The electric moment of heavy water in dioxane is 1.95 plus or minus 0.01 D, and the dipole-dipole interaction energy, as calculated from polarization measurements, is 6.1 plus or minus 0.3 ergs over the temperature range 30 deg to 50 deg . The molar decrement of the dielectric constant by the addition of dioxane is less for heavy water than that for water; the decrease becomes smaller in both cases with increasing dioxane concentration and temperature. In a mixture containing 81 mole% of heavy water the time of relaxation is double that of pure heavy water. The enthalpy of activation for dielectric relaxation in a mixture containing 50 mole% is nearly equal to that of heavy water in the pure state and seems to correspond to the rupture of one deuterium bond. In mixtures containing 35 to 81 mole% of heavy water, anomalous dispersson takes place at about -14.5 deg at a frequency of 1800 kc./sec. (auth)