This proposal will exploit the unique ability of neutron reflection to characterise the adsorption of a key additive on the surface of calcite from a non-aqueous solvent and the role that added water has in reducing the adsorption of this species. In particular we want to understand why simple fatty acids adsorb much more strongly to calcite (calcium carbonate) when adsorbed from oil than from water (approximately 30 times more strongly). To do this we need to 'see' what happens to the fatty acid and the water at the calcite surface as we change the sub phase gradually from oil to water. Only neutron reflection can do this.