
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