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- Exposed silver halide oxidizes the hydroquinone, which then oxidizes a nucleating agent in the film, which is attacked by a hydroxide ion and converts it via hydrolysis into a nucleating agent for silver metal, which it then forms on unexposed silver halide, creating a silver image.
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Silver is a chemical element; it has symbol Ag (from Latin argentum 'silver', derived from Proto-Indo-European *h₂erǵ'shiny, white') and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. [ 8 ] .
- Overview
- Properties, uses, and occurrence
- Compounds
silver (Ag), chemical element, a white lustrous metal valued for its decorative beauty and electrical conductivity. Silver is located in Group 11 (Ib) and Period 5 of the periodic table, between copper (Period 4) and gold (Period 6), and its physical and chemical properties are intermediate between those two metals.
Together with gold and the platinum-group metals, silver is one of the so-called precious metals. Because of its comparative scarcity, brilliant white colour, malleability, ductility, and resistance to atmospheric oxidation, silver has long been used in the manufacture of coins, ornaments, and jewelry. Silver has the highest known electrical and thermal conductivity of all metals and is used in fabricating printed electrical circuits and as a vapour-deposited coating for electronic conductors; it is also alloyed with such elements as nickel or palladium for use in electrical contacts. Silver also finds use as a catalyst for its unique ability to convert ethylene to ethylene oxide, which is a precursor of many organic compounds. Silver is one of the noblest—that is, least chemically reactive—of the transition elements.
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Silver ornaments and decorations have been found in royal tombs dating back as far as 4000 bce. It is probable that both gold and silver were used as money by 800 bce in all countries between the Indus and the Nile.
Silver is widely distributed in nature, but the total amount is quite small when compared with other metals; the metal constitutes 0.05 part per million of Earth’s crust. Practically all sulfides of lead, copper, and zinc contain some silver. Silver-bearing ores may contain amounts of silver from a trace to several thousand troy ounces per avoirdupois ton, or about 10 percent.
Unlike gold, silver is present in many naturally occurring minerals. For silver the more important deposits commercially are such compounds as the minerals tetrahedrite and argentite (silver sulfide, Ag2S), which is usually associated with other sulfides such as those of lead and copper, as well as several other sulfides, some of which contain antimony as well. Silver is found generally in lead ores, copper ores, and cobalt arsenide ores and is also frequently associated with gold in nature. Most silver is derived as a by-product from ores that are mined and processed to obtain these other metals. Deposits of native (chemically free, or uncombined) silver are also commercially important.
For silver the preeminently important oxidation state in all of its ordinary chemistry is the state +1, although the states +2 and +3 are known.
Silver compounds include silver chloride (AgCl), silver bromide (AgBr), and silver iodide (AgI). Each of these salts is used in photography. Silver chloride serves as the light-sensitive material in photographic printing papers and, together with silver bromide, in certain films and plates. The iodide is also used in the manufacture of photographic papers and films, as well as in cloud seeding for artificial rainmaking and in some antiseptics. All three halides are derived from silver nitrate (AgNO3), which is the most important of the inorganic silver salts. Besides these other salts, silver nitrate is also the starting material for the production of the silver cyanide used in silver plating.
- The Editors of Encyclopaedia Britannica
From a chemical standpoint, conventional black and white negative film is processed by a developer that reduces silver halide to silver metal, exposed silver halide is reduced faster than unexposed silver halide, which leaves a silver metal image.
The gelatin silver print or gelatin developing out paper (DOP) is a monochrome imaging process based on the light sensitivity of silver halides. They have been made for both contact printing and enlarging purposes by modifying the paper's light sensitivity.
Oct 1, 2011 · The most significant image change was made by Ardashir's son, Shapur I (241-270 A.D.) when the throne was eliminated and the altar was flanked by two holy figures. Later, mintmarks and regnal dates would appear.
Gelatin silver papers are commercially manufactured by applying an emulsion of light-sensitive silver salts in gelatin to a sheet of paper coated with a layer of baryta, a white pigment mixed with gelatin. The sensitized paper is exposed to light through a negative and then developed out—that is, made visible in a chemical reducing solution.
What is Silver? Silver is a soft, white metal that usually occurs in nature in one of four forms: 1) as a native element; 2) as a primary constituent in silver minerals; 3) as a natural alloy with other metals; and, 4) as a trace to minor constituent in the ores of other metals.
