Refractive indices and densities of acetone + methanol + water, acetone + methanol + 1-butanol and of the binary mixtures acetone + water, acetone + 1-butanol, methanol + water, and methanol + 1-butanol have been determined experimentally over the entire range of composition at the temperature 298.15 K and at atmospheric pressure. Derived excess properties were determined, variable-degree polynomials being fitted to the results. Methods for predicting ternary excess properties from the values of the corresponding three binary mixtures involved are tested and compared. An estimation of excess volumes is also evaluated using a modified Heller equation (Heller, 1965) which depends on the refractive indices of the mixture. Comparison of the predictions by different methods with the experimental values of the physical properties is made.