302 — Remarks on Tests for Cobalt. 
ble to be confounded with Arsenical fron; the latter is 
auatalis ed in four-sided prisms, terminated by diedral 
summits; and the ore in question is in four-sided prisms, 
also rinated by diedral summits, in many cases. In the 
arsenical iron these summits stand on the acute lateral edg- 
es, but in the ore in question, I am greatly deceived if these 
summits do not stand on the obtuse lateral edges; and some 
of the crystals are eg by four-sided pyramids. 1 
have not been able to find any octahedra, but have found | 
thombs. Nowcan as forms, in this instance, arise except 
from deeply truncated octahedra ?—but this I submit to 
GA een a e 
resence of cobalt, under all circumstances, CANNOT | 
be Se oath by fusion with borax; if oxide of iron, in com- 1 
paritively large portions, be mixed with cobalt, the colour | 
communicated to borax before the blowpipe is, as you found 
it, ‘‘only green, or reddish, aecording to the degree of di- 
th : lion;” and consequently this test of cobalt is not deserving | 
0) idence when such quantities of i iron are present; in- | 
deed, I am disposed to believe that it is of no value, when 
equal parts of iron and cobalt are mixed. Stromeyer, you 
recollect, found more than 74 per 100 of iron in an arsenie- 
al cobalt which he examined; and I am confident that, by 
the fusion of that ere with borax, a blue colour would not 
be communicated. It has always appeared tome agreat = 
misnomer to call such minerals “arsenical cobalt,’ wheh 
more than two thirds of them are iron! 
‘he following experiments I regard as decisive respect 
ing the value of boraz, before the “plowpipe, as a sufficient 
test or cobalt when iron is present in comparatively large 
portion 
£: Take a small bead of borax, rendered blue by a sub- 
stance known to be cobalt, and fuse it before the blowpipe 
with a little oxide of iron: the dlue colour instantly hs 
_ and is repiaced by a “ green or reddish colour, according a4 
‘to the degree of dilution.” y 
2. The same effect is produced by fusing a particle. of 
with oxide of iron, if the colour be sufficiently | diluted. 
‘ educe a minute portion of cobalt to powder, mix it 
“with about an equal quantity of protoxide ofiron,and expose 
Se en 
