The mucic acid test is used to identify the presence of the sugar galactose in food or in synthetics manufacture. When concentrated nitric acid is heated together with galactose, a dicarboxylic acid called mucic acid forms as a white precipitate, which counts as a positive result.
The mucic acid test gives a positive result with several galactose-containing substances such as lactose and dulcite. With these other sugars, there is no formation of a white precipitate when heated with nitric acid, but an acid that is soluble in water. To test the presence of other sugars, the Benedict's test, Barfoed's test and other tests in sugar analysis are usually conducted.