PROPERTIES OF GELATINE AND GLUE 211 



kataphoresis, precipitation, etc. According to this point of 

 view the particles of the disperse phase are surrounded by a 

 surface layer in which these ions are in much greater concen- 

 tration than in the volume concentration of the dispersion 

 medium. The hydrion and hydroxyl ion are particularly 

 liable to such adsorption. In the case of a lyophile colloid, 

 like gelatine, the charge may be either positive or negative, 

 according to the nature of the predominant ions in the 

 dispersion medium, and the amount of adsorption is deter- 

 mined by the concentration of these ions in accordance with 

 the adsorption law. 



In effect, therefore, the particles of the disperse phase 

 each carry an electric charge of the same nature, and as 

 similarly charged bodies repel one another, the particles of 

 the disperse phase will tend to separate and to occupy a 

 bigger volume. It is the author's opinion that this repulsion 

 of similarly charged particles is the cause of the swelling of 

 gelatine. The amount of charge and force tending to 

 swell is due possibly to several ionic adsorptions, which 

 may be considered to operate independently, and the power 

 of repulsion is determined by the nett charge, which in the 

 case of a " positive colloid " is positive, and in the case of a 

 " negative colloid " is negative. As ions possess different 

 electric charges, the charge on the disperse phase is subject 

 to the valency rule. 



Now the repulsive force between two similar and similarly 

 charged bodies is proportional to the amount of charge and 

 is inversely proportional to the square of the distance between 

 them. The amount of charge on a colloid particle will be 

 determined by the dispersity best signified by the specific 



surface (s) and by the operation of the adsorption law 



i 

 y=mac. The distance between the particles varies with 



the degree of swelling, and is determined by the cube root of 

 the volume of the gel (v). Hence if F be the force tending to 

 make the gelatine swell, we may write 



p "&" 



