96-04U

The phase transitions in binary fluids are investigated by means of the collective variables method with the reference system in the Gaussian approximation. The temperature dependence of the coefficients $\varepsilon _{1}(k=0)$ and $\varepsilon _{2}(k=0)$ ($\mathaccent "017E\relax k$ is a wave-vector) at the second power of the "relevant" collective variables (connected with the order parameters) of the diagonalized Hamiltonian is studied. The calculations are performed for the mixture of the equal diameter hard spheres interacting through Yukawa tails ($\phi _{aa}(r)$, $\phi _{bb}(r)$ and $\phi _{ab}(r)$). The influence of the "unlike" ($a-b$) interaction strength on the behaviour of the curves $\varepsilon _{1}(k=0,T)$ and $\varepsilon _{2}(k=0,T)$ ($T$ is a temperature) is demonstrated.