  Recent data on hadron multiplicities in central Pb+Pb collisions at 158A
GeV/c at mid-rapidity are analyzed within the concept of chemical freeze-out. A
non-uniformity of the baryon chemical potential along the beam axis is taken
into account. An approximate analytical solution of the hydrodynamic equations
for a chemically frozen Boltzmann-like gas is found. The Cauchy conditions for
hydrodynamic evolution of the hadron resonance gas are fixed at the thermal
freeze-out hypersurface from analysis of one-particle momentum spectra and HBT
correlations. The proper time of chemical freeze-out and physical conditions at
the hadronization stage, such as energy density and averaged transverse
velocity, are found.
