. The elements of physiological physics: an outline of the elementary facts, principles, and methods of physics; and their applications in physiology. Biophysics. chap, xxin.] THE PIPETTE AND SYPHON. 279 descends again the water is prevented passing back- wards by a valve c, while by the opening of other valves A and B it is permitted to pass through the piston, and is lodged in the upper part of the barrel. The re-ascent of the piston causes the piston valves to close, and the water is therefore driven out through the outlet tube. The pipette also illustrates the same principles (Fig. 121). I
. The elements of physiological physics: an outline of the elementary facts, principles, and methods of physics; and their applications in physiology. Biophysics. chap, xxin.] THE PIPETTE AND SYPHON. 279 descends again the water is prevented passing back- wards by a valve c, while by the opening of other valves A and B it is permitted to pass through the piston, and is lodged in the upper part of the barrel. The re-ascent of the piston causes the piston valves to close, and the water is therefore driven out through the outlet tube. The pipette also illustrates the same principles (Fig. 121). It is a glass tube blown out in the centre into a bulbous portion. One end is pro- longed into a fine point, the other is the full diameter of the tube, and is evenly ground. By applying the mouth to the wide end and sucking, the air is rarefied, and if the lower end be dipping in liquid, the liquid rises in the tube, and into the bulb. As soon as the desired quantity is drawn into the bulb, the upper end is quickly covered with the wet finger or thumb. The air is thus prevented from entering, and the pipette can be lifted out O' a1 of the fluid without any of its contents The Pipette, escaping. Any desired quantity can be per- mitted to escape by slightly moving the finger to permit the entrance of a little air. By this means part of the liquid in a vessel may be removed without disturbing the remainder. The syphon consists of a tube open at both ends but curved on itself, so as to have two limbs. It is so placed that one limb dips into the liquid to be removed, and the other discharges at a lower level (Fig. 122). By suction at the lower end the tube is first of all filled with the liquid, and then under the influence of atmospheric pressure, and the difference of levels, the flow will continue unless air be permitted to enter, or the levels become equal. Where the liquid to be withdrawn would be. Please note that these images are extracted from scanned page images that may ha
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