Computer‐automated measurement of high‐temperature vapor pressures by the simultaneous Knudsen torsion‐effusion method Available to Purchase

Data acquisition from high‐temperature vapor‐pressure measurements by the simultaneous mass‐effusion, torsion‐effusion method has been automated by interfaces to a laboratory computer. The apparatus consists of a torsion‐effusion pendulum suspended from a vacuum semimicrobalance. Rate of mass effusion is monitored by an analog interface to a retransmitting potentiometer on the chart recorder of the semicrobalance. Torque is measured by a digital interface to an array of photodetectors which register the torsion‐pendulum position by a reflected‐light method. Output from the balance is handled by one channel of an analog multiplexer and an analog‐to‐digital converter (ADC). The output from the ADC and the output from the torsion pendulum are fed to two channels of a digital multiplexer. With stored information about the torsion pendulum and the effusion cell, the computer calculates real‐time vapor pressures from both simultaneous measurements, and then the apparent molecular weight of the vapor. Early results from study of the vapor pressure over PbIn₂S₄(s)/Pb₂In₆S₁₁(s) are presented.