The Noro–Frenkel law is particularly useful for the description of colloidal and globular protein solutions, for which the range of the potential is indeed significantly smaller than the particle size. For these systems the thermodynamic properties can be re-written as a function of only two parameters, the reduced density (using the effective diameter as length scale) and the reduced second-virial coefficient B 2. The gas-liquid critical point of all systems satisfying the extended law of corresponding states are characterized by same values of B 2 at the critical point.