THE CHEMISTRY OF THE BODY. 17 



into a solution of a dye. The dye accumulates on the particles in the 

 paper, and the latter becomes more deeply coloured than the solution 

 into which it is dipped. 



The amount of adsorption is relatively much greater in dilute than 

 in strong solutions of the electrolyte. Its importance lies in the fact 

 that the velocity with which a chemical change takes place varies 

 with the concentration of the interacting substances. If two electro- 

 lytes, which can interact, are added to a colloidal solution, they 

 become concentrated on the surface of the colloidal particles, and at 

 these surfaces the reaction between them will proceed more rapidly 

 than if the colloid were absent. 



Solutions of colloids are called sols ; in certain circumstances the 

 particles may aggregate into larger masses, forming a precipitate, or 

 the solution may change to a jelly, called a gel. An example of this 

 process is the coagulation of protein by heat. 



