This part of ISO 1833 specifies a method, using hypochlorite, to determine the percentage of protein fibre, after removal of non-fibrous matter, in textiles made of binary mixtures of certain non-protein fibres and one protein fibre, as follows: — wool, chemically-treated wool, other animal-hair fibres, silk, regenerated protein fibres based on casein, and — cotton, cupro, viscose, modal, acrylic, chlorofibres, polyamide, polyester, polypropylene, glass and elastane. If several protein fibres are present, the method gives the total of their amounts but not their individual quantities.