  The variational theory of equilibrium boson system state to have been
previously developed by the author under the density matrix formalism is
applicable for researching equilibrium states and thermodynamic properties of
the quantum Bose gas which consists of zero-spin particles. Particle pulse
distribution function is obtained and duly employed for calculation of chemical
potential, internal energy and gas capacity temperature dependences. It is
found that specific phase transition, which is similar to transition of liquid
helium to its superfluid state, occurs at the temperature exceeding that of the
Bose condensation.
