COLUMBIUM AND TANTALUM COMPOUNDS. 223
bottom of the tube. The salt is insoluble in cold water but is
decomposed by hot water. It is slightly soluble in alcohol, less
so in ether, but dissolves readily in chloroform.
- Columbium and Tantalum Compounds from Columblte.
Columbium and tantalum, the most important elements in columbite and
tantalite, are separated from one another by crystallizing their potassium
double fluorides. Potassium tantalum heptafluoride, K 2 [TaF 7 ], is but spar-
ingly soluble, and crystallizes from a dilute solution, whereas potassium
columbium oxyfluoride, K 2 [Cb0F 6 ], separates only from a concentrated solu-
tion. This classic method was originated by Marignac in 1866, and is still
used almost exclusively; in this way the first perfect separation of the two
elements was obtained.
Concerning the history of these elements, it is of interest to note that
Hatchett, in 1801, first obtained from American columbite a peculiar acid
which ten years later was shown by the researches of Wollaston to be identi-
cal with a similar acid obtained by Eckeberg in 1802 from Swedish minerals
and named by him tantalic acid. The influence of Berzelius led to the adop-
tion of the name tantalum for the element. By more careful researches dat-
ing from 1844, H. Rose found in columbite a new element, columbium, and
of this he was the first to obtain pure compounds. He believed for a time
that a third element, which he named pelopium, was also present. Matters
were further complicated by the assumption by various investigators of other
elements in this group, and it remained for the work of Marignac to show
that all of the minerals worked with contained both columbium and tantalum
in varying proportions, and that the preparations studied up to that time
were, for the most part, mixtures.
Heat 100 g. of potassium bisulphate gently in a platinum dish
until it has reached a state of quiet fusion; allow the mass to
just solidify, and distribute 25 g. of finely powdered columbite
over its surface. Heat again with slowly rising temperature
until finally a clear melt is obtained. Allow the mass to cool, or
chill it by placing in cold water; break up the solid mass and
allow it to stand in water over night. Next morning pour off
the clear solution, and boil out the residue several times with
water containing a little hydrochloric acid. Finally collect the
residue on a plaited filter, wash it with hot water containing
hydrochloric acid, and dry it in the hot closet.
To purify this product completely, fuse it again with potassium
bisulphate exactly as before and wash the residue very thoroughly
with the dilute acid. Yield, 25 g. of a powder consisting of the
oxides of tantalum and columbium, and containing 30 to 50% of
water; the powder is usually entirely free from iron.