Ash, the material left after organic substances are burned. Most ash consists largely of lime (calcium oxide), soda ash (sodium carbonate), and potash (potassium carbonate), but may also contain sulfur, phosphorus, iron, and other chemical elements. Different plants and animals yield ashes of different composition. The burning of powdered coal, as in a power plant, yields very fine particles of ash called fly ash. It is used as a filler in plastics, as an absorbent material for cleaning up oil spills, and for a number of other industrial purposes. Wood ashes were once commonly used in producing lye for soapmaking and as a source of potash for fertilizing soil.