
264 The Principles of Thermodynamics
higher than linear growth, while for temperatures higher than this, the formula yields
a marginally lower than linear growth. It is clear from the formula that the curve must
touch the T-axis with zero slope, but this is very hard to see from the graph. Thus the
observed surface tension exponent is
β
=1.256, which is indeed greater than unity
as required by entropic considerations discussed earlier.
13.3 Critical behaviour of van der Waals theory
The vdW equation is easily the simplest equation of state for a system that displays
liquefaction of gases, as discussed at length in chapter 12. In fact, it was the first ...