122 SOILS: PEOPERTIES AND MANAGEMENT 



Approximate Internal Area exposed by Average Classes 

 OF United States Soils 



Coarse sands . . 

 Sands . . . . 

 Fine sands . . 

 Sandy loams . , 

 Fine sandy loams 

 Loams . . . . 

 Silt loams . . . 

 Sandy clays . . 

 Clay loams . . 

 Silty clay loams . 

 Clays . . . . 



Square Inches 

 PEK Gram 



91 



89 



79 



213 



294 

 307 

 417 

 430 

 458 

 653 



Square Feet 

 PER Pound 



286 



280 



248 



671 



699 



926 



967 



1313 



1354 



1442 



2057 



Aches per 



Acre-poot op 



3,500,000 Pounds 



23,055 

 22,549 

 20,014 

 53,965 

 56,180 



77,700 

 105,540 

 108,830 

 115,910 

 165,270 



It is at once apparent that the amount of surface 

 exposed by the soil grains of even a sand is tremendous. 

 It is not to be wondered at that the slowly soluble minerals 

 are able to supply sufficient food to the crop growing on 

 the soil, when such a large amount of surface is continually 

 available for chemical action. The figures presented for 

 an acre-foot of soil are almost too large for adequate com- 

 prehension. It is quite evident that the finer the soil, 

 the greater is the amount of internal surface. For ex- 

 ample, a sandy loam weighing 90 pounds to the cubic 

 foot would present 60,390 square feet of surface, while 

 a clay weighing 75 poimds to the cubic foot would expose 

 about 154,275 square feet. This is equivalent to 1.39 

 and 3.54 acres, respectively. 



87. The effective mean diameter of soil particles. — 

 It is very evident that the calculations presented above, 

 both as to the number of particles and as to the internal 



