249 
oj Columbium and Tantalum. 
White oxide - 4^ grains 
Oxide of iron - \ 
Oxide maganese 
The white oxides obtained from each of these minerals, are 
remarkable for their insolubility in the three common mineral- 
acids, as both Mr. Hatchett and M. Ekeberg have ob- 
served. 
In muriatic acid they cannot be said to be absolutely inso- 
luble ; but they are not sufficiently soluble for the purposes 
of analysis. 
In nitric acid they are also nearly, if not perfectly, inso- 
luble. 
In sulphuric acid, when concentrated and boiling, the oxide 
of columbium may be dissolved in small quantity, and so also 
may the oxide obtained from tantalite. 
The proper solvent, as has been observed by Mr. Hatchett 
and by M. Ekebebg, is potash ; and as it is not required to be 
in its caustic state, I employed the crystallized carbonate of 
potash on account of its purity and uniformity. Of this salt 
about eight grains seemed requisite to be fused with one of 
the oxide obtained from either of these minerals to render it 
soluble in water. 
Soda also combines with the oxide, and may be said to dis- 
solve it ; but a far larger proportion of this alkali is necessary, 
and a larger quantity of water. And although a solution may 
have been effected that is transparent while hot, it very soon 
becomes opaque in cooling, and finally almost the whole of 
the oxide subsides combined with a portion of the soda in a 
state nearly insoluble. 
