  Anomalous features for hypothetical Plasma Phase Transitions (PPT), which is
expected to occur in mixed hydrogen-helium plasma in interior of Jupiter and
Saturn, are under discussion. The characteristics of the Coulomb and density
corrections (the so-called non-ideality corrections) are reconstructed for
hydrogen-helium plasma in the vicinity of phase coexistence boundary of this
PPT in version of Saumon and Chabrier, using tabular data for hydrogen-helium
EOS of Saumon, Chabrier and VanHorn and some general thermodynamic relations.
Two previously unknown characteristics of the studied PPT have been estimated
based on these results: (i) -- the jump of the electrostatic potential across
the phase boundary of PPT (Galvani potential), and (ii) -- the scale of
non-congruency for this PPT (the differences in chemical composition of the
coexisting hydrogen-helium phases), which could be expected in H2/He mixture at
typical parameters of plasma in interior of Jupiter and Saturn. While the first
effect -- the potential of phase boundary -- turned out to be within the
typical scale of contact electrochemical potentials, $\Delta \varphi$ ~ 1-2 eV,
the second quantity -- the PPT non-congruency -- proved to be considerable
under Saturn and Jupiter conditions.
