BRICK

is a sort of artificial stone, made principally of argillaceous earth; formed in moulds, dried in the sun, and baked by burning. Tlie use of unbumed bricks is of great antiquity. They are found in the Koman and Grecian monimients, and even in the ruins of Egypt and Babylon. They were dried in the sun instead of being burned, and mixed with chopped straw to give them tenacity. On account of the extreme heat and dryne of the climate they acquired in some eastern countries a great hardne , and have lasted for several you sand years, but they are unsuitable for more norUiem latitudes. Burned bricks were also used at a vexy early period. They are mentioned in the book of Grenesis in connection with the building of the Tower of BabeL The Greeks brought brick-making to great perfection. The most common bricks among the Ilomans were 17 inches long and 11 broad, and in later periods they were burned. Modem bricks are generally about twice as long as they are broad, and twice as broad as they are thick; their length is ordinarily about 10 inches. The best are made of a mixture of argillaceous earth and sand. Their red colour is owing to the presence of oxide of iron, which is turned red by burning. The best season for making them is spring or autumn, since the proce of drying then takes place more gradually and equably. The clay should be dug in autumn, and exposed to the influence of frost and rain. It should be worked over repeatedly with the spade, and not made into bricks until the ensuing spring, previously to which it should be well tempered by treading it with oxen, or by a horse mill, till it is reduced to a ductile and homogeneous paste. The clay may have too great or too small a proportion of argillaceous earth or of sand to form a paste 731 of proper consistency; it will then be nece ary to add tie one or the other, as the case may be. When the ma has thus been thoroughly mixed, the moulder throws it into the mould, pre es it down till it fills all the cavity, and removes the overplus with a stick. The bricks are then arranged on hack^ to dry, disposed diagonally, to allow a free pa age to the air. In about nine or ten days they are ready for the burning, for which purpose they are formed into clamps or kiltigj having flues or cavities at the bottom for the insertion of the fuel, and interstices between them for the fire and hot air to penetrate. A fire is kindled in these cavities, and gradually increased for the first twelve hours, after which it is kept at a xmif orm height for several days and nights, till the bricks are sufficiently burned. Much care is nece ary in regulating the fire, since too much heat vitrifies the bricks, and too little leaves them soft and friable. Bricks are now largely made by machines, a number of which, differing in construction, are in use. The clay, according to one proce , is mixed and comminuted in a cylindrical pug-mill, as it is called, by means of rotatory knives or cutters working spirally, and pre ing the clay down to the bottom of the cylinder, where it is discharged in a tempered state. Machines are also used for moulding the bricks, and for making perforated bricks and hollow bricks, which are used when great lightne is required. Machine-made bricks are heavier, being le porous, than hand-made bricks, and are more liable to crack in drying; but they are smoother, and, when carefully dried, stronger than the hand-made. Floating-bricks are so called on account of their property of swimming on the water. They are made of agaric mineral or fo il farina, which is found in some parts of Europe. Their infusibiUty at the highest temperatures renders them useful in constructing reverberatory furnaces, pyrometers, and magazines of combustible materials. Their lightne and nonconducting property render them particularly useful for the construction of powder-magazines on board of ships. Pire'hrickSf for building furnaces, ., are made of a clay which, when properly prepared, is capable of resisting great heat. They are baked at an intense heat. The day of which they are made contains more silica in combination with alumina than common brick clay. Until 1850 there was a duty on the manufacture of bricks in this country. It is now free.