  In this paper we construct an effective field theory for a condensate of cold
Fermi atoms whose scattering is controlled by a narrow Feshbach resonance. We
show how, from first principles, it permits a hydrodynamic description of the
BEC-BCS crossover from which the equation of state, intimately related to the
speed of sound, can be derived. Specifically, we stress the non-universal
behaviour of the equation of state at the unitary limit of infinite scattering
length that arises when either, or both, of the range of the inter-atomic force
and the scale of the molecular field become large.
