[189] See Meyer, Monats. 1898, 20, 369 and 793.
[190] Compt. rend. 1908, 147, 1286; see also Urbain, ibid., 1910, 150, 913.
When the elements are considered in order of atomic weight, the coefficient reaches a maximum at neodymium in the cerium group, and again at dysprosium (or holmium) in the yttrium group:—[191]
| Element. | Atomic Weight. | Coefficient of magnetisation for the oxide. x × 10⁻⁶ | |
|---|---|---|---|
| Scandium | 44·1 | -0 | ·05 |
| Yttrium | 89·0 | -0 | ·14 |
| Lanthanum | 139·0 | -0 | ·18 |
| Neodymium | 144·3 | 33 | ·5 |
| Samarium | 150·4 | 6 | ·5 |
| Europium | 152·0 | 33 | ·5 |
| Gadolinium | 157·3 | 161 | |
| Terbium | 159·2 | 237 | |
| Dysprosium | 162·5 | 290 | |
[191] See Urbain and Jantsch, loc. cit.; the values for lanthana, scandia, and yttria were determined by Wedekind (see Meyer and Wuorinen, Zeitsch. anorg. Chem. 1913, 80, 7).
Erbium, thulium, ytterbium, and lutecium appear in descending order at the end of the series, but no figures are given.
The most interesting application of the property has been Urbain’s discovery of the new element Celtium (see [p. 207]).
The Equivalent Weight Determination
The determination of the mean equivalent weight, which was for the earlier chemists the only reliable method of controlling their fractionations, is still of considerable importance for this purpose, especially in the yttrium group, in which the differences in atomic weights are more considerable than among the cerium metals. Great importance, moreover, still attaches to these determinations, since they serve to fix the atomic weights; save that the methods used in an atomic weight determination are somewhat more elaborate and refined than those used when it is desired merely to test a fractionation, the same processes apply in both cases.
The methods which have been most commonly used are those based on a determination of the ratio R₂O₃ : R₂(SO₄)₃, and these are of two kinds, the synthetic and the analytical. The first, in which a known weight of the oxide is converted into the sulphate, has been most used for the most strongly basic oxides, since with these it is difficult to remove the last traces of sulphuric anhydride from the oxide by heat. The oxides are best obtained from the oxalates, which are precipitated from an acid solution of the nitrates, washed thoroughly with water, alcohol and ether in succession, dried, and ignited in a tarred platinum crucible. The oxide is best dissolved in dilute hydrochloric or nitric acid on the waterbath, a slight excess of sulphuric acid being added only when a clear solution has been obtained; the liquid is then heated gradually to 300°, and finally in the electric furnace at 450°-550° until constant in weight. If sulphuric acid be added directly to the weighed oxide, particles of the latter may become completely coated with the insoluble sulphate, and so escape the action of the acid.