Excess molar volumes V-m(E) and excess molar heat capacities C-p,m(E) have been measured through the composition range for quasi-binaries : [x{A = c-C6H12 or C6H5Cl or 1-C10H7Cl (1-chloronaphthalene)} + (1 - x){XCH(3)(CH2)(nu 2-2)CH3 + (1 - X)CH3(CH2)(nu 3-2)CH3}] for nu(2) = 16 or 10 and nu(3) = 7. V-m(E)(x) and C-p,m(E)(x) values for the quasi-binaries were fitted by means of empirical equations for each X and also to a ternary correlation equation covering the whole x and X ranges. Two similar tests of Bronsted’s Principle of Congruence have been applied : (1), at x = 0.5, V-m(E) and C-p,m(E) were plotted against the average alkane carbon number = X nu(2) + (1 - x)nu(3); these values were consistent, as required by the Principle with those obtained from a mixture of A with a pure alkane of carbon number nu = ; (2), V-m(E) and C-p,m(E) for (A + n-alkane mixtures of mole fraction X) were successfully compared, through the x range, with the V-m(E) and C-p,m(E) for (A + pure alkane) interpolated from literature values to the corresponding to the present X. The success of the Principle in the case of V-m(E) and C-p,m(E) is surprising since these quantities depend, respectively, on liquid "free volume" and alkane "orientational order" which are not obviously the same for a pure alkane and its congruent alkane mixture.