Any of three low-melting hygroscopic colourless solids. They are strong bases, smell of ammonia, and absorb water readily to form viscous liquids. Monoethanolamine, HOCH₂CH₂NH₂, is a primary amine, m.p. 10.5°C; diethanolamine, (HOCH₂CH₂)₂NH, is a secondary amine, m.p. 28°C; and triethanolamine, (HOCH₂CH₂)₃N, is a tertiary amine, m.p. 21°C. All are made by heating ethylene oxide with concentrated aqueous ammonia under pressure and separating the products by fractional distillation. With fatty acids they form neutral soaps, used as emulsifying agents and detergents, and in bactericides and cosmetics.