Hydrogen sulfide is the chemical compound with the formula H2S. It is a colorless gas with the characteristic foul odor of rotten eggs; it is heavier than air, very poisonous, corrosive, flammable, and explosive.Hydrogen sulfide often results from the bacterial breakdown of organic matter in the absence of oxygen gas, such as in swamps and sewers; this process is commonly known as anaerobic digestion. H2S also occurs in volcanic gases, natural gas, and in some sources of well water. It is also present in natural halite type rock salts, most notably in Himalayan Black Salt, which is mostly harvested from the mineral-rich ""Salt Range"" mountains of Pakistan. The human body produces small amounts of H2S and uses it as a signaling molecule.Dissolved in water, hydrogen sulfide is known as hydrosulfuric acid or sulfhydric acid, a weak acid.Swedish chemist Carl Wilhelm Scheele is credited with having discovered hydrogen sulfide in 1777.The British English spelling of this compound is hydrogen sulphide, but this spelling is not recommended by the International Union of Pure and Applied Chemistry or the Royal Society of Chemistry.In 2015, hydrogen sulfide under extremely high pressure (around 150 gigapascals) was found to undergo superconducting transition near 203K (-70 °C), the highest temperature superconductor known to date.