A carbon dioxide absorbing apparatus having a base containing adjacent inhalation and exhalation passages, a through opening or passage centrally located on the base and in communication with the inhalation passage, a gasket located on the base having a raised lip annular opening coaxial with the through...http://www.google.es/patents/US4353366?utm_source=gb-gplus-sharePatente US4353366 - Carbon dioxide absorber
