Hydrogen sulfide is the chemical compound with the formula H2S. It is a colorless chalcogen hydride gas with the characteristic foul odor of rotten eggs, it is poisonous and flammable. Hydrogen sulfide is produced from the microbial breakdown of organic matter in the absence of oxygen gas, such as in swamps and sewers. H2S occurs in volcanic gases, natural gas, in some sources of well water; the human body uses it as a signaling molecule. Swedish chemist Carl Wilhelm Scheele is credited with having discovered the chemical composition of 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. Hydrogen sulfide is denser than air. Hydrogen sulfide burns in oxygen with a blue flame to form sulfur water. In general, hydrogen sulfide acts as a reducing agent in the presence of base, which forms SH−. At high temperatures or in the presence of catalysts, sulfur dioxide reacts with hydrogen sulfide to form elemental sulfur and water.

This reaction is exploited in the Claus process, an important industrial method to dispose of hydrogen sulfide. Hydrogen sulfide is soluble in water and acts as a weak acid, giving the hydrosulfide ion HS−. Hydrogen sulfide and its solutions are colorless; when exposed to air, it oxidizes to form elemental sulfur, not soluble in water. The sulfide anion S2− is not formed in aqueous solution. Hydrogen sulfide reacts with metal ions to form metal sulfides, which are insoluble dark colored solids. Lead acetate paper is used to detect hydrogen sulfide because it converts to lead sulfide, black. Treating metal sulfides with strong acid liberates hydrogen sulfide. At pressures above 90 GPa, hydrogen sulfide becomes a metallic conductor of electricity; when cooled below a critical temperature this high-pressure phase exhibits superconductivity. The critical temperature increases with pressure. If hydrogen sulfide is pressurized at higher temperatures cooled, the critical temperature reaches 203 K, the highest accepted superconducting critical temperature as of 2015.

By substituting a small part of sulfur with phosphorus and using higher pressures, it has been predicted that it may be possible to raise the critical temperature to above 0 °C and achieve room-temperature superconductivity. Hydrogen sulfide is most obtained by its separation from sour gas, natural gas with a high content of H2S, it can be produced by treating hydrogen with molten elemental sulfur at about 450 °C. Hydrocarbons can serve as a source of hydrogen in this process. Sulfate-reducing bacteria generate usable energy under low-oxygen conditions by using sulfates to oxidize organic compounds or hydrogen. A standard lab preparation is to treat ferrous sulfide with a strong acid in a Kipp generator: FeS + 2 HCl → FeCl2 + H2SFor use in qualitative inorganic analysis, thioacetamide is used to generate H2S: CH3CNH2 + H2O → CH3CNH2 + H2SMany metal and nonmetal sulfides, e.g. aluminium sulfide, phosphorus pentasulfide, silicon disulfide liberate hydrogen sulfide upon exposure to water: 6 H2O + Al2S3 → 3 H2S + 2 Al3This gas is produced by heating sulfur with solid organic compounds and by reducing sulfurated organic compounds with hydrogen.

Water heaters can aid the conversion of sulfate in water to hydrogen sulfide gas. This is due to providing a warm environment sustainable for sulfur bacteria and maintaining the reaction which interacts between sulfate in the water and the water heater anode, made from magnesium metal. Hydrogen sulfide can be generated in cells via non enzymatic pathway. H2S in the body acts as a gaseous signaling molecule, known to inhibit Complex IV of the mitochondrial electron transport chain which reduces ATP generation and biochemical activity within cells. Three enzymes are known to synthesize H2S: cystathionine γ-lyase, cystathionine β-synthetase and 3-mercaptopyruvate sulfurtransferase; these enzymes have been identified in a breadth of biological cells and tissues, their activity has been observed to be induced by a number of disease states. It is becoming clear that H2S is an important mediator of a wide range of cell functions in health and in disease. CBS and CSE are the main proponents of H2S biogenesis.

These enzymes are characterized by the transfer of a sulfur atom from methionine to serine to form a cysteine molecule. 3-MST contributes to hydrogen sulfide production by way of the cysteine catabolic pathway. Dietary amino acids, such as methionine and cysteine serve as the primary substrates for the transulfuration pathways and in the production of hydrogen sulfide. Hydrogen sulfide can be synthesized by non-enzymatic pathway, derived from proteins such as ferredoxins and Rieske proteins. H2S has been shown to be involved in physiological processes like vasodilatation in animals, increasing seed germination and stress responses in plants. Hydrogen sulfide signaling is innately intertwined with physiological processes that are known to be moderated by reactive oxygen species and reactive nitrogen species. H2S has been shown to interact

An active protection system is a system designed to prevent line-of-sight guided anti-tank missiles/projectiles from acquiring and/or destroying a target. Electronic countermeasures that alter the electromagnetic, acoustic or other signature of a target thereby altering the tracking and sensing behavior of an incoming threat are designated soft-kill measures. Measures that physically counterattack an incoming threat thereby destroying/altering its payload/warhead in such a way that the intended effect on the target is impeded are designated hard-kill measures. Soft-kill measures are applied when it is expected that a sensor-based weapon system can be interfered with; the threat sensor can be either an artificial one, e.g. a solid-state infrared detector, or the human sensory system. Soft-kill measures interfere with the signature of the target to be protected. In the following the term signature refers to the electromagnetic or acoustic signature of an object in either the ultraviolet, visual, or infrared spectral range as well as cm-radar range, mmw-radar and sonar range.

