(for creatinine) to the suspected solution add a little of a dilute solution of sodium nitroprusside, and then carefully put in a few drops of a weak solution of sodium hydroxide; a ruby red color results, changing to blue on warming with acetic acid. (for nitric acid in the urine) distill 200 mL of urine with 0.2 part of sulfuric or hydrochloric acid, receiving the distillate in a potassium hydroxide solution. If m -phenyldiamine is added, a yellow color will form; if there is added pyrogallic acid in aqueous solution with a little sulfuric acid, the color will be brown; but sulfanilic acid in solution, followed in ten minutes by naphthylamine hydrochlorate, produces a red tint.