Laboratory measurements on the electrical properties of solid carbon dioxide (dry ice) were made over the frequency range 2.2 to 12 GHz. These give a dielectric constant which varies with density according to the Rayleigh mixing formula and is independent of frequency; at 1 g/cm3 the dielectric constant is 1.7. The loss tangent was below the sensitivity threshold of our measurement technique at all frequencies and densities used; we set an upper limit of 0.005.