Adsorption at a water surface. Part I

It has already been shown that the charge acquired by small air bubbles in water is due to the selective adsorption of ions by the surface molecules. The bubble surface is considered to consist of water molecules which are partly or completely orientated. These, owing to their polar nature, have a resultant electric field and therefore attract ions of one sign while repelling those of the opposite sign. In the case of water the orientation is such as to attract negative ions from the water. These ions are adsorbed on to the surface of the bubble and give it a negative charge. At the same time some of the negative ions already adsorbed will be removed by the thermal agitation of the liquid and an equilibrium state will eventually be reached in which the number striking the surface per second is equal to the number re-evaporated from it. This adsorption of negative ions is accompanied by the capture of positive ions from the liquid. Any such positive ion striking an adsorbed negative ion may be bound to it by the electrostatic attraction so that a number of the negative ions are covered by positive ions and the charge on the bubble is due to the remaining uncovered negative ions.