Natural yellowish cotton

In this connection it must be borne in mind that in some of these extraction tests on naturally coloured and raw cotton, flax, wool, hair, etc, an appreciable quantity of yellowish-brown colouring matter is removed, and that raw silks of a natural yellow or green colour exhibit special behaviour if subjected to some of these tests, eg, to treatment with concentrated acids ... 

Most natural fibers, such as cotton and linen, have a yellowish look when they are first manufactured because of the presence of natural impurities. They must be bleached to pure white before they can be dyed, printed, or sold as white fabrics. The commercial process of bleaching these fabrics is very similar to the process you used in this experiment. 

The only weU-estahhshed oxide of bismuth is Bi203, which occurs in nature as the mineral hismite. Bismuth(III) oxide exists as a yellow powder. A hismuth(V) oxide is known, but it is extremely imstahle. A hydroxide - Bi(OH)3 - can also be precipitated from solutions of bismuth salts it is a white to yellowish white amorphous powder which readily loses one molecule of water to form the yellow BiO(OH) (Cotton et al., 1999 Merck Index, 1996 Gmelin, 1932). 

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