The influence of an ultrasonic field on the rate of coagulation of negative AgJ‐sols by electrolytes

Abstract

AbstractThe rate of coagulation was determined by means of the Tyndall effect, measured by a photocell which was connected with a galvanometre. Plotting the deflection of the galvanometre against the time t, a curve was obtained the slope of which at t = 0 was called rate of coagulation.§ 1. The general features of the method are discussed. The particle radius is computed from the scattering power. This particle radius (0.8. 10−5 cm) represents the upper limit rather than the mean value.§ 2 and 3. The apparatus and the general course of the experiments are described.§ 4. The rate of coagulation in the absence of a sonic field conforms to Paine's equation. The coagulation is always accelerated by the sonic waves; this influence is negligible with high electrolytic concentration and becomes more pronounced with low electrolytic concentration.§ 5. The rate of the so‐called slow coagulation is almost linear in the concentration of the sol, but tends to increase more rapidly with this concentration if a sonic field is applied.§ 6. Experiments on the influence of the field strength.§ 7. It is shown that neither the cavitation nor the temperature rise are reponsible for the experimental results. Further, the kinetic energy of oscillation, the orthokinetic coagulation, the accumulation of the particles and the hydrodynamic interaction all are insufficiently effective to account for the influence of the sonic field. The most promising explanation of this influence at present seems to be the dipolar interaction of the particles (“migration dipoles”), which results from the distortion of the double layer.