T H E DIELECTRIC CONSTANTS O F SOME LIQUID HYDRIDES B Y R. C. PALMER AND HERMAN SCHLUNDT
Measurements of the dielectric capacity of liquid hydrides have been extended,' and values are reported here for the dielectric constants of liquid phosphine and stibine, and liquid and solid ammonia. The dielectric constant of liquid ammonia was determined independently in 1899 by Goodwin and ThompsonJ2 and Coolidge,s but we have found no record of a value for solid ammonia. As the dielectric constant of the solid was found t o be much lower than that of the liquid, and the value of the liquid increases with lowering of temperature, a maximum value must intervene. Like many other substances the change in dielectric capacity of ammonia is abrupt and occurs at the melting point. The maximum value of the liquid, at - 7 7 O , was determined. We were restricted, in our experiments, to the use of . solid carbon dioxide and ether under diminished pressure for obtaining low temperatures. We found the preparation and liquefaction of ammonia and phosphine relatively easy operations in comparison with stibine. Since the boiling point of liquid stibine is only -18O, and its melting point, -91.5', lies above the temperature of the cooling bath used, it seemed rather strange at first t o meet with failures in securing the required quantities of this liquid. Beautiful mirrors of antimony appeared upon the walls of the connecting tubes, but only a few drops of liquid would accumulate in the condenser. Evidently the large volume of hydrogen generated simultaneously swept the stibine through the small U tube condenser too rapidly. By modifying the generator and using a tiny Cf. Schaefer and Schlundt: Jour. Phys. Chem., 13, 669 (1909). Phys. Rev., 8, 38 (1899). Wied. Ann., 69, 125 (1899).
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spiral condenser the desired quantity of liquid stibine was ultimately obtained. The measurements were made with the well-known apparatus of Drude as modified by Schmidt.‘ As the hydrides in question are gases at ordinary temperatures and atmospheric pressure, the measurements were conducted with the liquids in sealed cells. The U form of cell previously used2 answered very well here. The cells were calibrated with the standard solutions of benzene and acetone, and acetone and water as given by D r ~ d e . At ~ least two independent determinations were made with different samples of each of the liquids and in cells whose dielectric capacity differed somewhat. The cells were recalibrated for each determination with freshly prepared samples of the solutions used as standards. The length of the stationary electric waves produced by the apparatus in air was determined and found to be 71.5 cm. Preparation of Compounds.--In preparing the hydrides stress was laid on securing pure samples in the liquid state. After the different parts of the apparatus,-generator, drying trains, condenser, measuring cells, manometers, etc., had been sealed together, dry air was passed through the apparatus for an hour or two, and finally the apparatus was exhausted with a Geryk pump. The chemical action was then started and the gas condensed in a small condenser surrounded by Thilorier’s mixture which could be kept under greatly reduced pressure if desired. The final measurements were conducted with samples that had been redistilled in vacuo. The ammonia used in these experiments was prepared by allowing a concentrated solution of potassium hydroxide t o drop upon a quantity of ammonium chloride in a suitable generator. The gas was dried in the usual way, and after condensation the liquid was distilled into the calibrated measuring cells, which had been previously sealed to the condenser. The cells were finally sealed off and transferred to the Drude Drude’s Ann., g, 919 (1902). Jour. Phys. Chem., 13, 671 (1909). Zeit. phys. Chem., 23, 270 (1899).
Diebctric Coastants o f Sowe Liqziid Uydmdes
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apparatus where several sets of readings were made with each sample at several temperatures. The samples of liquid phosphine used were free from the hydride, P,H,. Two of the specimens were prepared by the interaction of potassium hydroxide solution and phosphonium iodide, and a third was obtained by the interaction of aluminium phosphide and water as given by Matignon.' The gaseous phosphine was dried b y passing through towers containing phosphorus pentoxide, after passing through a cooling condenser t o remove traces of P,H,. The liquid phosphine was finally transferred t o the cells by distillation in vacuo. With the exception of the rubber stopper of the generator all connections were glass seals. The samples of pure liquid stibine used were prepared by the method of Stock and Doht,3 as later improved by Stock and G ~ t t r n a n . An ~ alloy consisting of one part antimony and two parts magnesium by weight was first prepared. The metals powdered to pass through a 40 M sieve were thoroughly mixed, placed in an iron tube, and heated in an atmosphere of hydrogen t o a bright red heat, being finally kept a t a dull red heat for about one hour. The alloy thus formed was easily removed from the tube, being in the form of a brown powder. In preparing the stibine, the finely powdered alloy was gradually shaken into cold diluted hydrochloric acid. sp. gr., 1.06, which had previously been boiled to free it from air. The acid was kept cold during the reaction by shaking the generator which was immersed in a mixture of ice and brine. Before passing through the drying tubes of calcium chloride and phosphorus pentoxide the gas passed through moist glass wool and water in a U tube to absorb traces of hydrochloric acid that might be carried over mechanically from the generComptes rendus, 130, 1314, 1393 (1900). details of preparation and photographs of the apparatus used as well as detailed data on the measurements are given by R. C. Palmer in his thesis for the degree of Chemical Engineer, University of Missouri, June 1910. a Ber. chern. Ges., Berlin, 35, 2 2 7 0 (1902). * Ibid., 37, 885 (1904).
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ator. With the exception of a piece of pressure tubing connecting the generator and drying train all connections were glass seals. Stock and Guttman experienced no difficulty in liquefying and solidifying stibine in a simple form of condenser immersed in liquid air. To liquefy stibine with Thilorier's mixture kept under diminished pressure we found it necessary to cool the gases in a spiral condenser ending in a small bulb at the bottom whose outlet passed up through the spirals and was surrounded by them. The liquid stibine was colorless and of high refractive power, and was easily transferred t o the cells by distillation. The cells were finally sealed off at constricted places. We met with no accidents in these operations. Stock and Guttman state that gaseous and even liquid stibine have a tendency to dissociate with explosive violence. To prevent any explosion in sweeping back throughout the whole apparatus when the measuring cells were sealed off, a stopcock was placed between the condenser and the cell. Only a faint antimony mirror appeared in the capillary tube where it was sealed off. The unstableness of stibine, however, was always manifest by the plating of antimony mirrors in different parts of the apparatus during an experiment. Results.-The values obtained for the dielectric constants arc summarized in the following table : Unless otherwise specified the values refer to the substances in the liquid state under their own vapor pressure at the temperature given. ____ _-
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Substance
Ammonia
