Thiosulfates photographic fixer

Silver Thiosulfate. Silver thiosulfate [23149-52-2], Ag 2 y is an insoluble precipitate formed when a soluble thiosulfate reacts with an excess of silver nitrate. In order to minimize the formation of silver sulfide, the silver ion can be complexed by haUdes before the addition of the thiosulfate solution. In the presence of excess thiosulfate, the very soluble Ag2(S203) 3 and Ag2(S203) 3 complexes form. These soluble thiosulfate complexes, which are very stable, are the basis of photographic fixers. Silver thiosulfate complexes are oxidized to form silver sulfide, sulfate, and elemental sulfur (see Thiosulfates). 

A simple and economical method for recovering silver residues by dissolution in used photographic fixer (thiosulfate) solution, then precipitation by addition of zinc powder, is detailed [1]. After the acid digestion phase of silver recovery operations, addition of ammonia followed immediately by addition of ascorbic acid as reducant gives a near-quantitative recovery of silver metal, and avoids the possibility of formation of silver nitride [2],... 

Ammonia complexes.. EflFect of complex formation on solubility. Cyanide complexes. The cyanide process of treating gold and silver ores. Complex halides and other complexes. Sodium thiosulfate as photographic fixer. Hydroxide complexes. Amphoteric hydroxides. Sulfide complexes. Equilibrium expressions for complex formation. Structural chemistry—tetrahedral, octahedral, square complexes. Existence of isomers. 

Would sodium cyanide be an effective substitute for sodium thiosulfate as a photographic fixer ... 

Sulfur Complexes. Silver compounds other than sulfide dissolve in excess thiosulfate. Stable silver complexes are also formed with thiourea. Except for the cyanide complexes, these sulfur complexes of silver are the most stable. In photography, solutions of sodium or ammonium thiosulfate fixers are used to solubilize silver hahdes present in processed photographic emulsions. When insoluble silver thiosulfate is dissolved in excess thiosulfate, various silver complexes form. At low thiosulfate concentrations, the principal silver species is Ag2(S203) 2j high thiosulfate concentrations, species such as Ag2(S203) 3 are present. Silver sulfide dissolves in alkaline sulfide solutions to form complex ions such as Ag(S 2 Ag(HS) 4. These ions are... 

Alkali fixers, especially those compounded with ammonium thiosulfate, are the most efficient and effective with modern emulsions in both film and paper. Although they have been used for scientific purposes since at least the 1930s, they have only recently become commercially available. Photographers Formulary TF-4 is the first to be widely distributed. The formula forTF-3, a fixer having similar properties but a shorter shelf life, is given in the Formulas section. 

Changing the fixer before it reaches exhaustion is critical for the longevity of photographic materials. Ammonium thiosulfate fixers will smell like ammonia when they are fresh, and... 

During the developing process of black-and-white film, silver bromide is removed from photographic film by the fixer. The major component of the fixer is sodium thiosulfate. The net ionic equation for the reaction is... 

This greatly increases the solubility of the silver bromide (Fig. 16.14). The formation of this complex ion is an important step in the development of photographic images thiosulfate ion is a component of the fixer that brings silver bromide into solution from the unexposed portion of the film. 

The structures of the sulfate and thiosulfate ions are compared in FIGURE 22.21. Thiosulfate salts are used industrially in the paper-making and textile industries and are the fixer solutions in the development of photographic film. 

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