One or more of the following actions may be taken to provide soft-kill: Reduction of signature Augmentation of signatureSoft-kill countermeasures can be divided into on-board and expendable countermeasures. Whereas on-board measures are fixed on the platform to be protected, expendable measures are ejected from the platform. Preemptive action of countermeasures is directed to prevent lock-on of a threat sensor to a certain target, it is based on altering the signature of the target by either concealing the platform signature or enhancing the signature of the background, thus minimizing the contrast between the two. Reactive action of countermeasures is directed toward break-lock of a threat homing in on a certain target, it is based on the tactics of augmentation, or reduction. One has to distinguish between infrared and radar countermeasures; the wavelength range between 0.8 and 5 μm is considered as Infrared, the frequency range between 2 and 18 GHz is considered as Radar. In the wake of shoulder-launched missile attacks against civilian passenger and cargo airliners in the early 2000s, various agencies investigated the feasibility of equipping countermeasures such as chaff and flares.

Many commercial carriers found the estimated price of countermeasures to be too costly. However, the Israeli airline El-Al, having been the target of the failed 2002 airliner attack, in which shoulder-launched surface-to-air missiles were fired at an airliner while taking off, began equipping its fleet with radar-based, automated flare release countermeasures from June 2004; this caused concerns in some European countries, regarding the possible fire hazard at civilian airports, resulting in banning such aircraft from landing at their airports. In 2007, Saab announced a new infrared countermeasure system called CAMPS that does not use pyrotechnic flares, thereby directly addressing these concerns. IR-decoy flares serve to counter infrared-guided surface-to-air missiles or air-to-air missiles and can be expelled from a craft according to an anticipated threat in defined sequences. To counter radar-guided missiles, chaff is used; these are copper nickel-coated glass fibers or silver-coated nylon fibers having lengths equal to half of the anticipated radar wavelength.

New systems, such as the BriteCloud expendable active decoy, use DRFM technology to generate a false target, luring the RF threat system away from the aircraft. Land and sea-based forces can use such countermeasures, as well as smoke-screens that can disrupt laser ranging, infrared detection, laser weapons, visual observation. Except for countering intercontinental ballistic missiles, hard-kill measures refer to measures taken in the so-called "end-game" shortly before a warhead/missile hits its target; the hard-kill measure in general physically affects the incoming warhead/missile by means of either blast and/or fragment action. The action may lead to: disturbance of the stability of a kinetic energy penetrator which will decrease its penetration ability as the deflection angle increases. Premature initiation of a shaped charge, but most improper initiation, thereby impeding optimum jet development of the metallic lining copper, in the shaped charge; the copper jet provides most of the anti armor capabilities of shaped charge weapons.

Destruction of the airframe of an inbound missile or shell. There are many examples of active countermeasures. For example, the Russian-made Arena system utilizes a Doppler radar to detect incoming threats and fires a top attack rocket to eliminate the threat; the Israeli Trophy system fires a shotgun-like blast to destroy the threat. An American system known as Quick Kill detects incoming threats using an Active Electronically Scanned Array, which assesses the threat, deploys a smaller rocket countermeasure. Another American system, known as Iron Curtain, utilizes two sensors to reduce false alarms and defeat threats inches from their target by firing a kinetic countermeasure designed to minimize collateral damage; the Russian T-14 Armata tank features the Afghanit active protection system, which includes a millimeter-wavelength radar to detect and intercept incoming anti-tank munitions, both kinetic energy penetrators and tandem-charges. The maximum speed of the interceptable target is 1,700 m/s, with projected future increases of up to 3,000 m/s.

According to news sources, it protects the

"Eight Arms to Hold You"' was a song recorded for the soundtrack to the film The Goonies. The song was recorded by a studio group called Goon Squad, put together by producer Arthur Baker, it was utilized in a scene in the film where the character Data puts a loud tape recorder into the mouth of an octopus to fend it off. The scene was deleted from the film and the song did not appear in the theatrical release of the film; the soundtrack producers had anticipated the track would be a big hit and so though it wasn't in the film, a single was released on both 12" and 7" vinyl. It reached number one on the Billboard Hot Dance Club Play chart and peaked at number eighty on the Hot R&B/Hip-Hop singles chart; the "octopus scene" was replaced for broadcast on the Disney Channel, in order to make up for time removed due to objectionable content. It was included in a deleted scenes featurette in the 2001 DVD release. Vocal Bonus Beat Dub Edit Dub