The heat capacity from 14 to 90deg;K and the enthalpies of transition and fusion have been measured for argonndash;oxygen mixtures containing 40.34 and 94.98 molpercnt; oxygen. A comparison of the spectroscopic and calorimetric entropy of the mixtures at their normal boiling points shows a discrepancy equal to the entropy of mixing of the pure components within the experimental error. For the 40.34percnt; mixture, a ldquo;humprdquo;hyphen;type transition not observed in xhyphen;ray work was present in the temperature range from 14ndash;25deg;K. For thebgr;ndash;ggr;transition in the 94.98percnt; mixture, positional as well as orientational disorder is occurring. The lattice model of Pople and Karasz for transitions and fusions in solids is entirely inadequate for the argonndash;oxygen system.
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