In the single tire construction the latter is liable to roll out of its bed where quick turns are made, but with the double tube this is not possible. [Illustration: Fig. 14. Illustrating Tire-removing Tool.] PUTTING ON AND TAKING OFF DOUBLE TUBES.--To do this properly with clincher tires is quite an art. A pair of blunt, round-ended levers is best for the purpose. The practice is to use cold chisels, screw drivers and like sharp or pointed tools. This is bad practice. A pair of levers, as shown in Fig. 14, can be made by any one, and you may be sure that their use will not be liable to jag a hole in the inner tube during the removal process. When the inner tube is put into the outer casing, or tire, as it is called, powdered talcum should be liberally applied, to the tube and also placed within the casing. The tube is then put in and carefully distributed and straightened out before the clinchers are put on. A little air blown into the tube will prevent it from being pinched under the flanges of the casing. The spare tubes should be inclosed in a receptacle of some kind which will exclude light, and protect them from heat. With the advent of the quick detachable rims of different forms these troubles have happily disappeared in the modern automobile. DAMAGES TO TIRES.--Many things must be provided for in the matter of tire keep. The thing most necessary to guard against is _punctures_, caused either by sharp stones, or nails. When a casing has a heavy protective tread the inner tube may not be effected, but it frequently happens that the outer casing is slitted for some distance, and the great pressure forces the thin wall of the inner tube into the slitted opening, and it is thus ruptured, not on account of its being punctured, but because the outer tire did not afford protection against the pressure. REPAIRS TO TIRES.--It is not a difficult job to repair tires, and the apparatus for doing it is very simple. Rubber, in its natural state, is a white, thick, milky juice, which after several heating and refining processes becomes dark and sticky. VULCANIZING.--When in this condition and properly mixed with sulphur, it may be vulcanized, which destroys the stickiness, and makes it firm and elastic. Vulcanizing is a kind of baking process, the maximum heat being about 275 degrees, but generally less. The time required is from 12 to 15 minutes, dependent on the thickness of the mass to be vulcanized. [Illustration: Fig. 15. Vulcanizer.] When the torn or cut portion of the tube or tire is carefully cleaned, it is filled with the plastic rubber, and the heater is applied. The heater, one form of which is shown in Fig. 15, is merely a shell with a heater connection, and this being partly filled with water, generates steam, the temperature of the shell being, of course, dependent on the pressure of the steam developed.