The Four-Sinker Densimeter: A New Instrument for the Combined Investigation of Accurate Densities and Sorption Phenomena of Pure Gases and Gas Mixtures

An apparatus for high-accuracy gas density and adsorption measurements over the range of temperature from (193 to 423) K and pressure from (0 to 15) MPa is described. This instrument is based on the two-sinker densimetry principle and incorporates a magnetic suspension balance. In addition to the two “density sinkers”, two “sorption sinkers” are weighed to investigate density and adsorption of a gas sample simultaneously. The design of the sinkers increases the resolution of density and adsorption investigations and enables the correction of sorption effects on density measurements. The complete apparatus, including the sinkers, the temperature and pressure measuring systems, and the measurement procedure, is described. For the density range investigated, the uncertainty (k = 2) is between (0.0034 to 0.019) kg \(\cdot\) $·$ m⁻³, corresponding to (0.060 to 0.011)%. The uncertainty (k = 2) in adsorption load is (0.16 to 0.26) \(\upmu\) $\mathrm{\mu }$ g \(\cdot\) $·$ cm⁻². Density measurements at T = (283 and 293) K and pressures up to 10 MPa of high-purity argon and nitrogen validate the instrument for density. Adsorption measurements of high-purity carbon dioxide and propane on a gold surface validate the instrument for adsorption investigation at T = (283 and 293) K and up to the saturation pressure of the investigated gas. The apparatus was used to measure the binary mixture (0.75 \(\text{CO}_2\) ${\text{CO}}_2$ + 0.25 \({\text{C}_3\text{H}_8}\) ${\text{C}}_3{\text{H}}_8$ ). In the future, the apparatus will also be used to accurately determine dew-point densities and pressures of pure gases and gas mixtures.