252 Dr. Wollaston on the Identity , &c. 
weighed at the same time, was as much as 7,8. I should, 
however, observe, that the specific gravities of three other 
fragments borrowed for this purpose were not so high, that 
of one being 7 ,65, of another 7,53, and of a third so low as 
7 > 15 - 
It is evident that no variation of mere proportion of the in- 
gredients can account for an increase of specific gravity from 
5,318 to 7,953, which are in the ratio of 3 to 4 ; for since 
columbite contains four fifths oxide, if the whole remain- 
ing one fifth part in weight of that oxide could be supposed 
added to the same bulk, without diminution of the quantities 
of iron and manganese, the specific gravity would not then 
exceed 7,1; and even if a weight equal to one third of the 
whole were thus added, without increase of bulk, still the 
aggregate would not quite equal the heaviest tantalite in spe- 
cific gravity ; but, on the contrary, the quantity of white oxide 
in this specimen certainly does not amount to six sevenths, and 
probably is not more than five sixths of the whole mass. 
The only chemical difference, by which this circumstance 
could be explained, would be the state of oxidation, which my 
experiments cannot appreciate ; but it may also arise in part 
from actual cavities in the mass of columbite, and in part from 
the state or mode of aggregation. 
