The complete phase diagrams in liquid range of mixtures of the nematic liquid crystal 4,4'-azoxyanisole (PAA) with n-dodecane, n-octadecane, and n-tetracosane have been determined. The experimental results are analyzed quantitatively in terms of a theory based on the Flory lattice model of nematic fluids. It is shown that all features present in the experimental phase diagrams are in accord with the theoretical predictions. Nearly quantitative agreement of theory and experiment can be reached if a concentration-dependent interaction parameter is used to describe the isotropic interaction between the nematic liquid crystal and the dissolved n-alkane.