OsO4; [20816-12-0]; FW 254.20
Solid vaporizes by sublimation. Should be used only under the hood. Affects eyes. Use eye protection.
EM Grade, glass ampoules in black paper. No sticky labels. Osmium purity >99.95%. Light sensitive.

Special note on handling Osmium Tetroxide (reference 5, appendices A:2.5, "Books" , Procedures in Electron Microscopy)

"Great care must be taken with osmium tetroxide. The crystals melt at 40°C and are extremely slow to dissolve in water. Both the crystals and diluted aqueous solutions give off fumes of osmium tetroxide, even at 0°C. It has an extremely low TLV (0.0002ppm). Osmium fixatives must therefore always be handled in a fume hood (cupboard), and because they act so rapidly, skin contact must be avoided at all times."

TLV= Eight hour average Threshold Limit Value measured in milligrams per cubic meter of air.