Amidol is a colorless

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macro ...

line compound with the molecular structure C₆H₃(NH₂)₂OH. It is a dihydrogen chloride

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...

and is used as a

photographic developer In the processing of photographic films, plates or papers, the photographic developer (or just developer) is one or more chemicals that convert the latent image to a visible image. Developing agents achieve this conversion by reducing the silve ...

. It was introduced as a developing agent for photographic papers in 1892. It is unusual amongst developing agents as it works most effectively in slightly acid conditions rather than the strongly alkaline conditions required for most other developers. As amidol ages it changes color to a dark red-brown. Developing dishes and equipment used to prepare amidol solutions are also frequently stained brown, a stain that is very persistent. Prints developed in amidol are typically a very warm brown-black colour, but overdevelopment can quickly lead to chemical fogging. Amidol's color change upon oxidation is used to advantage as a convenient

colorimetric Colorimetry is "the science and technology used to quantify and describe physically the human color perception". It is similar to spectrophotometry, but is distinguished by its interest in reducing spectra to the physical correlates of color ...

method for measuring the dissolved oxygen concentration in water supplies, rivers, etc.Westfall and Ellis, Determination of Water Quality, U.S. Govt. Printing Office (1848)

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References

{{reflist Photographic chemicals Anilines Phenols