The methods for the separation and purification of yttrium have recently been exhaustively examined by Meyer and Wuorinen.[401] They consider the chromate method suitable only if the terbium elements have already been removed. The ethylsulphate method is said to be tedious, whilst the ferrocyanide method indeed effects very rapid concentration, but with great loss. For purposes of concentration they find the most suitable method in the fractional hydrolysis of the phthalates; these salts are soluble in cold water, but hydrolyse when the solution is warmed, the most positive elements remaining of course longest in solution. For the final purification, they recommend fractional precipitation of the iodate from nitric acid solution; yttrium iodate being more soluble than the iodates of the erbium and ytterbium group, the latter collect in the first precipitates. [401] _Zeitsch. anorg. Chem._ 1913, ~80~, 7; Meyer and Weinheber, _Ber._ 1913, ~46~, 2672. Pure yttria is quite white, and gives rise to colourless salts, which in solution show no absorption spectrum in the visible region. A very large number of yttrium compounds have been prepared, of which sufficiently detailed accounts have been given in the general description of rare earth compounds. For an exhaustive treatment, the reader is referred to Abegg’s ‘Handbuch.’ The _metal_ has probably not been obtained in the pure state; impure yttrium has been obtained by Winkler[402] by the action of magnesium on the oxide, and by Cleve[403] by the action of sodium on a mixture of the chloride with common salt, and by electrolysis of the mixture of fused chlorides. It is described as a greyish metal, resembling iron in appearance; it oxidises in the air and readily decomposes boiling water. The _hydroxide_ is thrown down as a gelatinous precipitate by alkalies; ammonia throws down basic salts, but in presence of hydrogen peroxide an hydrated _peroxide_ is obtained. The _oxide_ absorbs carbon dioxide from the air, and liberates ammonia from ammonium salts. [402] _Ber._ 1890, ~23~, 772. [403] _Bull. Soc. Chim._ 1874, [ii.], ~21~, 344; Cleve and Höglund, _ibid._ 1873, [ii.], ~18~, 193; see also Popp, _Annalen_, 1864, ~131~, 359. The anhydrous _chloride_ has been prepared by many authors; it melts at a relatively low temperature, 680°, and is the most easily volatilised of all the rare earth chlorides. After fusion, it forms a mass of brilliant white lamellæ.[404] It is characterised by the ease with which it dissolves in pyridine. From aqueous solution it separates as the hexahydrate, YtCl₃,6H₂O, which melts at 160°. The _bromide_ separates from solution as the enneahydrate, YtBr₃,9H₂O; the _bromate_[405] also separates with 9 molecules of water of crystallisation. [404] _Compt. rend._ 1902, ~134~, 1308. [405] James and Langelier, _J. Amer. Chem. Soc._ 1909, ~31~, 913.