84 SOILS: PROPERTIES AND MANAGEMENT . 



covered by the life of man the necessary forces are not 

 active enough to have this effect ; consequently, as far 

 as the farmer is concerned the texture of the soil in his 

 field is subject to but slight alteration. A sand remains 

 a sand and a clay remains a clay, as far as practical con- 

 siderations are concerned. Changes in texture may be 

 made on a small scale by mixing two soils, but this is not 

 practicable in the field. 



63. Soil separates and mechanical analysis. — The 

 soil particles, varying in size as they do, may be separated 

 into arbitrary divisions, according to their diameters. 

 The various groups are designated as soil separates, and 

 the process of making the separation and determining 

 the percentage of each group present is called mechanical 

 analysis. There are a large number of classifications, or 

 groupings, of the soil particles, as well as several methods 

 of bringing about the actual separation. The grouping 

 and method of mechanical analysis most generally used 

 in this country is that devised by the United States Bureau 

 of Soils. 1 Other methods 2 are more nearly accurate, 

 but speed as well as precision is necessary in this work. 

 A Swedish classification 3 of soil particles has been adopted 

 by the Committee on Mechanical Soil Analysis, 4 appointed 



1 Briggs, L. J., and others. The Centrifugal Method of Soil 

 Analysis. U. S. D. A., Bur. Soils, Bui. 24. 1904. 



2 For a detailed discussion of all methods of mechanical 

 analysis, see Wiley, H. W. Agricultural Analysis, Vol. I, 

 pp. 195-276. Easton, Pa. 1906. 



8 Atterberg, A. Die Mechanische Bodenanalyse und die 

 Klassifikation der Mineralboden Schwedens. Internat. Mitt, 

 f. Bodenkunde, Band II, Heft 4, Seite 312-342. 1912. 



4 Schucht, F. Uber die Sitzung der Internationalen Kom- 

 mission fur die Mechanische und Physikalische Bodenunter- 

 suchung in Berlin am 31, October 1913. Internat. Mitt. f. 

 Bodenkunde, Band IV, Heft I, Seite 1-31. 1914. 



