Millon's reagent

A few drops of the reagent are added to the test solution, which is then heated gently.

A reddish-brown coloration or precipitate indicates the presence of tyrosine residue which occur in nearly all proteins.

[1] The test was developed by the French chemist Auguste Nicolas Eugene Millon.

[2] The reagent is made by dissolving metallic mercury in nitric acid and diluting with water, forming mercuric nitrate (Hg[NO3]2).

Therefore, the biuret test or the ninhydrin reaction are used along with it to confirm the presence of proteins.

Proposed formation of nitrosophenol ligand in the early stages of the Millon test.