Cystine amalgam reduction

If both cysteine and cystine are to be determined in a mixture, the cystine is first reduced with a sodiiun amalgam. In this reaction two moles of cysteine are formed from one mole of cystine. Thus one mole of cystine after reduction with the sodium amalgam consumes four moles of copper. 

Dewar published many papers on spectroscopy, partly with G. D. Liveing in Cambridge. Besides his work on pyridine (see p. 564) he published on the oxidation of phenol and the structure of unsaturated hydrocarbons, derivatives of meconic acid, cystine (with Gamgee), the conversion of quinoline (leucoline) into aniline, the quinoline series, the formation of hydrocyanic acid in the carbon arc burning in air, and the reduction of invett sugar by sodium amalgam, in which he found that both glucose and fructose are reduced, not fructose alone as Linnemann supposed (see p. 820). 

The method was also used for the determination of cysteine and glutathi but its application presents, mainly in biological materials, the doubts expressed in the previous paragraphs. For the determination of cystine a method is employed based on the reduction of cystine in an acidic medium with sodium amalgam or on the reaction with sulphite at pH 8-12 according to equation ... 

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