But if all this is of purely theoretical interest, the chemistry of our earth and its products is of immense practical importance. It may be _applied_, and the day of “industrial chemistry” is here. By studying the chemistry of soils, the farmer has been enabled to increase both the quality and the quantity of his crops. By employing artificial fertilizers, production has been greatly increased. An analysis of the earth’s strata has thrown great light upon geology. Analytical chemistry has proved of service in criminology,--by enabling experts to detect poisons, blood-stains, etc. (Unfortunately, it has also been applied detrimentally, in the manufacture of explosives, poison gases, etc., employed in war.) Dentistry and surgery have been rendered painless by the discovery of anæsthetics. The wholesale manufacture of illuminating gas has been instrumental in lighting millions of homes. The manufacture of steel, paper, ink, dyes, stains, paints, perfumes, bread, and a thousand-and-one useful articles of our daily lives has been rendered possible by the progress of chemical research. Artificial preservatives have enabled us to keep food-stuffs for long periods of time. By the discovery of the nature of iron rust, bridges, buildings, etc., have been preserved intact. Our food, our clothes, our very lives themselves, may be said to depend upon modern chemistry for their maintenance and preservation. Let us pass in rapid summary a few of these results. Let us take, for example, _glass_. Glass is made from silica. What is silica? It is a substance of remarkable infusibility, and is the oxide of silicon, which is a near neighbor of carbon. Glass is made by mixing sand, limestone and carbonate of soda or potash in large pots, and melting them together at a temperature of 3,500° F. The sand, being silica, combines with the lime of the carbonate of lime, to give silicate of lime, and with the soda (or potash) of the carbonate of soda (or potash) to give silicate or soda (or potash). These two silicates become intimately fused and form the glass, which remains liquid in the pot. It is then blown into various shapes or rolled into thin sheets for window glass. We know what an effect windows have had upon the comforts of modern life! By mixing together several metals, _alloys_ are obtained which very often have properties quite different from those of the substances which compose them. Thus: Bronze is a mixture of copper and tin; plumber’s solder is an alloy of lead and tin; brass is an alloy of copper and zinc; ferro-silicon is a union of silicon and iron, etc. Many of these alloys are of great utility in the various arts and sciences, as well as in manufacture.