  White dwarfs can be used as galactic chronometers and, therefore, provide
important information about galactic evolution if good theoretical models of
their cooling are available. Consequently, it is natural to wonder if all the
sources or sinks of energy are correctly taken into account. One of these
sources is partial differentiation of the chemical components of the white
dwarf upon crystallization. In this paper we use a new formalism to show that
if there is a redistribution of the elements inside the star, there is a net
release of energy that has to be radiated away and that slows down the cooling
rate of the white dwarf.
