  By proposing an Ansatz for the pressure (measured in terms of the bag
constant) of the hadronic gas in equilibrium, we have formulated a rather
simple method which allows one to analytically investigate the bulk
thermodynamic propertities in the vicinity of the phase transition. This makes
it also possible to take into account the nonperturbative vacuum effects from
both sides of the equilibrium condition. As an example of our approach, we have
calculated the crossover (critical or transition) temperature $T_c$ and the
critical chemical potential $\mu_c$ (as functions of the bag constant) from the
noninteracting quark-gluon plasma state equation. Our results for
$T_c(N_f=0)=241.5 MeV$ and $T_c(N_f=2)=160.6 MeV$ are in good agreement with
recent lattice data. The extensive densities such as the entropy density,
specific heat, etc. are calculated as well. A general scheme how to calculate
the latent heat, the critical density, etc. within the extended bad model is
also described and it is applied to the two models of the hadronic gas phase.
