UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY Heat capacity and thermodynamic properties of equilibrium sulfur to the temperature 388.36 K, and the heat capacity of Calorimetry Conference coppera

The heat capacity of specially prepared orthorhombic sulfur has been measured in a low-temperature adiabatic calorimeter. Measurements from T ~ 6 K to near the melting temperature transition at Tfug = 388.36 K are reported for equilibrium sulfur: for the orthorhombic modification from T » 6 K to the temperature of the orthorhombic-to-monoclinic transition Ttrg = 368.3 K, and for the monoclinic modification from Ttrs to Tfus . The molar entropy AjS^/R and molar enthalpy function A^.H^/RT for orthorhombic sulfur calculated from this data set are (3.843 ± 0.010) and (1.776 ± 0.005), respectively, where T = 298.15 K, T 1 0, and R = 8.31451 J-K^-mol' 1 . Four measurements of the, enthalpy of the orthorhombic to monoclinic phase transition were made with three samples. At Ttrs , the average value for the enthalpy of transition AcrsH° is (401.3 ± 0.8 J-mol" 1 ) . The heat capacity of the orthorhombic phase is given by the equation: Cp<n/ (J-K^-mol1 ) = 15.830 + 0.023036 (T/K) for the temperature interval (290 to 368.3) K, and that of the monoclinic phase by Cp , m/ (J-K^-mol1 ) = 11.8498 + 0.035197 (T/K) for the temperature interval (368.3 to 388.36) K. Previous determinations of the heat capacity of sulfur are discussed in the text.