What is "oso4"

Osmic \Os"mic\, a. (Chem.) Pertaining to, derived from, or containing, osmium; specifically, designating those compounds in which it has a valence higher than in other lower compounds; as, osmic oxide. Osmic acid. (Chem.)

1. Osmic tetroxide. [Obs.]

2. Osmic acid proper, an acid analogous to sulphuric acid, not known in the free state, but forming a well-known and stable series of salts (osmates), which were formerly improperly called osmites.

   Osmic tetroxide (Chem.), a white volatile crystalline substance, OsO4, the most stable and characteristic of the compounds of osmium. It has a burning taste, and gives off a vapor, which is a powerful irritant poison, violently attacking the eyes, and emitting a strong chlorinelike odor. Formerly improperly called osmic acid.

Tetroxide \Tet*rox"ide\, n. [Tetra- + oxide.] (Chem.) An oxide having four atoms of oxygen in the molecule; a quadroxide; as, osmium tetroxide, OsO4.