The high furnaces are provided with a continual overflow for the slag, which runs through a narrow gutter formed in the sand into a shallow pit, through which a small stream of water is kept running. By this chilling process the slag assumes the form of a fine gravel. An endless chain at once lifts the slag out of the pit and loads it upon cars. By grinding this material fine in a cement-mill, it is formed into an excellent sharp building-sand; the great bulk of it, however, is used, without further reducing its grain, for making bricks.

For this purpose it is mixed with one half of its bulk of mortar in a trough in which three shafts provided with long blades are revolving. It is then shoveled into the brick-machines, each of which turns out about twenty-five bricks a minute. These bricks are piled up in the open air for drying, and are ready for use after about six weeks. They continue to harden on exposure to the air, and are said to possess greater strength than ordinary burnt bricks. They are extensively used for all kinds of buildings, their light-gray color producing a very pleasing effect, and the roughness of their surface fitting them particularly well for retaining a coating of mortar. They can not be used, however, for foundation walls, as by the absorption of moisture their cohesive-ness is impaired.

The most interesting process is the following: As a thin stream of the fluid slag, falling from a narrow gutter, passes the nozzle of the steam-pipe, a jet of steam is blown through it, and by this simple process it is solidified in the form of most delicate fibres, resembling asbestos or spun glass; and it falls to the ground like a loose mass of grayish wool. This material is an excellent non-conductor of heat, and is used for covering steam-pipes, boilers, etc. The sole expenditure in its manufacture is that of the steam, the exact amount of which could not be ascertained. The material is sold for about $5 per cwt. The steam-pipe is about 1-1/2 inches in diameter, and the nozzle is simply a pipe, flattened and then curved into a semicircular form, in order to give the most advantageous shape to the steam-jet. The steam used has a pressure of about 50 lbs. per square inch.