Seismic waves may be attenuated in the Earth's outer core if it contains a slurry. The damping will be appreciable only if the time for the transition between solid and liquid is comparable with the period of the wave. This reaction time has been estimated for certain regions of the Earth's mantle as about 1 s. Here the same calculation is done for iron in the core giving a reaction time lower than 10−-9s. This means that waves will pass unattenuated at the phase speed appropriate to equilibrium between liquid and solid.