Ethylene oxide is a colorless gas at 25 C and is a mobile liquid at 0 C viscosity of liquid ethylene oxide at 0 C is about 5.5 times lower than that of water. The gas has a characteristic sweet odor of ether, noticeable when its concentration in air exceeds 500 ppm. Ethylene oxide is readily soluble in water, ethanol, diethyl ether and many organic solvents. Ethylene oxide, also called oxirane, is the organic compound with the formula C2H4O. It is a cyclic ether. This means that it is composed of two alkyl groups attached to an oxygen atom in a cyclic shape (circular). This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered ring consisting of two carbon and one oxygen atom. Because of its special molecular structure, ethylene oxide easily participates in the addition reaction, opening its cycle, and thus easily polymerizes. Ethylene oxide is isomeric with acetaldehyde. Although it is a vital raw material with diverse applications, including the manufacture of products like polysorbate-20 and polyethylene glycol that are often more effective and less toxic than alternative materials, ethylene oxide itself is a very hazardous substance: at room temperature it is a flammable, carcinogenic, mutagenic, irritating, and anaesthetic gas with a misleadingly pleasant aroma.