Limes are said to set when they will bear, without depression, a rod of 1
20 of an inch diameter loaded with ten or twelve ounces.
Note.—The following test was applied to every tenth cask of Rosendale cement used upon the masonry of the United States Dry Dock at the Brooklyn (N. Y.) Navy Yard. Cakes two inches in diameter and three fourths of an inch in thickness, after being immersed five days, were required to bear a rod of one twenty-fourth of an inch diameter loaded with fifty lbs. Two bricks united with the cement and immersed five days, were required to resist one hundred lbs. before separating. The following shows the progress of hardening. The force required to thrust a rod one twenty-fourth of an inch in diameter through a cake three fourths of an inch in thickness, was, after
| 24 hours, | 65 lbs. |
| 48 hours, | 70 lbs. |
| 72 hours, | 75 lbs. |
| 15 days, | 150 lbs. |
| 50 days, | 390 lbs. |
SAND.
267. Sand is the product of the decomposition of granitic and schistose rocks, and weighs, per unit of bulk, somewhat less than one half of the rock producing it; owing to the spaces between the grains. The amount of lime necessary to fill these spaces must be known before we can form a solid mass with the least lime. The amount of void may be found by filling a measure with sand, and then pouring in water: the volume of water is that of the spaces. In pebbles of one half inch in diameter the void amounts to about one half, in gravel about five twelfths, in common sand two fifths, and in very fine sand, one third. Clean sharp sand obtained from the beds of rivers is the best for mortars.
268. In mixing the ingredients for mortar, the lime is first spread on a platform and wet by sprinkling with water, which causes it to give off a great deal of heat and vapor, and fall into a powder. The sand is then applied, and the whole brought with water to a consistent paste.
The proportions for common mortar for dry work are
| Sand, | 1½ to 2 |
| Lime, | 1 |
It is well always to use a small quantity of cement; the parts which have in practice been found perfectly satisfactory are
| Cement, | 1 |
| Lime, | 3 |
| Sand, | 6 |