1. A. Michaelis and P. Becker, Ber., 15 (1882) 180.
2. C. L. Fields and J. R. Doyle, Thermochemica Acta, 8 (1974) 239.
3. R. L. Patnoe, D. A. Thesis, University of Northern Colorado, Greeley, Colorado, 1971.
4. G. Heller, Fortschr. Chem. Forsch., (1970) 206.
5. Ch. Tennyson, Fortschr. Mineral., 41 (1963) 64.