Hopcalite

a catalyst on which carbon monoxide (CO) is oxidized to carbon dioxide (CO₂) by atmospheric oxygen; a mixture of manganese, copper, and silver oxides.

Hopcalite is used in supplementary gas mask cartridges for work in an atmosphere containing dangerous concentrations of CO and in devices for controlling the CO content in a room. The action of these devices is based upon their sensitivity to the heat released during the catalytic oxidation of CO to CO₂. Water vapors ruin the catalyst. It is also ineffective at negative temperatures.