Mercury vapor streaming effect in McLeod gauges

In this paper the authors explain the experimental results, reported earlier, on the error made in measuring pressures below the vapor pressure of mercury with a McLeod gauge. Mercury vapor streaming effects the pressure measurement made by a cold trapped McLeod gauge. The percentage of errors in the pressure measured (i.e., Δp/P2%) agrees with Gaede’s transport theory and Takaishi’s kinetic theory of gas analysis of this problem. Below the vapor pressure of mercury the percentage error starts rising and rises to 10.3% forming a plateau and increases to 17%–19% below 2.67×10−3 Pa (2×10−5 Torr). This increase in pressure measurement error below 2.67×10−3 Pa (2×10−5 Torr) has been found to be in quantitative agreement with that predicted by Rambeau.