Methyl red

Overview
Methyl Red, also called C.I. Acid Red 2, is an indicator dye that turns red in acidic solutions. It is an azo dye, and is a dark red crystalline powder.

Methyl red is a pH indicator; it is red in pH under 4.4, yellow in pH over 6.2, and orange in between.

In microbiology, methyl red is used in the Methyl Red (MR) Test, used to identify bacteria producing stable acids by mechanisms of mixed acid fermentation of glucose. Cf. Voges-Proskauer (VP) test.

Murexide and methyl red are investigated as promising enhancers of sonochemical destruction of chlorinated hydrocarbon pollutants. 

Methyl red is classed by the IARC in group 3 - unclassified as to carcinogenic potential in humans. Its risk phrases are.