Niobium pentafluoride was prepared by fluorinating the metai with elemental fluorine at 300°. The melting point was found to be 78.9 ± 0.2°, the boiling point 233.3 ± 0.5°, and the heat of fusion was estimated to be 8600 cal./mole. A sample of the compound was distilled in a 20-plate column. The vapor pressure of the middle fraction was measured and may be expressed by equation (1). Using the value of the heat of fusion given above, the vapor pressure over the solid may lie expressed by equation ( 3). The liquid density was measured in the range of 86 to 125°and may be expressed by equation (4The following thermodynamic quantities for the vaporization process were calculated from the vapor pressure data and corrected for deviation from ideality by the density measurements:
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