In order to obtain the fundamental knowledge of the efficacy of the dispersor of air bubbles in water used in the case of transporting fish in life, four series of experiments as mentioned below were caried out on some problems concerning the rate of dissolution of air from the fine bubbles into water, and the effects of air bubbles on fish. The fine bubbles were exclusively obtained by passing compressed air through the wall of an unglazed pipe. The bubbles thus obtainable under a little excess of pressure in the pipe were very small in size and constant in amount.
(1) As the total number of bubbles in a vessel at an instant depends on the velocity of ascention of the bubbles in water, vcm./sec. the relation of v to their radii rcm. was preliminarily examined by direct measurement of both the quantities, and a new empirical formula was. obtained (Fig. 1): v2=4296×103.r3e-21.6r.
The temperature of water was 19°C in average.
(2) The rate of dissolution of oxygen into water, which had free surface or was aerated by fine bubbles, was studied by determining oxgen content in water Cc.c./L. at different tiems by WINKLER'S method. In all cases the oxygen content C at time t is approximately given by the theoretical formula
VdC/dt=KS/Z(C∞-C) or C=C∞-(C∞-C0)e-KS/ZVt,
where C∞, is the oxygen content in saturation at the temperature of water in the experiment; C0 the value of C at time O; V the total volume of water; S the total area of the surface of contact between water and air; Z the thickness of the transition-layer existing against the surface of contact; and K a constant (Fig. 2). The values of constant K/ZH (Hbeing the depth of water) in hour were calculated from the results of the experiment as follows:
K/ZH 0.0116/loge for the water having circular free surface of 15.35cm. in diameter, , , =0.027/loge for water aerated by fine bubbles of 0.00675cm. in radius,
and, , 0.0527/loge for, , , , , , , , , , , , 0.01cm, , , , , ,
The difference among these values suggests the fact that Z diminishes with the increasing velocity of ascending bubbles.
(3) The duration of adhesion of the bubbles on the body surface of 45 goldfish swimming in water was observed, counting at different times the number of bubbles n with reference to their radii. The result is given in Fig. 3.
(4) Two goldfish were so enclosed in a net that they might swim always in the water through which fine bubbles were ascending at the different rate Qc.c./cm.2min. After 1 hour (when Q=0.29, 4.38 and 8.8 c.c./cm.2min.) and 27 hours (when Q=2.5, c.c./cm.2min.) the fish were taken out from the mist of bubbles. No serious physiological effects were observed either in these hours or in the followed 1 month, during which the fish were cultured in a still water as usual.
