Pfund’s combination of the McLeod and Pirani pressure gages was studied with a number of gases. The calibration curves of pressure against galvanometer reading were found to be straight lines and, except for hydrogen, nearly interchangeable for all the gases used. By using a galvanometer of high sensitivity and introducing a compensating filament, the sensitivity of the gage was increased until a change in pressure of 1.5×10-9 mm of mercury would cause a change in deflection of 1 cm on the galvanometer scale.
Brief comments are made on the release of carbon monoxide and air from coconut charcoal and on the adsorption of air at low pressure by silica gel.
R. T. Cox, "A STUDY OF PFUND’S PRESSURE GAGE," J. Opt. Soc. Am. 9, 569-581 (1924)