def _coligative(self, rho, A, fav):
        """Miscelaneous properties of humid air

        Parameters
        ----------
        rho : float
            Density, [kg/m³]
        A : float
            Mass fraction of dry air in humid air, [kg/kg]
        fav : dict
            dictionary with helmholtz energy and derivatives

        Returns
        -------
        prop : dict
            Dictionary with calculated properties:

                * mu: Relative chemical potential, [kJ/kg]
                * muw: Chemical potential of water, [kJ/kg]
                * M: Molar mass of humid air, [g/mol]
                * HR: Humidity ratio, [-]
                * xa: Mole fraction of dry air, [-]
                * xw: Mole fraction of water, [-]

        References
        ----------
        IAPWS, Guideline on an Equation of State for Humid Air in Contact with
        Seawater and Ice, Consistent with the IAPWS Formulation 2008 for the
        Thermodynamic Properties of Seawater, Table 12,
        http://www.iapws.org/relguide/SeaAir.html
        """
        prop = {}
        prop["mu"] = fav["fira"]
        prop["muw"] = fav["fir"]+rho*fav["fird"]-A*fav["fira"]
        prop["M"] = 1/((1-A)/Mw+A/Ma)
        prop["HR"] = 1/A-1
        prop["xa"] = A*Mw/Ma/(1-A*(1-Mw/Ma))
        prop["xw"] = 1-prop["xa"]
        return prop
Miscelaneous properties of humid air

        Parameters
        ----------
        rho : float
            Density, [kg/m³]
        A : float
            Mass fraction of dry air in humid air, [kg/kg]
        fav : dict
            dictionary with helmholtz energy and derivatives

        Returns
        -------
        prop : dict
            Dictionary with calculated properties:

                * mu: Relative chemical potential, [kJ/kg]
                * muw: Chemical potential of water, [kJ/kg]
                * M: Molar mass of humid air, [g/mol]
                * HR: Humidity ratio, [-]
                * xa: Mole fraction of dry air, [-]
                * xw: Mole fraction of water, [-]

        References
        ----------
        IAPWS, Guideline on an Equation of State for Humid Air in Contact with
        Seawater and Ice, Consistent with the IAPWS Formulation 2008 for the
        Thermodynamic Properties of Seawater, Table 12,
        http://www.iapws.org/relguide/SeaAir.html