THE DIELECTRIC CONSTANTS OF SOME INOR- GANIC SOLVENTS RY HERMAN SCHLUNDT About four years ago I commenced the study of the dielec- tric constants of pure solvents. The work was undertaken at the suggestion of Professor Kahlenberg, and was carried out in the Laboratory of Physical Chemistry of the University of Wis- consin. The results obtained appeared in two numbers of the Journal of Physical Chemistry,* and in complete form as a Bulletins of the University of Wisconsin. The values of the dielectric constants of about sixty pure solvents were determined. The results obtained enabled me to point out some new relations existing between this physical con- stant and the constitution of the compounds investigated. Moreover, as the ionizing power of a large number of sol- vents chosen for the measurements had been studied by Kahlen- berg and Lincoln,+ Lincoln,s and Waldeq6 the results had a special bearing on the Nernst-Thomson rule, according to which a close parallelism exists between the dissociating power of solvents and their dielectric constants. A number of exceptions to the rule were pointed out, and a number of new examples were found which followed the rule. The inorganic solvents studied followed the rule in a general way, although the parallel- ism between the ionizing power and the dielectric constant was far from close in several instances. The dissociating power of inorganic solvents has been dili- * An abstract of this paper was presented before Section C of the A. A. A. S. on Dec. 31, 1903. Jour, Phys. Chem. 5, 157,503 (1901). Science Series, Vol. 11, No. 6, pp. 353-389 (1901). *Jour. Phys. Chem. 3, IZ (1899). Ibid. 3, 457 (1899). 6 Ber. chem. Ges. Berlin, 32, 2862 (1899) ; Zeit. anorg. Chem. 25, 209 (Igoo). Die Zect ric Constants 0f Inorganic So Zven ts 123 gently studied since the appearance of my results, by Walden and his pupils.' Frankland and Farmer2 have made a thorough study of the solvent and ionizing power of liquid nitrogen tetroxide. The,dielectric constants of the solvents studied by these investigators have, for the most part, not been determined. In view of this fact and the importance attached to the relation of the dielectric constants to the ionizing power of solvents, it appeared desirable to continue the study of the dielectric con- stants of pure solvents. The present report embrzces the results obtained for the dielectric constants of some halogen compounds of phosphorus, arsenic, and antimony. The values found for the dielectric con- stant of phosphorus, silicon tetrachloride, and nitrogen tetroxide are also included. Method and Apparatus The dielectric constants were measured by Drude's well- known method.3 The apparatus used in the former measure- ments4 served for this work. A vacuum tube containing hydro- gen was used to determine the settings for maximum resonance. This particular tube was selected from a lot of tubes belonging to the Department of Physics. Professor Stewart kindly placed at my disposal his extensive collection of Geissler and other vacuum tubes. I tested about thirty of them, but found none that gave better results than the hydrogen tubes. It was ob- served that the tubes of uranium glass, and the tubes containing fluorescent solutions were specially sensitive to the oscillations. They responded far more readily than the hydrogen tubes, but it is difficult to judge the position at which maximum resonance occurs. Two cells of the type used for the measurement of sub- stances having low or medium values for dielectric constants served for condensers. The apparatus was calibrated for each cell for values ranging from 2.26 to 20.5 with the standard I Zeit. anorg. Chem. 29, 371 (1902); Zeit. phys. Chem. 39, 220 (1901). Jour. Chem. SOC. 79, 1356 (1901). Zeit. phys. Chem. 23, 267 (1897). Jour. Phys. Chem. 5, 157 (1901). 124 Herman Schlundt liquids recommended by Drude. The capacities of the cells differed somewhat. Both were used for each of the solvents in making the measurements. The values given below represent ' the average of the two independent determinations thus obtained. Whenever the two values for any one substance differed from each other by 5 percent or more, the measurements were re- peated. The methods of preparing and rectifying the various sol- vents will be found under each particular solvent in the state- ment of results given below. In most cases the specific con- ductivity of the solvents was measured. The Kohlrausch method for measuring conductivities *of electrolytes was followed. The range of the apparatus at my disposal for these measure- ments was rather limited. Specific conductivities less than 2 X IO-^ could not be determined with accuracy. Experimental Results Phosphorus Trichloride. -The sample used for the measure- ments was Kahlbaum's preparation. It was redistilled, boiling at 73.9" C under a pressure of 738 mm. The value found for its D. C. at 18" was 3.72. This value is somewhat higher than the one obtained when this substance was formerly measI1red.I The present value, 3.72, is probably nearer the truth than the older value of 3.36 at 22' C. Phosphorm Tribrmide. - The sample was prepared by dropping bromine slowly on red phosphorus. The crude product was poured off from the red phosphorus remaining and was rectified by several distillations. The sample which served for the measurements had its boiling-point at I 73.5" under a pressure of 757 mm. Its density at 20") as compared with water at 4O, was found to be 2.8856. Its specific conductivity was less than I X IO-^. The value found for its D. C. at 20" was 3.88. Phosphorus Triiodide. - This compound was prepared by slowly adding a solution of yellow phosphorus in carbon disul- phide to the required amount of iodide dissolved in carbon disul- Jour. Phys. Chem. 5, 512 (1901). Dielectric Constants of Inorganic Solvents 125 phide. The greater portion of the carbon disulphide was then distilled off, Upon cooling, crystals of phosphorus triiodide formed in the residual solution. The mother-liquor was poured off, and the crystals dissolved in a fresh portion of carbon did- phide, which was distilled off in part as before. The mother- liquor was again poured off from the crystals, and the adhering solvent removed by warming the crystals to 40" under dimin- ished pressure, The red crystals of phosphorus triiodide were protected from coming in contact with moist air. The melting- point was found to be 55" C. The D. C. of the solid sample at 20" was found to be 3.66. For the liquid at about 65" C the value 4.12 was found for the D. C. The positions for maximum resonance were well defined. Arsenic Trichloride. -The D. C. of this compound in the liquid state had been previously measured.I Its D. C. was again determined and found to be 12.6 at 17", which agreesfairlywell with former value of 12.35 at 219. Kahlbaum's sample was used for the measurements. It was redistilled. Its boiling- point was 129.3" under a pressure of 753 mm. Its specific con- ductivity was 3.8 X IO-^. The D. C. of the solid compound was found to be 3.6 at about - 50" C. To solidify the sample the cell was introduced for a short time into a cooling mixture of solid carbon dioxide and ether kept in a small Dewar test-tube. The temperature of the bath was nearly - 55". C. After the cell had assumed the temperature of the bath it was taken out and quickly placed in the apparatus and a setting made. After cooling it again, another setting was made. This operation was repeated until IO settings were obtained. Arsenic Tribromide. -The sample used for the measure- ments was Kahlbaum's preparation. It was redistilled under a pressitre of 20-22 mm. The melting-point of the crystals was 31" C. The liquid had a faint yellow tinge. Its specific con- ductivity was less than 2 X IO-^. The value found for the D. C. of the liquid at 35" was 8.83. The solid gave the value 3.33 at 20". Jour. Phys. Chem. 5, 512 (1901). x I 26 Herman Schdundt Arsenic Triiodide. -Kahlbaum's sample was recrystallized from benzene. Small red crystals were obtained, whose melting- point was found to be 146'. The specific conductivity of the liquid at 150' was 3.1 X IO+. The value 5.38 at 18" was found for the D. C. of the solid sample. The D. C. of the liquid, at about I~o', was 7.0. Antimony Tyibyomide. - The compound was prepared by slowly adding bromine to a quantity of finely powdered anti- mony somewhat greater than the proportion required by the formula. The product was purified by several distillations. The boiling-point of the sample was 286.4' under 736 mm pres- sure, and its melting-point was 93". The liquid had a slight yellow tinge. The specific conductivity at 100' was 5 x 10-5. The D. C. of the liquid at about 100' was 20.9. The solidgave the value 5.05 at 20'. Antimony Tyiiodide. - The sample was prepared by bring- ing together finely powdered antimony and iodine in small quan- tities and gently warming. The product was distilled twice. Dark red crystals melting at 167' were obtained. The specific conductivity of the liquid at 175' was 1.1 X 10-4' The D. C. of the liquid at about 175' was found to be 13.9. For the solid at 20' the value 9.1 was found. Phosphorus. - A sample of Kahlbaum's yellow phosphorus which had been kept in the dark was freed froin adhering water by means of filter-paper.