=Gasoline Sad Irons.=--The use of gaseous or liquid fuel is always attended by an element of danger, because of the possibility of accidental explosion. The use of gasoline, the most highly volatile of all liquid fuels, has, however, come to be very generally used as a source of heat for domestic purposes. The danger of accident in the use of gasoline as a fuel for heating sad irons is largely due to ignorance of the involved mechanism or carelessness in manipulation. A knowledge of the principle included in their operation, together with an observance of the possible cause of accident, will reduce the element of danger to a negligible quantity. The use of gasoline sad irons has come into favor because of their convenience and economy in operation. These irons, in common with the use of gasoline in its other applications of heating and lighting, are made in a great many forms but the principle of operation is confined to two types. [Illustration: FIG. 203.--Gasoline flat-iron operated by a heated fuel tank.] [Illustration: FIG. 204.--Gasoline flat-iron showing the position of the cover while initial charge of gas is being generated.] _First_, those in which the gasoline is forced into the generator by the vapor pressure, from the heated supply tank; and _second_ those in which the pressure is caused by pumping air into the supply tank after the manner of the hollow-wire system of lighting. The first type of iron is illustrated in Fig. 203. The same iron is shown in Fig. 204, with the top in position for generating vapor pressure necessary to start the burner. The body of the iron A is a hollow casting, designed to receive the generator and burner in such position that the bottom portion of the iron may be uniformly heated. The generator and burner are shown in detail in Fig. 205, in which a sectional view is given of the parts, cut across lengthwise of the iron. In starting the burner for use, the tank is first filled--not quite full--of strained gasoline. The precaution of straining the gasoline should be taken, to prevent putting into the tank anything that will possibly choke the needle-valve. Alcohol is used for generating the vapor supply, because the flame does not black the iron and fill the room with smoke as in the case when gasoline is used for the purpose. When the alcohol is ignited, the cover is placed in position as shown in Fig. 204, so that the flame may heat not only the generator but also the tank. The object of heating the tank is that the heated gasoline may furnish pressure with which to force the gasoline into the generator. When the alcohol used for generating is almost burned out, the valve _F_ is slightly opened and the burner lighted. [Illustration: FIG. 205.--Sectional view of gasoline flat-iron generator and burner.]