R ecent publicatio ns from t.his laboratory d escribe some unus ual properties, such as crimping and helical coiling, induced by heterogeneous, chemical crosslin king of polycaprolactam fibers. The follo wing crosslinks are involved : yield one eq ui valent of formaldehyde for each equivalent of hydrolyzable methylene group. This permits t he application of the chromotropic acid method for determining formaldehyde to the estimation of t he number of crosslinks i n t he fib er, when used in co

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... unction with a previously reported conductometric m ethod for the determination of s uUhydryl group. A general method has bee n worked o ut, with special attention to sulfur-containing degradation products (of the crosslinks) that may interfere with the analysis.