![]() ![]() He observed that the effect was the same in thick tubes as in thin, and concluded that only those particles of the glass which are very near the surface have any influence on the phenomenon. ![]() Trans., 17), who ascribed the action to an attraction between the glass and the liquid. 551), Leonardo da Vinci must be considered as the discoverer of capillary phenomena, but the first accurate observations of the capillary action of tubes and glass plates were made by Francis Hawksbee ( Physico-Mechanical Experiments, London, 1709, pp. 402) made experiments to determine the greatest distance at which the effect of these forces is sensible, and he found for various substances distances about the twenty-thousandth part of a millimetre. It is only when the distance becomes exceedingly small that these forces become perceptible. These forces are quite insensible between two portions of matter separated by any distance which we can directly measure. The forces which are concerned in these phenomena are those which act between neighbouring parts of the same substance, and which are called forces of cohesion, and those which act between portions of matter of different kinds, which are called forces of adhesion. ![]() The action between the capillary tube and the water has been called capillary action, and the name has been extended to many other phenomena which have been found to depend on properties of liquids and solids similar to those which cause water to rise in capillary tubes. When such a tube of glass, open at both ends, is placed vertically with its lower end immersed in water, the water is observed to rise in the tube, and to stand within the tube at a higher level than the water outside. A tube, the bore of which is so small that it will only admit a hair (Lat. Because of this, there is a rise in the level of liquid inside the capillary as shown. CAPILLARY ACTION. Thus, in order to maintain the same pressure, the liquid in the capillary rushes into the capillary. The shape of liquid meniscus in the capillary is concave.īut the points B and D are at the same horizontal level. Because of this, there is a drop in the level of liquid inside the capillary as shown.Ĭonsider a capillary tube dipped in a liquid which wets the surface. Thus, in order to maintain the same pressure, the liquid in the capillary rushes out of the capillary. The shape of liquid meniscus in the capillary is upper convex.Īs the points A and C are at the same level, the pressure at both these points is the same, and it is the atmospheric pressure.īetween the points C and D, the surface is plane.īut the points B and D are at the same horizontal level. The pressure on the concave side is always greater than that on the convex side.Ĭonsider a capillary tube dipped in a liquid which does not wet the surface. Let p A, p B, p C, and p D be the values of the pressures at the points A, B, C, and D respectively. Iv) Point D is just below the plane surface and outside the capillary, and below the point C. Iii) Point C is just above the plane surface outside the capillary. Ii) Point B is just below the convex surface inside the capillary. I) Point A is just above the convex surface and inside the capillary. The phenomenon of rise or fall of a liquid inside a capillary tube when it is dipped in the liquid is called capillarity.Ĭonsider the points A, B, C, and D such that ![]() On the other hand, if the capillary tube is dipped in a liquid which does not wet its surface the level of liquid in the capillary drops. If one end of a capillary tube is dipped in a liquid which partially or completely wets the surface of the capillary the level of liquid in the capillary rises. ![]()
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