. Soil physics and management. .5 4, Illinois experiment station groups Coarse sand. Fine sand Coarse silt Medium Fine silt Clay 2,506 77,821 2,506,265 77,821,000 2,506,265,000 77,821,000,000 1, 3, 10, 5,596,597,275,0001 44, 1, 5, 21, 8. Shape of Particles.—Particles of many shapes and sizesexist in all soils. The shape varies with the origin. Soils formedfrom volcanic ash or dust are most irregular in
. Soil physics and management. .5 4, Illinois experiment station groups Coarse sand. Fine sand Coarse silt Medium Fine silt Clay 2,506 77,821 2,506,265 77,821,000 2,506,265,000 77,821,000,000 1, 3, 10, 5,596,597,275,0001 44, 1, 5, 21, 8. Shape of Particles.—Particles of many shapes and sizesexist in all soils. The shape varies with the origin. Soils formedfrom volcanic ash or dust are most irregular in shape and those ofwind origin are more nearly uniform. The former have many PHYSICAL PROPERTIES OF SOILS 179 elongated or lath-like particles, while those of wind origin aregenerally rounded. Figure 87 gives some of these difEerences, bothas to shape and size. The closeness of packing varies with the shapeof the soil grains. As a general rule, the more uniform the sizeand shape the closer the packing under normal Fig. 87.—(After Merrill.) A. Showing angular character of quartz particles in decom-posed gneiss. B. Quartz granules from beach sand. C. Showing outlines of shreds of vol-canic dust as! Been under the microscope. Rocks, Rock-Weathering and Soils, Merrill.(Courtesy Ma^millan Co.) 9. Arrangement of Particles.—There is no definite arrange-ment of particles in soils. Coarse sands approach more nearly uni-formity than any others. Theoretically, there are two general formsof packing or arrangement, the columnar, figure 88A, and oblique,figure 88B. If the soil particles were spheres and of uniform size,the columnar arrangement would give per cent of air spaee^ 180 SOIL PHYSICS AND MANAGEMENT while the oblique form would give per cent. The air spacewith columnar arrangement may be calculated very easily by takinga one-inch cubical box and tilling it with marbles of different sizes,varying from one inch to one-sixteenth inch in diameter, and com-
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