[382] Sitzungsber. kaiserl. Akad. Wiss. Wien, 1910, 119, IIa, 18.
[383] Publ. astrophys. Observ. Potsdam, 1909, 20, No. 60.
Thulium, Tm = 168·5
The thulia isolated in 1879 was described by Cleve[384] as pale rose in colour; in the following year, having obtained it in larger quantity, he found that it was white, and dissolved in acids to form colourless solutions which showed absorption bands in the red and blue. The spectra of the thulium compounds prepared by Cleve were examined by Thalèn,[385] who concluded that a new element was certainly present, though it had not been freed from ytterbium and erbium. Incidental observations on the new oxide were made by various investigators, but no extensive researches were carried out upon it until 1911, when James[386] published an account of the separation and purification by the bromate method, stating that after some 15,000 operations, his products remained unaltered; he gives, however, no spectroscopic determinations, though part of his material, spectroscopically examined by Sir William Crookes, was described as ‘Very good thulium, with a trace of ytterbium.’ In the same year Auer von Welsbach[387] published an account of a spectroscopic investigation, as a result of which he concludes that thulium is a mixture of at least three elements, of which the second, Tm II, agrees fairly well in properties, so far as the two accounts allow of comparison, with the thulium of James.
[384] Loc. cit.
[385] Compt. rend. 1880, 91, 376.
[386] J. Amer. Chem. Soc. 1911, 33, 1333.
[387] Zeitsch. anorg. Chem. 1911, 71, 439.
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.).