Bricks have been used as building material for many centuries, and no known substitute seems liable to make them less popular. They are durable, of good appearance, and compara tively cheap. The fact that brick masonry is but little affected by the chemical agents that often destroy stone is well known. As heat is used in the manufacture of brick, such material is well able to withstand the attack of fires that would destroy granite. While stone is no doubt preferred by many for its appearance, very pleasing effects may be obtained from the use of brick, and at considerably less expense.
Brick may be defined as a variety of arti ficial stone produced by baking clay. While made in a great many shapes and sizes, the blocks are generally of rectangular cross-section approximately by 4 by inches on the three sides. These small and regular dimen sions are factors that make handling, trans portation, and laying comparatively easy. No slow and expensive dressing is required; no heavy hoisting apparatus is necessary for load ing; and the separate loads can be made greater or smaller as occasion requires.
Composition of Brick. A pure clay, or one containing only silica and alumina, is seldom found, and, if used, would become distorted and 70 the dull reds that are characteristic of common brick. If oxide of iron is present in larger
percentage—say 10 per cent—the darker blue black shades result. Lime with iron produces a lighter brown or cream color; and magnesia has a somewhat similar effect.
(b) Clay containing constituents tending to produce a red color will become darker as more intense heat is added. Heat alone will not pro duce this effect, as is shown in the light-colored firebricks.
(c) In some processes of manufacture, sand is applied to the forms or moulds, to prevent the wet paste from sticking to them. If, as often happens, this sand is red, the brick that might otherwise be of light tint takes the color of the sand rather than that of the clay, and the out side is red.
The clay in this country suitable for brick making, is mostly glacial material that has been washed down by the streams and redeposited, while its character has undergone little or no change. This is called alluvial clay, and the larger pebbles and grains of gravel have been left behind by the stream while the fine clay was in suspension.