A better appearance may be given to cotton and many other fabrics by passing them through bleaching solutions. The most effective bleaching agent is bleaching powder, a white powder made by passing chlorine gas (made by heating common salt and sulphuric acid) into oxide of lime (CaO). Other bleaching agents, such as sodium sulphite (Na2SO3) and sodium peroxide (Na2O2), are sometimes used. The lime in the bleaching powder holds the chlorine gas. The cloth to be bleached is placed in a mixture of bleaching powder and water. The chlorine gas from the bleaching powder acts on the water forming hydrochloric acid and oxygen. The oxygen combines with the coloring matter and destroys it, thus leaving a white-surfaced fabric. Bleaching is a distinct chemical action and may weaken the fabric.

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