368 Fusion of Iridium and Rhodium. 
appeared porous immediately beneath the facets. When the mass 
was first fused, I found by the gravimeter the specific gravity to 
be 11:0, which coincides with the observations of Wollaston. 
Yet by acareful trial made at the U. S. mint by Mr. Eckfelt, 
after the second fusion, and the formation of the facet, the speci- 
fic gravity proved to be only 10°8. This is sufficiently explained 
by the porosity above mentioned. In fact the porosity to which 
rhodium and iridium are liable, may render it difficult to find = 
cimens of precisely the same apie gravity. 
In sectility, malleability and hardness, rhodium did not appear 
to differ much from iridium, but it is not of so palea white as 
iridium. The one has the pale white of antimony, the other the 
ruddy hue of bismuth. 
_ Osmiuret of iridium as existing in the native spangles associ- 
ated with platina ore, or as otherwise obtained, is far more diffi- 
cult of fusion than pure iridium. The propensity to assume the 
crystalline form, and to adhere to it, is even greater in this alloy 
than in the last mentioned metal. On first exposure to the most 
intense heat of the hydro-oxygen blowpipe, some slight appear- 
ances of fusion may be seen, and the spangles or grains may be 
magfe to cohere. Wevertheldes it yields very slowly, and requires 
an expenditure of gas too great to be incurred unless it were for 
the purpose of once well determining the question of its ultimate 
fusibility. This object was obtained completely as respects @ 
globule of forty-five grains in weight. The specific gravity of 
this globule appeared to be 20.4, but this result was evidently less 
than that which would have been obtained had there not been 
some minute cavities, which after splitting the globule, were de- 
tected by a magnifier. 
* The specific gravity of some large spangles of osmiuret of it 
dium from South American ore, was by Dr. Boyé found to be 
19-835. That of some grains heavier but not so flat, presented 
to me by Count Cancrine, was found to be 20.938. 
That the alloy of iridium with osmium should be more aifi- 
cult to fuse than pure iridium, leads to the inference that osmium 
must be the most infusible of the metals, although, like carbon, 
very susceptible of combustion, and capable, like that infusible 
non-metallic radical, of forreing a volatile peroxide. Of course 
its liability to oxydizement, would render it impossible to mee it 
by the hydro-oxygen Bers of which the efficacy requires the — 
