| Pounds per square inch. | |
|---|---|
| Granite | 10,000 to 16,000 |
| Limestone | 12,000 to 14,000 |
| Sandstone | 10,000 |
| Marble | 9,000 to 14,000 |
| Firm, hard burned brick | 2,600 |
| Yellow burned brick | 1,500 |
| Red brick | 1,200 |
| Pale-red brick | 900 |
| Chalk | 750 |
264. When stone cannot be found, brick forms an excellent substitute; being made from clay earths, which can be found in almost any locality. Bricks are well fitted for nice work, are cheap, and easy of transport. The French, at Algiers, have used concrete, rammed in boxes so as to make large cubes and other shapes. The structures built of this material are found to be very nearly if not quite as strong as those of natural rock.
LIMES, CEMENTS, MORTARS, AND CONCRETES.
265. Nothing is more important in the construction of masonry than good cement; and generally, no part of construction is intrusted to more ignorant persons. Under the above head are to be considered limes, cements, sands, common mortar, hydraulic mortar, and concrete.
266. Lime is obtained by burning off the carbonic acid from the pure limestones; when it is put up in air tight barrels and is unslacked lime. Natural cements are composed of pure lime mixed with argil, magnesia, iron, and manganese. Artificial cements are prepared by mixing with pure lime, calcined clay, forge scales, powdered bricks which are underburnt, and other materials of like nature. Cements made thus artificially, are as good as those naturally hydraulic.
Lime is termed rich, poor, hydraulic, and eminently hydraulic, according to its properties.
Rich or fat limes are those which double their volume in slacking and dissolve in fresh water to the last particle. They absorb about 300 per cent. of their weight of water.
Poor limes do not much increase their volume, do not dissolve completely, and absorb 200 per cent. of water.
Hydraulic limes set in fifteen or twenty days after immersion, and continue to harden as they grow older. After one year their consistency is about that of hard soap.
Eminently hydraulic limes set in five or six days, and continue to harden.