“ It burns when heated in air, and is soluble in warm concentrated sulphuric acid. Three oxides of columbium are certainly known, namely the dioxide, Cb2O2, the tetroxide, Cb2O4, and the pentoxide, Cb2O5, whilst a fourth oxide, columbium trioxide, Cb2O3, has been described by E. F. Smith and P. Maas (Zeit. f. anorg. Chem. 1894, 7, p. 97) . Columbium dioxide, Cb2O2, is formed when dry potassium columbium oxyfluoride is reduced by sodium (H. Rose, Pogg. Ann. 1858, 104, p. 312) . It burns readily in air, and is converted into the pentoxide when fused with acid potassium sulphate. ”

“ It forms a white silky mass which volatilizes at about 400° C. It deliquesces in moist air, and is decomposed violently by water. Columbium pentafluoride, CbF5, is obtained when the pentoxide is dissolved in hydrofluoric acid. It is only known in solution; evaporation of the solution yields the pentoxide. The oxyfluoride, CbOF3, results when a mixture of the pentoxide and fluorspar is heated in a current of hydrochloric acid. ”

“ The solution turns yellow in colour, and, when saturated, deposits a pasty mass of crystals. The salt separates from solutions containing hydrofluoric acid in large plates, which are greenish yellow in colour. ”