1. Gosudarstvennaya Farmakopeya SSSR, 9th ed., Moscow (1968), p. 6.
2. V. N. Bukin, Vitamins [in Russian], Moscow-Leningrad (1941), p. 220.
3. V. A. Devyatnin, Vitamins [in Russian], Moscow (1948), p. 152.
4. V. M. Berezovskii, The Chemistry of Vitamins [in Russian], Moscow (1959), p. 43.
5. T. Macek, Am. J. Pharm.,132, 443 (1960).