Hydrion is a trademarked name for a popular line of compound pH indicators, marketed by Micro Essential Laboratory Inc., exhibiting a series of color changes (typically producing a recognizably different color for each pH unit) over a range of pH values.
Although solutions are available, the most common forms of Hydrion are a series of papers impregnated with various mixtures of indicator dyes.
It is considered a "universal indicator".
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