For example, it is supposed that No. 3 sample, made up of 5 parts coarse sand. to 1 part cement, carries the same load as No. 6 (4 parts sand from the site to 1 part cement). If it costs $1.50 for one cubic yard of coarse sand, and 50 cents a yard to haul the sand away from the excavation, the coarse sand costs its for use $2.00 a cubic yard, or 7.4 cents a cubic foot. With cement at $2.00 a barrel, we have: It will thus be seen that it is cheaper to use the 4 to 1 mixture and the poorer sand from the site, than to haul it away, bring in other sand, and use less cement. If, on the other hand, it is found that it will require No. 5 to equal No. 3, it will be cheaper to haul away the excavated sand and haul in good sand.
Before breaking the bricks, they should be very carefully examined as to texture and firmness. Scratching with the finger-nail will show the general quality to the student after a short experience, so that experiment with weights is unnecessary after the student has become familiar with the appearance of good mortar.
After the bricks are broken, examine the fractures, and observe with a glass how well the spaces between the particles of sand are filled. Generally the results will be about in this order: No. 1 will show much greater strength than the corresponding No. 5. No. 2 and No. 6 will show less difference. Possibly No. 3 will break under less weight than No. 7; while No. 4 will go to pieces
much before No. S. The reason for this is readily detected under a glass. The imported coarse sand requires much more cement to fill the spaces. In No. 1 they are all filled; while in No. 4 there are large voids, which do not occur to such an extent in Nos. 7 and 8; the sand being finer allows smaller voids. Observe that the increase in the number of voids or small holes in the mass weakens the mixture.
Now try one other experiment. Get two forms from which fl inch cubes can be made; make a mixture of possibly 4 fine sand to 1 cement; mix one with a large amount of water, as is usually seen in ordinary work; and from this form a 4-inch cube. Mix for the other cube the same proportion, but with just enough water to change throughout the color of the mass. Crowd the mixtures into the form, both cubes to be compressed as much as possible; set the cubes aside, covered with a wet cloth for a week; then split with a cold chisel, and observe. The interior make-up of that mixed with a larger amount of water, is full of voids; that mixed with little water is com pact.
The question of sand is treated, as later the question of roofs will be, in a great deal of home-made detail, not only to get at the 'question of sand and roofs, but to illustrate how, with materials that are always at hand, results of great practical value may 1`e obtained.