Hydrogen sulfide is a colorless, extremely poisonous gas. The gas has a sweetish taste and a strong odor of rotten eggs. Chemical compounds containing sulfur produce hydrogen sulfide when they react with certain other chemical compounds. This is why the odor of hydrogen sulfide can be detected around decaying organic matter, such as garbage or sewage; when tarnish is removed from silver; in the exhaust of some buses and cars; and around some hot springs.
Hydrogen sulfide is flammable and burns with a pale blue flame. It dissolves slightly in water, forming a weak acid called hydrosulfuric acid. Chemists make hydrogen sulfide in the laboratory by combining such strong acids as hydrochloric acid with such metal sulfides as iron sulfide. They use the gas to analyze the composition of mixtures and to produce other compounds.
