OF VITAL PHENOMENA 67 



(second) to electrolytic dissociation in the case of silicic acid 

 which dissociates H ions or sulphur which partially oxidizes and 

 dissociates H ions, or (third) to absorption in case the particle 

 absorbed one ion of an electrolyte and not the other, and often 

 (fourth) to adsorption of ions. The ions that are responsible 

 for the electric charge of all particles are not known, but H ions 

 may be displaced from positive particles by organic cations. 



The electric charge of solid particles may be increased, de- 

 creased or reversed by the adsorption of ions. H ions and heavy 

 metal ions make particles more positive, whereas OH ions make 

 them more negative. In the neutralization of the charge of 

 particles, bivalent ions are more than twice as effective as mono- 

 valent ions and trivalent ions are much more than three times as 

 effective. This is what we should expect from the curve of 

 adsorption (Fig. 24), since two molecules are not twice as effec- 

 tive or three molecules three times as effective as one molecule. 



After reversing the charge of particles their adsorbing power 

 is reversed. Wool will take up very little acid dye until it is 

 made electropositive by the addition of free acid. 



