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Karr, " Physical Properties of Low-Boiling Phenols. the Interior, 1957, Information Circular 7802. F. p. 99.929 & 0.006 0.848" f 0.004" 40.84" f 0.01" F. p. 99.963 f 0.002 0-596 f 0.009 30.97 f 0.01 M. p. 99.917 & 0.020 0.749 f 0-040 12-16 f 0.01 F. p-99.963 f 0.021 0.915 f 0.051 34-65 f 0.01 M. p. 99.928 f 0.005 0.502 f 0.019 72-53 f 0.01 M. p. 99.972 f 0.002 0.576 f 0.030 24.52 f 0.01 M. p. 99.896 f 0.020 0.727 f 0.008 74.77 f 0.01 F. p. 99.886 f 0.008 0-558 f 0-016 45.56 f 0.01 M. p. 99.971 & 0.005 0.727 f 0.020 65-09 f 0.01 M. p. 99.960 f 0.004 0.520 f 0.059 63.24 f 0.01 I;. p. €or 100% purity 40.90" f 0.01" 30.99 & 0.01 34.69 -J= 0.02 72.57 f 0.02 24.54 & 0.01 74.85 f 0-02 45-62 & 0.01 65.11 f 0-01 63.27 f 0.02 (tf, 0 ) f 0-02Vapour pressure-temperature relationships, normal boiling points, values of (dtldp) 760 mm., and latent heats of vaporization. The vapour pressures of the liquid and solid xylenols were measured by ebulliometric and gas-saturation procedures previously described.4~ 1 3 ~~4 Detailed results for the six xylenols are given in Table 2.Antoine equations [i.e., equations of the form log,, P = A -B/(t + C)] were fitted to the data for higher temperatures, and the two-constant equation log,, P = A -B/(t + 273) was used for the lower temperature range. Table 3 gives the constants of these equations and Table 4 shows the normal b. p.s; values of (dt/dP),so-.

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The absorption spectra and thermodynamic dissociation constants at 25" C of pyridine, the three methylpyridines, the three ethylpyridines and the six dimethylpyridines in aqueous solution are presented. The wavelengths and extinction coefficients of the absorption peaks and the dissociation constants are discussed in relation to the chemical structure of the pyridine bases.

The second virial coefficients of pyridine, a-picoline, B-picoline, y-picoline, 2 : 6lutidine, benzene, toluene, o-xylene, rn-xylene, and p-xylene have been obtained by means of vapour compressibility measurements at temperatures in the neighbourhood of the normal boiling points of the compounds. The measurements are discussed in relation to the principle of corresponding states. The second virial coefficients have been combined with vapour pressure measurements previously made in this laboratory to derive the latent heats of vaporization of pyridine and its homologues; similarly, the latent heats of vaporization of benzene and its homologues have been calculated with the aid of existing vapour pressure data. Finally, the heats of formation at 25" C in the idea! gas state of pyridine and its homologues have been derived from previous measurements