The curvature of the surface of the liquid in a narrow tube leads to an apparent violation of the law of communicating vessels. If water lower in the presence of a narrow glassin (rice. 10.10, and), the water is drawn into the tube and its level is located at a height h above the water level outside the tube. The reason is, what laplacesche pressure p_L in the tube facing up.

It draws water up until then, until you are balanced by the hydrostatic pressure p_G of the water column in the tube height h, is t_G=pgh. Since p_L =2σ/R, when R_L =p have 2σ/R=pgh, where

In the complete wetting (Ɵ=0) the meniscus in a narrow tube has a hemispherical shape and the radius of the spherical surface R in (10.5) equal to the inner radius of the tube r; then

The incomplete wetting (Ɵ≠0) the radius of the meniscus R=r/cosƟ (rice. 10.10, in) and

From (10.5and, b) see, what height h the more, the smaller inner radius of the tube r. The rise of water has a significant value in the tubes, the inner diameter commensurate with the diameter of the voice (or even less); therefore, such tubes are called capillaries (from the Greek "capillaris" — hairline, thin). A wetting liquid in the capillary rises (rice. 10.10, and), a non-wetting — down (rice. 10.10, b). Phenomena, due to the retraction of wetting fluids into capillaries or by forcing the non-wetting fluids from the capillaries, called capillary phenomena.

In communicating vessels, one can observe different levels of liquid, if one of the vessels broad, and the other quite narrow (rice. 10.11, and — wetting liquid, b —non-wetting liquid).

The capillary phenomenon can be observed not only in the tubes, but in narrow cracks. If you omit in the water two glass plates so, so that between them formed a narrow slit, the water between the plates will rise, and the higher, the closer they are located. Capillary phenomena play an important role in nature and technology. Many tiny capillaries there are in plants. In the trees by capillary moisture from the soil rises to the tree tops, where through the leaves evaporates into the atmosphere. In the soil there are capillaries, those who already, the denser the soil. Water in the capillary rises to the surface and quickly evaporates, and the earth becomes dry. Early spring plowing destroys the capillaries, t. e. subsoil retains moisture and increases the harvest.

In the technique of capillary phenomena are of great importance, for example, in the process of drying of capillary-porous bodies and t. p. A large value of capillary phenomena in the construction business. For example, that brick wall is not syreli, between the house Foundation and the wall doing a strip of material, with no capillaries. In the paper industry have to consider the capillarity in the manufacture of various paper grades. For example, in the manufacture of writing paper it is impregnated with a special compound, bridging the capillaries. In the home of the capillary phenomenon is used in the wicks, in blotting paper, feathers for ink supply and t. p.