1. J. Roman, Manuel de sigillographie francaise (Picard, Paris, 1912).
2. Fr. Weech, Archiv. Zeitschr. 7, 280 (1882).
3. F. Philippi, Archiv. Zeitschr. 7, 284 (1882).
4. J. J. Dobbie and J. J. Fox, Trans. Chem. Soc., No. 105, 795 (1914).
5. M. Cassar, G. V. Robins, A. Alstin, and R. A. Fletton, Nature (London, U.K.), No. 303, 238 (1983).