PAVING AND DRAINING.] BUILDING 467 Fia. 14. Paving of Dutch Clinkers. >i T3 and JUS. surface is such that damp rarely shows through. The paving brick differs from the common brick only in thick ness, its dimension in that direction being rather less than 2 inches, in stead of 2|- inches, and in being rather harder and more compact. Dutch clinkers aro paving bricks, smaller and much harder than the English, and of a light yellow colour ; they are 6 inches long, 3 inches wide, and 1-| inch thick, and are always set on edge and herring-boned, that is, instead of being placed in parallel lines, they are set at right angles to each other, as in fig. 14, yet with a perfectly even face. Paving tiles are made O^- inches and 11^ inches square, though they are called 10-inch and 12-inch or foot tiles respectively, the former being 1 inch, and the latter 1|- inch thick ; they are set in courses, as stone paving would be, the alternating courses breaking joint. A sort of tiles called terro-metallic are manufactured for stabling and similar purposes. Here may be mentioned the extended manufacture of ornamental tiles. The tiles formed in intaglio and ena melled, similar to those used by the Moors in Spain, have enabled the architect to break through .the monotonous surface of brick buildings, and to introduce ornamental forms and colour without the necessity of resorting to plaster and stucco. From the geological position of London and many other towns, bricks must always be the prevailing material for building purposes ; such means, therefore, for the safe introduction of colour and ornament are especially desirable and should be carefully studied. With this, too, has come the extended use of ornamental brickwork by the introduction of moulded bricks of all forms, and of many colours, together with a material of a like nature, by which decorative work of a more ornamental character can be obtained, namely terra-cotta, or prepared clay moulded or wrought and then burnt in a kiln. Tiles as above referred to are made for mosaic and tesselated pavements in plain colours (some being enamelled), for halls, footways of land ings, conservatories, &c., also glazed tiles for hearths, and whito and toned tiles, with the encaustic tiles of many colours, for walls. The former are manufactured of all sizes, so that by the combination of certain forms and colours an endless variety of patterns are obtainable. For pavements they require to be carefully set in cement on concrete, and in cement on walls. Sewers and drains which are not cylindrical should be built with concave bottoms ; this keeps the stream more together, and enables it the better to carry its impurities along with it, whereas a flat-bottomed drain offers a large surface for the particles of soil to attach themselves to, and the stream of water being more scattered is less efficient in force. Drains near houses, and in other places where it may be necessary to open them at any time, may be of the form of which a, fig. 1, Plate XXI. is a section, with a flat covering of stone paving, or large paving tiles, set and jointed with cement. Gun-barrel drains, of 9-inch or 12-inch diameter, as at b, are the best in exposed situations, because they are the strongest ; but as there is no mode of cleaning, if they are too long to be raked, but by breaking them up, they should not be employed except, with a con siderable fall and a frequent or constant stream of water through them, as from a pump trough, rain-water trunks, &c. They are constructed on a barrelled centre of wood, which the bricklayer drags on as he advances with his work, finishing as ho goes. No drain should have an inclination or fall of less than one-quarter of an inch to a foot ; and where the stream is infrequent and dull, as much more would be a great advantage. Large sewers, which arc accessible from the ends, or from side entrances, Fid. 15. Section of Sewer. for men to clear or remove any accidental obstructions, are best made circular, elliptical, or egg-shaped, as in fig. 15. The last two shapes are gen ally preferred, because in proportion to the capacity the height is greater. The form in fig. 15 maintains the greatest possible depth with a small quantity of fluid, and combines this qualification with those of great strength to resist external pressure and large capacity with a given amount of materials. The form shown at c, fig. 1, Plate XXI., is now disused, though it was long advocated for sound work manship and regular joints. A rate of fall of 1 in 120, or 1 inch in 10 feet, is desirable, although less will suffice for a main sewer. Pipes or hollow cylinders of well-made and well-burnt Pipe glazed stoneware form the most efficient house-drains. drains - Such pipes are put together with great accuracy with sockets, so as to fit spigot and faucet fashion ; movable tops are provided so as to give access to them at any part required, without taking up and relaying the drain from one or other of its ends, as was so often the case with the old brick drain, Proper bends, junctions, syphons, &c., are also made of the same material. In using pipes for drains, it should be borne in mind that a little larger than large enough is better than the reverse of this. No pipes should be laid down for a house-drain of less bore than 6 inches, nor should earthenware be used for drains requiring a greater bore than 12 inches; the material is too weak to allow of more, and the material is not strong enough to stand more than a dead pressure. Glazed stoneware pipes are also employed for small sewers in side streets, or to take off the collected soil and water from a short row of houses into the main brick sewer, and thence to a water course or to a reservoir of a main drainage scheme. In building drains it is of great importance that proper Traps, traps should be constructed to prevent the ascent of foul air and the passage of vermin. At every sink there should be a bell-trap, and a well-trap within that, or near the hither end of the drain. Suppose a drain leading from a kitchen or scullery to the common drain of the house, in which it meets that which may come from the water- closet and other places. The bell-trap in the sink itself will prevent the return of smell when it is constantly in use, but it is liable to be left out, broken, or otherwise injured, or it may become dry by evaporation; it is, therefore, necessary to have a trap not so liable to such ordinary contingencies. Let a well be made 18 inches or 2 feet in diameter, square or round, and 2 feet 6 inches or 3 feet deep, across and below the level of the drain, as shown in plan, fig. 2, Plate XXL, and in longitudinal section, fig. 3 ; it must be built around with brick in cement, and be plastered on the inside with the same material, which will make it capable of retaining fluids. Uprightly across this well, and in the transverse direction of the drain, must be placed a sound piece of paving stone, so long that its ends may be inserted in the sides of the well, as shown in fig. 12, and so wide that its upper edge shall touch the covering of the drain, and that its lower may reach 6 or 9 inches down into the well below the bottom of the drain. Mortar or cement must prevent the passage of air between the upper edge of this trap-stone and the cover of the well and drain, and the trap is com plete. The water coming from the sink flows along the drain from a to b (fig. 3), where it falls into the well, and filling it up to that level it flows on again from c in the direction of d, to the cess-pool or common sewer from
which, however, no smell can return ; for the trap-stone