Tests for Brick

The transverse strength of shale paving or building brick is considerably larger than any of the above, being from 2,500 to 4,000 lb. per sq. in.

Shearing Strength.

The shearing strength of nine specimens of brick from five factories tested on the U. S. testing machine in 1894 gave a shearing strength equal to 10.1 per cent of the crushing strength flatwise; and sixteen samples from six factories, tested in 1895, gave 14.7 per cent. In the first lot the range was from 7 to 17 per cent; and in the second from 8 to 30 per cent. Apparently a higher com pressive strength is accompanied by a proportionally lower shearing strength; but the tendency is not very marked.

The size of common brick varies widely with the locality and also with the maker, and with the same maker the brick are likely to be larger as the working season advances, owing to the wear of the moulds or the die. Hard-burned bricks are smaller than soft-burned ones, owing to the greater shrinkage in burning; and this difference varies with the different kinds of clays.

In England the legal standard size for brick is 81X 41 X21 inches. In Scotland the average size is about 91 X 41 X31 inches; in Germany, 91X41 X21 inches; in Austria, 111 X51 X21 inches; in Cuba, 11 X51 X21 inches; and in South America, 121 X61 X21 inches.

In the United States there is no legal standard, and the dimen sions vary greatly. In 1887 the National Brick Makers' Association adopted standard sizes for brick, but in 1893 modified them slightly and in 1899 re-affirmed the latter dimensions, which are: Paving blocks are occasionally used as building bricks. The blocks range in size from 9 X 4 X3 to 9 X 5 X 4 inches, the former being much the more common.

Large brick are worth more per thousand than small ones, a seemingly small difference in the size of the individual brick making a greater difference in the volume of a thousand bricks than is usually supposed. If, reckoned according to the cubic contents, brick 8 X 4 X2 inches is worth $10 per thousand, brick 81 X41 X21 is worth $12.33 per thousand, and 81 X414 X21 is worth $15 per thou sand. In the first case a difference of n inch on each dimension is worth $1.16 per thousand, and in the second case, $1.25.

Further, where bricks are laid by the thousand, small bricks are doubly expensive.

In 1905 the average selling price of brick in the several States was as in Table 9.* Prices have been gradually rising for eight years.