SURFACE AREA OF SOIL PARTICLES 



83 



gives: (1) The area in square feet of one gram of the 

 soils represented by the curves on page 78. (2) The 

 surface area per pound of the same soil. (3) The ap- 

 proximate weight per cubic foot of the material in the 

 field. (4) The approximate area of surface in one cubic 

 foot of these soils as they occur in the field. 



The surface area of the particles in a given weight 

 of soil may be calculated from the formula. 



S = ttD2N. 

 Where S = Surface area in square centimeters. 

 D = Mean diameter in centimeters. 

 N = Number of particles in the class or separate. 



Thus in the calculation on page 81 there were found 

 to be approximately 47,500 particles in 3.5 grams of 

 medium sand. Their surface area, provided the particles 

 were spherical, would be: 



S = tt.0375 2 X 47,500 = 212 sq. cm. =32.8 sq. in. 



Table XII. Internal Surface Area of Field Soils in Square 

 Feet (Analysis of first seven represented by curves on page 78) 



Area per gram 

 Sq. ft. 



Coarse sand 



Medium sand . . . 



Sandy loam 



Fine sandy loam . 



Silt loam 



Clay loam 



Clay 



Sand hill 



Hobart clay 



0.8900 

 1.0440 

 1.8000 

 1.6G00 

 2.9600 

 4.0250 

 4.4130 

 0.0708 

 7.2820 



II 



Area per 

 pound. 

 Sq. ft. 



405.0 



473.0 



816.0 



756.0 



1,340.0 



1,825.0 



2,000.0 



32.2 



3,316.0 



III 



Approximate 



weight per 



cubic foot. 



Pounds 



100 

 96 

 83 

 82 

 77 

 75 

 71 



110 

 60 



IV 



Surface area 



per cubic foot 



Sq. ft. 



40,500 

 44,500 

 66,600 



62,000 

 104,000 

 130,500 

 142,000 

 3,540 

 200:000 



