£5° Dr. Wollaston on the Identity 
When a solution of the white oxide, obtained from either 
of these minerals, has been made, as above, with potash, the 
whole may be precipitated by the addition of an acid, and will 
not be redissolved by an excess of sulphuric acid, of nitric, of 
muriatic, succinic, or acetic acids. 
But there is a further agreement in the properties of these 
two minerals, which appears above all others to establish their 
identity ; for though they are both so nearly insoluble by any 
excess of the mineral adds, yet they are each completely 
dissolved by oxalic acid, by tartaric acid, or by citric acid ; and 
the solution of each is subject to the same limitations ; for if 
the precipitate has been dried, it is become intractable, and 
can scarcely be dissolved again till after a second fusion with 
potash. 
If to the alkaline solution of either of them there be added 
infusion of galls, prussiate of potash, or hydrosulphuret of 
potash, no precipitate occurs ; but when a sufficient quantity 
of acid has been added to neutralize the redundant alkali, the 
infusion of galls will then occasion an orange precipitate ; but 
prussiate of potash causes no precipitate, nor does the hydrosul- 
phuret precipitate the oxide, although the solution may become 
turbid from precipitation of sulphur by a redundant acid. 
The characteristic precipitant of columbium is consequently 
the infusion of galls ; but in the employment of this test cer- 
tain precautions are necessary. For as an excess of potash 
may prevent the appearance of this precipitate, so also may 
a small excess of oxalic or tartaric acids prevent precipitation, 
or dissolve a precipitate already formed. A larger excess of 
citric acid seemed requisite for that purpose, and would also 
dissolve the gallat of columbium. In each case the precipi- 
