Bleaching photography

Hydrogen peroxide in aqueous solution has many uses, because the products from its reaction are either water or oxygen, which are generally innocuous. The chief use is bleaching of textiles, both natural and synthetic, and of wood pulp for paper. Other uses are the oxidation of dyestuffs, in photography and in the production of... 

The reducing action of sulphurous acid and sulphites in solution leads to their use as mild bleaching agents (for example magenta and some natural dyes, such as indigo, and the yellow dye in wool and straw are bleached). They are also used as a preservative for fruit and other foodstuffs for this reason. Other uses are to remove chlorine from fabrics after bleaching and in photography. 

In the traditional silver halide dye-forming and dye-bleach processes, metal complex dyes are not normally used.62,63 However, metal complex azo dyes have been claimed15 for use in color diffusion transfer photography employing non-diffusible magenta dye-releasing dyes which, upon development of the silver halide layer, release a diffusible magenta dye (Scheme 7). 

Sodium sulfite (Na SO ) is an antioxidant, used as a preservative except with meats. It is also used for water treatment and in photography and textile bleaching. 

Potassium oxalate, along with calcium oxalate, is found in leaves and roots of certain plants. It is used for cleaning and bleaching straw and for removing stains. It also is used in photography, in clinical tests, as a secondary pH standard, and in wet chemical analysis. The analytical apphcation involves standardization of many oxidizing agents in titrimetric analysis. 

Uses of the halide acids.—The hydrochloric acid formed as a by-product in tne manufacture of sodium sulphate from sodium chloride is sufficient to meet commercial requirements, and accordingly the acid is cheap. The largest amount of hydrochloric acid or hydrogen chloride is used in the manufacture of chlorine and chlorine products—hypochlorites, bleaching powder, and chlorates. It is also used in the manufacture of many of the metal chlorides—zinc, tin, etc. This acid is also used for general purposes in laboratories, in analytical and metallurgical work, in the manufacture of colours. Smaller quantities are used medicinally. Hydro-bromic acid or the bromides and hydriodic acid or the iodides are used medicinally, in photography, and in analytical chemistry. Hydriodic acid is an important... 

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