In the process of generation the tank is filled with gasoline and pressure applied with the air pump. The tanks described in Fig. 189 might be used to advantage with this plant but the one shown in Fig. 197 is so constructed that the larger tank is used for storage of gasoline. The gasoline is pumped directly into the smaller tank which alone is kept under pressure. The pump _P_ is enclosed in the large tank; at any time it is desired to replenish the supply of gasoline, it is only necessary to open the valve _V_ and pump the necessary supply into the small tank. This transfer may be done at any time without danger from escaping gasoline vapor. [Illustration: FIG. 197.--Diagram of central-generator tube system of gasoline lighting.] The process of generating the gas is best understood by reference to Fig. 198, which shows the internal construction of the generator. The liquid gasoline is admitted at the bottom through the small pipe _W_, and then enters the space 4, where it is vaporized. The initial flow of gas is generated by heating the generator with an alcohol flame from the iron cup 1, which surrounds the generator. When the generator is heated the gasoline admitted to the generator is immediately vaporized; when, by turning the handle 6, the needle valve 5 opens a small orifice through which the heated gasoline vapor escapes into the tube 7, above. The blast of vapor issuing from the orifice carries with it air of sufficient volume to render the gasoline vapor an explosive mixture that when burned in the mantle will be reduced to CO₂ gas. When the initial heating by the alcohol flame is exhausted, sufficient gas has been generated so that part of it may be used as a sub-flame in the gas burner 9, to keep the generator heated. The gas is conducted to the burner from the main tube 11, through the pipe 12-14, as indicated by the arrows. The burner 9 surrounds the generator and the size of the flame is regulated by the valve 15, which is opened an amount sufficient to admit the necessary gas to the burner. To start the generator, the cup 1 is filled with alcohol and ignited. The needle valve 2 is now opened by turning the hand-wheel 3, admitting gasoline into the generator chamber 4, where the vaporization of the gasoline takes place. The flame from the burning alcohol will heat the generator in about a minute. When the generator is hot, the needle valve 5 is opened slightly, by turning the lever 6, and the gasoline vapor under high pressure blows into the tube 7. As the gasoline vapor is blown into the tube 7, air is drawn in through the opening 8, as indicated by the arrows. The generator is practically a large Bunsen tube from which the mixture of gasoline vapor and air is conducted to the burners by a connecting pipe. [Illustration: FIG. 198.--Cross-section of the generator for the tube system of gasoline lighting.]