In each of the groups , in the absence of an indication to the contrary, a substance is classified in the last appropriate place. In this subclass: Within each one of main groups , a mixture of substances is classified at least according to the essential ingredient. If more than one ingredient is essential, the mixture is classified, in the absence of an indication to the contrary, according to the essential ingredient which belongs to the last appropriate place in the sequence of substance. Treatment by mixtures of substances covered by two or more of main groups is classified in each appropriate main group. In this subclass, the treatment of textiles, not provided for elsewhere in class , is classified according to the following principles: Treatment of textiles characterised by the treating agent in groups . Treatment of textiles characterised by the process in group . Processes using enzymes or micro-organisms in order to: liberate, separate or purify a pre-existing compound or composition, or to treat textiles or clean solid surfaces of materials are further classified in subclass . TREATMENT OF FIBRES, THREADS, YARNS, FABRICS, OR FIBROUS ARTICLES with inorganic substances with non-macromolecular organic substances graft polymerisation with macromolecular substances BIOCHEMICAL TREATMENT PHYSICAL TREATMENT TREATMENT CHARACTERISED BY THE PROCESS TREATMENT OF FEATHERS PRODUCING MULTI-LAYER FABRICS In this group, the following term is used with the meaning indicated: "treatment" means, in the absence of an indication to the contrary, the treatment which leads to the end product, e.g. treatment with barium sulfate can mean treatment with barium chloride and with sulfuric acid in two separate steps. If a compound used in the treatment is characterised by itscation, classification for this aspect is made in main group only and not in groups ; metallisation by treatment with a metal salt, followed by reduction, is classified in group . In this group, it is desirable to add the indexing codes of group . In this group, the following term is used with the meaning indicated: "treatment" means, in the absence of an indication to the contrary, the treatment which leads to the end product, e.g. treatment with chloroacetic acid can mean treatment with chloroacetylchloride and saponification in two separate steps. In this group, it is desirable to add the indexing codes of group . In this group, the following term is used with the meaning indicated: "treatment" means, in the absence of an indication to the contrary, the treatment which leads to the end product, e.g.: treatment with polyvinylalcohol can mean treatment with polyvinylacetate and subsequent saponification in a separate step; treatment with aminoplast can mean the delayed cure process or the treatment with precondensation products, or with e.g. urea and with formaldehyde in two separate steps. In this group, it is desirable to add the indexing codes of group . In this group, it is desirable to add the indexing codes of group . In this group, it is desirable to add the indexing codes of group . Examples: the swelling of cellulose with alkaline hydroxides is classified in groupand indexed in group ; the treatment of cellulose with amines is classified in groupand indexed in group ; the treatment of polyester fibres with polyesters is classified in group and indexed in group ; the treatment of wool with pepsin is classifiedin group and indexed in group ; the treatment of cellulose with silicon tetrachloride in the form of a foam is classified in groups, and indexed in group . Blends of fibres are indexed according to each constituent fibre.