SAND Sand will be considered only in connection with cement (Port land cement). See notes under caption, "Cement." The province of sand with cement is similar to that of brick in masonry, on a. small scale. The cement acts in the same capacity as the mortar surrounding the brick. If a brick could be made the size of the com plete wall there would be no need for mortar, but as it cannot, mortar is required to fill thoroughly all spaces between the bricks and to adhere to each tenaciously so as to form one solid mass. If on the sides of the brick should be placed thin layers of soft clay, the bond would be broken, inasmuch as the clay would not cling tenaciously to the brick and would prevent contact with the mortar; therefore, to obtain a good brick wall, each brick must be clean and free from coating of foreign material, so that the contact with the mortar will be complete.
To return to sand—in the same way, each particle must be entirely separate from any other, and must be free from foreign coatings which would prevent its contact with the cement or would cause the particles to cling together so as to prevent the thorough coating of each particle with cement. The usual requirement for sand to be used with cement is that it shall be clean, coarse, and sharp; and that rarely should over three volumes of sand be used to one volume of cement. In our case, however, we must be more economical—we find in our pits a soft, fine sand, which, while it separates well, resembles ground clay when rubbed between the fingers. Before throwing it out as useless and paying a round price for sand hauled in, let us see what can be done with it.
flake frames of wood screwed together which will provide 32 moulds for cement bricks 2 inches long, with ;-inch section, by using two long strips i-inch square divided by i-inch divisions so as to leave 2 inches clear between each, all to be oiled. In these spaces we are to mould our small bricks for test. (See Fig. 1.) Obtain some clean, coarse, sharp sand for comparison, and also some of the fine soft sand from the site; carefully mix (dry) enough cement with sand to form four bricks of each kind, first in proportions of 3 sand to 1 cement, then of 4 sand to 1 cement, then of 5 sand to 1 cement, and lastly of 6 sand to 1 cement—eight batches in all, one half of which will be of sand from the site, the other of im ported sand. Each batch should be mixed with greatest thorough
ness in order that every side of every particle of sand shall become coated; then add just enough water to thoroughly dampen, and crowd the mixtures into the moulds (which should be laid on a smooth plank, for bottom), compressing each as much as possible. If water appears on top, it will indicate that too much has been used in mixing. Then there will be four bricks of each batch. Place on each an identifying mark— Cover with a clamp cloth to prevent evaporation; and after one day, draw out the screws holding the forms, and put the bricks for two weeks in a damp place, covered with a wet cloth or in water. Obtain two good, smooth planks about 3 feet long by 1 foot wide; go to a neighboring foundry, and obtain permission to use their scales and a few hundred pounds of pig iron; lay down one plank on a perfectly level bed, and place the number S brick on their sides. (See Fig. 2.) In order to get an even bearing it is well to place below and over the cement bricks one layer of soft building paper; above place the second plank with great care, seeing that it has a firm, even bearing at each of the four bricks. Carefully lay pig iron above, beginning at the middle, and fill each way, never loading one end before or with a much heavier load than the other. Carefully watch the bricks; note when they crack; and when they crumble, weigh the pig iron and note the results.
As above, test each of the remaining seven sets of bricks.
It is safe for ordinary dwellings to select the cheapest materials and mixture which will carry under such conditions 500 poundsof iron.