The Coefficients of Viscosity and of Slip of Air and of Carbon Dioxide by the Rotating Cylinder Method

Abstract

Coefficients of viscosity of air and of C${\mathrm{O}}_{2}$, determined by the constant deflection method.---With the rotating cylinder apparatus designed by Millikan and used by Gilchrist, Harrington, Yen and Stacy in measurements of high precision, a new determination has been made of the coefficient of viscosity of dry air. The value obtained, ${\ensuremath{\eta}}_{23}=1822.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$, is only 1/40 per cent less than the standard value of Harrington. The coefficient of viscosity of C${\mathrm{O}}_{2}$ obtained by the same method comes out ${\ensuremath{\eta}}_{23}=1471.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$. The gas used was from c.p. NaHC${\mathrm{O}}_{3}$, and since, after purification by freezing, various samples gave concordant results, this value is thought to be correct to within 1/20 per cent. Comparison with the results of Breitenbach indicates that all his values, though relatively correct, are 1.5 per cent too high.Coefficients of slip for rough and smooth surfaces in air and C${\mathrm{O}}_{2}$ were computed from values of the apparent coefficients of viscosity measured by this method for pressures of 0.5 to 0.1 mm. For an old shellac surface, the values came out in both air and C${\mathrm{O}}_{2}$ only 3 per cent greater than the theoretical lower limit computed by Millikan for a completely diffusing rough surface, in agreement with Stacy's result; while for a surface coated with watch oil, the coefficients in air and C${\mathrm{O}}_{2}$ were respectively 21 and 12 per cent higher, in good agreement with the corresponding values found by Millikan's oil drop method. For clean and scratched brass surfaces intermediate values were obtained.Fatigue of a watch spring steel wire, twisted under load.---In five years the period decreased 0.09 per cent, showing a gradual stiffening. A twist of 8\ifmmode^\circ\else\textdegree\fi{} for half an hour caused a temporary zero shift of 0.004\ifmmode^\circ\else\textdegree\fi{}.