THE SWELLING OF ORGANIZED BODIES 73 



stances and cell-walls when hardened in alcohol lose the power of swelling 

 in water, in this respect behaving like porous bodies the pores of which 

 have become rilled with air as the alcohol evaporated. When a pile of 

 glass plates is placed in water, each plate becomes slightly separated from 

 its neighbours as capillary water penetrates between the plates, and the 

 height of the whole pile is slightly increased. For the same reason 

 imbibition causes in a finely porous sphaero- crystal a degree of swelling, 

 the extent of which is determined by the amount of cohesion existing 

 between the radially-arranged acicular crystals of which it is composed. 



The amount of swelling, and, indeed, all the phenomena of imbibition, 

 capillarity and absorption are manifestations of the same natural forces 

 as are exhibited in the phenomena of surface-tension \ Surface-tension 

 energy, or in other words, the attraction existing between the water and 

 the imbibing substance, causes the former to penetrate between the com- 

 ponent particles of the latter, and force them asunder as far as the cohesion 

 existing between the component particles of the given substance will allow. 

 Since, however, the distance through which the energy of surface-tension 

 can act is excessively small 2 , the power of swelling, as well as the expansive 

 force which the swelling may exert, rapidly diminishes as the amount of the 

 imbibed water increases. The first molecules of water are absorbed with 

 extraordinary energy, and undergo considerable compression, but as imbi- 

 bition progresses the force of absorption rapidly decreases, and further 

 expansion ceases before the films of water which separate the component 

 parts of the imbibing substance from one another have attained a measur- 

 able thickness 3 . 



The same general relationships hold good, whether the component 

 elements separated by the water of imbibition are molecules, micellae, 

 or groups of micellae, or whether the micellae or micellar groups are 

 themselves capable of swelling. 



In addition, chemical union, partial solution, and other factors may 

 be correlated with imbibition phenomena, while from the differences which 

 have been shown to exist between solution and swelling, it follows that 

 in most cases, though not necessarily in all, a sharp distinction may be 

 drawn between the swelling due to simple imbibition and that due to 

 processes of solution 4 . The swelling which substances may undergo in 



1 Pfeffer, Studien zur Energetik, 1892, p. 163. 



a See for example Winkelmann, Handbuch d. Physik, 1891, Bd. I, p. 476. 



3 For the phenomena of swelling and the theoretical conclusions which may be deduced from 

 them, see Nageli, Starkekorner, 1858, p. 333 ; Reinke, Bot. Abhandlung von Hanstein, 1879, Bd. iv, 

 p. i ; Rodewald, Landw. Versuchsst., 1894, Bd. XLV, p. 201. For theory of swelling, Reinke, Nach. 

 d. Ges. d. Wiss. zu Gottingen, 1894, p. i. 



* A. Meyer (Unters. u'ber die Starkekorner, 1895, p. 139^ distinguishes in starch between the 

 swelling of imbibition and the swelling due to solution. 



