BRICK, a rectangular mass of clay and sand, dried in the sun or baked in a kiln and used for building purposes. To mold wet clay into cubes for the erection of walls and houses was one of the first efforts at architecture. There still exist in perfect preservation sun dried bricks made by the Babylonians and Egyptians over 4,000 years ago. On some of these are inscriptions relating to the cause of their making, family history, etc. In many cases,.straw was mingled with the clay in order to give it greater coherence. The story of the Egyptian taskmasters and the brick-making Israelites, told in Exodus i, 14; v, 4-19, is too well known for further reference here. Scarcely less ancient than these Babylonian and Egyp tian bricks are the °adobe° bricks of Yucatan and Mexico. There are in Colorado, Arizona, New Mexico, Texas and California hundreds of these 'dobe houses, some of them more than 300 years old and still inhabited. The Aztecs and other American aborigines were adepts at using this material and constructed wonderful architecture out of it. The present Indian town of Laguna, in New Mexico, illustrates the decadence of this art, which the Spanish found so perfect in old Mexico.
Bricks are made of clay and sand, molded and dried or burned. Sometimes a proportion of other substances may enter into their com position. Iron is usually present in clay soils, and the iron oxide gives the red color famil iarly seen in common brick. A brick may be darkened by overburning, or if underburned it is known as salmon brick from its light color. By introducing lime as a constituent the color may be lightened, and the sand-lime brick is nearly pure white. A little magnesia in the mixture yields a brown brick. A number of the mineral oxides may be mixed with the raw materials to secure the different popular tints. Rough-faced bricks have come into consider able use as affording a pleasing contrast to the once popular smooth or pressed brick.
In New England brick are commonly made x 33/4 x 234, which when laid with a quarter inch of mortar, gives walls of 12 or 16 inches. Western brick are more usually
854 x 4y& x 2%, giving a slightly thicker wall, but popular where most of the construction is the length of a single brick or two courses.
Good brick should be uniform in size and color. If a brick is overburned, it is not only darker but smaller and may shrink as much as 3/16ths of an inch. Well-made brick should not absorb more than 1/10th of its weight of water, but some are so porous that they absorb 25 per cent; such are suitable only for filling and should never be exposed to the weather. A first-quality brick should withstand a weight of 1,600 pounds placed on it centrally when the ends are supported,under one inch of the length or when laid over a 5g-inch gap; brick have been made that would bear almost five tons under such a test.
Brick clay consists largely of hydrated sili cate of alumina, with iron in varying quantities, and sand or free silica. It varies greatly in adhesiveness, hardness and value. The hand method of working the clay into brick is still used by many small yards in the United States. One or two men can mold and kiln about 50, 000 rough bricks in a season, though under favorable conditions they may make consider ably more. The clay is usually dug in the autumn and allowed to freeze and thaw until spring, thus disintegrating the mass thoroughly through the action of frost. It is then either spaded until all lumps are removed or put into a horse-power pug-mill, where it is ground up more thoroughly. The mold is simply a box, open at both ends, the size of the brick desired. The protruding clay is planed off with a straight-edge, and the cube of wet clay is then allowed to dry in for some hours before it is placed in a kiln for firing. This latter process usually takes from 10 to 15 days and must be carefully attended to, so that the brick shall not become cooled until the operation is finished. After cooling, stacking and counting, they are ready for the market.