The theory of a nonideal gas developed by N. N. Bogoliubov is applied for a semiclassical description of nonlinear dynamics of Bose condensate density. Analytical calculations lead to temperature dependence of heat capacityCvtypical of superfluid4Heat temperatures below and above the superconducting transition temperatureTcexcept for the interval1.6 K<T<2.2 K. ©1998 American Institute of Physics.