SKCZTA    SKCZTA    SKCZTA    SKCZTA    SKCZTA    SKCZTA    SKCZTA    
          **********************************************
                    **************************
                              ******

SUBROUTINE SKCZTA (T, CZ, SDEN, ISKWRK, RSKWRK, ACT)
Returns the activities of the species, given the pressure,
temperature and concentrations.

INPUT
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
CZ(*)     - Real array, gas-phase and surface species concentrations,
            and bulk species activities;
            dimension at least KKTOT, the total species count.
            The first KKGAS gas-phase concentrations are moles/cm**3,
            the next KKSURF site concentrations are moles/cm**2, and
            the final KKBULK entries are bulk species activities.
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
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.