Remarks on Tests for Cobalt. 301 
1 
C. Alumina, - ABB Bs hi iii seed 2:923 
D. Lime, - 2) 28,000 jie - ~ - 7.865 
97.999 | 19.086 
100.000 roi leneme 
2.001 Loss. 1.314 
Arr. XXV.—Remarks on the common methods of detect- 
ing Cobalt. By. Prof. J. F. Dana, of Dartmouth Col- 
lege. | 
[The following letter was addressed by Prof. Dana to 
the Editor, in consequence of doubts expressed by the 
latter, as to the genuineness of some specimens of arsenical 
cobalt, whose locality was announced in the last number 
of this Journal. It is but fair to say, that those doubts are 
now removed, so far, at least, as the question of the ewtst- 
ence of cobalt in this ore is concerned.— Ed. | 
Dartmouth College, Hanover, 
NM. H. June 19th, 1824. 
{To the Editor. | 
\ 
Dear Sir, 
Ir gives me much pleasure to acknowledge the receipt of 
your favour of the 15th instant; [ am happy to hear that 
you received the ‘‘.Arsenical Cobalt,” and particularly 
happy to learn that your health permits you to make any 
experiinents. [had made some preliminary experiments 
on the ore of which you now have a specimen, and intend 
a full analysis of it as soon as I can satisfy myself of any 
good method of separating arsenic, cobalt and iron, perfect- 
ly, from each other—three metals, each of which adheres 
to the others with the most obstinate pertinacity. The Fran- 
conia ore contains these three metals, and also gives indica- 
gions of sulphur. 1 am aware that Arsenical Cobalt is lia- - 
