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The densities of D20/H20 mixtures relative to pure D20 and H20 have been measured with a Mettler-Paar vibrating densitometer at 10, 25, and 40 °C. The excess volumes calculated from the densities are very small and, within experimental precision, are independent of temperature. They are described by the relation (X = atoms of D/(atoms of + atoms of D)), ^/ 1) = X(1 -X) [(15.7 The results are not in agreement with the high-precision dilatometric measurements of Bottomley and Scott but are in agreement with older pycnometric determinations. Reasons for the differences are discussed in detail. The isotope effect on the partial molar volume of NaCI in a mixture of HOH and DOD was found to be proportional to the atom fraction, D/(D + H). The results are discussed in terms of the theory of isotope effects in condensed phase systems. The volume effects of HOH, DOD, and HOD are rationalized in terms of isotope effects on oxygen mean-square amplitudes by using a model due to Leadbetter.

The heats of mixing for binary mixtures of n-butyl amine with water, methyl alcohol, ethyl alcohol, n-propyl alcohol, and n-butyl alcohol at 40.00 ± 0.01 °C determined in a twin-type calorimeter can be fitted in an equation of the form AHmwhere x2 is the mole fraction of n-butyl amine; Xi is the mole fraction of the second component; B, C, and D are constants. The mixing is accompanied by evolution of heat, and the exothermic effect follows the order CH3OH > H20 > C2H5OH > n-C3H7OH > n-C4H9OH.As part of our program of research to investigate the effect of a gradual change in the size and shape of the substituent hydrocarbon group on the thermodynamic properties of a mixture of highly polar liquids, we present the results of studies on the heats of mixing of n-butyl amine with water, methyl alcohol, ethyl alcohol, n-propyl alcohol, and n-butyl alcohol.

Excess volumes are reported for the title solutions across the entire concentration range at 25 and 45 "C. For the solution of isotopic isomers, C&/C6&, the excess volume shows a complicated concentration dependence with a minimum of about -6 X m3/mol near X c , = 0.8 (25 "C). The effect is sensitive to trace water content. For benzene/cyclohexane solutions the volumetric isotope effects display simpler concentration dependences. Thus, the difference, pC6Hg/C6Hl2 -pCeDs,CsH12, within experimental error shows simple minima at Xbenzene = 0.5 of about -7 x (25 "C) and-12 x IO4 (45 "C) m3/moi. After comparing the present results for C6H6/C6H12 solutions with those of previous workers, we discuss isotope effects in terms of the theory of isotope effects on the properties of condensed phases.m3/mol near Xch = 0.33 and a maximum of about 2 x Experimental SectionDensities were measured with a Mettler-Parr DMA-60 vibrating densitometer using techniques previously described by us.&' The hydrocarbons were reagent grade and were further purified by fractional distillation. Deuteriocarbons were reagent grade. Tests for organic impurities in both hydrocarbon and deuteriocarbon samples were made by gas chromatography. The most likely impurity affecting the partial molar volumes is water. The problems which it introduces and our analysis of them are discussed at length in the next section. Hydrocarbons were kept on the vacuum line, over sodium, in closed vessels in the degassed state. In making up solutions, we transferred the degassed liquids via vacuum distillation into the mixing vessel and weighed them (still in the degassed state, i.e., Hook4) for the SOlUtiOnS C&j/C&,

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