ADDITIVITY OF THERMODYNAMIC PROPERTIES OF ORGANIC-COMPOUNDS IN CRYSTALLINE STATE .2. HEAT-CAPACITIES AND ENTHALPIES OF PHASE-TRANSITION OF ALKYL DERIVATIVES OIL UREA IN CRYSTALLINE STATE

The heat capacities and enthalpies of phase transitions for urea and 1 3 alkyl derivatives of urea [methyl-, 1,1-dimethyl-, 1,3-dimethyl-, et hyl-, (1-methylethyl)-, tetramethyl-, 1,1-diethyl-, 1,3-diethyl-, buty l-, (1,1-dimethylethyl)-, 1,3-bis(1,1-dimethylethyl)-, tetraethyl-, oc tyl-, and (1-methylpropyl)urea] in the temperature range from 5 to 320 K have been measured by adiabatic calorimetry. The thermodynamic func tions of these compounds were obtained from smoothed heat capacity val ues. The results were used to show that an additive scheme for the cal culation of the thermodynamic properties of crystals of alkyl derivati ves of urea, without taking into consideration the phase distinctions in crystals, gives reasonable accuracy.