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On Crystallized Oxyd of Chromiwm. 353 
_ The crystals which I have examined with the following re- 
sults, were obtained from a furnace which had been long in ope- 
ration for the production of chromate of potassa from the mineral 
chromic iron. A portion of the furnace having been taken down 
for repairs, I found small but exceedingly brilliant:erystals lining 
isseminated 
the cracks and fissures between the fire bricks an 
- @: ab=141° 38’ 24” (mean of 5 measurements.) 
Calculating from a:R, the angle a: a} =141° 15, and R: as 
= 96° 50’; and.gs the plane. a} is exceedingly small, this result is 
More probably ids than that given above from measurement. 
he angle a: R gives for the angle of the rhombohedron 85° 22’, 
which is but little less than that given for specular. iron. The 
axis = 1-39045, The crystal according to Naumann’s notation 
has the descriptive, expression, OR, R,-4R, R®. 
The crystals have the hardness of sapphire, equal to 9 on the 
Scale of Mohs. Lustre metallic. Color black ; opaque ee 
ite plates, which are green by transmitted light. The powder 
ort als 
_ The mass of the bricks and the portions on which the sesqui- 
oxyd has crystallized, is charged with soluble yellow chromate of 
Potash, and in many or all of the specimens the green color of 
the uncrystallized oxyd can be seen. 
Srconp Series, Vol. X, No. 30.—Nov,, 1850. 45 
