THE SAVINGS OF SCIENCE. 809 



inulating at the rate of nearly 8,000,000 tons per annum, its bulk being 

 some three times that of the iron from which it has been separated. 

 It forms a heavy incumbrance to iron-masters, demanding the pur- 

 chase of large tracts of land whereupon to deposit it, while the invest- 

 ment is, of course, wholly unremunerative. There are one or two ex- 

 ceptions to this rule, where the slag is tipped into the sea, and serves 

 to form land for the works, and where some of the iron-works supply 

 slag for the construction of breakwater and training walls. The 

 quantity thus utilized, however, on the Tees is but about 600,000 tons 

 per annum, forming only a small proportion of the whole yield of 

 the district. 



In early times, slag was broken up by hand, and used for road- 

 making, and it so continues to be used, where it can be had without a 

 heavy cost for transport ; but there is only a limited demand for this 

 purpose. On the Continent, where stone is scarce, slag plays a promi- 

 nent part in road-making, as in Silesia and other similarly situated dis- 

 tricts. Another direction in which many attempts have been made 

 to utilize slag, both at home and abroad, is to adapt it for constructive 

 purposes, and various schemes have been devised for transforming 

 the highly refractory slag into bricks, sand, and other materials for 

 building. 



It is also applied to the manufacture of artificial stone, and molded 

 into chimney-pieces, window-heads, balustrading, and outside orna- 

 mental builders' work generally. The stone is composed of two and 

 a half parts of finely pulverized slag, and two and a half parts of 

 ground brick, to one part of Portland cement. The mixture is run 

 into molds, and sets quickly, the articles being ready for the market in 

 four or five days. Besides bricks and stone articles, the slag is used 

 for making mortar, cement, and concrete. The mortar is a mixture of 

 slag and common lime, the cement being composed of the same mate- 

 rials, with the addition of iron oxides. 



Another useful purpose for which it has been successfully utilized 

 is that of glass manufacture. The vitreous character of slag indicates 

 a resemblance to glass in its composition. It does, in fact, contain the 

 principal components of glass, but not in proper proportions, and those 

 in which it is deficient have therefore to be added, with others which 

 are not present. Bottles made of this slag by the Britten Patent Glass 

 Company were shown at the Paris Exhibition in 1878, and received 

 honorable mention. 



Another application is to the manufacture of slag-wool. By the 

 action of strong jets of steam, the slag is transformed into a fibrous 

 whitish silicate cotton, which, being metallic, is incombustible, like 

 asbestos. In the construction of new houses with Mansard-roofs, the 

 space between the interior lath, or paneling, and the exterior covering 

 of zinc, slate, or tin, is filled with this slag-wool, which protects from 

 the risror of frost in winter and the intense heat in summer. If in 



