Measurement of the (pressure, density, temperature) relation of two (methane + nitrogen) gas mixtures at temperatures between 240 and 400 K and pressures up to 20 MPa using an accurate single-sinker densimeter Chamorro, C.; Segovia, J.; Martín, M.; Villamañán, M.; Estela-Uribe, J.; Trusler, J.; The Journal of Chemical Thermodynamics 2006, 38, 916-922