  Thermodynamic properties of hot and dense hadronic systems with a hard-sphere
interaction are calculated in the Boltzmann approximation. Two parametrizations
of pressure as a function of density are considered: the first one, used in the
excluded volume model and the second one, suggested earlier by Carnahan and
Starling. The results are given for one-component systems containing only
nucleons or pions, as well as for chemically equilibrated mixtures of pions,
nucleons and delta resonances. It is shown that the Carnahan-Starling approach
can be used in a much broader range of hadronic densities as compared to the
excluded volume model. In this case superluminal sound velocities appear only
at very high densities, in the region where the deconfinement effects should be
already important.
