Pressure measurements in the 0.01-30 torr range with an inclined-piston gauge

An inclined-piston pressure gauge is described that will supply a long-standing need in thermochemical research for accurate vapour-pressure determinations in the low and intermediate pressure range. Residual friction between the piston and the cylinder is minimized by a unique oscillatory method that is free of end thrust on the piston and allows full sensitivity of the gauge to be realized. The axial component of the weight-to-area ratio of the piston is determined by measuring the angle of declination with a goniometer that can be read to 1 sec. Accuracy of the gauge proper is estimated to range from 0.001 to 0.012 torr from lower to upper pressure limits respectively. Vapour pressure results on ice, water, 1-heptanethiol, 1-decanethiol, and hexafluorobenzene are described.