Density of Potassium Chloride

Abstract

The density of potassium chloride has been determined by the method of "crystal suspension" in a liquid mixture of bromoform, $n$-hexanol, and $n$-pentanol. The density of the liquid mixture at the average suspension temperature of fifty-three different crystals was taken as the density of the potassium chloride. The value determined was: ${\rho }_{28.098{}_{}{}^{\circ }{}_{}{}^{}\mathrm{C}}=1.98651\mathrm{}\pm 0.00002 \frac{\mathrm{g}}{\mathrm{ml}}$ which when corrected to 25°C gave: $\{{\rho }_{25{}_{}{}^{\circ }{}_{}{}^{}\mathrm{C}},=1.98721\mathrm{}\pm 0.00002 \frac{\mathrm{g}}{\mathrm{ml}}\}\{=1.98715\mathrm{}\pm 0.00002 \frac{\mathrm{g}}{{\mathrm{cm}}^3}.\}$ It was found that six precipitations of potassium chloride from aqueous solutions with hydrogen chloride were necessary to effect purification to constant density (±4×${10}^{-6\mathrm{}}$ g/ml). Exposure of crystals to the atmosphere was found to produce some manner of surface contamination which resulted in a change of density by as much as 7×${10}^{-4\mathrm{}}$ g/ml within two hours. Storage of crystals over phosphorus pentoxide under vacuum eliminated this effect. An annealing of crystals for four hours at 50° below the melting point with gradual cooling over a period of four hours was found necessary to obtain agreement of suspension temperatures among different crystals. By combination of density and x-ray data, atomic weights have been calculated. The values of the atomic weights of fluorine and calcium were found to be 18.9967±0.0010 and 40.0851 ±0.0011, respectively. In the crystals of calcite, lithium fluoride, and potassium chloride which were used to obtain the data underlying these calculations, there is no evidence for a secondary structure as proposed by Zwicky.