The nitrates show an interesting case of isomorphism with the corresponding bismuth nitrate hydrates.[276] The stable form of the neodymium salt is the hexahydrate, Nd(NO₃)₃,6H₂O, whilst the pentahydrate, Nd(NO₃)₃,5H₂O, is labile. Of the bismuth salts, on the other hand, the pentahydrate is stable whilst the hexahydrate is labile; but mixed crystals of both pairs may be obtained, the stable neodymium hexahydrate with the unstable bismuth compound, and the stable bismuth pentahydrate with the labile neodymium salt.
[276] Bodman, Ber. 1898, 31, 1237.
Many double carbonates are obtained by dissolving the normal carbonate in excess of the precipitant. The absorption spectra of these solutions, which have a blue colour, are abnormal and very intense, and have been suggested as a basis of quantitative estimation.[277]
[277] Muthmann and Stutzel, Ber. 1899, 32, 2653.
The acetylacetone derivative forms violet crystals, melting at 144°-145°.
A large number of organic salts of neodymium have been prepared by James, Hoben, and Robinson.[278]
[278] J. Amer. Chem. Soc. 1912, 34, 276.
Atomic Weight.
—The earlier determinations of this constant were carried out by the sulphate method, the synthetic process being usually employed. Auer von Welsbach, at the time of the discovery of praseodymium and neodymium,[279] gave the values 143·6 and 140·8 respectively for their atomic weights. Brauner, who carried out a determination in 1898,[280] showed that these numbers should be interchanged, and gave the value 143·63 for neodymium. Boudouard,[281] employing the analytical sulphate method, obtained the value 143·05, whilst in the same year Jones[282] gave the value 143·6. A second determination by Brauner[283] gave the value 143·89. All these values are undoubtedly too low, the material being probably contaminated with other earths.
[279] Loc. cit.