AbstractThe phase‐equilibria data of the propane‐hydrogen sulfide system has been previously investigated from 32°F. to the critical locus. Since this represents about one‐half of the phase data, the primary purposes of the present study were to complete the data to the solid‐liquid‐vapor region which starts about —125°F. and to verify the results of other investigators at the higher temperatures.Five mixtures of propane‐hydrogen sulfide were studied, ranging from 8.6 to 78.3% propane, with the dew‐ and bubble‐point method. A temperature‐composition diagram for six isobars from 400 to 20 lb./sq. in. abs. presents most of the essential data. Vaporization equilibrium constants are tabulated together with thex‐ydata for these isobars. The data of Kay and Rambosek (3) and Steckel (4) were verified to within 2% except near the vicinity of the azeotrope.A new method was used to fix the temperature of the azeotrope for two of the five mixtures and a sixth mixture. The determination of the azeotropic temperatures was made by a graphical method in which the differences between the dew‐ and the bubble‐point pressures for each mixture were plotted against the temperature. The minimum value of the curve corresponds to the temperature of the azeotrope. The application of this method to the data of Kay and Rambosek (3) gave results which were in agreement with this study, while the original results by these authors as determined by an indirect method were in poor agreement.A measure of the reliability of the composition, temperature, and pressure data of the solid‐liquid‐vapor region was indicated when checks within 5% were found with Da