<unk>  (or hydrogen sulphide) is the chemical compound with the formula<unk> .  This colorless, toxic and flammable gas is responsible for the foul odour of rotten eggs and flatulence.
It often results from the bacterial break down of organic matter in the absence of oxygen, such as in swamps and sewers (anaerobic digestion). It also occurs in volcanic gases, natural gas and some well waters. The odor of<unk>  is commonly misattributed to elemental sulfur, which is in fact odorless.<unk>  has numerous names, some of which are archaic (see Table).
Hydrogen sulfide
Dimethyl sulfide
Acrolein
Peroxide
Superoxide
Hydrogen chloride
Nitrosamine
Carbon dioxide