173.158. If SO, = 80, Yb = 173.016. The true number cannot be far from 173. ERBIUM. Since the earth which was formerly regarded as the oxide of this metal is now known to be a mixture of two or three different oxides, the older determinations of its molecular weight have little more than historical interest. Nevertl eless the work done by several investigators may properly be cited, since it sheds some light upon certain important problems. First, Delafontaine's* early investigations may be considered. A sulphate, regarded as erbium sulphate, gave the following data. An oxalate was thrown down from it, which, upon ignition, gave oxide. The percentages in the fourth column refer to the anhydrous sulphate. In the last experiment water was not estimated, and I assume for its water the mean percentage of the four preceding experi Bahr and Bunsen † give a series of results, representing successive purifications of the earth which was studied. The final result, obtained by the conversion of oxide into sulphate, was as follows: .7870 grm. oxide gave 1.2765 grm. sulphate. 61.653 per cent. oxide. Hoeglund, following the method of Bahr and Bunsen, secured these results: Humpidge and Burney* give data as follows: 1.9596 grm. Er2(SO4)3 gave 1.2147 grm. Er2O. 61.987 per cent. 66 1.1781 66 61.965 66 Mean, 61.976, .0074 Combining all four series we get the subjoined general mean for the percentage of oxide in sulphate. Bahr and Bunsen's single experiment is given the probable error of one experiment in Hoeglund's series: = From the mean of all, Er = 170.379, .082; or, if 0 = 16, Er 170.770. From Bahr and Bunsen's determination, Er = 168.683; and from Humpidge and Burney's highest, Er = 171.428. The foregoing data were all published before the composite nature of the supposed erbia was fully recognized. It will be seen, however, that three sets of results were fairly comparable, while Delafontaine evidently studied an earth widely different from that investigated by the others. Since the discovery of ytterbium, some light has been thrown on the matter. The old erbia is a mixture of at least three earths, to one of which, a rose-colored body, the name erbia is now restricted. For the atomic weight of the true erbium *Journ. Chem. Society, Feb., 1879, p. 116. Cleve* gives three values, but without data concerning weighings or methods. Doubtless the oxide was converted into sulphate, and the calculations were made with SO, = 80: 166.00 166.21 166.25 Mean, 166.153 With SO, 79.874, this becomes 165.891, and if only O = 16, 166.273. These figures are undoubtedly the nearest yet reached to the true value. According to Thalén,† who reasons from spectroscopic evidence, the erbium of Hoeglund was largely ytterbium. TERBIUM, SAMARIUM, PHILIPPIUM, DECIPIUM, THULIUM, HOLMIUM, AND SORET'S EARTH X. Concerning these substances, real or alleged, the data are exceedingly vague. For phillippium Delafontaine‡ gives an atomic weight approximating to 123 or 125, and in the same memoir decipium is put at 171. It seems probable that philippium may be identical with Cleve's holmium and the metal of Soret's earth X, while decipium comes near Cleve's thulium, for which the discoverer gives a value of about 170.7.|| If decipium and thulium are identical, or if either proves to be erbium or ytterbium contaminated with the other, then we shall have a triad of metals with atomic weights ranging from Er = 166 to Yb = 173, strikingly parallel with lanthanum, cerium, and didymium. If we take the natural arrangement of the elements as tabulated after Mendelejeff's plan, somewhat modified in Roscoe and Schorlemmer's "Treatise on Chemistry,§ we find that such a triad should exist, and, furthermore, that another similar group ought to lie between indium and tin. The latter triad should have atomic weights ranging from 114 to 117; and here possibly, or else forming a triad with yttrium, the other metals of this group may lie. COLUMBIUM.* The atomic weight of this metal has been determined by Rose, Hermann, Blomstrand, and Marignac. Rose† analyzed a compound which he supposed to be chloride, but which, according to Rammelsberg, must have been nearly pure oxychloride. If it was chloride, then the widely varying results give approximately Cb 122; if it was oxychloride, the value becomes nearly 94. If it was chloride, it was doubtless contaminated with tantalum compounds. = Hermann's results seem to have no present value, and as for Blomstrand's,§ I am not able to get at a copy of his original memoir. The results of the latter chemist are thus summed up in Becker's "Digest." Three chlorine estimations in the pentachloride give, in mean, Cb = 96.67. Eleven weighings of columbic acid from the same compound make Cb 96.16. Other experiments on sodium columbate lead Blomstrand to regard 95 as the most probable value. = Marignac¶ made about twenty analyses of the potassium fluoxycolumbate, CbOF,.2KF.H,O. 100 parts of this salt give the following percentages: *This name has priority over the more generally accepted "niobium," and therefore deserves preference. = From the mean percentage of Cb,O,, Cb 93.217. O 16, this becomes 93.431. Cb = 2 If From the mean between the extremes given for K,SO,, 93.812. If O= 16, this becomes 94.027. = As Deville and Troost's* results for the vapor density of the chloride and oxychloride agree fairly well with Cb = 94, we may adopt this value as approximately correct. TANTALUM. The results obtained for the atomic weight of this metal by Berzelius,† Rose, and Hermann || may be fairly left out of account as valueless. These chemists could not have worked with pure preparations, and their data are sufficiently summed up in Becker's "Digest." Marignac§ made four analyses of a pure potassium fluotantalate, and four more experiments upon the ammonium salt. The potassium compound, K,TaF, was treated with sulphuric acid, and the mixture was then evaporated to dryThe potassium sulphate was then dissolved out by water, while the residue was ignited and weighed as Ta2O. 100 parts of the salt gave the following quantities of Ta2O and K2SO, ness. Б |