CHAPTER VI 



A NOTE OX ADSORPTION 



A very important corollary to, or amplification of the theory 

 of surface tension is to be found in the modern chemico-physical 

 doctrine of Adsorption*. In its full statement this subject soon 

 becomes complicated, and involves physical conceptions and 

 mathematical treatment which go beyond our range. But it is 

 necessary for us to take account of the phenomenon, though it 

 be in the most elementary way. 



In the brief account of the theory of surface tension with which 

 our last chapter began, it was pointed out that, in a drop of liquid, 

 the potential energy of the system could be diminished, and work 

 manifested accordingly, in two ways. In the first place we saw 

 that, at our liquid surface, surface tension tends to set up an 

 equilibrium of form, in which the surface is reduced or contracted 

 either to the absolute minimum of a sphere, or at any rate to the 

 least possible area which is permitted by the various circumstances 

 and conditions ; and if the two bodies which comprise our system, 

 namely the drop of liquid and its surrounding medium, be simple 

 substances, and the system be uncomplicated by other distributions 

 of force, then the energy of the system will have done its work 

 when this equilibrium of form, this minimal area of surface, is 

 once attained. This phenomenon of the production of a minimal 

 surface-area we have now seen to be of fundamental importance 

 in the external morphology of the cell, and especially (so far 

 as we have yet gone) of the solitary cell or unicellular organism. 



* See for a further but still elementary account, Michaelis, Dynamics of Surfaces, 

 1914, p. 22 seq.; Macallum, Oberfldchenspcmnttng und Lebenserscheinungen, in 

 Asher-Spiro's Ergebnisse der Physiologic, xi, pp. 598-658, 1911; see also W. W. 

 Taylor's Chemistry of Colloids, 1915, p. 221 seq., Wolfgang Ostwald, Grundriss der 

 Kolloidchemie, 1909, and other text-books of physical chemistry; and Bayhss's 

 Principles of General Physiology, pp. 54-73, 1915. 



