In the present study, the magnitude and range of the hydrophobic interaction (which is the predominating force causing the coalescence of air-bubbles in pure water) was calculated from the critical thickness of rupture of a free metastable horizontal water film in air. Application of a modified DLVO theory enabled values of the pre-exponential hydrophobic interaction parameter (C) and the decay length (Do) to be estimated. The experimental data confirmed the long range nature of the hydrophobic force. In addition, it was found that the decay length and interaction parameter was reduced in KCl and this appears to be consistent with the fact that salts act to prevent the coalescence of airbubbles in water.