  Upon melting, the molecules in the crystal explore numerous configurations,
reflecting an increase in disorder. The molar entropy of disorder can be
defined by Bolzmann's formula dSd = Rln(Wd) where Wd is the increase in the
number of microscopic states, so far inaccessible experimentally. We found that
the Arrhenius frequency factor A of the electron diffraction signal decay
provides Wd via an experimental equation A = AINTWd where AINT is an inelastic
scattering cross-section. The method connects Clausius and Boltzmann
experimentally and supplements the Clausius approach, being applicable to a
femtogram quantity of thermally unstable and biomolecular crystals. The data
also showed that crystal disordering and crystallization of melt are
reciprocal, both governed by the entropy change, but manifesting in opposite
directions.
