Ultrasonic velocities in binary liquid mixtures of benzene, toluene, o-xylene, m-xylene, p-xylene, cyclohexane, pyridine, nitrobenzene, o-nitrotoluene, aniline, o-chloroaniline, methylaniline, benzylamine, acetone, ethylacetate, amyl acetate, acetic anhydride, acetophenone, dioxane and diphenyl ether with triethylamine as a common component have been determined using a variable path interferometer. The molecular sound velocity has been found to vary linearly with concentration in all cases excepting the mixtures of nitrobenzene, o-nitrotoluene and o-chloroaniline. In all these binary systems molecular compressibility varies linearly with concentration. The validity of Nomoto's empirical formula for sound velocity is discussed.The excess compressibility conforms to the empirical relation, pqn1n2 = A+B(n1-nnz)+C(n1-n2)' where / 3 is the excess compressibility, nl, n2 are molar fractions of the common component 1 and the second liquid 2. A, B, C, the constants characteristic of each system, have been evaluated and reported. The excess compressibility of equimolar solutions for different systems is found to vary regularly with the difference in boiling points of the component liquids.
