A colourless flammable gas, C2H4O; m.p. –111°C; b.p. 13.5°C. It is a cyclic ether (see epoxides), made by the catalytic oxidation of ethene. It can be hydrolysed to ethane-1,2-diol and also polymerizes to …-OC2H4-O-C2H4-…, which is used for lowering the viscosity of water (e.g. in fire fighting).