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This paper documents the construction details and experimental procedures for the continuously weighed pycnometer used in our laboratory to measure fluid properties such as densities, saturation pressures, phase boundaries, and isothermal compressibilities. This apparatus consists of a cell suspended from an electronic balance at all times and a variable volume bellows cell which is used to adjust the confined sample density within an isothermal enclosure. The principal advantages of this apparatus are rapid measurement and relatively high accuracy. Some experimental results are presented to illustrate capability. The accessible experimental ranges are 100−450 K up to 200 MPa; measurement accuracy is 0.1% or better.

This paper reports PVT measurements for five gravimetrically prepared mixtures of CO 2 + N 2 from 225 K to 450 K at pressures up to 70 MPa. These results have been determined using a continuously-weighed pycnometer. A detailed error analysis indicates that the accuracy of the densities is better than (0.1%. Additional PVT data for CO 2 + N 2 mixtures have been measured by Netherlandse Gasunie, Ruhrgas, and Gaz de France as reported by Jaeschke and Humphreys (1990).

A flexible foil mixer is described which is gravity driven and which assists in the preparation of gas mixtures of accurately known composition. This mixer, which is simple, inexpensive, and easy to construct, does not limit the operating temperature and pressure ranges of the containment vessel.

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