separates, is decomposed by sulphuric acid, or by continued boiling
with water (C. Marignac; see also G. Kruss and L. F. Nilson, _Ber._
1887, 20, p. 1676). It is a white amorphous infusible powder, which
when strongly heated in sulphuretted hydrogen, yields an oxysulphide.
Several hydrated forms are known, yielding salts known as
_columbates_. A _percolumbic acid_, HCbO4.nH2O, has been
prepared by P. Melikoff and L. Pissarjewsky (_Zeit. f. anorg. Chem._
1899, 20, p. 341), as a yellow amorphous powder by the action of
dilute sulphuric acid on the potassium salt, which is formed when
columbic acid is fused in a silver crucible with eight times its
weight of caustic potash (_loc. cit._). Salts of the acid H3CbO8
have been described by C. W. Balke and E. F. Smith (_Jour. Amer. Chem.
Soc._ 1908, 30, p. 1637).

_Columbium trichloride_, CbCl3, is obtained in needles or crystalline
crusts, when the vapour of the pentachloride is slowly passed through
a red-hot tube. When heated in a current of carbon dioxide it forms
the oxychloride CbOCl3, and carbon monoxide. _Columbium
pentachloride_, CbCl5, is obtained in yellow needles when a mixture of
the pentoxide and sugar charcoal is heated in a current of air-free
chlorine. It melts at 194 deg. C. (H. Deville) and boils at 240.5 deg.
C. It is decomposed by water, and dissolves in hydrochloric acid.
_Columbium oxychloride_, CbOCl3, is formed when carbon tetrachloride,
and columbic acid are heated together at 440 deg. C.: 3CCl4 + Cb2O5 =
2CbOCl3 + 3COCl2, and also by distilling the pentachloride, in a
current of carbon dioxide, over ignited columbic acid. It forms a
white silky mass which volatilizes at about 400 deg. 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. It forms many double salts with other metallic
fluorides.

_Columbium oxysulphide_, CbOS3, is obtained as a dark bronze coloured
powder when the pentoxide is heated to a white heat in a current of
carbon bisulphide vapour; or by gently heating the oxychloride in a
current of sulphuretted hydrogen. It burns when heated in air, for