Acetic anhydride is a colourless, volatile liquid having an odor like that of glacial acetic acid, but stronger. It is very corrosive and its vapors are extremely irritating to the eyes and lungs. Care should therefore be exercised in working with it, and any spilled upon the hands should be immediately washed off. It is a condensation of two molecules of acetic acid with elimination of water. The reaction, however, is reversible, and there is always present some acetic acid due to action of water.