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Nigrosin (CI 50415, Solvent black 5) is a mixture of synthetic black dyes made by heating a mixture of nitrobenzene, aniline, and hydrochloric acid in the presence of copper or iron.
N 1615 (OTTO) Nigrosine (alcohol soluble) Cas 8005-02-5 - used in tests for viability because living cells exclude the dye, but it enters dead cells.