EFFECT OF ELECTROLYTES ON BUBBLE COALESCENCE

THE foaminess of ocean waves, relative to fresh water, has long been a ttributed to the effect of salts in reducing bubble coalescence9. This phenomenon is exploited in extraction processes using froth flotation 1, in which the extraction efficiency increases as the bubble size get s smaller. But whereas the bubble-stabilizing effect of surfactants is well understood, the effect of salts is not; the fact that salts decr ease the surface tension of water and that they are desorbed from the air-water interface would, if anything, be expected to destabilize bub bles. 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 i nhibition occurs only upon the 'matching' of a two-valued empirical pr operty assigned to each anion and cation. We believe these observation s can be explained only by the local influence of the ions on water st ructure, possibly in a way related to the hydrophobic interaction2-8.