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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.