1. Browning undPalmer, Z. anorg. Chem.62, 218 (1909).
2. A. Gatterer, Ricerche Spettroscopiche,1, 201 (1946). Spectrochim. Acta,3, 214 (1947).
3. R. A. Lomakin, Z. anorg. u. allg. Chem.187, 75 (1930).
4. K. E. Mann, Aluminium23, 140 (1941).
5. K. Pfeilsticker, Spectrochim. Acta1, 424 (1940).