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THE POPULAR SCIENCE MONTHLY.

furnished is about four hundred feet. They are all connected by a tunnel, five feet in diameter inside, and walled with brick, which has been constructed in the impervious clay seventy-six feet below the upper limit of artesian flow. From the "wet chamber" of this tunnel, in which the water is collected, it is pumped for distribution over the city. The character of the water is shown by the most careful tests to be of the best.

 

Science in Iowa.—The paper of most general interest in the Proceedings of the Iowa Academy of Sciences for 1887, 1888, and 1889, is the annual address for 1888 of President Herbert Osborn. It reviews what has been accomplished in Iowa in the various fields of science, and gives a forecast of the directions in which work in the future may be conducted with most immediate advantage. The first Iowa Academy of Sciences, which existed from 1875 to 1884, was the means of encouraging investigation in many parts of the State, and secured the publication of a number of valuable papers. The present Academy, of which R. Ellsworth Call is secretary and treasurer, was organized in 1887. Besides this body, the Iowa Assembly of the Agassiz Association, the State Agricultural and Horticultural Societies, Agricultural College and Weather Service are mediums for scientific publication on subjects appertaining to their respective spheres. Anthropological work has been furthered by the Davenport Academy of Sciences. Much has been done by the geological surveys and by individual naturalists from 1819 on. Continued geological studies and the development of the weather service are indicated as the leading lines on which future scientific work may be prosecuted. The proceedings of the three years covered by the volume contain many excellent special papers.

 

Uses of Slag.—-The slags produced in iron-making vary in composition according to the ore that is used, but are all alike in that their chief constituents are silica, lime, and alumina. From the chemist's point of view they are a kind of impure glass, and they in so far resemble glass that when rapidly cooled they are apt to fly to pieces. The uses to which slag has been longest put are the production of slag-sand by running the molten material into water and the preparation of bricks and mortar from it; and the casting of it into blocks, which are chiefly used in paving. The regular, smooth surface of these blocks is an objection to their use; but this is obviated, and the ideal cleavage surface is obtained by casting them double with a notch around the middle, where they are broken by a sharp blow. Besides being toughened and more dense, the slag, when annealed, has a strong affinity for Portland cement, and unites with it into a concrete of remarkable toughness, which is one of the best pavement materials of its class. The slag, broken by machinery, is largely used in England for road-making; for this purpose, the material should contain about equal proportions of lime and silica and seven or eight per cent of alumina. "Slag-wool," or "silicate cotton," is obtained by turning a jet of steam or an air-jet upon the stream of molten slag as it issues from the furnace. By this the slag is dispersed or broken up into countless small, bead-like particles, each of which, as it flies away, carries behind it a delicate thread of finely drawn or "spun" slag. This substance has several valuable properties. It is extremely light, and absolutely fire-proof; is a non-conductor of heat and sound; and is so porous that it will absorb large quantities of water, and readily retains the same for a considerable time. The last property is important in the use of the substance as a fireproofing material; for, when water is pumped into a burning building, it is held by the slag-wool as by a vast sponge, and will evolve steam sufficient in itself to extinguish the flames, or at least assist powerfully in doing so. It is also an antiseptic; and this property, in conjunction with its great porosity, seems to render it specially applicable for medical purposes. Slag cements are prepared largely at several factories on the continent of Europe. To make them, the slag-sand, dried, is ground fine, mixed with slaked lime, and stamped, and the whole intimately mixed in a "homogenizer" of special construction. The slag cement is lighter than Portland cement, takes longer to set, and is cheaper. It is held in great favor in Germany, though it is not, perhaps,