In section C, the definitions of groups of chemical elements are as follows: Alkali metals: Li, Na, K, Rb, Cs, Fr Alkaline earth metals: Ca, Sr, Ba, Ra Lanthanides: elements with atomic numbers 57 to 71 inclusive Rare earths: Sc, Y, Lanthanides Actinides: elements with atomic numbers 89 to 103 inclusive Refractory metals: Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W Halogens: F, Cl, Br, I, At Noble gases: He, Ne, Ar, Kr, Xe, Rn Platinum group: Os, Ir, Pt, Ru, Rh, Pd Noble metals: Ag, Au, Platinum group Light metals: alkali metals, alkaline earth metals, Be, Al, Mg Heavy metals: metals other than light metals Iron group: Fe, Co, Ni Non-metals: H, B, C, Si, N, P, O, S, Se, Te, noble gases, halogens Metals: elements other than non-metals Transition elements: elements with atomic numbers 21 to 30 inclusive, 39 to 48 inclusive, 57 to 80 inclusive, 89 upwards Section C covers: pure chemistry, which covers inorganic compounds, organic compounds, macromolecular compounds, and their methods of preparation; applied chemistry, which covers compositions containing the above compounds, such as: glass, ceramics, fertilisers, plastics compositions, paints, products of the petroleum industry. It also covers certain compositions on account of their having particular properties rendering them suitable for certain purposes, as in the case of explosives, dyestuffs, adhesives, lubricants, and detergents; certain marginal industries, such as the manufacture of coke and of solid or gaseous fuels, the production and refining of oils, fats and waxes, the fermentation industry (e.g., brewing and wine-making), the sugar industry; certain operations or treatments, which are either purely mechanical, e.g., the mechanical treatment of leather and skins, or partly mechanical, e.g., the treatment of water or the prevention of corrosion in general; metallurgy, ferrous or non-ferrous alloys. In the case of operations, treatments, products or articles having both a chemical and a non-chemical part or aspect, the general rule is that the chemical part or aspect is covered by section C. In some of these cases, the chemical part or aspect brings with it a non-chemical one, even though purely mechanical, because this latter aspect either is essential to the operation or treatment or constitutes an important element thereof. It has seemed, in fact, more logical not to dissociate the different parts or aspects of a coherent whole. This is the case for applied chemistry and for the industries, operations and treatments mentioned in Notes (1)(c), (d) and (e). For example, furnaces peculiar to the manufacture of glass are covered by class and not by class . There are, however, some exceptions in which the mechanical (or non-chemical) aspect carries with it the chemical aspect, for example: Certain extractive processes, in subclass ; The chemical purification of air, in subclass ; Chemical methods of fire-fighting, in subclass ; Chemical processes and apparatus, in class ; Impregnation of wood, in subclass ; Chemical methods of analysis or testing, in subclass ; Photographic materials and processes, in class , and, generally, the chemical treatment of textiles and the production of cellulose or paper, in section D. In still other cases, the pure chemical aspect is covered by section C and the applied chemical aspect by another section, such as A, B or F, e.g., the use of a substance or composition for: treatment of plants or animals, covered by subclass ; foodstuffs, covered by class ; ammunition or explosives, covered by class . When the chemical and mechanical aspects are so closely interlocked that a neat and simple division is not possible, or when certain mechanical processes follow as a natural or logical continuation of a chemical treatment, section C may cover, in addition to the chemical aspect, a part only of the mechanical aspect, e.g., after-treatment of artificial stone, covered by class . In this latter case, a note or a reference is usually given to make the position clear, even if sometimes the division is rather arbitrary. This class does not cover mechanical features provided for elsewhere, e.g. mechanical working , kilns . In this subclass, the following terms or expressions are used with the meanings indicated: "fillers" includes pigments, aggregates and fibrous reinforcing materials; "active ingredients" includes processing aids or property improvers, e.g. grinding aids used after the burning process or used in the absence of a burning process; "mortars", "concrete" and "artificial stone" are to be considered as a single group of materials, and therefore, in the absence of an indication to be contrary, they include mortar, concrete and other cementitious compositions. LIME, MAGNESIA; SLAG ; CEMENTS MORTARS; CONCRETE; ARTIFICIAL STONE Compositions Fillers Active ingredients , Porous products Influencing or modifying the properties of mortars After-treatment CERAMICS Clay-wares Other ceramics Joining Porous products After-treatment TREATMENT OF NATURAL STONE In groups , in the absence of an indication to the contrary, classification is made in the last appropriate place. Active ingredients which react with cement compounds for forming new or modified mineralogical phases and are added before the hardening process, as well as cements added as additives to other cements, are classified in groups . In groups and , it is desirable to add the indexing codes of group . Any ingredient of compositions of mortars, concrete or artificial stone, classified in groups according to the last place rule, and which itself is determined to be novel and non-obvious, must also be classified in the last appropriate place in groups . Any ingredient of compositions of mortars, concrete or artificial stone, which is not identified by the classification in groups according to the last place rule, and which is considered to represent information of particular interest for search, may also be classified in the last appropriate place in groups . This can for example be the case when it is considered of interest to enable searching of compositions using a combination of classification symbols. Such non-obligatory classification should be given as "additional information". For example, a well defined Portland cement mortar mixture containing clay as an essential or characterising filler is classified in group and may also additionally be classified in group . In groups , it is desirable to add the indexing codes of group . In this group, in the absence of an indication to the contrary, compositions are classified according to the constituent present in the highest proportion by weight. In this group, magnesium is considered as an alkaline earth metal. In this group, a composite is considered as a sintered mixture of different powdered materials, other than sintering aids, the materials being present as separate phases in the sintered product. In this group, fine ceramics are considered as products having a polycrystalline fine-grained microstructure, e.g. of dimensions below 100 micrometers. The production of ceramic powder is classified in this group in so far as it relates to the preparation of powder with specific characteristics. Any ingredient of a refractory mortar composition containing a hydraulic cement, e.g. aluminous cement, classified in group , which is considered to represent information of interest for search, may also be classified in the last appropriate place in groups . This can, for example, be the case when it is considered of interest to enable searching of compositions using a combination of classification symbols. Such non-obligatory classification should be given as "additional information". For example, such an additional classification in group may be given for an organic retarder added to the mortar composition. The products covered by this group are usually referred to as "carbon-carbon composites". Porous mortars, concrete, artificial stone or ceramic ware characterised by the ingredients or compositions are also classified in groups . In this group, the following terms or expressions are used with the meanings indicated: "mortars", "concrete" and "artificial stone" cover materials after primary shaping. Treating, e.g. coating or impregnating, a material with the same material or with a substance which ultimately is transformed into the same material is not considered after-treatment for this group but is classified as preparation of the material, e.g. a carbon body impregnated with a carbonisable substance is classified in . In groups , in the absence of an indication to the contrary, classification is made in the last appropriate place.