Of the water used, four liters are found in the elutriating vessels and nine liters in the receiving vessel No. 5. The apparatus is left standing for an hour until the liquid in the elutriators is clear and the portions in each vessel are received on weighed filters dried at 125°, and the weight of each portion determined. It is recommended that the loss on ignition of each part be also determined. The separated particles thus secured are classified as follows: No. 1. Débris and gravel. No. 2. Coarse sand. No. 3. Fine sand. No. 4. Clayey sand. No. 5. Finest parts or clay. Although the method of Nöbel has been much used, the results which it gives are entirely misleading. The convection currents produced in the conical vessels by the passing water and the flocculation of the soil particles prevent any sharp separation into classes of distinct hydraulic value. The process may be useful for a qualitative test, but its chief claim to a place in this manual is in its historic interest arising from its use in the first attempts at silt analysis. =215. Method of Dietrich.=[148]—The difficulties attending the silt separation by the Nöbel method, led Dietrich to construct an apparatus in which the sides of the elutriating vessels were parallel, but these vessels, with the exception of the first, were not set in an upright position. [Illustration: FIGURE 29. DIETRICH’S ELUTRIATOR. ] The apparatus (Fig. 29) consists of a series of cylindrical vessels connected by rubber tubing. The elutriators are of the following dimensions: No. 1. Seventeen centimeters long, 2.8 centimeters in diameter, position upright. No. 2. Thirty-four centimeters long, four centimeters in diameter, inclined 67°.5. No. 3. Fifty-one centimeters long, 5.2 centimeters in diameter, inclined 45°. No. 4. Sixty-eight centimeters long, 6.4 centimeters in diameter, inclined 22°.5. The rubber tubes passing from one vessel to the other are furnished with pinch-cocks so that each one of the elutriating vessels can be shut off from the others and independently removed from the circuit. The stream of water is made to pass through the apparatus under a constant pressure of one meter. Only the fine earth, boiled with water or hydrochloric acid, is to be placed in the apparatus. The part coming through a sieve with a mesh 0.67 millimeters is to be used and placed in No. 1. About thirty grams of soil, are employed for each elutriation. Before adding the soil, the air is completely removed from all parts of the apparatus by connecting it with the water supply and allowing it to be filled with water. The rate of flow is controlled by the orifice of the last effluent tube and the analyst is directed to continue the operation until the effluent water collected in the beaker glass (5) is clear. The particles then remaining in each of the vessels are collected separately.