The behavior of a colloidal silica dispersion in the mixed solvent of H2O or D2O and 2-butoxyethanol (C4E1) is studied as a function of solvent composition and particle volume fraction. Under certain conditions, the silica particles undergo a phase transition (gas/liquid) that is reversible on dilution or cooling. Small angle neutron scattering measurements are performed on one-phase samples, and the resulting scattering curves are modeled using appropriate forms of the pair interaction potential. In D2O, the silica particles are highly charged and stabilized by Coulombic repulsion. As the C4E1 content of the solvent is increased, Coulomb forces are diminished and the particles behave as hard spheres. At higher C4E1 concentrations, attractive interparticle interactions become important and the particles behave like sticky hard spheres. The sticky hard sphere parameters obtained from fits to the scattering data compare well to those required by theory to match the observed phase boundary.