1. H. K. Alber, Ind. Engng. Chem., Analyt. Ed.12, 764 (1940).
2. M. Sobotka, Mikrochem.36/37, 407 (1951).
3. J. M. Clavera undF. Moreno Martin, An. Soc. españ. Fisica Quim.32, 690 (1934).
4. G. R. Clemo undA. McQuillen, J. Chem. Soc. London1935, 1220.
5. C. J. Ksanda undH. E. Merwin, Amer. Mineralogist.24, 482 (1939).