This part of ISO 1833 specifies a method, using sulfuric acid, to determine the mass percentage of chlorofibres and certain other fibres, after removal of non-fibrous material, in textiles made of mixtures of cotton, viscose, cupro, modal, lyocell, acetate, triacetate, polyamide, polyester, elastomultiester, certain acrylic and certain modacrylic fibreswith chlorofibres based on homopolymers of vinyl chloride, polypropylene, elastolefin, melamine and polypropylene/polyamide bicomponent. The modacrylics concerned are those which give a limpid solution when immersed in concentrated sulfuric acid (Á = 1,84 g/ml at 20°C).] 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.