Alkaline iron oxide for the purification of gas

1. This chapter does not cover: (a) separate chemically defined elements or compounds with the exception of the following: artificial graphite (heading 3801); insecticides, rodenticides, fungicides, herbicides, anti-sprouting products and plant-growth regulators, disinfectants and similar products put up as described in heading 3808; products put up as charges for fire-extinguishers or put up in fire-extinguishing grenades (heading 3813); certified reference materials specified in Note 2 below; products specified in Note 3(a) or 3(c) below; (b) mixtures of chemicals with foodstuffs or other substances with nutritive value, of a kind used in the preparation of human foodstuffs (generally heading 2106); (c) slag, ash and residues (including sludges, other than sewage sludge), containing metals, arsenic or their mixtures and meeting the requirements of Note 3(a) or 3(b) to Chapter 26 (heading 2620); (d) medicaments (heading 3003 or 3004); or (e) spent catalysts of a kind used for the extraction of base metals or for the manufacture of chemical compounds of base metals (heading 2620), spent catalysts of a kind used principally for the recovery of precious metal (heading 7112) or catalysts consisting of metals or metal alloys in the form of, for example, finely divided powder or woven gauze (Section XIV or XV). 2. (A) For the purposes of heading 3822, the expression 'certified reference materials' means reference materials which are accompanied by a certificate which indicates the values of the certified properties, the methods used to determine these values and the degree of certainty associated with each value, and which are suitable for analytical, calibrating or referencing purposes. 3. Heading 3824 includes the following goods which are not to be classified in any other heading of the Nomenclature: (a) cultured crystals (other than optical elements) weighing not less than 2.5 g each, of magnesium oxide or of alkali or alkaline-earth metal halides; (b) fusel oils; Dippel's oil; (c) ink removers put up in packings for retail sale; (d) stencil correctors, other correcting fluids and correction tapes (other than those of heading 9612), put up in packings for retail sale; (e) ceramic firing testers, fusible.