Osmic acid is used to test for fats and oil. Procedure. To small quantity of oil or fat in a test tube add 1% of osmic acid and boil. Result. A Black precipitate shows the presence of oil or fat
n. A crystalline oxide of osmium that is a volatile caustic and strong oxidizing agent, the aqueous solution of which is used as a stain for fat and myelin and as a general fixative for electron microscopy.
Osmic Acid or Osmium Tetroxide (OsO4): A selective stain for unsaturated lipids and for lipoproteins such as myelin, which it stains black. Also used as a fixative, especially for electron microscopy.