upper bearings of these standards serve for the fly-wheel shaft p and the lower for the beam-shaft q. The work of the piston is transmitted to the fly-wheel shaft by the beam r, which swings around the shaft q, and the two drawing-rods, /, and /. The other constituents of the motor are the same as in the two-cycle motor.

Fig. 197 presents Spiel's petroleum motor. The engine is horizontal and single-acting, standing on a solid base, with the reservoir of oil above. The organs of admission, distribution and exhaust are worked from an auxiliary shaft, geared from the main shaft in the usual way. The exhaust is opened by a cam and levers from this shaft, and ignition is by a flame carried in a slide valve, working at the back of the cylinder; the Spiel being probably the only oil-motor firing the charge in this way. A portion of the compressed charge of oil and air in the cylinder passes through a grooved passage to a chamber in the slide valve which, as the slide is moved by a cam on the auxiliary shaft, is brought opposite a permanent

flame in the valve-cover, and fired. A spring effects the return movement of the slide-valve, when released by the cam, and the lighted mixture is brought in line with the cylinder port, when the remainder of the charge is fired. The pressures of the charge in the cylinder, and of the flame in the ignition port, are equalized by means of a small passage connecting them.

The oil is drawn from the reservoir and injected into the cylinder by a small pump, the piston of which is worked by a cam, lever and spring from the auxiliary shaft. The airadmission valve is also in connection with a cross-head attached to this pump. At the bottom of the pump is a double-seated horizontal lift valve, usually held open by a spring, in which position it communicates freely with the oil reservoir above. When the plunger pump is driven down, carrying with it the cross-head, the air-valve is first lifted, and air enters a mixing chamber at the back of the cylinder. As the piston continues to descend, the horizontal valve is closed and a passage opened from the pump into the mixing chamber.

The pump sends a jet of petroleum-spirit into the air, and in its passage it is broken into spray by striking against a projection. Thus the out (admission) stroke of the motor piston sucks into the cylinder a stream of air mixed with petroleum spray. The engine has a ball governor which, if the speed be too great, interposes a small projection between the valverod of the pump and the levers working it. The two become locked and cannot move, and the valve remains open, admitting air only to the cylinder, until the projection falls back, and the speed is reduced.

The consumption of oil with the motor making 180 revolutions per minute is about 1 lb. per horse-power per hour. With a 14 horse-power Spiel engine, having a cylinder diameter of 91⁄2 inches, with 18 inches stroke, and making 160 revolutions per minute, the consumption of naphtha was 0.81 lb. per horse power per hour. The specific gravity of the oil used was about 0.725.

The Priestman petroleum motor uses almost any kind of heavy petroleum, but is not suitable for light, volatile oil. It is described by Mr. Bryan Donkin, Jr.,' as follows: "It works best with common petroleum, having a specific gravity of 0.800 and flashing point of 100° F., but it may also be driven with heavy Scotch paraffin of 0.820 specific gravity and flashing point 150° F. Even common creosote of still lower density is available, but there are practical difficulties in the way of using it. Of course, the heavier the oil the thicker the residuum will be, and the more carbon is deposited in the engine, the oftener it must be cleaned. Nor can these very heavy oils be properly treated in an engine cylinder, by raising the temperature. If the oil is too much heated it is converted into oil gas instead of vaporized spray, and tarry deposits accumulate in the working parts. The proper temperature of the charge of oil vapor and air on entering the cylinder has been determined by experiments at from 170° to 300° F., according to the size of the engine. The proportions are 191 cubic feet

1A Text-Book of Gas, Oil. and Air Engines. London, 1894.

of air to 0.015 cubic inch of oil vapor for a 1 horse-power .engine.

"The horizontal motor cylinder of Priestman's engine is divided from a compression space, the proportional volumes of the two being-clearance or compression, 88 cubic inches; volume described by the piston, 191 cubic inches for a 1 horsepower nominal engine. The piston works on to a crank shaft through a connecting rod. At the back of the cylinder are two valves-inlet and exhaust. The exhaust is worked by an eccentric on the auxiliary shaft revolving at half the speed of the crank shaft, to which it is geared by wheels in the usual proportion. In the Priestman, as in most other oil-engines, ordinary lift-valves are used of a simple type. Unless almost perfect combustion is obtained, there is much more deposit than in gas engines. The simpler the valves, the less liable they are to become clogged.

"The most important parts of the engine are the vaporizer and spray-maker. The oil tank is under the crank shaft, and, when full, is sufficient to last for two or three days. A glass gauge shows the level of the oil. A small air pump is worked by an eccentric which also drives the exhaust valve. The air to supply this pump is filtered through gauze and cotton wool, and is then compressed into the oil tank at a pressure of 8 to 15 lbs. per square inch above atmosphere. This pressure forces two streams of oil and air into the spray-maker, from whence they are injected into the vaporizer. The oil is drawn from the bottom of the tank, the compressed air from the top, above the level of the oil, and both pass through a six-way cock. When this cock is set upright, the supply of oil and air to the spray-maker is cut off; when the cock is turned to the right they are admitted, and when set to the left they pass to a small lamp below the vaporizer, used to heat it when starting the engine.

"The spray-maker is one of the most ingenious parts of the motor. The oil and air are injected into the vaporizer through two concentric nozzles. The pulverization of the oil and its

complete mixture with the air depend on the shape of the nozzles, and their exact form has only been determined by. numerous experiments. The oil passes through the central tube in a small stream, and, on being ejected from the mouth of the nozzle, spreads out in a fan shape. The annular air nozzle surrounds the central oil orifice, and the air is turned back with considerable force to meet the issuing of oil at more than a right angle, the result being that both are violently driven out in a spray as fine as required. The oil and air from the spray-maker enter at the pressure of the air-pump. At the same time the in-stroke of the motor piston lifts the non-return valve and draws into the vaporizer a supply of air from the outside through a throttle valve. This auxiliary charge enters through a number of fine holes in the circular air passage of the vaporizer and a filtering layer of cotton wool. The sudden inrush of fresh air sweeps forward the oil and air with it into the cylinder.

"The vaporizer is divided into two parts. In the first the oil and compressed air are mixed with, and broken up by, the air admitted through the above-mentioned throttle valve; in the second the charge is completely vaporized by the heat from the exhaust gases, which, at a temperature of about 600° F., are led through a pipe round the vaporizing chamber before being allowed to escape into the atmosphere. Thus, there are two admissions of air-one to the spray-maker under pressure from the oil tank, the second at atmospheric pressure to the vaporizer through the throttle-valve. In each case the oil is sprayed, and is thus twice pulverized before the actual vaporization by heat begins. Unless the heat from the vaporizer were also applied to the oil spray, it would condense and separate from the air before reaching the cylinder. The vaporizer is contained in the frame of the engine, under the cylinder. The speed of the engine is regulated by means of a spindle above the throttle valve. It contains a small V-shaped opening through which the oil is admitted from the tank to the spraymaker, and the wing of a valve is keyed to the lower part of the