IMBIBITION ( from Lat. iminbcre, to drink in, from in. in bibere, for *pibere, to drink, Skt. pa, to drink, Olr. ihim, I drink). The phys ical process of swelling of solids by the absorption of liquid. it is exhibited most freely by organized bodies, i.e. those formed by living beings, which have therefore a characteristic structure, but is not confined to them. The swelling depends on a separation of the structural units of the hotly, which are believed to be not its molecules, but rather molecular complexes. Imbibition, there Ptre, differs from solution in that the separation of the particles is not so extensive. and when the water is removed by evaporation or otherwise they return to their original relations, so that the body regains its previous form and structure. After solution, on the contrary, the separated molecules may rearrange themselves completely. In a normal condition all parts of plants hold large quantities of water imbibed in their sub stance. Even in the walls of wood-eells, the least watery material, there is usually 50 per cent. of water, while in the protoplasm there may be as much as 95 per vent. halved, the plant may be considered as a mass of water held between the structural particles of the cells composing it and exceeding in volume the material by which it is so held. This condition alone makes it, possible for plants to obtain materials from the water and air about them. See Anstalt-nos, IN PLANTS.
The force of imbibition depends upon the sur face tension of the water and upon the relation be tween the molecules of water and those particles of the swellinz body whose cohesion is thereby overt-one. When a dry starch-grain imbibes water, heat is developed (on :lemma of the com pression of the water) to an amount which indi cates (according to Rodewald) a pressure of over 2500 atmospheres. The force exerted by a confined swelling body is at first enormous, but becomes rapidly weaker as the particles are sep arated farther anti farther. Correspondingly, water is held loosely when abundant, hut more and more tenaciously when only a little is im bibed. Thus. when a hit of laminarM is com pletely swollen, water can be removed from it by slight pressure; V.lien it holds 170 per cent. of water it requires a pressure of 16 atmospheres to extract water; when only 93 per cent. is present a pressure of 200 atmospheres is needed. Appli cations of the force of swelling tire made in split ting stone by wooden wedges driven in and then wetted; in shortening ropes by wetting; in the use of laininaria for surgical distension, etc. 'Ile phenomena of imbibition afford the chief for theories concerning the molecular struc ture of organized bodies. See COLLOIDS.