COUPLING CONSTANT AND CHEMICAL SHIFTOF TETRAFLUOROBORATE ION
results applicable to very dilute solutions only. I n Table I11 it cnn be seen that at NaCl concentration of 0.11 m, where XCY = 0.566, the comparison between observed transport numbers and those calculated with eq 10 is already less satisfactory. In the two other cases where Stokes' original eq 9 has been verified at high concentrations (3 N HC1 and 1 N LiCl), S is negative and eq 10 again does not apply. It thus appears that the older Fuoss-Onsager theory underlying eq 9 describes the electrophoretic retarda-
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tion effect in aqueous solutions much better than the recent revised treatment. The refinements in this revised treatment of electrolyte conductance will show up to full advantage if the restriction XCY HzO acetoneHz0 > DMSO-H20 from high field to low field. The effect of the organic solvent component is more clearly seen in Figure 4. We have maintained the concentration of BF4- ion in moles/1000 g of solvent constant but varied the ratio of water-organic solvent. As the organic solvent component increases in concentration, widely divergent chemical shift changes are observed. DMSO causes a large low-field shift and JB-Falso decreases on adding DMSO. The behavior in DMSO-water mixture is unique and cannot be explained on the basis of hydrogen-bonded interactions at the BF4- ion. We suggest as before the specific solvation of the protolysis product of DMS027-30 at the BF4- ion.
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Acknowledgments. We thank Professor D. M. Grant for sending us the relevant parts of the Ph.D. Thesis of Dr. I
