1. n. [Drilling Fluids]

A pH indicator used in alkalinity titration of mud filtrate and water samples. The indicator is yellow in solutions above pH 4.3, and red below pH 4.3. "M" alkalinity is the titration volume measured using the methyl orange indicator. Methyl orange is often replaced in test kits by bromocresol green.

See: alkalinity test,  bromocresol green,  phenolphthalein,  titration