code: def Zl(self):
          r'''Compressibility factor of the chemical in the liquid phase at the
          current temperature and pressure, [dimensionless].
  
          Utilizes the object oriented interface and
          :obj:`thermo.volume.VolumeLiquid` to perform the actual calculation of
          molar volume.
  
          Examples
          --------
          >>> Chemical('water').Zl
          0.0007385375470263454
          '''
          Vml = self.Vml
          if Vml:
              return Z(self.T, self.P, Vml)
          return Nonf Zl(self):
          r'''Compressibility factor of the chemical in the liquid phase at the
          current temperature and pressure, [dimensionless].
  
          Utilizes the object oriented interface and
          :obj:`thermo.volume.VolumeLiquid` to perform the actual calculation of
          molar volume.
  
          Examples
          --------
          >>> Chemical('water').Zl
          0.0007385375470263454
          '''
          Vml = self.Vml
          if Vml:
              return Z(self.T, self.P, Vml)
          return None
docs: r'''Compressibility factor of the chemical in the liquid phase at the
          current temperature and pressure, [dimensionless].
  
          Utilizes the object oriented interface and
          :obj:`thermo.volume.VolumeLiquid` to perform the actual calculation of
          molar volume.
  
          Examples
          --------
          >>> Chemical('water').Zl
          0.0007385375470263454