A simple experiment illustrates the principle. Any boy who has made fireworks, or dabbled in chemistry, knows that paper--one of the most inflammable of substances--after being soaked in a solution of saltpetre, will not flame, but smoulders quickly at the touch of fire; hence the name touch-paper, which is used to ignite fireworks. Some of these salts, then, prevent the fabric from flaming, and also reduce the burning to slow smouldering, the explanation being apparently this,--when the fabric is dipped in solutions of certain salts, tiny crystals are deposited among the fibres on drying, and the inflammability is diminished; but the effect of the salt upon the fabric has to be considered, and some, such as sulphate of ammonia, will decompose when the goods are ironed with a hot iron. This necessary operation of the laundry, however, does not affect tungstate of soda; and all the dresses of a household could be rendered non-inflammable and largely incombustible by dipping them in a solution of this salt. The proportions would be about one pound of the tungstate to a couple of gallons of water. For starched goods, the best way to use the tungstate would be to add one part of it to three parts of the starch, and use the compound in the ordinary manner. Various methods have been adopted for fire-proofing wood, the strong solution of silicate of soda being one of the best. Asbestos paint is also useful, if it does not peel off, a little trick to which it seems addicted. By another method, the wood is soaked for three hours in a mixture of alum, sulphate of zinc, potash, and manganic oxide, with water and a small quantity of sulphuric acid. But while the inflammability of wood may be removed, it is questionable if it can be rendered entirely incombustible. In short, the problem of absolutely preventing fires by rendering substances perfectly fireproof has yet to be solved, if, indeed, it is capable of solution. But if fire cannot be entirely prevented, could not some method be devised of automatically quenching the flames directly they break forth? Such a method would appear like the prerogative of the good genii of a fairy fable, and beyond the reach of ordinary mortals. But science and human ingenuity which tell so many true "fairy tales" have made some approach to this also. The device is known popularly as "sprinklers," and is contrived somewhat in this way:-- Lines of water-pipes are conducted along the ceilings of the building, and are connected with the water supply through a large tank on the roof. To these pipes, the sprinklers are attached at distances of about ten feet. They are, in some cases, jointed with a soft metal, which melts at a temperature of about 160 degrees; the valve then falls, and the water is sprayed forth into the apartment.