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The Collaborative International Dictionary

Hydrogen \Hy"dro*gen\, n. [Hydro-, 1 + -gen: cf. F. hydrog[`e]ne. So called because water is generated by its combustion. See Hydra.] (Chem.) A gaseous element, colorless, tasteless, and odorless, the lightest known substance, being fourteen and a half times lighter than air (hence its use in filling balloons), and over eleven thousand times lighter than water. It is very abundant, being an ingredient of water and of many other substances, especially those of animal or vegetable origin. It may by produced in many ways, but is chiefly obtained by the action of acids (as sulphuric) on metals, as zinc, iron, etc. It is very inflammable, and is an ingredient of coal gas and water gas. It is standard of chemical equivalents or combining weights, and also of valence, being the typical monad. Symbol H. Atomic weight 1.

Note: Although a gas, hydrogen is chemically similar to the metals in its nature, having the properties of a weak base. It is, in all acids, the base which is replaced by metals and basic radicals to form salts. Like all other gases, it is condensed by great cold and pressure to a liquid which freezes and solidifies by its own evaporation. It is absorbed in large quantities by certain metals (esp. palladium), forming alloy-like compounds; hence, in view of quasi-metallic nature, it is sometimes called hydrogenium. It is the typical reducing agent, as opposed to oxidizers, as oxygen, chlorine, etc.

Bicarbureted hydrogen, an old name for ethylene.

Carbureted hydrogen gas. See under Carbureted.

Hydrogen dioxide, a thick, colorless liquid, H2O2, resembling water, but having a bitter, sour taste, produced by the action of acids on barium peroxide. It decomposes into water and oxygen, and is manufactured in large quantities for an oxidizing and bleaching agent. Called also oxygenated water.

Hydrogen oxide, a chemical name for water, H?O.

Hydrogen sulphide, a colorless inflammable gas, H2S, having the characteristic odor of bad eggs, and found in many mineral springs. It is produced by the action of acids on metallic sulphides, and is an important chemical reagent. Called also sulphureted hydrogen.

H2S (radar)

H2S was the first airborne, ground scanning radar system. It was developed for the Royal Air Force's Bomber Command during World War II to identify targets on the ground for night and all-weather bombing, allowing attack outside the range of the various radio navigation aids like Gee or Oboe, which were limited to about . It was also widely used as a general navigation system, allowing landmarks to be identified at long range.

The early variants of the transmitter/ receiver equipment were officially known as TR3159 (H2S Mk. I/ASV VIB) or TR3191 (H2S Mk. II). These operated in the S band at a wavelength of 9.1 cm (3 GHz) using the early cavity magnetron designs developed in 1940. After it was found the resolution of these sets was too low to be useful over large cities like Berlin, in 1943 work started on a version operating in the X band at 3 cm (10 GHz). A wide variety of these H2S Mk. III versions were produced before the Mk. IIIG was selected as the late-war standard. The US Radiation Laboratory also produced an X band system, the H2X, developed from a prototype H2S that was provided during the Tizard Mission.

On its second operational mission on 2/3 February 1943, an H2S was captured almost intact by German forces. Combined with intelligence gathered from the surviving crew, they learned it was a mapping system and were able to determine its method of operation. This led to the introduction of the FuG 350 Naxos radar detector, which enabled Luftwaffe night fighters to home on the transmissions of H2S. The British learned of Naxos and a great debate ensued over the use of H2S. However, calculations showed that losses during this period were actually less than before; the use of H2S as a night fighter detector saved more bombers than Naxos claimed.

Development continued through the late-war Mk. IV to the 1950s era Mk. IX that equipped the V bomber fleet. The Mk. IX was tied into both the bombsight and navigation system to provide a complete long-range Navigation and Bombing System (NBS). In this form, H2S was last used in anger during the Falklands War in 1982 on the Avro Vulcan. Some H2S Mk. IX units remained in service on the Handley Page Victor aircraft until 1993, providing fifty years of service.


H2S may refer to:

  • Dynali H2S, a Belgian helicopter design
  • Hydrogen sulfide (HS), a chemical compound
  • H2S radar, the first airborne ground-mapping radar, used during World War II
  • How to Succeed in Business Without Really Trying, a 1952 book and 1961 stage musical adapted from the book