more or less of the fine coal is taken out of the main stream of coal as it passes over the upper screen.

The supply to each of the side elbows is regulated by a dividing rib which can be placed at different points in the opening so that the flowing stream of coal will be divided up in different proportions between the tubes going to the side elbows.

While there are means supplied, as described, for making different adjustments of regulation of the speed, as well as the dividing means for supplying the coal to the different zones in the firebox, the adjustable features generally of this stoker are designed with the idea of permitting a definite setting to be determined, and then permitting the stoker to operate at that setting of speed or coal delivery, so that, so long as the locomotive is worked at the point requiring that particular amount or distribution of the coal, the stoker will need no additional

attention on the part of the fireman other than to see that the coal is being fed properly to the opening above the screen in the tender.

In designing the Street stoker the firing problem of itself was considered as of first importance; that is to say, the keeping of the fire in direct relation to all of the conditions of operation of a modern. locomotive, especially that of securing the absolute maximum output and satisfactorily caring for the abrupt changes required of the power plant, yet it can be said that the general scheme of firing is in line. with the best recommended practice and must contribute toward economy, although in a different manner from that of the underfeed method, and at the same time make it possible to burn fuel that could not be used for hand firing.

I beg leave to quote in this connection a few paragraphs from Technical Paper No. 80, issued by the Department of the Interior, Bureau of Mines, which particularly commends this method of firing, especially as to its possibilities for successfully burning slack coal:

"Soft or bituminous coal should be fired in small quantities at short intervals, the quantity that should be fired varying with the size of the grate and the intensity of the draft.

"Small and frequent firing makes the coal supply more nearly proportional to the air supply, which in most hand-fired furnaces. is nearly constant. They also reduce the formation of crust on the fires and the chance of holes in the fuel bed. With small and frequent firings better combustion is obtained.

"When a fresh charge of bituminous coal is spread over an incandescent fuel bed, the coal is heated rapidly and twenty to forty per cent of the combustible matter is distilled off in the form of gases and tar vapors. This distilled combustible matter requires for its combustion additional air. It can be readily understood that the heavier the charges, the larger amount of volatile combustible driven off two to five minutes after firing.

"To burn the volatile combustible, about fifteen times its weight of air needs to be supplied. Therefore, immediately after firing, a large quantity of air should be admitted over the fire, and this quantity should be gradually reduced as the distillation of the volatile combustible nears completion. The larger the quantity of fresh coal fired at a time, the larger the volume of air needed for the complete combustion of the volatile matter.