The _nitrate_ cannot be obtained anhydrous; the normal hydrate, Yt(NO₃)₃,6H₂O, loses 3 molecules of water at 100°, but further heating converts it into basic salts. A _basic nitrate_, 3Yt₂O₃,4N₂O₅,20H₂O, is described by James and Pratt[406] as stable at ordinary temperatures, and in contact with solutions of the normal nitrate. The _sulphate_ octohydrate is isomorphous with analogous compounds of the rare earth elements, and with the _selenate_, Yt₂(SeO₄)₃,8H₂O; the latter compound can also form an enneahydrate. The _phosphate_, YtPO₄, occurs in nature in the mineral xenotime, and has been obtained in the laboratory in the crystalline form; many other phosphates have been prepared. The _platinocyanide_, Yt₂[Pt(CN)₄]₃,21H₂O, has the characteristic red colour with greenish-blue fluorescence. [406] _J. Amer. Chem. Soc._ 1910, ~32~, 873. Many _organic yttrium salts_ have been prepared by James and Pratt[407] and by Tanatar and Voljanski.[408] [407] _J. Amer. Chem. Soc._ 1911, ~33~, 1330. [408] _Vide Abstr. Chem. Soc._ 1910, ~98~, i. 809. ~Atomic Weight.~--The numbers obtained by the investigators who have determined this constant vary to such an extent that considerable uncertainty attaches to the value, 89·0, at present accepted by the International Committee. The determinations carried out prior to 1870 gave such diverse results that they are of little use in fixing the constant; since that date, all the investigations, with the exception of the most recent, have given values below 90, the sulphate method being generally employed. Cleve and Höglund,[409] in 1883, carried out six determinations by the synthetic method; their results were concordant, and gave the mean value 89·57. Brauner considers this result if anything too low, as traces of undecomposed acid sulphate may have been present in the anhydrous sulphate. The same method was employed again by Cleve in 1884;[410] the mean of twelve very concordant results gave the number 89·11. [409] _Loc. cit._ [410] _Compt. rend._ 1883, ~95~, 1225. Much stress is laid by Brauner[411] on an unpublished determination of Marignac, carried out with material entirely free from terbia, which gave the value 88·88. H. C. Jones in 1895[412] carried out two series of determinations with material purified by Rowland’s method, _i.e._ precipitation with potassium ferrocyanide;[413] the results in both series were very concordant, the synthetic method giving the value 88·95, the analytical method the value 88·97. This work has been taken by the International Committee as the basis for the accepted value. According to Brauner, the ferrocyanide method does not give perfectly pure material.[414] [411] Abegg’s _Handbuch_, III. i. 328. [412] _Amer. Chem. J._ 1895, ~17~, 154. [413] Rowland, _Chem. News_, 1894, ~70~, 68; compare also Crookes, _ibid._ ~70~, 81-82. Bettendorff (see Böhm, _Die Darstellung der seltenen Erden_, I. 480) has also used the method.