Additive
Additive, a chemical substance added to a material—usually in small amounts—to impart or enhance desirable properties or to lessen or suppress undesirable properties. Among the most familiar products in which additives are used are gasoline, lubricating oils, rubber, and foods.
For example, dye is added to gasoline to give it color, which is necessary for identification purposes. Other gasoline additives prevent or reduce gum formation, rusting, and spark-plug fouling. Additives in lubricating oils provide the proper viscosity. The use of additives in vulcanized rubber greatly retards its oxidation. There are hundreds of additives used in foods to improve their nutritive value, retard spoilage, or enhance their flavor.