Murexide test is a color test for uric acid and some other purines. The (solid) sample is first treated with small volume of a concentrated acid such as hydrochloric acid, nitric acid, which is slowly evaporated away; subsequent addition of ammonia (NH) gives a purple color if uric acid was present, due to formation of murexide, or a yellow color that turns to red on heating if xanthine or its derivatives are present.