The interaction of fluorine with metallic oxides at cold temperatures yields metallic fluorides and oxygen; metallic oxyfluorides, such as MoO 2 F 2 , may also be formed. Nonmetallic oxides either add fluorine, for example SO 2 + F 2 = SO 2 F 2 , or the oxygen in the oxides is replaced by fluorine, for example, SiO 2 + 2F 2 = SiF 4 + O 2 . Glass reacts very slowly with fluorine, except in the presence of water, when the reaction proceeds rapidly. Water interacts with fluorine according to the reaction 2H 2 O + 2F 2 = 4HF + O 2 , a process accompanied by the formation of OF 2 and hydrogen peroxide, H 2 O 2 . The nitrogen oxides NO and NO 2 combine readily with fluorine, forming nitrosyl fluoride, FNO, and nitroxyl fluoride, FNO 2 , respectively. Carbon monoxide combines with fluorine on heating to form carbonyl fluoride: CO + F 2 = COF 2 .