Thulia is described by James as a dense white powder, with a greenish tinge, which ‘emits a carmine coloured glow, when carefully made to incandesce.’ The salts have a greenish tint, very susceptible to traces of erbium; addition of erbium compounds turn the solution first yellowish-green, then colourless, and finally pink. von Welsbach describes Thulium II as forming an almost white sesquioxide, which, when heated in the flame, gives a purplish light quickly succeeded by a splendid characteristic glow; the salts are pale yellowish-green by daylight, emerald-green by artificial light, the colour being almost complementary to that of erbium salts. In solution, salts of Tm II give the bands at 685 and 464 ascribed by James and other workers to thulium. Until further researches on these interesting results are published, the elementary nature of thulium cannot be considered definitely settled; it appears probable, however, that homogeneous salts of a definite element were obtained by James. The following salts are described by James (_loc. cit._). The _chloride_, TmCl₃,7H₂O, separates at ordinary temperatures from the concentrated solution of the oxide in hydrochloric acid as greenish crystals, very soluble in alcohol and water. The _bromate_, Tm(BrO₃)₃,9H₂O, forms pale bluish-green hexagonal prisms, isomorphous with the analogous salts of the group. The _sulphate_ and _nitrate_ separate as the octohydrates. The precipitated _oxalate_ has the formula Tm₂(C₂O₄)₃,6H₂O, and is soluble in excess of alkali oxalate. The _acetylacetone derivative_ was prepared by dissolving the precipitated and well-washed hydroxide in alcoholic acetylacetone; it recrystallises from absolute (?) alcohol as the dihydrate, Tm₂(C₅H₇O₂)₆,2H₂O. The _phenoxyacetate_, Tm₂(C₆H₅·O·CH₂·COO)₆,6H₂O, was obtained in a similar manner by addition of the hydroxide to a solution of phenoxyacetic acid in dilute alcohol. ~Atomic Weight.~--Cleve gave the value 170·7 for this constant, but his material was very impure. In a footnote to a paper published in 1907, Urbain[388] pointed out that the value could not be above 168·5. Analyses of the salts prepared by James agree fairly well with the theoretical values calculated on this basis, but a systematic determination with pure material has not yet been made. The International Committee (1912) have adopted the value 168·5. [388] _Compt. rend._ 1907, ~145~, 760. ~Detection.~--The element can be detected in solution by its absorption spectrum, the most intense bands being in the neighbourhood of λ = 685, and λ = 464. For provisional arc spectra see Exner and Haschek, and for spark spectra Auer von Welsbach (loc. cit.) and Eder and Valenta.[389] [389] _Sitzungsber. kaiserl. Akad. Wiss. Wien_, 1910, ~119~, II_a_, 103. ~Ytterbium~ (Neoytterbium, Aldebaranium), Yb = 172·0. ~Lutecium~ (Cassiopeium), Lu = 174·0.