This part of ISO 1833 specifies a method, using sulfuric acid, to determine the percentage of chlorofibres, after removal of non-fibrous material, in textiles made of binary mixtures of — chlorofibres based on homopolymers of vinyl chloride (after-chlorinated or not) and — cotton, viscose, cupro, modal, acetate, triacetate, polyamide, polyester, certain acrylic and certain modacrylic fibres. [The modacrylics concerned are those which give a limpid solution when immersed in concentrated sulfuric acid (ρ = 1,84 g/ml).] This method can be used, particularly in place of the methods described in ISO 1833-12 and ISO 1833-13, in all cases where a preliminary test shows that the chlorofibres do not dissolve completely either in dimethylformamide or in the azeotropic mixture of carbon disulfide and acetone.