(for uric acid) the substance tested is treated with nitric acid, evaporated, and moistened with diluted ammonia solution; if uric acid is present, murexide will be formed, and a purple color is produced. Called also murexide test. (for xanthine) warm with freshly prepared chlorine water containing a trace of nitric acid until gas ceases to be produced; contact with gaseous ammonia develops a pink or purple color. (for xanthine bodies) dissolve in warm chlorine water, evaporate, and treat with diluted ammonia solution; a pink or purple color will form, changing to violet on the addition of sodium or potassium hydroxide solution.