  The free energy of mixing and the entropy of mixing for Cu$_{x}$Al$_{1-x}$
liquid binary alloys have been systematically investigated by using the
electronic theory of metals along with the perturbation approach at a
thermodynamic state $T=1373$ K. The interionic interaction and a reference
liquid are the fundamental components of the theory. The interionic interaction
is described by a local pseudopotential. A liquid of hard spheres (HS) of two
different effective diametres is used to describe the reference system for
alloys. The results of the calculations for energy of mixing agree well with
the available experimental data. Calculation of entropy of mixing is parameter
free and, the agreement with experiment, in this case, is found to be fairly
good.
