The burner is heated so that when more gasoline is turned on, this heat will change the gasoline to gas. If the burner is not hot enough to do this, the gasoline flowing from the pipe will flow down into the cup and the stove will burn with a smoky flame which becomes higher and higher and looks very alarming. When this happens, the valve should be closed, and the fire permitted to burn all the gasoline which has collected in the cup. This may be sufficient to heat the burner. Test after the fire has gone out, by lighting a match, turning on the gasoline and touching the lighted match to the burner. If all right, it will burn with a blue flame; if not, it will burn with a yellow flame. If the yellow flame is noticed, turn out the fire by closing the valve, and let the burner get cold before attempting again to light it. See that the burner has not become clogged with soot or dirt. Then proceed to re-light the stove. [Illustration: FIG. 17-_a_. Cross-section of gasoline stove showing burner.] Air must be mixed with the gasoline to make it burn with a blue flame. The air enters the burner through the same tube that the gasoline flows into the cups when the burner is cold. In the burner are small holes for the escape of the gas mixed with air, and here the blue flame should appear, and nowhere else. If it appears elsewhere, the burner is not working properly. Sometimes the gas ignites at the point where the air is mixed with it. The fire should then be turned out and the stove re-lighted immediately. If the little holes where the flames should be, or if any other part of the stove is clogged with soot, it will not burn as it should. It must be cleaned. _A dirty gasoline stove is dangerous._ =32. Filling the Gasoline Stove.= Never get oil on the tank or any part of the stove while filling it. If oil is spilled, wipe it up before igniting the stove. Do not fill the tank when the stove is lighted or when there is a fire anywhere near the tank. If the fire has been burning, close all the valves and wait until it goes out before opening the tank. Close the valve from tank to pipe before filling. Fill the tank and cover it before lighting the stove again.