1. Britton ..J. Chem. Soc., 1926, 269.
2. --, Battrick ..Ibid., 1932, 196.
3. Mellor..A Comprehensive Treatise on Inorganic and Theoretical Chemistry, Longmans, 1924,5, 570.
4. Thomson..Phil. Mag., 1811,37, 278.
5. Spencer ..The Metals of the Rare Earths, Longmans, Green & Co., 1919, p. 39.