CHAPTER XII 

 IMBIBITION 



Protoplasm takes in water by imbibition. In general, imbibi- 

 tion is the taking in of water and consequent swelling by gels. 

 Most organic gels, such as cellulose, agar, gelatin, and starch, 

 swell when in water. They are, therefore, known as jellies, in 

 distinction from coagula. Gels (jellies and coagula) usually 

 possess high elasticity in the true physical meaning of the word 

 (an extreme case is that of glass), but extensibility, or capacity 

 to be stretched, is primarily a property of jellies. Extensibility 

 and imbibition thus distinguish jellies from coagula. Turgescence 

 is a term commonly used to denote swelling through the taking 

 in of water. Inorganic gels, such as pumice stone and silica 

 gel, which do not swell, are nonturgescent. Such gels may take 

 up water even more readily than do jellies, but they do not exhibit 

 that one indissociable property of imbibition, viz., swelling, and 

 its inevitable companion imbibition pressure. (Solvation and 

 hydration are sometimes used as synonyms of imbibition.) 



Imbibition pressure is a familiar expression in biology and col- 

 loidal chemistry. The volumetric increase due to the swelling of 

 jellies is great, and the magnitude of the pressures developed 

 may be enormous. The considerable increase in volume of a gel, 

 due to swelling, is illustrated in the case of the stalk of the sea- 

 weed Laminaria, which will swell several hundred per cent when 

 soaked in water after drying. Starch, in taking up water, may 

 develop a pressure of several thousand pounds per square inch. 

 The stupendous pressure developed by imbibition is illustrated in 

 the use of wood by the Egyptians to dislodge huge blocks of 

 stone. 



A more delicate operation is that involving the slow separation 

 of the bones of a skull by the swelling pressure of wetted peas 

 filling the skull. The cracks in a bo t or in a wooden bucket 

 are closed by the imbibition pressure of wood. Wooden parts of 

 certain machinery must be kejit permanently wet for use. The 



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