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A universal indicator is a pH indicator made of a solution of several compounds that exhibits several smooth color changes over a wide range pH values to indicate the acidity or alkalinity of solutions.
Although there are several commercially available universal pH indicators, most are a variation of a formula patented by Yamada in 1933. Details of this patent can be found in Chemical Abstracts. Experiments with Yamada's universal indicator are also described in the Journal of Chemical Education.