"stance of the pipe is uniformly and extremely dense, which, consequently, gives it immense strength, and ensures a durability which cannot belong to a more por"ous, though thicker, tile.

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"The clay is brought from the pug-mill so dry that, "when squeezed through the machine, not a drop of water "exudes, moisture is, indeed, scarcely apparent on the "surface of the raw pipe. Hence, the tiles undergo little or no change of figure while drying, which takes place very rapidly, because of their firm and slight substance." Tempering. After the fine clay is relieved of the water with which it was washed, and has become tolerably dry, it should be mixed with the sand, or other tempering ma

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terial, and passed through the Pug-Mill, (Fig. 42,) which will thoroughly mix its various ingredients, and work the whole into a homogeneous mass, ready for the tile machine. The pug mill is similar to that used in brick-yards, only, as the clay is worked much stiffer for tiles than for bricks, iron knives must be substituted for the wooden pins. These knives are so arranged as to cut the clay in every part, and, by being set at an angle, they force it downward toward the outlet gate at the bottom. The clay should be kept at the proper degree of moisture from the time of tempering, and after passing through the pug-mill it should be thoroughly beaten to drive out the air, and the beaten mass should be kept covered with wet cloths to prevent drying.

Fig. 42.-PUG-MILL.

Moulding the Tiles.-Machines for moulding tiles are

of various styles, with much variation in the details of their construction, but they all act on the same general principle; that of forcing the clay through a ring-shaped aperture in an iron plate, forming a continuous pipe, which is carried off on an endless apron, or on rollers, and cut by wires into the desired lengths. The plates with the ring-shaped apertures are called dies; the openings are of any desired form, corresponding to the external shape of the tiles; and the size and shape of the bore, is determined by the core or plug, which is held in the centers of the apertures. The construction of the die plates, and the

manner of fastening the plugs, Fig. 43.-PLATE OF DIES. which determine the bore of the tiles, is shown in Fig. 43. The view taken is of the inside of the plate.

The machine consists usually of a strong iron chest, with a hinged cover, into which the clay is placed, having a piston moving in it, connected by a rod or bar, having cog-teeth, with a cog-wheel, which is moved by horse or hand power, and drives the piston forward with steadiness, forcing the clay through the openings in the die-plate. The clay issues in continuous lines of pipe. The machines most in use in this country are connected directly with the pug-mill, and as the clay is pugged, it at once passes into the box, and is pressed out as tiles. These machines are usually run by horse-power.

Mr. Barral, in his voluminous work on drainage,* describes, as follows, a cheap hand machine which can be made by any country wheelwright, and which has a capacity of 3,000 tiles per day (Fig. 44):

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"Imagine a simple, wooden box, divided into two compartments. In the rear compartment there stands a "vertical post, fastened with two iron bolts, having heads

*Drainage des Terres Arables, Paris, 1856.

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"at one end, and nuts and screws at the other. The box "is thus fixed to its support. We simply place this support on the ground and bind its upper part with a rope "to a tree, a stake, or a post. The front compartment is "the reservoir for the clay, presenting at its front an orifice, in which we fix the desired die with a simple bolt.

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"A wooden piston, of which the rod is jointed with a "lever, which works in a bolt at the top of the supporting "post, gives the necessary pressure. When the chest is "full of clay, we bear down on the end of the lever, "and the moulded tiles run out on a table supplied with "rollers. Raising the piston, it comes out of the box, "which is again packed with clay. The piston is replaced. "in the box; pressure is again applied to the lever, and so on. When the line of tiles reaches the end of the "table, we lower a frame on which brass wires are "stretched, and cut it into the usual lengths."

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The workmen must attend well to the degree of moisture of the clay which is put into the machine. It should be dry enough to show no undue moisture on its surface as it comes out of the die-plate, and sufficiently moist not

to be crumbled in passing the edge of the mould. The clay for small (thin) tiles must, necessarily, be more moist than that which is to pass through a wider aperture; and for the latter there may, with advantage, be more sand in the paste than would be practicable with the former.

After the tiles are cut into lengths, they are removed by a set of mandrils, small enough to pass easily into them, such as are shown in Fig. 45, (the number of fingers

Fig. 45.-MANDRIL FOR

corresponding with the number of rows of tiles made by the machine,) and CARRYING are placed on shelves made of narrow strips sawn from one-inch boards, laid with spaces between them to allow a free circulation of air.

TILES FROM MACHINE.

Drying and Rolling.-Care must be taken that freshly made tiles be not dried too rapidly. They should be sheltered from the sun and from strong winds. Too rapid drying has the effect of warping them out of shape, and, sometimes, of cracking the clay. To provide against this injury, the drying is done under sheds or other covering, and the side which is exposed to the prevailing winds is sometimes boarded up.

For the first drying, the tiles are placed in single layers on the shelves. When about half dried,—at which time they are usually warped more or less from their true shape, it is well to roll them. This is done by passing through them a smooth, round stick, (sufficiently smaller than the bore to enter it easily, and long enough to project five or six inches beyond each end of the tile,) and,— holding one end of the stick in each hand,―rolling them carefully on a table. This operation should be performed when the tiles are still moist enough not to be broken by the slight bending required to make them straight. After rolling, the tiles may be piled up in close layers, some

four or five feet high, (which will secure them against further warping,) and left until they are dry enough for burning, that is, as dry as they can be made by exposure to the air.

Burning.-Tiles are burned in kilns in which, by the effect of flame acting directly upon them, they are raised to a heat sufficient to melt some of their more easily fusible ingredients, and give to them a stone-like hardness.

Kilns are of various construction and of various sizes. As this book is not intended for the instruction of those who are engaged in the general manufacture of tiles, only for those who may find it necessary to establish local works, it will be sufficient to describe a temporary earthen kiln which may be cheaply built, and which will answer an excellent purpose, where only 100,000 or 200,000 tiles per season will be required.

Directions for its construction are set forth in a letter from Mr. T. Law Hodges, of England, to the late Earl Spencer, published in the Journal of the Royal Agricultural Society for the year 1843, as follows:

"The form of the clay-kiln is circular, 11 feet in diame"ter, and 7 feet high. It is wholly built of damp, clayey "earth, rammed firmly together, and plastered, inside and "out, with loam (clay ?). The earth to form the walls is dug

out around the base, leaving a circular trench about four "feet wide and as many deep, into which the fire-holes of "the kiln open. If wood be the fuel used, three fire-holes

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will be sufficient; if coal, four will be needed. About "1,200 common brick will be wanted to build these fireholes and flues; if coal is used, rather fewer bricks will "be wanted, but, then, some iron bars are necessary,"six bars to each fire-hole.

"The earthen walls are four feet thick at the floor of "the kiln, seven feet high, and tapering to a thickness of two feet at the top; this will determine the slope of the

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