If the solution appears yellow precipitate, indicating that there are three or five hydroxyl-containing flavonoids. (3) Lead acetate reaction: 2 ml test solution was took to the test tube, then added a drop of lead acetate solution to the color reaction in the test tube, the change of the color observed, and it can check whether there are total flavonoids. If the solution appears yellow precipitate, explain the flavonoids containing hydroxyl groups.