The _chloride_, NdCl₃,6H₂O, is obtained by crystallisation from aqueous solutions; it is also precipitated by addition of water to an alcoholic solution. It forms large deliquescent rose-coloured crystals; 100 parts of water at 13° dissolve 246·2 parts of the salt, the saturated solution having the density 1·741; at 100°, 511·6 parts are dissolved. The solution resembles those of the other chlorides of the group in that it readily dissolves the rare earth oxalates. When heated in a current of hydrogen chloride of 130°, the hexahydrate yields a monohydrate, NdCl₃,H₂O; at 160° the anhydrous chloride is obtained as a very deliquescent rose-coloured powder, which melts at a red heat to a clear red liquid. The anhydrous chloride forms an additive compound NdCl₃,12NH₃, when exposed to the action of ammonia at low temperatures;[274] by gradually heating this, a large number of other additive compounds are formed, containing smaller quantities of ammonia. [274] Matignon and Trannoy, _Compt. rend._ 1906, ~142~, 1042. The anhydrous _iodide_, NdI₃, has been obtained[275] by passing hydrogen iodide over the heated anhydrous chloride, and also by heating the carbide in iodine vapour. It fuses to a black liquid, which at a higher temperature suddenly becomes transparent. [275] Matignon, _ibid._ 1905, ~140~, 1637. The _bromate_, Nd(BrO₃)₃,9H₂O, which is exactly similar to the analogous compound of praseodymium, forms rose-coloured hexagonal prisms, melting at 66·7°. The _sulphate_, Nd₂(SO₄)₃,8H₂O, is isomorphous with the corresponding salt of praseodymium, but is considerably less soluble. Only the one hydrate is known. 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.