@property<EOL><INDENT>def SGg(self):<DEDENT>
Vmg = self.VolumeGasMixture(T=<NUM_LIT>, P=<NUM_LIT>, zs=self.zs, ws=self.ws)<EOL>if Vmg:<EOL><INDENT>rho = Vm_to_rho(Vmg, self.MW)<EOL>return SG(rho, rho_ref=<NUM_LIT>) <EOL><DEDENT>return None<EOL>
r'''Specific gravity of a hypothetical gas phase of the mixture, .
        [dimensionless]. The reference condition is air at 15.6 °C (60 °F) and 
        1 atm (rho=1.223 kg/m^3). The definition for gases uses the 
        compressibility factor of the reference gas and the mixture both at the 
        reference conditions, not the conditions of the mixture.

        Examples
        --------
        >>> Mixture('argon').SGg
        1.3800407778218216