712 



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 impervi- 

 ous clay seventy-six feet below the upper 

 limit of artesian flow. From the " wet cham- 

 ber " 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 vari- 

 ous fields of science, and gives a forecast of 

 the directions in which work in the future 

 may be conducted with most immediate ad- 

 vantage. 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 publica- 

 tion 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 Assem- 

 bly 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 fur- 

 thered by the Davenport Academy of Sciences. 

 Much has been done by the geological sur- 

 veys and by individual naturalists from 1819 

 on. Continued geological studies and the 

 development of the weather service are in- 

 dicated as the leading iines 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 ©f 

 view they are a kind of impure glass, and 

 they in so far resemble glass that when rap- 

 idly 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 prepara- 

 tion of bricks and mortar from it ; and the 

 casting of it into blocks, which are chiefly 

 used in paving. The regular, smooth sur- 

 face 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 affini- 

 ty 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 con- 

 tain about equal proportions of lime and 

 silica and seven or eight per cent of alumina. 

 " Slag- wool," or " silicate cotton," is ob- 

 tained 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 im- 

 portant in the use of the substance as a fire- 

 proofing 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 prop- 

 erty, in conjunction with its great porosity, 

 seems to render it specially applicable for 

 medical purposes. Slag cements are pre- 

 pared 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, 



