Osmium tetroxide is widely used to oxidise alkenes to the vicinal diols, adding two hydroxyl groups at the same side (syn addition). Osmium tetroxide is also a widely used staining agent used in transmission electron microscopy (TEM) to provide contrast to the image.
O 1346 (OTTO) Osmic acid, solution, 2% w/v Cas 20816-12-0 - used as a secondary fixative of tissues.