CAUSES OF THE MOTION OF JUICES. 349 



absorbed with force enough to ovei'come the pressure of 

 the atmosphere froin three to six times ; in other words — 

 to sustain a column of water in a wide tube 100 to 200 ft. 

 high. {Comptes Hendvs, 50, p.'Sll.) 



Absorbent power is influenced by temperature. Warm 

 water is absorbed by wood more quickly and abundantly 

 than cold. In cold water starch does not swell to any 

 striking or even perceptible degree, although considerable 

 liquid is imbibed. In warm water, however, the case is 

 remarkably altered. The starch-grains are forcibly burst 

 open, and a paste or jelly is formed that holds many times 

 its weight of water. (Exp. 27, p. 65.) On freezing, the 

 particles of water are mostly withdrawn from their adhe- 

 sion to the starch. The ascent of liquids in narrow tubes 

 whose walls are unabsorbent, is, on the contrary, dimin- 

 ished by a rise of temperature. 



Adhesive or Capillary Attraction. — The absorption of 

 a liquid into the cavities of a porous body, as well as its 

 rise in a narrow tube, are but expressions of the general 

 fact that there is an attraction between the molecules of 

 the liquid and the solid. In its simplest manifestation 

 this attraction exhibits itself as Adhesion, and this term 

 we shall employ to designate the kind of force under con- 

 sideration. If a clean plate of glass be dipped in water, 

 the liquid touches, and sticks to, the glass. On withdraw- 

 ing the glass, a film of water comes away with it. If two 

 squares of glass be set \vp together upon a plate, so that 

 they shall be in contact at their vertical edges on one side, 

 and one-eighth of an inch apart on the other, it will be 

 seen, on pouring a little water upon the plate, that this 

 liquid rises in the space between them several inches or 

 feet where they are in very near proximity, and curves 

 downwards to their base where the interval is large. 



Capillary attractio7i — the common designation of the 

 force that causes liquids to rise in fine tubes — is the same 

 adhesion which is manifested in all the cases of .absorp- 

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