  For a number of mixtures of rate gases at high pressures, sound speed minima
are experimentally observed depending on the concentration. This behavior has
not yet been explained. We have studied the behavior of a mixture of argon and
helium using computer simulation. Sound speed minima have been discovered at a
certain concentration, which is in good agreement with experimental data. It is
shown that this behavior is due to the fact that the P and T parameters for gas
mixtures are near the Frenkel line, separating the states of "rigid" and
quasi-gas fluid.
