The Viscosity of Gaseous Isobutane and Its Initial Density Dependence1

Results of new relative high-precision measurements on gaseous isobutane are reported. Six series, each differing in density, were performed in a quartz oscillating-disk viscometer from 297 to 627 K and for densities between 0.010 to 0.048 mol } L&1. Isothermal values recalculated from the original experimental data were evaluated with a first-order expansion, in terms of density, for the viscosity. Reduced values of the second viscosity virial coefficient derived from the zero-density and initial-density viscosity coefficients agree with the represen- tation of the Rainwater Friend theory when using energy and length scaling factors specific for the iInteractions of the isobutane molecules. With the same scaling factors an individual correlation in the limit of zero density was devel- oped including only a few values from the literature. The uncertainty of the zero-density viscosity correlation is estimated to be \0.40.