to be effective on a given ore slurry, the collectors are chosen based upon their selective wetting of the types of particles to be separated. a good collector will adsorb, physically or chemically, with one of the types of particles. this provides the thermodynamic requirement for the particles to bind to the surface of a bubble. the wetting activity of a surfactant on a particle can be quantified by measuring the contact angles that the liquid/bubble interface makes with it. another important measure for attachment of bubbles to particles is induction time. the induction time is the time required for the particle and bubble to rupture the thin film separating the particle and bubble. this rupturing is achieved by the surface forces between the particle and bubble.