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In earlier papers (R. J. Meyer, Zeit. Anorg. Chem., 1908, Ix., 134; R. J. Meyer and Herbert Winter, Zeit. Anorg. Chem., 1910, Ixvii., 398) it has been shown that scandium can be comparatively easily isolated from the wolframite ores from Zinnwald-Attenberg or from the Sadisberg copper mine. The method which has hitherto been employed for the preparation of the pure earth may be described in outline as follows: i. The hydrochloric acid solution of the wolframite oxides was precipitated whilst boiling with hydrofluosilicic acid. ii. The fluorides thus precipitated were converted into sulphates by means of sulphuric acid, and the hydroxides were separated from the solutions by the addition of ammonia. iii. The solution of the hydroxides in hydrochloric acid was treated with sulphuretted hydrogen and then precipitated with sodium thiosulphate. iv. After the thiosulphate had been decomposed with hydrochloric acid, the solution was finally precipitated with oxalic acid. By this series of processes all the substances accompanying scandium in wolframite, viz., lead, calcium, iron, manganese, as well as the other rare earths belonging chiefly to the yttrium earths, are removed, and only thorium accompanies scandium through all the stages of the purifi. cation. The complete separation of thorium and scandium presents very special difficulties, owing to the remarkable similarity of their chemical properties, which is by no means to be expected in view of the great distance between them in the periodic table. But after many unsuccessful attempts Dr. Speter found a method of separating them, depending upon the insolubility of the scandium sodium carbonate, of composition Sc2Na8(CO3)76H2O, which separates from boiling soda solution. When subjected to spectroscopic examination, the scandium oxide thus obtained is found to be quite free from thorium, and this is in agreement with the fact that the distinct radio-activity of the impure products is no longer electrometrically measurable in the preparations which have been purified in the form of the sodium double carbonate. Moreover, the thorough examination of the spectra did not reveal the presence of any other impurities. This was all the more remarkable because atomic weight determinations always gave values which approximated to 45, while Nilson, the discoverer of scandium, had obtained the value 44'1 in four very concondant determinations. A further purification was then attempted by the fractionation of scandium acetyl-acetonate, but the atomic weight remained unchanged. However, it did not seem advisable to take the value 45 as final, until it had been found that it undoubtedly remained constant after the application of further methods of purification. Meanwhile, R. J. Meyer and M. Speter (Chem. Ztg., 1910, No. 35; R. J. Meyer, Zeit. Anorg. Chem., 1911, Ixxi., 65) had found that iodic acid is an excellent reagent for separating thorium from mixtures with other earths. The method depends upon the precipitation of thorium iodate from strong nitric acid solution by means of a large excess of potassium iodate. Based upon this a quantitative determination of thorium in presence of other earths could be worked out. When the experience thus obtained was applied to the separation of thorium from scandium oxide containing thorium, the result was different from that 13 obtained in earlier experiments with other methods. The details of the method will be given fully elsewhere, and here it will be described in outline only :-By means of an excess of potassium iodate, thorium iodate is precipitated from a nitric acid solution as a flocculent amorphous precipitate. But in presence of a large excess of scandium it is appreciably soluble in scandium iodate, and hence the thorium can be separated quantitatively only if the addition of a large excess of potassium iodate has reduced the solu bility to such an extent that some of the scandium iodate is simultaneously precipitated. When the liquid containing the precipitates has stood for some time, it is found that the amorphous thorium iodate is mixed with distinctly crystalline scandium iodate. The complete separation of the thorium cannot be ensured unless this method of procedure is adopted. Different specimens of scandium oxide, which had previously been freed from other impurities as described above, were separated from thorium by this method. Determinations of the atomic weight gave the following result :— thorium with iodic acid the atomic weight was reduced to Thus by strongly treating the scandium containing the value given by Nilson, 441. If the alteration from the lower is caused only by the elimination of the last trace of value previously obtained, viz., 45, to a value one unit thorium, this must show that o5 per cent of Tho2 in scandium oxide cannot be directly detected either chemically or physically. As a matter of fact, as Prof. Eberhard, of the Astrophysical Observatory in Potsdam, has had the kindness to prove, the arc spectrum of the oxide of atomic weight 45 is in every respect identical with that of the oxide of atomic weight 44, purified by means of iodic acid. On the other hand, the thorium in the precipitate obtained in the iodate separation can of course be detected in the usual way. These precipitates consist of thorium and scandium; no unknown lines can be detected in the spectrum, so that in any case these experiments give no warrant for the suggestion previously made that scandium of atomic weight 45 might contain an unknown element. Thus spectrographic and electrometric methods have proved not sensitive enough to detect o'5 per cent of thorium oxide. (The sensitiveness of the spectrographic method of detecting thorium is impaired by the fact that only lines of feeble intensity appear in the spectrum; it is the same with cerium). On the other hand, it is interesting to notice that the magnetic method, the great sensitiveness of which in its application to the analysis of the rare earths has already been pointed out by Urbain, cxlvii., 1286; Urbain, Comptes Rendus, 1910, cl., 913; does not fail (Urbain and Jantsch, Comptes Rendus, 1908, 1911, clii., 141). Prof. Urbain, of Paris, was kind enough to determine the magnetic susceptibility of two preparations of scandium oxide, the first of which, of atomic weight 45, had been purified by sodium carbonate, and the second, of atomic weight 44, by iodic acid. The actual determinations were carried out by Mademoiselle Feytis, whose valuable work in this region is well known, and to whom we offer our hearty thanks. The coefficients of magnetisation, x, referred to unit weight are as follows: Thus the impure product of atomic weight 45 is very feebly paramagnetic, while the purer product, of atomic weight 44, is diamagnetic. This fact is of general interest. Mainly owing to the work of du Bois and his pupils, and of St. Meyer, it is known that the group of the rare earths from cerium to ytterbium is strongly paramagnetic, reaching a maximum, as Urbain has proved, in dysprosium. In contrast to this group, the individual members of which cannot be allocated in the Periodic Table owing to the |