SKDRDC    SKDRDC    SKDRDC    SKDRDC    SKDRDC    SKDRDC    SKDRDC    
          **********************************************
                    **************************
                              ******

SUBROUTINE SKDRDC (KSPEC, P, T, ACT, SDEN, ISKWRK, RSKWRK, DKDC)
Returns the partial derivative of the production rates of the
species with respect to the concentration of species KSPEC.

INPUT
KSPEC     - Integer scalar, species index
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
DKDC(*)   - Real array, partial of the production rates of the
            species with respect to the concentration of species
            KSPEC;
            dimension at least KKTOT, the total species count.
               cgs units, moles/(cm**2*sec) / (units of KSPEC)