Experimental vapor pressure and critical point of sodium

The pressure tube method employed previously to determine the high temperature vapor pressure and the critical point of cesium, rubidium, and potassium, was improved and used on sodium. The critical pressure was determined directly as 256.4 bars (3719 psia) with a standard deviation of 0.09 percent. Vapor pressure was determined experimentally from 1255 K (1800 F) up to the critical point. The value selected for the critical temperature was 2503.3 K (4506 R), which is the lowest temperature at which the critical pressure was observed. Regression analysis showed that the data over the full range were slightly better fitted by LnP = 10.627840 to 11936.171/T to 0.03997216 LnT (for P in Bars and T in K) than without the LnT term. This equation has a standard deviation of 1.1 percent from the data points