This paper presents several studies essentially on the solid/liquid interface. The studied system is the liquid binary mixture water- 2,5dimethylpyridine (2,5DMP) in contact with an amorphous silica (Aerosil type). The study of wetting along the two-liquid bulk phases coexistence in contact with silica allows the determination of a wetting transition temperature, which is an important parameter for the adsorption behavior at coexistence. The adsorption isotherms in a diluted phase and in a concentrated phase present some very significant features. In diluted solutions the isotherms show a succession of plateaus; these transitions of layers persist in concentrated phases presenting a sequence of maxima and minima of relative adsorption (Gibbs adsorption) of 2,5DMP with respect to water. In concentrated solutions, they interfere with the prewetting that gives an original shape to the isotherms in concentrated solutions. These adsorption measurements were completed by activity measurements which allow one to obtain the chemical potential of mixtures and linked information. The whole study shows the behavior of colloidal suspensions close to bulk phase changes.