THERMODYNAMICS OF AMMONIUM HALOGENATED OSMATES .1. HEAT-CAPACITY AND THERMODYNAMIC PROPERTIES OF (NH4)(2)OSCL6 AT TEMPERATURES FROM 6 K TO 325 K

The heat capacity of ammonium hexachloroosmate (NH4)(2)OsCl6 was measu red at temperatures from T = 6 K to 325 K by adiabatic calorimetry. Tw o small anomalous regions were observed in the heat-capacity against t emperature plot. The lower one, from 80 less than or equal to (T/K) le ss than or equal to 140, had an excess molar enthalpy of (21.19 +/- 0. 04).R.K and an excess molar entropy of (0.198 +/- 0.006).R. The upper one, from 200 less than or equal to (T/K) less than or equal to 300, h ad an excess molar enthalpy of (19.51 +/- 0.04).R.K and an excess mola r entropy of (0.076 +/- 0.006).R. Smoothed values of the standard mola r thermodynamic quantities for pure (NH4)(2)OsCl6 are tabulated up to T = 350 K.