As shown in Fig. 205, the generator _G_ is a brass tube, inclosing the valve-stem _G_, which terminates in the needle-valve _V_. This valve regulates the supply of gas admitted to the burner and is operated by the hand-wheel _F_. When the gasoline in the tank has been heated the necessary amount, the vapor in _G_ is allowed to escape through the valve _V_. The vapor is discharged into the Bunsen tube, and with it the air is carried in through the openings _E_, from both sides of the iron. The burner is a brass tube, slotted as shown at _H_, through which the gas escapes, forming a short flame of large area close to the part of the iron to be heated. The size of the flame is regulated by the hand-wheel _F_. The tank is entirely closed, the plug _P_ being provided with a lead washer to insure a tight joint. The plug is further provided with a soft metal center which acts as a “safety-plug” in case of overheating. Should the iron at any time become too hot, the soft metal center will melt and the released pressure in the tank will put out the burner flame. The soft metal center may be renewed with a drop of solder. In case the safety-plug at any time is melted, the hot gasoline will spurt from the opening and immediately vaporize. This of course would, in a short time, produce an explosive atmosphere which if ignited would be dangerous. In case of accident the iron should be carried to the open air and the flame smothered with a cloth. =Alcohol Sad Irons.=--Irons of the same style are also made in which alcohol is used as a fuel. The alcohol irons differ in construction from those using gasoline only in the amount of air that is mixed with the vapor. In general appearance the two styles look very much alike, but in the alcohol iron one of the intakes _E_ is entirely closed and the other opening is partially closed. [Illustration: FIG. 206.--Gasoline flat-iron operated by an air-pressure fuel tank.] The operation of these irons is identical to those using gasoline, but they are preferred by those who fear the use of that fuel. In reality there is little difference in the danger attending the use of the two liquids. It is only fair to say, however, that the use of any highly volatile fuel is attended with some danger when used carelessly, but with a reasonable amount of care and a knowledge of the mechanism of the machine in use the danger is of minor consequence. In Fig. 206 is illustrated another style of gasoline sad iron, the working principle of which is the same as those already described but the supply tank is not heated to give pressure to the gasoline in the tank. In this iron the tank is located at one side of the iron and pressure is applied with an air pump as in the hollow-wire system of lighting. The burner is generated after the manner of the others and operated in exactly the same manner. The chief difference is that the possibility of excessive pressure through overheating is eliminated.