Hopcalite is a mixture of copper and manganese oxides used as catalyst to convert carbon monoxide into carbon dioxide when exposed to the oxygen in air A variety of composition for are known Hopcalite II is approximately 3 1 manganese dioxide copper oxide Hopcalite I is a mixture of 50 MnO 30 CuO 15 Co 2 O 3 and 5 Ag 2 O