  We consider the topological susceptibility for an SU(N) gauge theory in the
limit of a large number of colors, $N \to \infty$. At nonzero temperature, the
behavior of the topological susceptibility depends upon the order of the
deconfining phase transition. The most interesting possibility is if the
deconfining transition, at $T=T_d$, is of second order. Then we argue that
Witten's relation implies that the topological susceptibility vanishes in a
calculable fashion at $T_d$. As noted by Witten, this implies that for
sufficiently light quark masses, metastable states which act like regions of
nonzero $\theta$ --- parity odd bubbles --- can arise at temperatures just
below $T_d$. Experimentally, parity odd bubbles have dramatic signatures: the
$\eta'$ meson, and especially the $\eta$ meson, become light, and are copiously
produced. Further, in parity odd bubbles, processes which are normally
forbidden, such as $\eta \to \pi^0 \pi^0$, are allowed. The most direct way to
detect parity violation is by measuring a parity odd global asymmetry for
charged pions, which we define.
