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.