Nitroglycerin (explosive), powerful explosive, formula C₃H₅(NO₃)₃, derived from glycerin by treatment with a mixture of concentrated sulfuric and nitric acids. It is a heavy, oily, colorless or light-yellow liquid, of specific gravity 1.60, with a sweet, burning taste. It gives two crystalline forms, one melting at 2.8° C (37° F), the other at 13.5° C (56.3° F). It solidifies at 12° C (53.6° F). Nitroglycerin burns quietly when heated in air, but explodes when heated above 218° C (424° F) or when heated in a closed vessel. It is very sensitive to shock and therefore dangerous to transport. Although discovered in 1846, nitroglycerin was not used as an explosive (see Explosives) until the Swedish engineer and inventor Alfred Nobel used it in making dynamite in 1866. Nitroglycerin is a common explosive today and is usually mixed with an inert, porous material such as sawdust. When detonated, it produces about 10,000 times its own volume of gas. It is 8 times as powerful as gunpowder in proportion to relative weight, and 13 times as powerful in proportion to relative volume. Nitroglycerin is used medically, in doses of 0.2 to 0.6 mg, as an agent to cause dilation of blood vessels.