The surface tension sigma of inorganic electrolyte aqueous solutions at a given concentration c follows the Hofmeister series. The explanation of this phenomenon was sought in the increased adsorption of certain ions due to specific ion-surface interactions. However, the ion-specific dependence of the activity coefficient gamma(+/-) on c also influences sigma, and its contribution to the ion-specificity of sigma prevails. Thus, the surface tension of potassium salts follows the order sigma(KOH) > sigma(KCl) > sigma(KNO3), which turns out to be a direct corollary of the corresponding activity coefficients series: gamma(KOH) > gamma(KCl) > gamma(KNO3). In fact, the adsorption of NO3- at the water surface is lower than that of OH- and Cl-! If the bulk ion-specific effects are correctly evaluated, Schmutzer's classical model predicts accurately the surface tension of a large number of inorganic salt solutions in a wide concentration range, without adjustable parameters. This model accounts for image and hydration forces. Comparison with tensiometric data shows that other ion-surface interactions play a role only in the adsorption of ions of bare radius larger than a threshold value of about 1.95 angstrom (e.g. HCOO-, I-, SCN-). (c) 2012 Elsevier Inc. All rights reserved.