Excess and interaction second virial coefficients have been measured in the temperature range 290-320 K for 20 binary gaseous systems. Several of these systems have previously been studied by Brewer.' The present values are in excellent agreement with his results. The excess virial coefficients have been used to calculate excess molar enthalpies of mixing at 300 K. of a mixture BE B , , , -( X~B~~S ~2 B 2 2 ) Note that BE = 2x,x28.
Equivalent conductances and transference numbers were determined in dilute aqueous solutions of isotactic and atactic poly(styrene sulphonic acid) and of the corresponding sodium salts. The polyion mobilities in the polyacid and polysalt solutions differed significantly although the mobilities were independent of the stereoregularity of the polyion. The results obtained are interpreted in terms of the counterion association and of the counter ion retardation models.
The association of Li+ with SCN" has been studied in several aprotic solvents by 15N and 7Li NMR. The chemical shift variations are interpreted by an ion pairing equilibrium (dimethylformamide) or by a dimerization equilibrium (dimethyl carbonate, ether). A decrease of 16 with concentration is observed and this result shows the formation of N-bonded species in both cases. However, in tetrahydrofuran, the slight increase of " with concentration indicates the formation of small amounts of S-bonded species. This result is confirmed by the appearance of a weak absorption band at a frequency (2087 cm"1) which is much higher than for SCN" or for N-bonded species.
The optical rotatory dispersion curves in the visible region of the quinine salts of isotactic and atactic poly(styrene sulphonic acid) solutions show significant differences. The absorption spectrum of proflavine is changed in an identical manner by the addition of isotactic and atactic polyacids at low sulphonic acid residue/dye ratios. However, at high sulphonic acid residue/dye ratios at room temperature the proflavine has a lower extinction in the presence of the isotactic polyacid than in the presence of the atactic sample. At temperatures above 60°C the different quantitative effects of the isotactic and atactic polyacids on the proflavine absorption diminish. The results are discussed in terms of conformational differences between isotactic and atactic poly(styrene sulphonic acid) molecules in solution.
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