usually the fusing-point of cone 1 or 2, while for buff-burning clays it is commonly necessary to go to cone 7 or 8 to make the brick steel-hard.

The following table gives the physical characters of several clays used for pressed brick in New Jersey.

Physical properties of some New Jersey clays used for front brick.

In New Jersey the Raritan, Pleistocene and Cohansey formations supply materials for the manufacture of pressed brick. The Raritan clays found around Perth Amboy were formerly much used for making pressed brick, but at the present time comparatively few are manufactured in this district, although much Raritan clay is shipped to other States to be used for this purpose. They are commonly molded in stiff-mud machines and re-pressed. The Pleistocene (post-Glacial?) clay loams were much used in former years for making red pressed brick, and are still employed to some extent. They cover large areas around Trenton, in Mercer county, but, owing to their shallowness, much of the material has been removed. Similar loams are found in western Burlington and Camden counties. The Cohansey clay is often found to make a good buff-burning brick, with either the stiff-mud repressed, or dry-press process, but trouble is experienced now and then in making the bricks flash well. These Cohansey clays are available in Burlington, Camden; Atlantic, Cumberland, and Ocean counties. They are not fire clays, and can barely be classed as semirefractory, but burn to a good hard buff brick at cones 6 to 8. They are utilized for this purpose at present at Winslow Junction, Mays Landing and Rosenhayn.

Enameled brick.-The clays used for these are similar to those employed in the manufacture of pressed brick. There are two

factories in the State making enameled brick, and both employ a mixture of fire clays from the Middlesex county district.

Glazed brick are made only to a slight extent in New Jersey. The clays used are similar to those employed for enameled brick.

METHODS OF MANUFACTURE.

The methods employed in the manufacture of common and pressed brick are usually very similar, the differences lying chiefly in selection of material, the degree of preparation, and the amount of care taken in burning. The manufacture of bricks may be separated into the following steps: preparation, molding, drying and burning.

PREPARATION.

In brickmaking some preparation of the clay is commonly necessary, since few clays can be sent direct from the bank to the molding machine, although some common brick manufacturers in New Jersey reduce the preparation process to a minimum.

Weathering. Many clays are prepared by weathering, especially if they are to be used in the manufacture of pressed brick. This is done by distributing the clay in a thin layer over some flat surface not more than 2 or 3 feet in thickness and allowing it to lie there exposed to frost, rain, wind, and sun. This results in a slow but thorough disintegration or slacking. present, tend to rust, and are thus more easily seen and rejected, while pyrite, if present, may also decompose and give rise to soluble compounds, which form a white crust on the surface of the clay. Although some clays are weathered, yet in great part their preparation is done by artificial means.

Iron nodules, if

Dry crushing.-When the clay or shale is to be disintegrated or crushed, it is commonly done dry, and the machine employed varies with the character of the material. Hard shale is usually disintegrated in a jaw crusher, which consists of two movable jaws that interact, and are set closer together at their lower than at their upper ends. Where a soft shale, or a hard, tough, dry clay

is to be used, dry pans are often employed. These consist of a circular pan, in which there revolve two iron wheels on a horizontal axis. The wheels turn because of the friction against the bottom of the pan, the latter being rotated by steam power, and in turning they grind by reason of their weight, which ranges from 2000 to 5000 pounds. The bottom of the pan is made of removable, perforated plates, so that the material falls through as soon as it is ground fine enough. Two scrapers are placed in front of the rollers to throw the material in their path. The diameter of a dry-pan may range from 6 to 9 feet. For a 9-foot pan with rollers 48 inches in diameter and 12 inches face, the total weight would be about 20 tons, while the weight of the two rollers with their shafts and boxes is about 61⁄2 tons. From 12 to 16 horsepower are required to operate the pan. The capacity of such a machine will depend on the size of the screen meshes, and character of raw material, whether hard or soft, dry or moist. For a medium shale, it is possible to grind 8 tons per hour through a 8-inch screen and about 12 tons through a 1/4-inch screen.

Disintegrators represent a third type of machine used for breaking up clay or shale, and, where used, are commonly found to be quite effective. Their capacity is large, but much power is also required to drive them. A disintegrator has several drums, or knives on axles, revolving rapidly within a case, and in opposite directions. As the lumps of clay are dropped into the machine they are thrown violently about between the drums and also strike against each other, thus pulverizing the material completely and rapidly. Such machines can pulverize from 8,000 to 28,000 pounds of material, such as shale or gypsum, in one hour, and require from two and one-half to four horsepower per ton per hour.

Rolls (Pl. XXIV, Fig. 2) are often employed for breaking up clay and pebbles, and, where dry material is used, they are quite effective, but if damp clay is put through them, as is done at some yards, the lumps are simply flattened out. Rolls are also supposed to break up any stones that may be present in the clay. The surface of the rolls is smooth, corrugated or toothed, or tapering. The two rolls revolve in opposite directions and with differential velocities of 500 to 700 revolutions per minute.