Vapor Pressure of Metallic Calcium

Abstract

Vapor Pressure of Calcium, 500-700° C., from Rate of Evaporation in Vacuum.—A drawn wire of calcium was coiled into an open helix and placed in a glass tube which was then evacuated and heated to a definite temperature for a definite time. From the loss of weight due to evaporation the vapor pressure was computed by using a formula derived from the kinetic theory but involving a correction factor for the reflection of molecules by the walls of the hot tube. This factor was assumed to be a constant of the apparatus and was determined by making measurements for zinc and cadmium whose vapor pressures are known. The calcium used had 1.6 per cent. Mg and 1.25 per cent. Ca${\mathrm{Cl}}_2$. The values obtained for 500 to 700° C. are well represented by the formula: $log p = 9.73-\left(\frac{\mathrm{I}0,\mathrm{I}70}{T}\right)$, the corresponding equations for zinc and cadmium being $9.4\mathrm{I}-\left(\frac{7070}{T}\right)$ and $9.02-\left(\frac{5940}{T}\right)$ respectively.