CKRHEX    CKRHEX    CKRHEX    CKRHEX    CKRHEX    CKRHEX    CKRHEX    
          **********************************************
                    **************************
                              ******

SUBROUTINE CKRHEX (K, RCKWRK, A6)
Returns an array of the sixth thermodynamic polynomial
coefficients for a species, or changes their value,
depending on the sign of K.

INPUT
K         - Integer scalar, species index;
            K>0 gets A6(*) from RCKWRK,
            K<0 puts A6(*) into RCKWRK.
RCKWRK(*) - Real    workspace array; dimension at least LENRCK.

OUTPUT
A6(*)     - Real array, the 6th thermodynamic polynomial
            coefficients for species K, over the number
            of fit temperature ranges; dimension at least (MXTP-1),
            where MXTP is the maximum number of temperatures used
            to divide the thermodynamic fits.