We used a pressure membrane extractor (Model 1020, Soil Moisture Equipment Corp.) to study the silica content at equilibrium with the decreasing pore sizes of amorphous silica. The principle is to extract the aqueous solution through a sequential process from the larger (micrometric) pores to the thinner (some nm) pores. Each extraction step is followed by an equilibration period. The measurements confirmed earlier observations [1,2] that the concentration in dissolved silica decreases when the extraction pressure increases. The direct conclusion is that the silica solubility is pore-size dependent. These results are interpreted with the Young- Laplace relationship, at constant silica-solution surface tension, which means to attribute an elasto-capillary pressure to the solid.