  We discuss structural and thermodynamical properties of Baxter's adhesive
hard sphere model within a class of closures which includes the Percus-Yevick
(PY) one. The common feature of all these closures is to have a direct
correlation function vanishing beyond a certain range, each closure being
identified by a different approximation within the original square-well region.
This allows a common analytical solution of the Ornstein-Zernike integral
equation, with the cavity function playing a privileged role. A careful
analytical treatment of the equation of state is reported. Numerical comparison
with Monte Carlo simulations shows that the PY approximation lies between
simpler closures, which may yield less accurate predictions but are easily
extensible to multi-component fluids, and more sophisticate closures which give
more precise predictions but can hardly be extended to mixtures. In regimes
typical for colloidal and protein solutions, however, it is found that the
perturbative closures, even when limited to first-order, produce satisfactory
results.
