code: def _coligative(self, rho, A, fav):
          
          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
docs: 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