PHYSICOCHEMICAL ORGANIZATION OF THE PLANT 7 



everj^ hydrosol, there may be observed reciprocal repulsion of 

 the colloidal particles carrying the same charge and likewise 

 their reciprocal attraction, which is natural to all bodies. The 

 magnitude of the reciprocal repulsion determines the degree of 

 the stability of the colloidal system, while the reciprocal attrac- 

 tion, on the other hand, contributes to their aggregation into a 

 complete mass of the micelles forming the dispersed phase. 

 This mass is either precipitated or may rise to the surface. The 

 separation of th€ dispersed phase from the dispersion medium is 

 termed ' 'coagulation" and may be caused by various factors. 



One of these factors is the increase in concentration of elec- 

 trolytes that neutralize the charge of the colloidal particles. As 

 this neutralizing effect is caused by the adsorption of oppositely 

 charged ions on the surface of the micelles, coagulation occurs 

 only after the adsorption of a definite amount of ions, carrying 

 a definite charge. The charge is determined by the valence of 

 the ions; hence the general rule that the coagulating effect 

 increases with the increase in valence. The same activity is 

 shown by trivalent ions at lower concentrations than with 

 bivalent ions and by bivalent ions at lower concentrations than 

 with univalent ones (Hardy's rule). 



When several electrolytes are added simultaneously to colloids, 

 very often, instead of reciprocal increase of the effect, there may 

 be observed an antagonism of ions. The addition of one kind 

 of ions decreases the coagulating action of the others. Many 

 investigators explain this antagonism by the fact that in a mix- 

 ture of electrolytes colloidal particles adsorb both oppositely 

 charged and identically charged ions, thus increasing their 

 charge. 



Another coagulating factor may be the increase in concen- 

 tration of the colloid ; with excessive decrease of the intermicellar 

 spaces, the forces of reciprocal attraction may surpass the forces 

 of electrical repulsion. One may mention also the senescence 

 of the colloids, when the degree of dispersion gradually decreases. 



3. Properties of Proteins and Other Hydrophilic Colloids. 

 Gels and Jellies. Structure of the Cell Wall and of the Proto- 

 plasm. — Protein substances as well as several other closely allied 

 hydrophilic colloids represent one of the most important group 

 of colloids from the viewpoint of investigation of living substance, 

 the protoplasm. 



