232 CHEMISTRY OF PLANT LIFE 



This latter consideration seems to be the factor of largest influence 

 in colloidal catalysis. 



But in addition to the increased rate of reaction in the surface 

 layer due to the increased energy available there and to the 

 increased concentration of dissolved substances, there is the pos- 

 sibility that the act of concentration itself bring into play molec- 

 ular forces which give rise to a resultant increase in chemical 

 potential, or chemical affinity, of the reacting materials, such as 

 has been observed to result in other concentrated solutions. A 

 discussion of the theoretical and mathematical considerations 

 upon which this conception is based would be out of place here, 

 but there is ample experimental evidence to indicate its soundness. 



Further, as has been pointed out, colloidal phenomena are 

 essentially due, in large part at least, to the electric charges on 

 the dispersed particles. Electric charges accumulate at the 

 surface of any charged body. Hence, the surface layers in any 

 colloidal system carry its electric charges in highest concentration, 

 ar\d all of the chemical changes which are stimulated by electrical 

 phenomena are most strongly influenced at the surface boundaries 

 between the different phases of the system. This latter considera- 

 tion affords a satisfactory explanation of the well-known depressing, 

 or stimulating, action of electrolytes, especially acids and bases, 

 upon the enzymic catalysis of protoplasmic reactions. 



These few, brief statements are sufficient to indicate how 

 extensively the chemical activities of colloidal protoplasm are 

 influenced by the phenomena arising from the surface boundaries 

 between different materials, which are present in such enormous 

 extent in a colloidal gel. Surface boundary phenomena hi a 

 heterogeneous system, such as we have seen protoplasm to be, 

 provide the possibilities for many reactions which would other- 

 wise take place very slowly, if at all. Mere subdivision of the 

 protoplasmic materials into the film, or foam, structure brings into 

 play energies which may predominate over all other types of 

 energy in the system. Here, too, effects may be extraordinarily 

 modified by slight changes in environment, which effects could 

 not be "explained by any considerations which govern ordinary 

 chemical reactions. Here, we deal with adsorption and other 

 colloidal phenomena, rather than with ordinary stoichiometric 

 combinations. 



Indeed, it is not too much to say that the differences between 



