A study has been made, using a static method, of the solubility of seven low-m.-wt. hydrocarbon vapours in two non-volatile liquids (dinonylphthalate and squalane) in the temperature range 20-40°C. It has been shown that spreading the liquid on kieselguhr does not affect the equilibrium state, but speeds up the attainment of equilibrium. The results are expressed in terms of the activity coefficients of the low-m.-wt. components and it is shown that all systems studied can be interpreted by means of equations of the Miller-Guggenheim or Flory-Huggins type. The interaction parameters so deduced provide additional evidence for differences between the energies associated with aliphatic-aliphatic, aliphatic-aromatic and aromatic-aromatic contacts in solution.

Replicate gas-liquid chromatographic based specific retention volumes, activity coefficients, and interaction parameters of ten solutes with poly(dimethylsiloxane) (PDMS) solvent at 303 K are reported. The average relative standard deviation of the former (three GLC columns) is 0.82%. The values moreover compare favorably with those reported previously for four PDMS used commonly as stationary liquids in analytical GLC. Static-determined activity coefficients and interaction parameters are also reported and compared with the GLC results. The internal consistency of the former lies within ±1.2%, while the averages of these agree with the GLC values to within ±0.5%, thus providing validation of the latter. Previously reported discrepancies between static and GLC-based activity coefficients and interaction parameters with PDMS solvents are therefore attributed to experimental artifact rather than fundamental principle.

The activity coefficients of benzene, cyclohexane, n-pentane, n-hexane, n-heptane and n-octane in the involatile solvents, dinonyl phthalate and squalane, have been determined over a solute mole fraction range 0.05 to 0.4 at 30°C using a vacuum microbalance. The results are analysed in terms of the Flory-Huggins equation by regarding the interaction parameter as an empirical quantity dependent on the composition of the solution. Values of the solute activity coefficient at infinite dilution in the solvent are derived from the analysis for comparison with values from gas-liquid&romatographic determinations. The technique is relatively quick compared to classical methods of determining activity coefficients of such systems and shown to be capable of good precision.

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