Holthof modifies the apparatus of Schöne by putting into the lower mouth of the elutriator a little mercury so that the particles of earth are deposited upon its surface and are thus better agitated and washed by the current of water. =218. Mayer’s Modification of Schöne’s Method.=—An improvement of Schöne’s apparatus in the direction of greater simplicity has been tested by Mayer[150] with satisfactory results: The apparatus, (Fig. 34), consists of a glass vessel having a glass stop-cock at the bottom for admitting the water. For a distance of twenty centimeters the sides of the tube are parallel and the diameter about one centimeter. Next for a distance of fifty centimeters the tube is conical expanding at a regular rate until the internal diameter reaches five centimeters. For a distance of ten centimeters the vessel is again strictly cylindrical and it is in this cylindrical portion that the separation of the different constituents takes place. The vessel is then rapidly narrowed until it carries the stopper A two centimeters in diameter. This stopper carries two glass tubes, one F bent downward to conduct the overflow into the receiving vessels, and one H for the purpose of regulating the rate of overflow by the height of the column of water therein. The orifice of the overflow tube F should be so regulated that with a pressure of five centimeters water in H, one liter shall pass over in ten minutes. [Illustration: FIGURE 34. SCHÖNE’S APPARATUS FOR SILT ANALYSIS, MODIFIED BY MAYER. ] If the separation be conducted in an apparatus thus mounted and graduated with a pressure of two centimeters in H all that portion of the soil which can properly be called clay will pass over. The fine earth, that is, earth in which all coarse particles have been removed by proper sifting, is used in ten-gram lots for each experiment. The residue, after the separation is complete, consists of pure sand or at least pure sand mixed with humus. Before the fine earth is placed in the apparatus, the calcium carbonate therein is removed with hydrochloric acid. The treatment with hydrochloric acid, however, is not to be recommended in soil containing many undecomposed particles of calcium carbonate or dolomite for then large additions to the silt output might be made from these particles, which could not be regarded as coming from the soil as it actually exists. For alluvial soil, however, previous treatment with hydrochloric acid is recommended unconditionally.