On heating it glows suddenly between 500° and 600°C.,[66] losing all its helium, and with decrease in density (5·619 to 5·375). At the same time it gives out a considerable amount of heat—8·09 C.[67] for 1 gm. (see [p. 38]).
[66] Ramsay and Travers, Zeitsch. physikal. Chem. 1898, 25, 568.
[67] The heat of combustion of a gram of hydrogen is 342 K.
Sipylite.
—Essentially a columbate of rare earth metals, with oxides of tantalum, tungsten, zirconium, uranium, iron and calcium, and some water. Mallet, the discoverer, gives the formula as R₂O₃,Cb₂O₅, the basic oxides including, besides the rare earths, Cb₂O₅ with Ta₂O₅ and WO₃, and some water. An alternative formula, making it a complex pyro-salt, is also given, but from its great similarity in form and angles to fergusonite, the first formula is preferred. Strutt finds that it contains not only uranium, radium and helium, but also thorium in considerable quantity (ThO₂ = 4·9 per cent.), a fact which had been overlooked by Mallet. The rare earths contain a high proportion of erbia.
It is tetragonal, c = 1·4767, (001) ∧ (101) = 55° 54´. The crystals are octahedral, with the form p {111}; p ∧ p´ = 79° 15´, p ∧ p´´ = 128° 50´. Cleavage distinct ∥ p. It is usually granular and amorphous. Colour brownish-black to brownish-red, lustre resinous. Brittle. Hardness 6; sp. gr. 4·89. Translucent.
Its behaviour on heating has been already mentioned (see [p. 39]); it is infusible. Boiling hydrochloric acid partially dissolves it; the solution gives the turmeric test for zirconium, and on diluting and adding metallic tin a sapphire-blue colour is developed, due to the columbium present. Boiling concentrated sulphuric acid decomposes it slowly.
It is found in Amhurst Co., Virginia, adherent to the allanite which occurs there in large quantities. It was discovered there by Mallet in 1877, who named it, on account of the columbium (niobium) present, from Sipylus, one of the sons of Niobe.[68]
[68] See Mallet, Amer. J. Sci. 1877, [iii.], 14, 397.
In this class, also, are to be included the following minerals (see [list]):