... > SECTION XVI - MACHINERY AND MECHANICAL APPLIANCES; ELECTRICAL EQUIPMENT; PARTS THEREOF; SOUND RECORDERS AND REPRODUCERS, TELEVISION IMAGE AND SOUND RECORDERS AND REPRODUCERS, AND PARTS AND ACCESSORIES OF SUCH ARTICLES > CHAPTER 84 - NUCLEAR REACTORS, BOILERS, MACHINERY AND MECHANICAL APPLIANCES; PARTS THEREOF > 8421 Centrifuges, including centrifugal dryers; filtering or purifying machinery and apparatus, for liquids or gases > Filtering or purifying machinery and apparatus for gases > Other > Other > Machinery and apparatus for filtering or purifying other gases > By a catalytic process