Brick
a well known building material. Bricks are really a kind of coarse, porous, unglazed pottery, made from common clay. Almost any reasonably clean clay answers the purpose. It must be free, however, from limestone pebbles, lest the burning convert them into lime which would later absorb water and slake, causing the brick to chip or split open.
Brickmaking is not a complex process. Brick clay, fuel, and water are the essentials. If necessary, the clay is first screened to free it from pebbles. It is then ground, mixed with water, and worked into a plastic, stiff mud in a mill or large wooden barrel in which paddles driven by machinery stir the mass thoroughly. The well kneaded clay is pushed out at the bottom, and is molded or cut into bricks. The largest brick machines turn out 30,000 bricks a day. The green bricks are stacked up under light sheds to harden for a few days. Care must be taken not to let them dry too fast lest they crack.
The air-dried bricks are then built up in large kilns properly constructed to allow the flames to race through channels at suitable intervals. Wood or coal and, in some localities, gas, is used for fuel. The firing should be light at first and should increase gradually in intensity. For common brick the heat should reach 1,800 deg. F., and for paving brick the heat should be more intense. The more intense the heat, the more the ingredients, especially sand, which is present in all brick clay, are melted together in a glassy fusion. Fire bricks, in fact, are made of clay containing a large degree of sand and are fired to such a degree of heat that they are afterward virtually fireproof and will neither crack nor warp. They are brittle, however, and in a wall require to be backed by common brick.
The red color of some bricks is due usually to the presence of iron. The redder the brick, the more iron. Dark brown brick also owes its color to burnt iron. Yellow and cream colored brick derive their color from lime and iron.
An ordinary brick is 2 X 4 X 8 inches. Bricks are manufactured, sold, and laid in walls usually at a price per thousand. A chimney builder plans his dimensions in multiples of four inches, allowance being made for mortar. In addition to the regular size, bricks of a thousand conceivable shapes and sizes may be ordered for special cases. There are about 8,000 manufactories in the United States, turning out, it is estimated, 25,000,000,000 bricks annually. About $2,000,000 worth are exported.
The earliest brickmaking of which we have remains was doubtless carried on by the Babylonians and Egyptians in the grain producing valleys of the Euphrates and the Nile, where both timber and stone were lacking. Sun-dried bricks 4,000 years old may be found in a state of excellent preservation. Straw was used to give the bricks greater coherency. For a story of the Egyptian taskmasters who forced the Israelites to gather their own straw from the stubble fields, see Exodus i: 14; v: 4-19.