Chemical substances are divided into classes and categories. In brief, chemical substances include, acids (inorganic acids and organic acids), alkali (bases), colors, dyes, and pigments, cyanides, detergents, dopants, fillers, food contaminants, gases (cryogenic gases, industrial gases), metals and metal compounds, oxidizers, pesticides, radioactive chemicals, solvents, and many more. (Readers will find more information in chemistry textbooks.)