Brady's reaction. Precipitate from a positive test for a carbonyl compound with Brady's reagent (2,4-dinitrophenylhydrazine sulphate in methanol) in chemical analysis. When added to a sample containing the organic carbonyl group (aldehydes or ketones), a characteristic precipitate of 2,4-dinitrophenylhydrazone is formed. This may be coloured from yellow (as here) to deep red, depending on the carbonyl.