NUMBER OF SOIL PARTICLES 81 



of uniform diameter and weight, the number in a given 

 mass of soil may be calculated from the following 

 formula: 



N _ W _ W 



^rR3 X 2.65 7rD 3 x2.65 

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Where N = Number of particles. 

 W = Weight of soil used. 

 R = Mean radius in centimeters. 

 D = Mean diameter in centimeters. 

 AttR' = Volume of sphere. 



For example, the mean diameter of the medium sand 

 class is .0375 centimeters, and in 3.5 grams of this 

 material there would be 



3 5 3 5 



N = 7^375 ^ X2~65 = ^000737 " 47 ' 500 particleS 

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From the mechanical analysis which gives the weight 

 of each class of particles in a given amount of soil, the 

 number of particles of each size may be calculated 

 by use of the above formula, and the sum of the particles 

 in each class gives the total number in the sample. 



Table X. Number of Particles in One Gram of Pure Soil 

 Separate, Supposing that All Particles Are Spherical 



Diameter in Number of particles 



m.m. in one gram 



Fine gravel 2.000-1.000 252 



Coarse sand 1.000-0.500 1,723 



Medium sand 0.500-0.250 13,500 



Fine sand 0.250-0.100 132,000 



Very fine sand 0.100-0.050 1,687,000 



Silt 0.050-0.005 65,100,000 



Clay 0.005-0.000 45,500,000,000 



F 



