Measurement of the Critical Parameters and the Saturation Densities of Dimethyl Ether

On the basis of the direct visual observation of the meniscus disappearance and reappearance in an optical cell, 17 saturated liquid densities and 8 saturated vapor densities of dimethyl ether were measured in the temperature range from 301.816 K to the critical temperature, corresponding to a density range from (66.75 to 654.54) kg·m-3. The maximum uncertainties of the saturated liquid and vapor densities are ±0.15 kg·m-3 and ±0.10 kg·m-3, respectively. The uncertainties of temperature were estimated to be within ±5 mK. The critical temperature Tc and density ρc were determined as (400.378 ± 0.005) K and (272 ± 2) kg·m-3 by taking into consideration the meniscus disappearance and reappearance as well as the intensity of the critical opalescence. The critical pressure was (5356 ± 10) kPa extrapolated from the vapor pressures data with the Wagner equation. We have also determined the critical exponent β and the critical amplitude B on the basis of a correlation of the vapor−liquid coexistence curve.