Positive test for sulfate ions in a solution. This white precipitate of barium sulfate indicates that the original solution contains sulfate. Before this, a few drops of nitric acid were added to the test solution, followed by a few drops of barium chloride solution. The barium reacted with the sulfate to form this insoluble barium sulfate, which precipitates instantly. See clips K004 2737-9 for all the stages in this test.