Abstract
The authors identify the topological or configurational degrees of freedom in dense liquids as continuous line defects, labelled by the two-element group Z2. These defects are absent in perfect solids, and yield a topological contribution to the latent heat of melting. The topological entropy is universal (for dense atomic liquids) and equals R ln 2 per mole, as observed experimentally. The same value is obtained for the topological, molar entropy of melting of (loose) covalent liquids. The topological entropy of sublimation of atomic substances is also calculated to be 4.69 R per mole.