│ ——————————————│ ——————————————│ —————————————— │ 10,228,547,439│ 14,735,778,341│ 19,638,258,585 ─────────────────┴─────────────────┴─────────────────┴───────────────── =245. Estimation of the Surface Area of Soil Particles.=—The approximate extent of surface area of the soil grains in one gram of soil can be calculated from the foregoing by the following formula:[163] π(_d_)²_n_ in which _d_ is the mean of the diameters of any group in centimeters, and _n_ is the number of particles in the group. The following table gives the approximate extent of surface area of the particles in one gram of soil calculated from the preceding table: APPROXIMATE EXTENT IN SQUARE CENTIMETERS, OF SURFACE AREA IN ONE GRAM OF SOIL. Soil number. ————— —————— —————— —————— —————— —————— Diameter, millimeters. 1 2 3 4 5 6 1.5 0.0 0.0 0.4 0.0 0.0 0.1 0.75 1.8 0.6 1.8 12.8 0.1 0.1 0.375 24.3 17.7 8.4 36.5 31.0 0.7 0.175 35.8 52.6 11.4 31.1 5.3 1.4 0.075 21.3 35.3 47.3 97.9 35.8 22.2 0.03 218.8 38.3 228.9 112.0 301.4 232.7 0.0075 67.4 62.5 248.9 130.8 273.5 353.4 0.00255 390.8 800.5 1355.0 2072.0 2976.0 3965.0 ————— —————— —————— —————— —————— —————— Total 760.2 1007.5 1902.1 2493.1 3593.1 4575.3 =246. Logarithmic Constants.=—The following logarithmic constants have been used in the calculation of the approximate number of grains per gram and of the surface area, using 2.65 in all cases as the specific gravity of the soil. Diameter. (_d_) Approximate number of grains. Surface area. log.(π(_d_)³_w_)/(6) log.(_d_)²π 0.15 centimeters \̅3.6703 \̅2.8493 0.075 „ \̅4.7674 \̅2.2473 0.0375 „ \̅5.8641 \̅3.6451 0.0175 „ \̅6.8711 \̅4.9831 0.0075 „ \̅7.7674 \̅4.2473 0.003 „ \̅8.5734 \̅5.4513 0.00075 „ \̅1̅0.7674 \̅6.2473 0.000255 „ \̅1̅1.3616 \̅7.3101