SKDEN     SKDEN     SKDEN     SKDEN     SKDEN     SKDEN     SKDEN     
          **********************************************
                    **************************
                              ******

SUBROUTINE SKDEN  (P, T, ACT, SDEN, ISKWRK, RSKWRK, DEN)
Returns a real array of species densities.

INPUT
P         - Real scalar, pressure.
               cgs units, dynes/cm**2
T(*)      - Real array, temperature(s); dimension is determined by
            the application program to be the total number of
            species temperatures, nominally 1.
               cgs units, K
ACT(*)    - Real array, activities of the species;
            dimension at least KKTOT, the total species count.
            The first KKGAS activities are mole fractions,
            the next KKSURF activities are site fractions
               (species density normalized by the site density;
                surface concentration in moles/cm**2 is
                ACT(K)*SITE_DENSITY / # sites per species), and
            the next KKBULK activities for bulk phase species
            should be from 0 to 1, and should sum to 1 for each
            phase.
SDEN(*)   - Real array, site densities for the site types;
            dimension at least NPHASE, the total phase count,
            but the subroutine only uses site phase entries,
            NFSURF <= N <= NLSURF.
               cgs units, moles/cm**2.
ISKWRK(*) - Integer workspace array; dimension at least LENISK.
RSKWRK(*) - Real    workspace array; dimension at least LENRSK.

OUTPUT
DEN(*)    - Real array, densities for the species;
            dimension at least KKTOT, the total species count.
               cgm units, gm/cm**3 for gas-phase species
                          bm/cm**2 for surface species
                          gm/cm**3 for bulk species

            NOTE:  mass densities are not required to be input to
                   the Interpreter for bulk-phase species.
                   If they are input, they are returned by this
                   subroutine.  If not, DEN = -1.0 for the bulk
                   species