1. Bourcet, P.: Bull. Soc. chim. Paris 33, 572 (1905); cf. Z. analyt. Chem. 89, 428 (1932).
2. Knichoviecka, J.: Bull. trav. pharm. Etat No. 4, 6 (1925).
3. Machtou, R.: J. Pharmac. Chim. 13, 329 (1931); cf. Z. analyt. Chem. 89, 427 1932).
4. Maricq, L.: Bull. Soc. chim. Belgique 40, 361 (1931); cf. Z. analyt. Chem. 89, 427 (1932).
5. Oliveri-Mandala, E., and E. Calderaro: Gazz. chim. ital. 51, I, 324 (1921); cf. Z. analyt. Chem. 89, 427 (1932).