A salt formed when a fatty acid reacts with a metal oxide or hydroxide. Fatty acids and lime, Ca(OH)2, form emulsifiers for oil muds. Fatty acids reacted with sodium hydroxide [NaOH] or potassium hydroxide [KOH] are laundry soaps, some used as foamers for air drilling. Fatty acids and aluminum hydroxide form soaps used as greases and as defoamer chemicals.