Machine-made Brick. Brick is frequently described as "machine made"; but this is very indefinite, since all grades and kinds are made by machinery.
When brick \k' generally burned in the old-style up-draught kiln, the classification according to position was important; but with the new styles of kilns and improved methods of burning, the quality is so nearly uniform throughout the kiln that the classification is•less important. Three grades of brick are taken from the old-style kiln : Arch or Clinker Bricks. Those which form the tops and sides of the arches in which the fire is built. Being overburned and par tially vitrified, they are hard, brittle, and weak.
Body, Cherry, or Hard Bricks. Those taken from the interior of the pile. The best bricks in the kiln.
Salmon, Pale, or Soft Bricks.. Those which form the exterior of the mass. Being underburned, they are too soft for ordinary work, unless it be for filling. The terms salmon and pale refer to the color of the brick, and hence are not applicable to a brick made of a clay that does not burn red. Although nearly all brick-clays burn red, yet the localities where the contrary is true are sufficiently numer ous to make it desirable to use a different term in designating the quality. There is not necessarily any relation between color, and strength and density. Brick-makers naturally have a prejudice against the term soft brick, which doubtless explains the nearly uni versal prevalence of the less appropriate term salmon.
The form or use of bricks gives rise to the following classification : Compass Brick. Those having one edge shorter than the other. Used in lining shafts, etc.
Feather-edge Brick. Those of which one edge is thinner than the other. Used in arches; and more properly, but less frequently, called voussoir brick.
Front or Face Brick. Those which, owing to uniformity of size and color, are suitable for the face of the walls of buildings. Some times face bricks are simply the best ordinary brick; but generally the term is applied only to re-pressed or pressed brick made especially for this purpose. They are a little larger than ordinary bricks.
Sewer Brick. Ordinary hard brick, smooth, and regular in form.
Kiln-run Brick. All the brick that are set in the kiln when burned.
Hard Kiln-run Brick. Brick burned hard enough for the face of outside walls, but taken from the kiln unselected.
Rank of Bricks. In regularity of form re-pressed brick ranks first, dry-kiln brick next, then stiff-mud brick, and soft-mud brick last. Regularity of form depends largely upon the method of burning. The compactness and uniformity of texture, which greatly fluence the durability of brick, depend mainly upon the method of moulding. As a general rule, hand-moulded bricks are best in this respect, sinew the clay in them is more uniformly tempered before being moulded; but this advantage is partially neutralized by the presence of sand-seams. Machine-moulded soft-mud bricks rank next in compactness and uniformity of texture. Then come machine moulded stiff-mud bricks, which vary greatly in durability with the kind of machine used in their manufacture. By some of the machines the brick is moulded in layers (parallel to any face, according to the kind of machine) which are not thoroughly cemented, and which separate under the action of frost. The dry-clay brick comes last. However, the relative value of the products made by different pro cesses varies with the nature of the clay used..
Size and Weight of Bricks.
The variations in the dimensions of brick render a table of exact dimensions impracticable.
As an exponent, however, of the ranges of their dimensions, the following averages are given: Baltimore front Wilmington front 81 in. X 41 in. X 2i1 in.
Washington front Croton front.... 82 in. X 4 in. X 21 in.
Maine ordinary. 71 in. X 3* in. X 2-2- in.
Milwaukee ordinary. 81 in. X za in. X n in.
.North River, N. 8 in. X 31 in. X 21 in.
English 9 in. X 41 in. X 21 in.
• The Standard Size as adopted by the National Brickmakers' Asso ciation and the National Traders and Builders' Association is for com mon brick 81 X 4 X 21 inches, and for face brick 81 X 4t X 21 inches.