The Principles of Thermodynamics

Phases and Their Equilibria 199

whereas Helium-4 is Bosonic. From a purely thermodynamic perspective, this dis-

tinction can not be made use of. Helium-4 exists in four phases, solid, vapor, and two

liquid phases. There are two triple points and one isolated critical point.

FIGURE 10.7 Helium-4 Phase Diagram.

The accompanying figure displays the

phase diagram of Helium-4. What is to-

tally new from the Helium-3 case is that

now there is a continuous line of criti-

cal points separating the two liquid phases.

This is called the

λ

-transition line because

the specific heat curve at each of these

critical points resembles the greek symbol

λ

. At each of these