As before mentioned, the lime used for making bricks is selenitized, the following being the analysis of the raw gypsum employed in the process:-

The process of brick-making, as now carried on, is extremely simple, and, as already shown, inexpensive; but it was here that the greatest difficulties were met with. There was no machinery to be purchased that could work the slag-sand into bricks, in the state in which it arrived from the blast furnaces. In the earlier attempts, the sand had to be prepared in a fine state, the result being a superior class of bricks, but at a cost so great as to exclude them from the market. Wood had therefore to design and construct brick-presses and • other machinery that could work the sand, as it came from the slag-sand machines, directly into bricks. The success of this machinery at once rescued the Cleveland Slag Co. from an early collapse, but not before a large amount of money had been spent and some 2 years wasted.

In designing the press, the following points had to be kept in view, viz.: unusual depth of brick moulds, as the sand (being spougy) is exceedingly compressible; great pressure, in order to consolidate the slag; as well as great care in mixing the lime in fixed proportions to the sand-too much lime tending to burst the bricks, whilst too little seriously affects the hardening.

For Artificial Stone

One other manufacture from slag is carried on at the Cleveland Slag Works, which, although it does not consume much, is still of interest, viz., artificial stone. It is moulded into chimney-pieces, window-heads and sills, balus-trading, wall coping, and other ornamental work for builders, as well as for paying for footpaths, stables, etc. The stone is composed of 2 1/2 parts finely-pulverized slag, and 2 1/2 of ground firebrick, to 1 of Portland cement; the mixture is run into moulds, and sets quickly, the articles being ready for the market in 5 or 6 days.

A sort of concrete brick has been made by the Moss Bay Iron Co., Workington, from hematite Bessemer slag. These bricks have been made by a process differing entirely from the system adopted by Wood at Middlesbrough. The slag employed at Moss Bay is pulverized from the cold solid mass under heavy edge-runners, which crush the material into fine dusty shingle; it is then lifted by elevators into French burr-stones, and ground down as fine as sand. From the stones it passes through a worm conveyer to a brick-press, during which about 25 per cent. of common river-sand is added, with sufficient water to thoroughly damp it, without any addition of lime; again showing, in a remarkable degree, the extraordinary setting nature of the slag after the chemical combination with the water and exposure to the air have taken place. These bricks are taken from the press and placed under cover for a few days, when they are put out in the open air to harden. They are of excellent shape, grey colour, and become exceedingly hard. Large quantities have been employed in building the Moss Bay Steel Works, and appear to be standing remarkably well.

The cost, however, is very heavy, owing to the difficulty of preparing the slag, and the wear and tear of the machinery; the excessive weight also precluding the sale at any great distance from the works. The large amount of lime, combined with the silica and alumina in the Bessemer slag, quite accounts for the setting properties. The bricks continue to harden for years, and appear to arrive at a kind of crystalline fracture, which damp greatly accelerates.