Found 2 items, similar to Congo red.
English → English (WordNet) Definition: congo red congo red n : a red-brown azo dye especially as a chemical pH indicator (congo red is red in basic and blue in acidic solutions)
English → English (gcide) Definition: Congo red Congo red \Congo red\ (Chem.) An artificial red dye from which the Congo group received its name. It is also widely used either in aqueous solution or as test paper ( Congo paper) for the detection of free acid, which turns it blue. [Webster 1913 Suppl.]