78 



DISPERSE SYSTEMS 



ing values were calculated : 119, 142, 169, 201. This and 

 numerous other experiments confirm quantitatively the theory 

 that the Brownian movement is the result of molecular impacts. 

 After this adjustment of concentration to level has been reached, 

 no other change seems to take place. To this cause may be 

 attributed a share at least of the responsibility for the stability 

 of colloidal solutions. 



The electrical properties of a colloidal dis- 

 persion may have much to do with the 

 permanence of the suspension. Each 

 colloidal particle carries a definite charge 

 seemingly dependent on the hydrogen ion 

 concentration of the dispersing medium. 

 The colloid generally has a greater con- 

 ductance than the intermicellar liquid itself. 

 This is due to the unequal adsorption of 

 ions of electrolytes present in the disper- 

 sion medium and in some instances by 

 ionisation of the colloid itself. By virtue 

 of this charge the particles of the disperse 

 phase will act like ions and will migrate 

 through the solution to any point of op- 

 posite charge. This electrical migration is 

 called cataphoresis (Figs. 9 and 10). 



Diffusion of Electrolytes. 



Cataphoresis should not be confused with 

 the electrical diffusion of electrolytes into 

 gels. That dissolved substances diffuse into 

 or out of gels was a fact familiar to Graham. 

 The rate of diffusion may be altered by the 

 addition of certain substances to the gel. 

 A gel, after treatment with sodium 

 sulphate, glucose, alcohol, glycerol, etc. 

 (dehydrating agents), offers considerable 

 resistance to the diffusion of electrolytes. 

 Urea, iodides, and chlorides, on the 

 other hand, cause acceleration of the rate of diffusion. These 

 added substances cause alteration in the relative amounts of 

 water held by dispersoid and dispersant and so produce alterations 

 in the more liquid phase. The degree of continuity of liquidity 

 is a causative factor in the velocitv of diffusion. 



FIG. 11. Adsorptive stratifi- 

 cation of silver bichromate in 

 an agar gel. (Bradford, Bio- 

 chemical Journal.) 



