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GARY

739

GAS-ENGINE

a figure of St. George on horseback meeting the dragon; the star; and the ribbon. The order consists of the sovereign and 25 knights and such descendants of George II as shall be elected, besides distinguished foreigners. The Prince of Wales, son of the ruling sovereign, is always a member. The members write the title K. G., Knight of the Garter, after their names. See Sir Harris Nicolas' History of British Orders of Knighthood.

Gary, Ind., about 22 miles southeast of Chicago on Lake Michigan, was established by the U. S. Steel Corporation in 1906 in connection with the location of the largest plant in the west. Within two years what _aad oeen sand dunes and swamp was occupied by a modern well-built city of several thousand inhabitants with a modern school ^ system worked out on such original and practical lines that it was known throughout the country. Population about 20,000. See SCHOOL SYSTEM AT GARY.

Gas, a term applied to a vapoi which cannot be condensed to a liquid at ordinary temperatures and pressures. Thus, in the ordinary conditions of the atmosphere, air is a gas, and other gases are oxygen, hydrogen, nitrogen etc. Gases have small densities as compared with liquids and solids; air, which is about 14 times as dense as hydrogen, is only about ^ as dense as water. Gases have no definite surface boundary, but occupy any space within which they may be confined. With a given quantity of gas, the smaller the containing vessel the greater the pressure exerted on its walls; and it is true, for all practical purposes, that twice a given pressure reduces a given volume one half. If two gases be brought together, they will gradually mix with one another, even though the mixing has to take place in opposition to gravity. Thus, if a bottle of carbonic acid be connected by even a slender tube with a bottle of hydrogen placed above it, some of the heavy carbonic acid will make its way into the upper bottle, and a corresponding volume of the light hydrogen will descend into the lower, and within a few days the two gases will be completely mixed. The same thing will result even if the two gases be separated by a thin membrane or a piece of unglazed porcelain. Gases may, in many cases, be dissolved in liquids, as ammonia and carbonic-acid gas.

Of gases used for lighting or heating, there are various kinds. The most common kind is coal-gas, made from bituminous or soft coal. The principle of the manufacture of coal gas may be seen in the following experiment: Powder a little coal and put it into the bowl of a common, long tobacco-pipe; then cover the top with moist clay, let it clry, and then heat the bowl. Soon there

will come out at the end of the pipe a yellow smoke, which is coal-gas, and this will burn when a light is brought to it; in the pipe is left some coke or carbon. In manufacturing this gas, instead of tobacco pipes, large ovens of brick or iron are used, called retorts. Large works may have a hundred furnaces, each of which has from five to ten retorts. The gas is purified by various processes from the other products of the coal, as tar and ammonia.

Other kinds of lighting gases are oil-gas, made from heavy mineral oils or, as in Australia, from waste mutton-fat, and used sometimes to light railroad-cars and steamships; water-gas, made by passing steam through glowing coke; wood-gas and peat-gas. Besides these artificial gases, an important gas, both for heating and lighting, is natural gas, which issues from the earth in many places. This gas has long been used in China, and near the Caspian Sea there are several so-called eternal fires which are supported by gas escaping from the soil. But it is chiefly in North America that natural gas has been found and used. It came into notice in connection with the digging of oil-wells, and was for a long time looked upon as a disadvantage. The general use of it for burning began only iu 1872 in Pennsylvania. Many of the gas-wells lasted only four or five years, but some then sunk are still in use. Two years later manufactories began to use it, and one smelting company now uses a million cubic feet every hour. Natural gas is also found in Ohio, Indiana, Kentucky, Kansas-Dakota and (slightly) in California. It is believed by many that it will soon be exhausted. See Miller's Chemical Physics. See NATURAL GAS.

Gas=Engine, an engine driven by the force produced by the explosion of a mixture of air and a gas. A gas-engine is a form of internal-combustion engines, because the fuel, the gas, is burnt in the cylinder of the engine. The first gas-engine used practically was that of Lenoir (1860). Air and gas were drawn into the cylinder in suitable proportions, and, as soon as the inlet-valve was closed, the mixture was exploded by an electric spark. The cylinder was kept cool by a water-jacket. The engine was not economical. It used from four to five times as much as a good modern gas-engine. In 1866 Otto and Langen invented a gas-engine which used only about half the gas that Lenoir's engine did. The explosion occurred in a vertical cylinder under a piston which was driven up. The piston then came down under atmospheric pressure, and was in gear with the shaft only during the dowj stroke, so that the work was done only OR the down stroke. It was very noisy and did not eome into general use. In 1876