In a beaker of water, if air is introduced from the bottom, air bubbles are produced and rise to the surface of water (Fig. 27.1 A) as the density of air bubble is much less than that of water. Similarly air bubbles also rise if air is introduced in a pulp containing solid particles. If a solid particle of high density adheres to the air bubble, air bubble along with solid particle rise to the surface because the apparent density of air bubble and the adhered solid particle is less than that of water. If many number of solid particles are adhered to the air bubble, still air bubble rise to the surface (Fig. 27.1B) as the apparent density of air bubble and adhered solid particles is less than that of water due to relatively large volume of air bubble. This concept is the basis for froth flotation operation.