This part of ISO 1833 specifies a method, using formic acid, to determine the percentage of polyamide fibre, after removal of non-fibrous matter, in textiles made of binary mixtures of - polyamide and- cotton, viscose, cupro, modal, polyester, polypropylene, chlorofibre, acrylic or glass fibre. It is also applicable to mixtures with wool and animal hair, but when the wool content exceeds 25 %, the method described in ISO 1833-4 should be used.