The Coefficients of Viscosity and Slip of Carbon Dioxide by the Oil Drop Method and the Law of Motion of an Oil Drop in Carbon Dioxide, Oxygen, and Helium, at Low Pressures

Coefficient of viscosity for carbon dioxide, determined by the oil drop method, was found to be 1.478×{}10^-4 for 23^∘{} C and 76 cm pressure. This agrees well with Van Dyke's value 1.472×{}10^-4 obtained by the constant deflection method. The constant A in the modified form of Stokes' law came out 0.815.Motion of oil droplets in carbon dioxide, oxygen, and helium, at low pressures.---Measurements in these gases were extended to pressures of 1.9, 2.0, and 10 mm respectively, and to values of l/a, ratio of mean free path to oil drop radius, of 76, 130, and 71, respectively. The empirical correction factor to Stokes' law suggested by Knudsen and by Millikan, viz. f(l/a)=1+(l/a)(A+Be^-Ca/l) was found to hold for all. Moreover the value of ($A+B$) comes out the same for all within the experimental error, and equal to 1.175. The gases were carefully purified. A new atomizer for use at these low pressures was developed; otherwise the apparatus and methods were the same as those used by Ishida. Comparison with motion of large ions. The formulas of Lenard and Langevin for large ions are both the same as the empirical law for droplets, but the Wellisch formula cannot be extended to droplets whose mass is large with respect to the mass of a molecule.