
220 The Principles of Thermodynamics
the nature of the systems went into that. In particular, details like whether a system
is magnetic or not also did not enter those considerations. Of course, for magnetic
systems, one must include B
e
in addition to (P,T) as the independent variables. As
explained in chapter 10, it is the magnetic Gibbs potential G
M
that has to be used
for determining the equilibrium conditions, rather than the usual Gibbs potential G.
More precisely, it is the magnetic Gibbs potential per unit mass g
M
that needs to
be used. As explained in chapter 10, the contribution of the magnetic field energy
density
B
2
e
2
μ
0
need not be explicitly in ...