Abstract
(1). When treated with nascent hydrogen, cystine and cysteine alone among amino acids react to iodine very actively in acid solution and at room temperature.
(2). A method for the determination of cystine is described. The principle is to titrate cysteine produced by the reduction of cystine, with a standard iodate solution in presence of iodide and acid.
(3). The quantitative method must be done under strictly comparable conditions as regards the concentrations of acid, cysteine and the temperature of the solution etc.
