Cobalt filter

The cobalt filter, or more specifically the cobalt-on-alumina filter, was effective when used as a catalyst to remove carbon monoxide from cigarette smoke, but the cobalt was "poisoned" (rendered ineffective) after being exposed to the moisture contained in tobacco. Philip Morris developed an external cobalt filter that could be used adjacent to a cigarette, which avoided exposing the cobalt filter directly to the moisture contained in the tobacco. One filter was good for one 20-pack of cigarettes, according to the testimony of William Anthony Farone in the case of Betty Bullock vs. Philip Morris and DuPar's Restaurant.