2507per monomole of polyelectrolyte. Values of AHD were taken from the beiat available literature source;21 the missing data for iodic, p-toluenesulfonic, and trichloroacetic acids were obtained from other source^.^^^^^ As can be seen, the experimental results are spread out like a fan around the theoretical straight line. We must not forget, however, that the infinite line charge theory on which eq 4 is based is strictly valid only for extremely dilute solutions, whereas the experiments were carried out at finite concentrations. Also, the corrected values of AHm are only approximations for the enthalpy of transfer given by eq 4. As expected, the agreement between theory and experiment gets better at lower concentrations ( Figure 5), a finding which has been observed also in many previous studies. Although the nature of the counterions is definitely expressed even at concentrations as low as 0.006 mol/L, one may expect that their individuality will disappear at extreme dilution.Acknowledgment. The partial financial support of the Research Council of Slovenia is gratefully acknowledged.Densities of NaCl solutions in H20 and D20 have been measured with high precision at 15,30, and 45 "C by using a Mettler/Paar densitometer. The data in H20 are compared with the best results of earlier workers. Solvent isotope effects onbpparent molar volumes of NaCl solutions are large and, within experimental error, are proportional to m'/2. They are interpreted in the context of available extended Debye-Huckel theories and cliscussed in terms of the molecular structure of the solvents.

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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The deuterium isotope partition coefIicient CL has been detcrinined as a function of total pressure, temperature and degree of deuteriation for niethylcy~lol~exanc/hydrogen over Ni/A1203 Good agreement with theory has been obtained for the dcpcndencc on temperature but not for that on total pressurc or on the degree of deuteriation 1)