THE SOIL PARTICLE 73 



methods take days for completion ; secondly, it is simple, and 

 the techniqiie of the separation is easily acquired ; thirdly, in 

 the decantations no very large amount of water is accumulated 

 with the separates, except for the clay, and thus the time and 

 cost of evaporation is reduced. The clay, moreover, may be 

 as accurately determined by difference as loy direct methods, 

 thus allowing a further saving of time. While the method 

 is accurate only within one per cent., it is sufficiently precise 

 for all practical purposes. 



41. Physical characters of the soil separates.— It is im- 

 mediately apparent that as these groups vary in size they 

 must exhibit properties, especially physical ones, which are 

 widely different. These properties should in turn be imparted 

 to the soil of which the separates form a part. If a person is 



2. Air (CusiimaiL's^ air elutriator) . 



f Gravity (Schone 's * elutriator 

 and Hilgard's^ cliurii elutria- 



3. Water < 



In motion j tor), 



I Centrifugal (Yoder's* Centrifu- 

 [ gal elutriator) . 

 Gravity (Osborne's beaker 

 method and Atterl)erg's' modi- 

 At rest -l fied silt cylinder). 



Centrifugal (Bureau of Soils 

 method) . 



For a detailed discussion of all methods of mechanical analysis see 

 Wiley, H, W., Agricultural Analysis, Vol. I, pp. 195-276,* Easton, Pa., 

 1906. 



^ Cushman, A. S. and Hubbard, P., Air JSl%tr%ation of Fine Powders; 

 Jour. Amer. Chem. Soc, Vol. 29, No. 4, pp. 589-597, 1907. 



^Sehone, E., tfter ScJiIammansalyse ; Bui. Soc. Imperiale des Natural- 

 istes de Moscow, 40, Part 1, p. 324, 1867. tJler Schlammanalyse und 

 einen neuen BcMammapparat ; Berlin, 1867. Also see Wiley, H. W., 

 Agricultural Analysis, Vol. I, pp. 231-241; Easton, Pa., 1906. 



^Hilgard, E. W., Methods of Physical and Chemical Soil Analysis; 

 Ann. Rep. Calif. Agr. Exp. Sta., pp. 241 257, 1891-1892. 



*Yoder, P. A., A N^ew Centrifugal Soil Elutriator; Utah Agr. Exp. 

 Sta., Bui. 89, 1904. 



* Appiani, G., uher einen Sehlammapparat fur die Analyse der Boden- 

 und Thonarten; Eorseh. a.d. Gebiete d. Agri-Physik, Band 17, Seite 291- 

 297, 1894. Atterberg, A., Die Mechanische Bodenanalyse und die Klassi- 

 fihation der Mmeralboden Schwedens; Internat. Mitt. f. Bodenkunde, 

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



