
210 The Principles of Thermodynamics
curve is practically flat as demanded by Nernst theorem, to be discussed in a later
chapter).
11.3.1 Anomalous freezing curves
An examination of even the small number of phase diagrams shown in chapter 14
tells us that not all freezing curves have positive slope in the P-T plane. A prime case
is that of water itself, whose freezing curve has a negative slope, although very small
in magnitude. The latent heat in going from solid to liquid is positive in this case.
But what is anomalous about water is the behaviour of its density below 4
◦
C;the
density decreases with temperature. More specifically, at the freezing point ...