The first indication of the complexity of Marignac’s Ytterbium was furnished on spectroscopic grounds by Auer von Welsbach in 1905;[390] he showed that a separation could be effected by the fractional crystallisation of the ammonium double oxalates from concentrated ammonium oxalate. Three years later[390] he published a full account of his method, gave atomic weight determinations, and mapped the spectra of the two new elements. In 1907, Urbain[391] independently effected a separation by the fractional crystallisation of the nitrates from nitric acid, and proposed the names Lutecium (from the old name for Paris) and Neoytterbium for the elements. [390] See _Monats._ 1908, ~29~, 204. [391] _Compt. rend._ 1907, ~145~, 759. The two new elements resemble one another so closely in chemical properties that the account given by Astrid Cleve in 1902[392] of the compounds of the old ytterbium applies in practically every detail to the new elements. The oxides are white, and yield colourless salts, showing in solution no absorption bands in the visible region. [392] _Zeitsch. anorg. Chem._ 1902, ~32~, 129. The _oxides_, R₂O₃, though perfectly white, are coloured yellow or brown by the faintest traces of thulium. They are attacked by acids only slowly in the cold, but dissolve readily on warming; lutecia is slightly the less strongly basic. The _chlorides_ crystallise with six molecules of water, and are extremely soluble and deliquescent; when heated in a stream of hydrogen chloride, they form oxychlorides of the type ROCl. The _platinocyanides_ crystallise with 18 molecules of water, and have the characteristic appearance of the analogous compounds of the yttrium elements. The _sulphates_ crystallise at all temperatures as the normal octohydrates, and are moderately easily soluble in water; conductivity measurements show that they are partially hydrolysed in solution. The _nitrates_ crystallise from concentrated aqueous or nitric acid solutions as the tetrahydrates; by evaporation of the aqueous solutions over sulphuric acid, the trihydrates are obtained. These compounds are anomalous among the rare earth nitrates, by reason of their low water content. The neutral _carbonates_ are thrown down by ammonium carbonate as the tetrahydrates; if a stream of carbon dioxide be led into aqueous suspension of the hydroxides, _basic carbonates_ of the formula R(OH)CO₃,H₂O, are obtained. The _oxalates_ are precipitated as the decahydrates; they are readily soluble in excess of alkali oxalate. Many other salts of the old ytterbium have been prepared.