A systematic investigation is made of the consequences of the pseudopotential theory of metals on the thermodynamic properties of metallic liquids, including mixtures. We obtain expressions for the internal energy, the Gibbs free energy, and excess chemical potentials of general metallic mixtures with any number of constituents. We recommend on this basis optimum pseudopotentials for all liquid alkali metals. We obtain good agreement for the excess chemical potental of lithium in selected alloys. Finally, on the basis of metallic theory, we obtain a new scaling law for the critical constants of liquid metals which seems to be well satisfied by the metals of the groups I and IIIa, except perhaps for lithium and thallium.