T H E DIELECTRIC COXSTANT O F LIQUID PHOSGENE BY HERMAN SCHLUA’DT AND ALBERT F. 0. GERMANN
Beckmann and Junker1, in a study of the ebullioscopy of phosgene solutions, have pointed out that phosgene probably belongs to the group of solvents which, like benzene, possess little or no ionizing power. This conclusion was based on the observation that phosgene conforms to the rule adhered to by the members of this group, that certain organic acids, such as acetic and benzoic, are associated to double molecules when dissolved in it, while their anhydrides are not. Germann recently found, on the other hand, that solutions of aluminum chloride in liquid phosgene conduct the elect,ric current, the solvent being decomposed into carbon monoxide and chlorine in the process2. He has measured the conductivity of these solutions, and has found that the maximum conductivity is nearly one hundred thousand times the specific conductivity of the pure solvent, and hence it may be inferred that phosgene hardly belongs to the class of non-ionizing solvents, but rather to that of weakly ionizing solvents. I n this connection a knowledge of the dielectric constant was of interest. But no measurements of this constant were available. Thwing’s method3 of calculating the dielectric constant did not furnish a solution of the problem, for depending on the interpretation made of its structure, Germann4 has pointed out that liquid phosgene may have a dielectric constant in the neighborhood of 3.6 or in the neighborhood of 24.
Experimental Approximately two hundred cubic centimeters of technical phosgene, as supplied by Edgewood Arsenal, were purified in an all-gla~sapparatus by a method similar to that described by Germann and Gagos5,the only essential variation consisting in the use of a distilling tube in which effervescent evaporation instead of surface evaporation was employed for the fractionation of the sample. Fifty cubic centimeters of pure phosgene were thus obtained, whose vapor tension at zero remained constant a t 5 5 7 mm. during distillation. For the measurements of the dielectric constant, Drude’s method6 with the modifications made by Schmidt’ was used. Four condenser bulbP, numbered I , 2 , 4 and 7, of which numbers I and 2 happened to have identical capacities, were filled with the purified phosgene. Two other bulbs were filled with impure phosgene, and the dielectric constant measured in order anorg. Chem. 5 5 , 371 (1907). Science, 61, 7 0 (1925). Z. physik. Chem. 14, 286 (1894). J. Phys. Chem. 28, 879 (1924). J . Phys. Chem. 28, 965 (1924). Z. physik. Chem. 23, 267 (1897). Ann. Physik. (4), 9, 919 (1902).
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3 54
HERMAN SCHLUNDT AND ALBERT F. 0. GERMANN
to determine the effect of the impurities usually present in technical phosgene as prepared by the Chemical Warfare Service. I t was found that the dielectric constant of the pure and of the impure phosgene was very nearly the same. For the calibration of the condenser bulbs, thiophene free benzene, and solutions of specially purified acetone in benzene were used, the dielectric constants of which are given by Drudel for use as standards. Five standards were prepared, three having valuee for the dielectric constant below that of phosgene, and two above. These values were plotted against the bridge readings for maximum resonance, and by interpolation of the bridge readings obtained with the four samples of pure phosgene, four values of the dielectric constant of liquid phosgene a t 22' and oo were obtained. Each bridge reading used in the curves is the average of ten concordant observations, five by each of two observers.
TABLEI Bridge Readings D. C. of cell liquid at 22'
Cell
6.82 5.04 3.53 2.94 2.25
46.58 49.60 51.65 52.87 54.30
c0c12(22°) C0C12(o0)
49,72
2
Cell 4
Cell 7
46.77 49.29
39.50 43.32 47,48 49.28 51.50 45.25 44.05
30.86 35.97 41.12 43.86 47.05 38.35 37.37
Cell
I
51.65 52.93 54.36 50.35 49.62
50.25
Table I records the values used to deduce the dielectric constant of phosgene, and will be self-explanatory. Table I1 contains the values for phosgene as read from the curves, dielectric constant values plotted against scale readings.
TABLEI1 Dielectric Constant of Liquid Phosgene Cell
22O
O0
I
4.368 4.352
4.704
2
4 7
Average Loc. cit.
4.320 4.312 4.338
4.832 4.760 4.600 4.724
355
DIELECTRIC CONSTANT O F PHOSGENE
The four cells show remarkable agreement in the value given for phosgene a t 2 2 O , but the agreement is much less good a t oo, because the tubes had to be taken from the cooling bath and transferred t o the apparatus, where temperature changes began to occur. The temperature coefficient calculated, - 0.470 per degree a t 2 2 O , is sufficient,lyaccurate, however, for most purposes.
Conclusion The dielectric constant of liquid phosgene has been found at 4.34 k . 0 2 , and the temperature coefficient, -0.4% per degree.
22OC.
to be
Acknowledgment Our thanks are due to members of the Chemical VC'asfare Service for supplying us with liquid phosgene for this investigation. University o j Missouri and Stanford University, Cal$ornia.
