The World War reversed this story, especially in its later phases. The greater part of the war was fought with implements and machines prepared in peace either for war or for peaceful purposes. Such implements were the aeroplane, submarine, truck, automobile and gasoline motors in general. The first gas attack, which was simply an adaptation of the peacetime use of the chemical chlorine, inaugurated the change. Gas was so new and instantly recognized as so powerful that the best brains in research among all the first class powers were put to work to develop other gases and other means of projecting them upon the enemy. The result was that in the short space of three and one-half years a number of substances were discovered, or experimented with anew, that are aiding today and will continue to aid in the future in the peaceful life of every nation. Chlorine is even more valuable than ever as a disinfectant and water purifier. It is the greatest bleaching material in the world, and has innumerable other uses in the laboratory. Chloropicrin, cyanogen chloride and cyanogen bromide are found to be very well adapted to the killing of weevil and other similar insect destroyers of grain. Hydrocyanic acid gas is the greatest destroyer today of insect pests that otherwise would ruin the beautiful orange and lemon groves of California and the South. [Illustration: FIG. 120.] Phosgene, so extensively used in the war both in cloud gas and in shell, is finding an ever increasing use in the making of brilliant dyes—pinks, greens, blues and violets. On account of its cheapness and simplicity of manufacture, it has great possibilities in the destruction of rodents such as rats around wharves, warehouses and similar places that are inaccessible to any other means of reaching those pests. Since phosgene is highly corrosive of steel, iron, copper and brass, it cannot be used successfully in places where those metals are present. Instead of phosgene for killing rodents and the like in storehouses and warehouses, cyanogen bromide has been developed. This is a solid and can be burned like an ordinary sulphur candle. It is much safer for the purpose of fumigating rooms and buildings than is hydrocyanic acid gas when so used. This is for the reason that cyanogen bromide is an excellent lachrymator in quantities too minute to cause any injury to the lungs. It will thus give warning to anyone attempting to enter a place where some of the gas may still linger.