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THEORY AND PRACTICE OF ENGINEERING,

♦Book II.

CHAP. IV.

BRICKS AND TILES.

Where stone cannot be procured, bricks form an admirable substitute, being easily madefrom clay or argillaceous earth, which is found in most situations where stone is wanting:some advantages are derived from the use of this material over stone, which is not ob-tained from the quarry in a state or shape fitted for use, whilst the brick is of a con-venient size, and easily carried to the place where it is employed. An absorbent brickreadily adheres to the mortar in which it is bedded, and in a short time becomes a solidmass; whilst it often happens that hard stones are less adhesive, and their surfaces do notcombine with the mortar in which they are laid.

Unburnt bricks are of great antiquity : the first were probably masses of clay, dried in theair by exposure to the sun ; afterwards these masses were moulded into regular and uniformshapes, improved also in strength by mixing chopped straw with them : such bricks werenot calculated to resist the humidity of our climate, although some found among the ruinsof Babylon are as durable as if they had been burnt, which is entirely owing to the drynessof the air.

The remains of what is considered a part of the famous tower of Babel are perhapsamong the most ancient specimens of unburnt brick ; these bricks are 12 inches square,and 4 Inches in thickness, are bedded in bitumen mixed with sand, the joints of which areabout 8 inches in thickness; and although they have stood the exposure to the dryness andheat of the climate, when soaked in water have quickly decomposed, which is sufficient proofthat straw, reed, and such vegetable matter mixed with the clay, do not constitute a soundbrick : at Bagdad, where the bitumen is obtained from a lake in the neighbourhood, bricksare still used in most of the buildings.

The immense edifices of unburnt brick constructed by the Egyptians remain almostentire : one distant about 10 leagues from Cairo , and measured by Dr. Pococke, in 1788,was about 150 feet in height, with its base rectangular, one side being 210 feet and the other157 feet. This brick pyramid was supposed to be that mentioned by Herodotus as builtby Asychius, who is said to have inscribed on it the following : “ Do not disparage myworth, by comparing me with pyramids composed of stone : I am as much superior to themas Jove is to the rest of the deities ; I am formed of bricks, made of mud that adheredto the ends of poles, and drawn up from the bottom of the lake.”

These bricks are composed of a black, argillaceous earth, containing small pebbles, shellsand chopped straw, and were of two dimensions, the largest 15 inches long, 7 inches broad,and about 4J inches thick.

The Greeks as well as the Romans used, as we have seen, unburnt bricks: Vitruvius mentions the wall of Athens, on the sides towards Hymettus and Pentelicus; the walls of thetemples of Jupiter and Hercules, the columns and entablature of which were of stone ; thepalace of King Attalus at Tralles, that of Croesus at Sardis, and of Mausolus at Halicar-nassus : that author also describes the manner in which unburnt bricks were made, andobserves that gravelly, pebbly, or sandy clay is unfit for the purpose, and that the mostproper is a red earth, of a chalky nature, or containing sand; and that the proper season formaking them is the spring and autumn, as they dry more equally. When plaster is laidon bricks which are not perfectly dry, they shrink, and the plaster no longer adheres tothem : the inhabitants of Utica would allow no bricks to be used which were not at leastfive years old, and had been approved by a magistrate.

The three sorts of bricks in use were the doron, the tetradoron, and the pentadoron.

The word doron signifies palm, designating a^ift that might be borne on the palm ofthe hand, and it is supposed that the Roman palm was equal to it. The tetradoron is acube of four palms, and the pentadoron five : there were half bricks of each sort: the leastthickness the Greeks are supposed to have given to their walls was that of the doron, or onebrick, to their ordinary walls a brick and a half, and to their thickest two bricks. Inbuilding a wall there are alternate courses of whole bricks and half bricks, so that the jointsare regularly broken.

In neither Athens nor Rome are found any remains of unburnt bricks, and the form ofthose mentioned by Vitruvius is not quite certain, though it is generally believed that theywere cubical; it does not seem very practicable to build a wall and keep the coursesregular where the three varieties are to be used ; they seem intended for as many differentkinds of work. The unburnt bricks still used by the nations of the east are made by treadingthe clay with the feet, and mixing chopped straw, after it has been duly prepared; it is then