THE foaminess of ocean waves, relative to fresh water, has long been attributed to the effect of salts in reducing bubble coalescence9. This phenomenon is exploited in extraction processes using froth flotation1, in which the extraction efficiency increases as the bubble size gets smaller. But whereas the bubble-stabilizing effect of surfactants is well understood, the effect of salts is not; the fact that salts decrease the surface tension of water and that they are desorbed from the air-water interface would, if anything, be expected to destabilize bubbles. Here we report the results of experiments conducted to study the stabilization of bubbles by salts. We find that bubble coalescence is inhibited by some salts whereas others have no effect and that this inhibition occurs only upon the 'matching' of a two-valued empirical property assigned to each anion and cation. We believe these observations can be explained only by the local influence of the ions on water structure, possibly in a way related to the hydrophobic interaction2-8.