In the sifting process it will be found that so soon as the finer grain-sizes of the sand are approached, the sieve fails to act satisfactorily; the more so, the more clay was originally contained in the material. The fine particles flock together, forming little pellets, which refuse to be separated by the sieve. This difficulty can, of course, be partly overcome by previously separating the clay from the sand by means of water, as detailed above; but even then it will be found that so soon as the grain-sizes fall much below ¹/₅₀ of an inch (½ millimeter) the same difficulty is experienced, so long as the sand is dry. By playing a small stream of water upon the sieve, however, all the particles beyond the ¹/₅₀₀ of an inch may be successfully separated from the coarser portion; and for many practical purposes the separation need be carried no farther. _Use of Water for Separating Finest Grain-Sizes._—The scientific investigator, however, must of necessity proceed to separate the finer grain-sizes from each other, since, as will presently be shown, they influence the tilling qualities of the soil to a much greater degree than do the coarser particles. Such farther separation can be accomplished only by the aid of water. _Subsidence Method._—When a small amount of soil is stirred up in water, and is afterward allowed to stand for some time, the different grain-sizes will settle consecutively in accordance with their sizes (or weights); the smallest ones settling latest, and the clay only remaining suspended, as stated above. So long, however, as any considerable amount remains suspended in the water, the latter is not only denser but especially more viscid than if the clay were absent. In order therefore to obtain correct results by any method involving the use of water, it is necessary to remove the clay before proceeding to the separation of the granular sediments. This, as has been already stated, is approximately accomplished by allowing the soil, when diffused in water after proper disintegration, to settle for 24 hours from a column of water 200 mm. high, whereby all grain-sizes, of and above .01 mm. diameter are removed from the turbid liquid. This sedimentation is then repeated until after 24 hours the water becomes clear. The clay is then determined in the “clay water” by evaporation or precipitation; the granular sediments may then be successfully separated by sedimentation.