  We analyze the density distribution and the adsorption of solvent hard
spheres in an annular slit formed by two large solute spheres or a large solute
and a wall at close distances by means of fundamental measure density
functional theory, anisotropic integral equations and simulations. We find that
the main features of the density distribution in the slit are described by an
effective, two--dimensional system of disks in the vicinity of a central
obstacle. For large solute--solvent size ratios, the resulting depletion force
has a straightforward geometrical interpretation which gives a precise
"colloidal" limit for the depletion interaction. For intermediate size ratios
5...10 and high solvent packing fractions larger than 0.4, the explicit density
functional results show a deep attractive well for the depletion potential at
solute contact, possibly indicating demixing in a binary mixture at low solute
and high solvent packing fraction.
