X-ray diffraction patterns of binary mixtures of normal tricosane and tetracosane at 20 degrees C (powder method) show the presence of two new phases, here denoted beta’ and beta(1)’. The crystal structure of these phases is orthorhombic; the structure of the beta’ phase is isomorphous with the tricosane beta’ phase observed after the delta transition. With increasing temperature and concentration, the experimental observations, both by X-ray diffraction and differential thermal analysis, made it possible to modify the binary phase diagram of n-C-23-n-C-24.