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Absorption

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  p-125

2025-11-08

703

 Whenever a liquid is brought in contact with a porous solid, and wets it, the liquid immediately begins to pass into the pores of the solid; this process is called absorption. Blotting paper absorbs ink, and a lamp wick, oil. When once absorbed, the liquids cannot be entirely removed by pressure. A sponge can never be pressed dry, but becomes dry only when evaporation takes place. It is evident that absorption is a capillary phenomenon and that every pore in a porous substance acts as a capillary tube.

Demonstration. - Procure a small porous cup such as is used for a battery cell, and fit in the open end a rubber stopper with one hole. In the stopper fit one end of a glass tube T, bent as in Fig. 1. Pour mercury into the end of this tube and let it come to rest at A: The heights in the two branches can be made the same by letting a little air out of the cup. Lower the cup into a beaker of water and observe the change in the level at A.  Explain this action. Measure this pressure by putting a scale back of the tube at A.