red. For lighting up, however, the fire is started in a clear grate, as usual, and the month's average (November) of fuel, including lighting up, is 12-2 pounds of oil per mile and 11 pounds of coal, or a total of 23-2 pounds of fuel. Nine other engines of the same class and the same range of duties averaged 34 pounds of coal per mile for the same month. Thus one pound of oil was practically equivalent to two pounds of coal.

Mr. Holden states that his early experiments convinced him that, for oil burning to be a success, the apparatus for the purpose must be independent of any firebox alterations, or, indeed, of anything which would prevent instant return to coal or solid fuel, or its use in lighting up. Hence his special injector to break up the oil into a fine spray without the use of brick work, hitherto common as a means of giving an extended surface of exposure to the oil. This breaking up of the oil is enhanced by the several small ring jets which converge on the issuing jet of oil, and both spread and mix it with air and diffuse the flame throughout the firebox, so preventing local heating.

The injector, entirely of gun metal, is clearly shown in section in fig. 21. Oil

enters at the side some way back of the steam nozzle and outside this. Steam, therefore, comes inside a thin ring of oil at the mixing nozzle and through the inner tube comes the vacuum brake air which, expanding as it becomes heated, still further aids the breaking up of the oil into spray. The ring jets of steam induce a further supply of air on the exterior of all, and so is obtained an alternation of air, oil, and air, which promotes admixture and thorough combustion. The whole inside of the injector is removable and can be replaced with a spare set in a few minutes when running. Removal of the brake hose connexion allows the injector nozzle to be cleared by a wire while actually at work, this being the main reason of the through passage which has been utilized, also for the purposes of the vacuum brake. As the engines of the Great Eastern Company were the first express engines

to burn liquid fuel, the general dimensions of No. 760 class, fig. 22, will perhaps be of interest. They are as follows

Blast nozzle, 5ĝin. in diameter, reducible to 5 in. for coal burning when required. Specific gravity of liquid fuel, 1·09 to 1·11, according to mixture.

Minimum gradient 1 in 70 at Bethnal Green.

It should be added that the brackets of the oil regulating valves were movable vertically, though this is not clear in the figure. The two brackets were connected to a hand wheel common to both, and were dropped by a single movement of the wheel, thus shutting off both oil valves and putting them again in action without varying their individual adjustment. Later arrangements differ somewhat, the combined motion being given by a lever as in fig. 23.

This single wheel is used for the station stoppages, after which each injector can be set going again exactly as before the stop, so dispensing with fresh regulation. The injector steam to be dry comes from high up in the dome. The variable blast nozzle is shown open as for oil burning.

When liquid fuel has been and is employed in locomotive work, the absence of a bed of incandescent fuel on the grate is a cause of very serious temperature

B

range in the firebox when the oil is shut off at stops. Where a solid fire is maintained on what may be termed the combined system, there is always an incandescent fire to prevent undue cooling when the oil is stopped, and this appears in itself alone a valuable feature in the system, quite apart from the question of lighting up in the ordinary way and the power of using solid fuel if necessary at any time so to do. The burner or atomizer is shown in figs. 21, 24. Fig. 24 is the stationary form, and consists of a cone body A to the interior of which the oil is admitted through a specially designed regulating valve B. Inside the body an annular steam jet is introduced, which possesses a central passage for assisting in the supply of air and also for enabling a wire to be passed through the burner without shutting off either oil or steam. At the front, just behind the nozzle, a hollow ring (C) is attached, and to this steam is admitted and allowed to escape from six very fine jet holes, for better atomizing and distributing the oil. The jets induce a considerable current of air, which is mixed with the spray as it emerges from the nozzle and ensures complete and smokeless combustion. The steam supplied to the ring

STEAM

A

Fig. 24.

ATOMIZER.

HOLDEN'S STATIONARY TYPE

is taken through a branch from a small regulating valve attached to the rear of the burner, so that only one pipe is required from the boiler; the small jets in front of the ring are at different angles, which have been found to be most efficient in practice.

The valve B used for regulating the flow of the oil fuel is of special construction, found desirable after many attempts with different forms of cocks and valves. To pass regular quantities of thick viscous fluid through the "crooked passage" formed by the half open plug of a common cock is impossible, and, consequently, some form of "Straightway" valve is necessary. In the example, a small reservoir of oil is formed by the body of the valve, and a tube with a slit in it is moved up and down inside. The proportion of cut exposed in the oil reservoir regulates the supply. With this valve very fine adjustments in the flow of oil fuel are possible.

The Holden apparatus is now largely used on stationary, locomotive and marine boilers. The Roumanian Government alone have over 250 locomotives fitted on this system.

In fig. 25 is shown the firebox, about 8 feet long, of an American locomotive, which may be compared with the firebox of the Great Eastern Railway locomotive. In this American box the tube plate and sides of the box are lined with brick, and there are two air inlets at the bottom of the box opening into the ash pit which has the usual front and back dampers. In these narrow boxes there is only room for one atomizer. Oil alone is intended to be used in this furnace, and the area of brickwork is necessarily larger than in the mixed system, where the bars are covered with more or less self-incandescent fuel. The fire-brick arch, which has been but slowly adopted in American coal burning engines, is of necessity a part of the oil burning furnace. In some locomotives there is also a small arch over the atomizer to