Surface tension of liquids and capillary phenomena

If the attraction between liquid and solid molecules is stronger than the attraction between the liquid’s own molecules, the liquid wets the solid (water – glass, soapy water – skin); if weaker, it does not wet (mercury – glass, water – oily feather). A wetting liquid has a concave surface near the vessel wall (the meniscus curves upward), a non-wetting one a convex surface. Very narrow tubes are capillaries; a wetting liquid rises in a capillary, a non-wetting one sinks. The rise stops when the surface tension force F = σ·2πr equals the weight of the column mg = ρ·πr²h·g, so h = 2σ/(ρgr). The smaller the radius, the greater h. Capillary phenomena appear in the rise of water in plants, in the evaporation of soil moisture and in the dampening of foundations; loosening the soil breaks the capillaries and keeps the moisture.