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Recent measurements have shown1 that the compressions of benzene and a number of its monosubstituted derivatives over considerable ranges of pressure may be well represented by the Tait equation2where k is the decrease in volume per unit volume when the pressure is raised from Pq to P kilobars. B, a function of the temperature, is a constant characteristic of the liquid or liquid mixture, and C is a constant independent of temperature and the same for all the derivatives of benzene we have examined. In this paper we shall give data on the thermal expansions of the liquids mentioned in the title, give more complete compressibility data, and discuss some of the thermodynamic quantities derivable from these measurements, including the pressure-temperature coefficient {dP/dT')v which, following Hildebrand,3 4we shall denote as y, and especially the energy-volume coefficient (dE/d V)T. ExperimentalThe compressions of the liquids to various pressures up to 1000 bars were measured at 25,45, 65 and 85°in vitreous silica piezometers in our latest pressure apparatus,1 and depend on the same constants for vitreous silica and mercury that were employed in the investigation of benzene.5The specific volumes of the liquids at atmospheric pressure were measured at intervals of 10°between 25 and 85°in a weight dilatometer of the type used by Burlew8 and by Pesce and Holeraann.' The dilatometer, made of vitreous silica, is shown diagrammatically in Fig. 1. Its chief merits are simplicity and ease of manipulation. By following Bttrlew's design of having the open end of the capillary above the dilatometer, we were able to avoid the complicated thermostat used by Pesce and Holeinann, and by having an opening at the top of the dilatometer bulb we were able to fill it readily with solutions whose (1) R, E. Gibson and O. H, Loeffler, J. phys. Chem.t 43, 207 (1939).(2) This equation in the differential form was proposed by Tait in 1881 to fit the compressibility data for water. It was rederived by A. Wohl [Z. physik. Chem., 99, 234 (1921)], who applied it to some organic liquids, and it was later applied successfully to the existing data on a large number of liquids by H. Carl [ibid., 101, 238 (1922)]. who showed that the constant C did not depend on the temperature.(3) W.

The various criteria as to the quality and sufficiency of platinization in the measurement of the conductance of electrolytes are discussed and compared; and a test based on the variation of apparent resistance with frequency is recommended.2. The addition of lead acetate to the platinizing solution, as recommended by Kohlrausch, is helpful. Cambridge, Mass.

Synopsis It is shown that the factor of safety against undrained failure of a slope cut in an ideal normally consolidated clay whose undrained shear strength increases linearly with depth, depends not upon the height but only upon the inclination of the slope, the ratio and the bulk density of the clay. The calculation of the factor of safety is facilitated by the use of a stability number which is related to the slope inclination alone: this relation is presented graphically in the Paper. Il est démontré que le coefficient de sécurité qui joue dans la rupture d'une pente taillée dans une argile normalement consolidée dont la résistance au cisaillement à teneur en eau constante augmente d'ne façon linéaire avec la profondeur, dépend non de la hauteur mais seulement de l'angle de la pente, du rapport et de la densité apparente de l'argile. Le calcul du coefficient de sécurité est rendu plus arisé par l'emploi d'un facteur de stabilité qui n'est lié qu'a l'angle de la pente: ce rapport est représenté graphiquement dans l'article.

was found to be 1.630, and its mean compressibility between 6000 and 12,-000 bars at about 22°, 4.8 X 10-6 per bar. A method for calculating the heat of fusion from solubility data gives a value which is in fair agreement with that determined from the initial slope of the melting curve, the average value being 32 cal. per g. of NaCl-2H20.A secondary pressure increase, that is, a continued rise of pressure following a sudden increase, was observed at pressures near the maximum on the curve, and an explanation is given for this phenomenon.

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