In the apparatus of Harada,[176] Fig. 59, the separating vessel _a_ is made of thick glass furnished with a glass stopper above and a glass stop-cock _h_ below. The separating liquid and silt are placed in the pear-shaped vessel _a_, the stopper inserted, and the whole well-shaken. As soon as a ring of clear liquid is seen between the sinking and floating silt, the lower end of the apparatus is brought near the bottom of a conical glass _b_, the cock _h_ opened and the heavy silt allowed to fall out. Very little of the liquor will flow out because of the air pressure. Should an air bubble enter the apparatus and be held at the stop-cock, it should be made to ascend by gently tapping. When all the heavy silt has passed into the conical glass, the cock _h_ is closed and some water poured over the solution and silt in _b_. The separatory apparatus is now raised until the beveled end of it is in the water layer, when the water at once rises to _h_ and thus washes all the silt particles adhering to the glass into _b_. The liquid in _a_ may then be diluted by inverting the apparatus, adding the required amount of water through _h_, again shaken after closing _h_, and another separation secured as before. This apparatus is somewhat easier to manipulate than Thoulet’s but does not admit of the same quantitative dilution of the separating liquid. [Illustration: FIG. 60 a. FIG. 60 b. FIG. 60 c. BRÖGGER’S APPARATUS. ] =271. Apparatus of Brögger.=—All silt separations in narrow tubes are open to the objection of permitting more or less flocculation. Some of the lighter particles are thus carried down by the heavier, and, on the other hand, some of the heavier float with the lighter. This disturbing action Brögger[177] seeks to avoid by the following device, Fig. 60, a, b, c. The length of the apparatus is forty-six centimeters, and its greatest diameter 3.5 centimeters. The opening in the large stop-cock A is the same diameter as that of the apparatus at that point. The cubical content of the apparatus with A open and B closed is about seventy-five cubic centimeters. In conducting the separation the cock B is closed, the separating liquid and silt introduced, A being open, the stopper K inserted and the whole well-shaken. In the first separation, the silt S, lying over B is contaminated with some of the lighter particles S′₂, while the lighter particles above A, S₂, are mixed with some of the heavier particles, S′₁. After closing A the apparatus is again well-shaken and inverted as in Fig. 60 b. The two parts of the silt will now undergo another separation as indicated. The apparatus is now carefully inclined as in c, when the various grades of silt will flow in the directions indicated by the arrows, but without mixing, passing each other on opposite sides of the apparatus. When the movement is complete, A is carefully opened, the apparatus still being held as in c, and the light silt formerly between A and B will flow above A, while the heavy