Fig. 19.—Horizontal Double Opposed Engine
In some tractors, notably the Fordson, no pump is used; the water circulates because it is heated. This is called a thermo-syphon system. When the engine runs, the water in the cylinder jackets becomes heated; as hot water is lighter than cold water, it rises and flows out of the jackets to the radiator, its place being taken by cool water from the bottom of the radiator. This circulation continues as long as the water in one part of the system is hotter than the water in some other part of the system.
The lubrication of an engine is described and explained in [Chapter X].
Fig. 20.—“Monarch” Engine
CHAPTER IV
FUELS AND CARBURETION
In order that a thing may burn, it must be provided with oxygen. Oxygen is found in air, so it is usual to say that air is necessary in order that anything may burn.
To prove this, light a candle and place an empty bottle over it, upside down; in a very short time the oxygen in the bottle will be used up, and the flame will flicker and get smoky, and finally die out. If a card is laid on the chimney of a coal-oil lamp so that it covers the opening, that flame also will flicker, get smoky and go out.
In order to deaden the fire in a stove, the dampers are closed to prevent air from entering; the fire is kept alight by the very small quantity of air that leaks in below the fire-box. When the drafts are opened the fire will burn up brightly because a plentiful volume of air can then enter.