The vapor viscosities of both normal and isopentane have been measured by the rotating cylinder method at different pressures ranging from a few millimeters pressure to the saturated vapor pressures all at 25°C. Twenty-eight measurements are given for normal pentane and thirty-seven for isopentane with an estimated accuracy of 0.2 percent. The plotted values for each compound shows a linear decrease with pressure, the slopes being nearly the same. The results may be expressed for normal pentane $\eta =(677.2-0.0084p)\mathrm{}\times {10}^{-7\mathrm{}}$ poises; for isopentane $\eta =(696.5-0.0077p)\mathrm{}\times {10}^{-7\mathrm{}}$ poises where $p$ is the pressure of the vapor in millimeters of mercury.

• Received 26 January 1932

DOI:https://doi.org/10.1103/PhysRev.40.281