INTRODUCTORY STATEMENT.

Probably few persons have any conception of the many different applications of clay in either its raw or burned condition. These varied uses can be best shown by the following table, compiled originally by R. T. Hill1 and amplified by the writer:

Domestic.-Porcelain, white earthenware, stoneware, yellow ware and Rockingham ware for table service and for cooking; majolica stoves; polishing brick, bath brick, fire kindlers.

Structural.-Brick: common, front, pressed, ornamental, hollow, glazed, adobe; terra cotta; roofing tile; glazed and encaustic tile; draintile; paving brick; chimney flues; chimney pots; doorknobs; fireproofing; terra-cotta lumber; copings; fence posts.

Hygenic.-Urinals, closet bowls, sinks, washtubs, bathtubs, pitchers, sewer pipe, ventilating flues, foundation blocks, vitrified bricks.

Decorative. Ornamental pottery, terra cotta, majolica, garden furniture, tombstones.

Minor uses. Food adulterant; paint fillers; paper filling; electric insulators; pumps; fulling cloth; scouring soap; packing for horses' feet; chemical apparatus; condensing worms; ink bottles; ultramarine manufacture; emery wheels; playing marbles; battery cups; pins, stilts and spurs for potters' use; shuttle eyes and thread guides; smoking pipes; umbrella stands; pedestals; filter tubes; caster wheels; pump wheels; electrical porcelain; foot rules; plaster; alum.

Refractory wares.-Crucibles and other assaying apparatus; gas retorts; fire bricks; glass pots; blocks for tank furnaces; saggers; stove and furnace bricks; blocks for fire boxes; tuyeres; cupola bricks; mold linings for steel castings.

1 Mineral Resources U. S., 1891, p. 475, Washington.

Engineering works.-Puddle; Portland cement; railroad ballast; water conduits; turbine wheels; electrical conduits; road metal.

Nearly all of the more important products are made in New Jersey, and these branches of the industry are treated in some detail in the following pages.

Classification of clays based on uses.-Clays are sometimes classified according to their uses into the following groups:

Kaolins or China clays.-Those burning white and used in manufacture of white earthenware or porcelain.

Fire clays. Buff-burning clays of refractory character used chiefly for fire brick.

Stoneware clays.—Semirefractory clays, which burn to a dense body and possess good plasticity and tensile strength.

Pipe clays. Nonrefractory clays, of good plasticity, and which are vitrifiable.

Brick clays.-Impure clays, usually red-burning.

These do not by any means represent all the names commonly met with in the clay-working industries. For this reason it may be well to give at least the more important ones below.

Kaolins.-A term applied to white-burning residual clays, used in the manufacture of white earthenware, porcelain, wall tiles, white floor tiles, paper making, etc.

Ball clays.-White-burning, plastic, sedimentary clays, used chiefly in the manufacture of the fine grades of pottery, viz.: those having a white body.

Ware clay. A term applied to ball clays mined near Woodbridge.

Fire clay.-A term loosely applied to clays considered suitable for making fire brick. No standaid of refractoriness has been adopted in this county, and many clays are called fire clays which have absolutely no right to the name. Fire clays are often classed as No. I and No. 2 grades. Since the term is so loosely used, and, furthermore, as even in New Jersey there is no uniform usage of the name, in this report the fire clays have been grouped as highly refractory, refractory, semirefractory (p. 100), and no clay fusing below cone 27 is considered a fire clay. The terms No. I and No. 2, when used, refer to the designations given by

the clay miner, and often mean no more than that the clay is the best or second best dug by him.

Stoneware clays.-Under this term are included such clays as are adapted to the manufacture of stoneware. They must, therefore, possess good plasticity, dense-burning qualities and preferably good tensile strength. The lower grades of stoneware are often made from a nonrefractory clay, but the better grades, and in New Jersey even the common ones, are generally made from a No. 2 fire clay.

Sagger clay. This is a term applied to clays which are used in a mixture for making the saggers, in which the white ware and other high grades of pottery are burned. They are commonly rather siliceous in their character, although some may be used on account of their bonding power and freedom from grit to hold the more porous grades together. As far as the physical properties go, the sagger clays are not, therefore, represented by any one type. Their refractoriness varies from that of a refractory to a semirefractory clay.

Wad clay. This is a low grade of fire clay, which is used for grouting the joints between the saggers, when they are set up in bungs in the kilns. It is dug at several localities in Middlesex and Mercer counties.

Terra-cotta clay. This term does not mean very much and is used rather indiscriminately to indicate different beds of clays, which are being dug for the manufacture of terra cotta. In the majority of cases they are semirefractory clays of buff-burning character, sometimes sandy, at other times dense-burning. At one or two places a red-burning clay is dug for terra-cotta manufacture. The wide difference in character between two of them is shown elsewhere in this report.

Retort clay. A dense-burning, plastic, semirefractory clay, used chiefly in the manufacture of stoneware. In New Jersey the term is restricted to the Woodbridge district.

Pipe clay. This is a term applied to almost any fine-grained plastic clay. Strictly speaking, it would refer to a clay used for making sewer pipe.

Brick clay. This includes all impure, nonrefractory clays suitable for the manufacture of common brick.

Pot clay.-A clay used for the manufacture of glass pots, and consequently representing a very dense-burning fire clay. In refractoriness it ranges from a highly refractory to a refractory clay.

Paper clay. This term is generally applied to fine-grained white clays that can be used in paper manufacture.