INDUSTRIAL AND ENGINEERING CHEMISTRY
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* I n the case of phenanthrene and naphthalene the results given here are often very different from those obtained by Nelson and Senseman. Inspection of Fig. 2 indicates that, judging from the standpoint of the log P vs. 1/T curves, the data of Nelson and Senseman are somewhat in error for these substances. I n the case of phenanthrene this may be due to the use of an impure product. The melting point of the phenanthrene used by them was 100.Oo C. This, calculated from the melting point curve (unpublished data), is equivalent to at least 5 per cent of anthracene, the presence of which would tend to raise the boiling point and lower the vapor pressure.
VoI. 15, No. 11
given here for comparison: carbazol, 338.06 and 351.5;' fluorene, 305.08and 295.0;$ acenaphthene, 277.5.lO In a recent article Mortimerll reviewed the principles relating the vapor pressures and sublimation pressures with the heats of vaporization, sublimation, and fusion. The data given in Table VI11 are pertinent to the calculation of the vapor pressures of these substances. This calculation is accomplished by introducing the appropriate values for the constants C and S , found in Table VIII, in the equation, log P = C - S / T , in which P is the pressure in millimeters a t the absolute temperature T . The corresponding constants for the calculation of the sublimation pressures of anthracene and carbazol are also included. Similar sublimation pressure data might have been given for the other substances, but on account of the greater extrapoIation (lower melting point) the calculation of sublimation pressures for these substances is less accurate. TABLE VI11 SUBSTANCE Naphthalene Acenaphthene Fluorene Phenanthrene Anthracene Carbazol Anthracene (solid) Carbazol (solid)
FIG. 2
,*-*~ :1.
,
The presence of impurities, however, wili not account for the differences in the case of naphthalene. It is the opinion of the writers that the method used by Nelson and Senseman is at fault, at least for substances which may decompose, in one particular. The heating bath wed by them was arranged to give very slow cooling. The writers have found that if cooling takes place too slowly there may be sufficient decomposition of these substances, after the confining liquid stops boiling and before equilibrium is reached, to cause appreciable differences in the measured pressure. At temperatures near the boiling point, equilibrium is reached more quickly and the two sets of data are in fair agreement, the observed boiling points being identical for naphthalene. Apparently, no measurements of 'the vapor pressures of acenaphthene, fluorene, ahd carbaz01~are given in the literature. The following points have been recorded, and are Since this paper was written Senseman and Nelson, THISJOURNAL, The boiling point is found by the authors to be 353' C.; Senseman and Nelson obtained 354.76' C. 6
16, 382 (1923),have published data on this substance.
Absolute Boiling Point
491.0 550.3 571.0 611.5 615.0 626
.... ....
S
C 7.901 8.033 8.089 7.771 7.910 8.280 10.972 10.982
Calories per Mol
10,450 12,010 12 510 12'660 13'100 14:310 19,990 20,710
Column 5, Table VIII, contains the values of the molecular latent heats of vaporization (or of sublimation). The values for the heats of vaporization have been calculated from the expression L = 4.23 X S. The constant 4.23 has been used instead of 4.58 (1.9885 X 2.303), because it has been shown'l that the constant 4.58 gives results which are about 8 per cent greater than those determined calorimetrically. The heats of sublimation for anthracene and carbazol were calculated by adding the molecular latent heats of vaporization and of fusion. Finally, a comparison of the calculated sublimation pressures of anthracene may be made with the experimental results given by Niederschulte.12 It was found that the experimental points given by this observer fell quite closely t o the calculated log P vs. 1/T curve, the deviations being both positive and negative. These calculated sublimation pressures are incIuded in Table VII. Stelzner'3 has also determined the pressures of anthracene at temperatures below the melting point. Access was not had' totthe original article, but it is quite evident that the determinations were made on a solution of anthracene rather than on the solid, because the data fall upon the extrapolated vapor pressure curve rather than upon the sublimation pressure curve. 6
7 8 9
10
11 12
Graebe and Glaser, Ber., 5, 12 (1872). Chemical Rubber Handbook, 1920, p. 161. Barbier, Ann. chim. fihys. 151,7 , 479 (1876). Chemical Rubber Handbook, 1920, p. 185. Behr and van Dorp, Ann. Chem. Pharm., 172, 263 (1874). J. Am. Chem. Soc., 44, 1429 (1922). I,andolt and Bbrnstein, Tabellen, 1912, p. 394; Dissertation, Erlan-
gen, 1903. 1s Landolt and Bbrnstein, Tabellen, 1912, p. 394; Dissertation, Erlangen, 1901.
Dr. Sosman Honored OF the Geophysical Laboratory,
R. B. Sosman, has been appointed by the National Research Council as American Member on the Permanent Committee for the Standardization of PhysicoChemical Symbols of the International Union of Pure and Applied Chemistry. The other members of the committee are: Ernst Cohen, University of Utrecht, chairman; Alexander Findlay, University of Aberdeen; and Charles Marie, Sorbonne.
