2. To insure neat work the bricks must be uniform in size and the surfaces true and square to each other, with sharp edges and angles.
3. Good bricks should be quite hard and burnt so thoroughly that there is incipient vitrification all through the brick. A sound, well-burnt brick will give out a ringing sound when struck with another or with a trowel. A dull sound indicates a soft or shaky brick. (This is a simple and generally sufficient test for common bricks, as a brick with a good ring is ordinarily sufficiently strong and durable for any ordinary work.)
4. A good brick should not absorb more than one-tenth of its weight of water. The durability of brickwork that is exposed to the action of water and frost depends more largely upon the absorptive power of the bricks than upon any other condition; hence, other conditions being the same, those bricks which absorb the least amount of water will be the most durable in outside walls and foundations. As a rule the harder a brick is burnt the less water it will absorb. "Very soft, underburned bricks will absorb from 25 to 35 per cent, of their weight of water. Weak, light red ones, such as are frequently used in filling in the interior of walls, will absorb about 20 to 25 per cent., while the best bricks will absorb only 4 or 5 per cent. A brick may be called good which will absorb not more than 10 per cent."*