Gasoline being a highly volatile liquid will vaporize at temperatures as low as -10°F., but as the temperature is higher vaporization will be more rapid. In a confined space, at relatively low temperature, such as the carburetor of a gas machine, the vaporization will at first be very rapid; but after the more highly spiritous portion has been evaporated, a considerable part, even of the lighter grades, will be vaporized very slowly. In the cold-process machines, only the lighter grades can be used with success and even then, in inefficient machines, a portion of the lesser volatile gasoline will have to be thrown away. For this reason and for others that will appear later, it is advisable to consider very closely the working properties of the entire plant. In order to obtain gas that will always be of the same quality and at the same time use gasoline in an efficient manner, the gas machine must be composed of three essential parts: the blower, the carburetor and the mixer. The blower is that part of the machine which supplies air for absorbing the gasoline vapor and maintaining a constant pressure on the system. It is usually made in the form of a rotary pump, the motive power for which is a heavy weight. The pump may, however, be driven by water pressure furnished by city water pipes or other water supply. The carburetor is a tank which contains the supply of gasoline and is so constructed as to permit the air from the blower to most readily take up the gasoline vapor. It should be so arranged that when the contained gasoline becomes old and less volatile, the air may remain in its presence a sufficient time to become saturated by slow absorption. The mixer is that part of the machine which regulates the amount of gasoline vapor contained in the gas entering the distributing pipes. In order to satisfactorily perform its function, it should be so arranged as to permit a constant amount of gasoline vapor to enter the mixture which composes the finished gas. This amount should be such as to produce a bright clear flame in an open gas jet. If the gas contains too great an amount of gasoline vapor, the flame will smoke. If too little gasoline vapor is present, the flames will be pale and lacking in heat. [Illustration: 1 Carburator 2 Mixer 3 Blower 4 Weight 5 Gas Range 6 Water Heater 7 Water Tank FIG. 183.--Cold-process system of gasoline lighting with kitchen range and water heater.]