Slag.
1. (Metallurgy.) Vitreous mineral matter removed in the reduction of metals. The scoria from a smelting-furnace. At some furnaces on the Continent of Europe the slag is sold. It is run directly into wagons, or prepared by granulation in water, and is used for making cement and artificial stone, and in the manufacture of alum and crown glass. At the iron-works of Aulnoye, in Belgium, the slag is cast into slabs for pavements, garden-rollers, and other things. For the former purpose, molds are excavated in the ground around the furnace, and trenches cut to conduct the liquid slag to them The material is allowed to cool very slowly; its interior is then found to be compact and homogeneous, the exterior consisting of a vitreous crust. The masses are often divided by fissures, but may be cut and dressed into smaller blocks. Mr. Woodward, of Darlington, England, has patented a method of manufacturing bricks from slag. The slag from the furnace is run into a series of molds on a revolving table. After removal from the molds, the bricks are annealed in a kiln or furnace, and are ready to be used for any of the purposes to which common brick are applied. The fracture is said to be close and firm, and they are capable of standing an intense heat. They resist a crushing force of 3 to 4 tons to the inch, and it is claimed can be made at less than half the cost of common brick, though there is considerable loss by breakage. In another process, invented by Hartmann in Hanover, the slag is granulated by allowing it to flow into a shallow pit, through which a stream of water runs. The material may then be ground fine and used as a building sand. For making bricks, it is mixed, in its coarsely granular state, with half its bulk of water, in a kind of pug-mill. The bricks are molded by machinery, and dried in the open air; in about six weeks they are ready for use. They are said to be stronger than ordinary bricks, and peculiarly adapted for receiving mortar, owing to their rough surface. Their cohesiveness is, however, impaired by the absorption of moisture. An incombustible non-conducting fibrous material is also prepared by blowing a jet of steam, at a pressure of about 50 pounds, through a thin stream of slag as it falls from a narrow gutter leading from the furnace. By this process it is solidified in the form of delicate fibers resembling asbestus or spun glass. From the appearance of the mass it has received the name of slag-wool. It is used as a covering for steam-pipes, boilers, etc. See slag-wool.
2. (Founding.) The fused sullage and dross which accompanies the metal in a furnace, and which it is the business of the skimmer to hold back from the ingate. It is essentially a very base silicate of iron. Cinder; scorioe; clinker.
