  Thermodynamical properties of an interacting boson system at finite
temperatures and zero chemical potential are studied within the framework of
the Skyrme-like mean-field toy model. It is assumed that the mean field
contains both attractive and repulsive terms. Self-consistency relations
between the mean field and thermodynamic functions are derived. It is shown
that for sufficiently strong attractive interactions this system develops a
first-order phase transition via formation of Bose condensate. An interesting
prediction of the model is that the condensed phase is characterized by a
constant total density of particles. The thermodynamical characteristics of the
system are calculated for the liquid-gas and condensed phases. The energy
density exhibits a jump at the critical temperature.
