The corresponding later investigations of Rudzinski (Ann. Agr. Inst. Moscow, Vol. 9, No. 2, pp. 172-234; Exp. Sta. Record, Dec. 1904, p. 245) and of Mazurenko (Jour. Exp. Landw. 1904, pp. 73-75; Exp’t Stn. Record, Dec. 1904, p. 344) fully corroborate Loughridge’s conclusions, for typical soils of European Russia. In the arid or irrigation regions, however, the case is different, for the reason that much of the decomposed rock-substance remains adherent to the surface of the larger grains, and plastic clay is formed to a much less extent. Much available plant-food may therefore, in arid lands, be present even in rather coarsely sandy soils almost devoid of clay; such as in humid climates would be likely to be found wholly barren. (See chapt. 19). PHYSICAL ANALYSIS OF SOILS. _Use of Sieves._—Down to a certain point the separation of the soil into its several grain-sizes may be accomplished by means of sieves. We may thus separate coarse gravel from fine gravel and from sand; and the latter may itself be separated into several sizes by the same means. This presupposes, of course, that the soil has been previously prepared for the purpose by crushing the lumps consisting of aggregates of finer particles, that in the operation of tillage would again be resolved into their fine constituents, or be penetrated by roots. But this preparation of the soil for sifting must not be carried beyond the point mentioned, for a grain consisting of particles somewhat firmly cemented together will under ordinary conditions play in the soil precisely the same part as a solid sand-grain, and must not therefore be broken up, if the soil is to be examined in its natural condition. The pressure of the fingers or of a rubber pestle is as far as trituration should go. The disintegration of these compound particles by means of acids, as prescribed and practiced by the French soil chemists, may wholly change the physical nature of the soil by the breaking-up of mechanical aggregations which in the usual course of tillage would remain intact. This is especially true of strongly calcareous soils, and particularly those containing calcareous sand. The sieves used for this purpose should not be ordinary wire sieves, but should have bottoms of sheet brass perforated by _round_ holes of the various diameters desired, of fractions of inches, or preferably of millimeters. For the finer grain sizes, silk bolting cloth is used by the U. S. Bureau of Soils.