The Heat of Sublimation of Carbon

By using the most likely figures for the heat of dissociation of the ${\mathrm{C}}_2$ molecule (5.5 and 7.0 volts), it is shown that in saturated carbon vapor at temperatures from 4150 to 4700°K the partial pressures of both atoms and molecules are of the same order of magnitude. Statistical computations of the vapor pressure of solid carbon at these temperatures show that either the absolute vapor pressure as determined experimentally is entirely wrong or the pressure-temperature dependence is considerably in error. On the assumption that the absolute pressures are approximately correct, the heats of sublimation at 0°K into atoms and into molecules are 161 and 176 Cals. and 195 and 189 Cals. respectively for the 5.5 and 7.0 volt dissociation energies. The true values probably lie within these limits.