rect, but heat capacities are not available in the literature. However, we think that such a correction would not substantially modify our values of excess entropy. This view is supported by comparison with the Ga-Bi system (9) which is analogous to the Ga-Pb system in many aspects. In fact, excess entropies are positive in bismuthrich alloys (-0.07 e.u. at 90 at. % Bi) and negative at intermediate compositions (-0.2 e.u. at 30 at. % Bi). This is not surprising, because lead and bismuth are neighbors in the sixth period of the Periodic Table and have similar properties as shown in Table III. As one can see, the difference in electronegativity for Ga-Bi alloys is greater than or at least equal to that for Ga-Pb alloys. Taking into account the errors which affect the electronegativity values, one could attribute the differences of excess entropies between Ga-Bi and Ga-Pb alloys to electronic peculiarities. This seems supported by the maximum mixing enthalpy of Ga-Pb alloys which is larger than that of Ga-Bi alloys (920 and 504 cal/g-atom, respectively)• At present, we cannot regard the excess entropies of Ga-Pb alloys as more reliable than those of Predel and Stein for our assumption on Newman-Kopp law validity.Further calorimetric measurements of mixing enthalpies at 1143K should be carried out to get entropy values from direct experimental data.
Literature Cited(1) Elliott, R. P., "Constitution of Binary Alloys," 1st suppl., McGraw-Hill, New York, N.Y., 1965. (2) Freeman, R. D., "Momentum Sensors," In "The Characterization of High Temperature Vapors," J.
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