(for carbon monoxide in the blood) add to the blood 20 volumes of water and sodium hydroxide in solution; if CO is present, it becomes cloudy and then red, and eventually flakes of red float on the surface. (for cholesterol) dissolve the sample in chloroform and add an equal volume of strong sulfuric acid; if cholesterol is present, the solution becomes bluish red and slowly changes to a violet red, and the sulfuric acid becomes red, with a green fluorescence. (for indole) to the solution to be tested add a little nitric acid, and drop in slowly a solution of potassium nitrite (2 per cent): a red color shows that indole is present, and a red precipitate is afterward formed. (for creatinine) to the yellow solution obtained in the Weyl test , add an excess of acetic acid and heat; a green color results, which turns to blue.