More Repeatable Moser and Poltz McLeod Gauge

Abstract

Modifications in design and operation are described which increase the repeatability of measurements made with Moser–Poltz McLeod gauges. Larger capillary chambers (≃1-mm diam and height) have been used which when combined with new reading techniques, attention to cathetometer use, awareness of electrostatic charge effects, and vibration, give a repeatability of 0.06 to 0.1 mm (95% confidence level) in reading h1–h2 in the operating equation P=v/(V1–V2)(h1–h2). This compares to the 0.2 to 0.4 mm realized earlier. Possible systematic errors due to heating of the gas by the light source and depression of mercury surfaces in operation when pertinent volumes are usually determined with water (undepressed surfaces) are discussed. Operational photographs, taken through a high-power cathetometer eyepiece, of the light reflected from the mercury surface are presented.