Steam, reaction with hair

Setting of wool and hair by either steam or hot alkaline solutions is a very old technique [54]. Steam is also very effective for producing a permanent set. Alkali and steam are known to cleave the disulfide bond in keratins [55-57] and alkaline treatments are reputed to be the most effective hair-straightening compositions because they provide the most permanent set (see the section on hair straightening in this chapter). The reaction with hydroxide is summarized by Equation E. Because sulfenic acids are generally unstable species [58], they have been suggested as intermediates that can react with the nucleophilic side chains in the keratin macromolecules [56]. 

Human hair (Note i) is freed from foreign matter (Note 2), washed well with a lukewarm solution of soap (Note 3), then twice with cold distilled water, and dried. This washing removes the natural oils from the hair (Note 4). Two kilos of the dry, washed hair is pushed into a 12-I. round-bottom Pyrex flask, and 4 1. of 20 per cent hydrochloric acid (Note 5) is added. An air-cooled reflux condenser, consisting of a wide glass tube, is attached to the flask. The hair is hydrolyzed by heating on the steam bath (Note 6) until the biuret reaction is entirely negative this requires one hundred twenty to one hundred forty-four hours. 

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