  We discuss free-free radio emission from ionized gas in the intergalactic
medium. Because the emissivity is proportional to the square of the electron
density, the mean background is strongly sensitive to the spatial clumping of
free electrons. Using several existing models for the clumping of ionized gas,
we find that the expected free-free distortion to the cosmic microwave
background (CMB) blackbody spectrum is at a level detectable with upcoming
experiments such as the Absolute Radiometer for Cosmology, Astrophysics, and
Diffuse Emission (ARCADE). However, the dominant contribution to the distortion
comes from clumpy gas at z < 3, and the integrated signal does not strongly
constrain the epoch of reionization. In addition to the mean emission, we
consider spatial fluctuations in the free-free background and the extent to
which these anisotropies confuse the search for fluctuations in 21 cm line
emission from neutral hydrogen during and prior to reionization. This
background is smooth in frequency space and hence can be removed through
frequency differencing, but only so long as the 21 cm signal and the free-free
emission are uncorrelated. We show that, because the free-free background is
generated primarily at low redshifts, the cross-correlation between the two
fields is smaller than a few percent. Thus, multifrequency cleaning should be
an effective way to eliminate the free-free confusion.
