450 On Iridium and Osmium. [Dec. 
oxide exhales; a property which Fourcroy and I made known in 
‘February 1804. 
This metal being volatile, or rather oxidating very easily at a 
low temperature, it has not been posssible to fuse it, and, conse- 
quently, to know its colour and its specific gravity, 
~ As to ifs colour, if we can judge from some appearances, I con- 
ceive, that it is blue. The following are these appearances, The 
instant that osmium is precipitated by zine from its solution, the 
liquid assumes a purple tint, which becomes soon the finest blue. 
‘This blue matter at last separates from the liquid, and precipitates 
in a powder which appears black. 
When we heat osmium thus precipitated from zinc, and washed 
and dried, we obtain, as we shall see hereafter, white oxide, which 
is volatilized into the neck of the retort, where it crystallizes; 
then a light crust of matter, which is blue by reflected light, and 
green by refracted. The portion not volatilized appears black. 
Yet it is possible that the blue colour does not belong to the metal 
itself, but to a suboxide. 
Osmium, which has been heated in a retort, takes, when rubbed 
against a hard and polished body, a surface of a copper-red, like 
indigo rubbed. 
As we have not been able to obtain osmium hitherto, except in a 
fine powder, it appears to us light; but if it could be melted, it 
would perhaps be as heavy as some of the metals known before it. 
We have no experiments which show that osmium is volatile ; 
because the little of it which we have hitherto possessed has only 
enabled us to heat it in glass vessels not capable of bearing much heat 
without melting. But it is probable that in a higher 1 temperature 
it would be volatile; for we have not hitherto any examples of 
metals furnishing volatile oxides ,which are not volatile themselves. 
The blue sublimate which forms in the upper part of vessels in 
which osmium is heated, strengthens this probability, 
When we heat osmium in contact of air, it soon disappears 
entirely; but we ought not to consider this phenomenon as a simple 
volatilization of the metal. It is a true combustion, easily distin- 
guished by the suffocating odour of oxide of osmium diffused in 
the air. 4 
I exposed to heat a gramme of osmium in a luted retort, the 
capacity of which was about 12 cubic inches, and which terminated 
in a tube plunged into water, in order to collect the vapours which 
should not.condense. 
The bottom of the retort was not red-hot, before very beautful 
white brilliant crystals were deposited in the neck of the vessel. 
Some time after, and.in proportion as the heat increased, a blue 
crust was deposited on the upper part of the retort. 
The formation of these matters, and especially of the first; soon 
ceased ;, because the contact of air was necessary for it, which soon 
failed in. so small a vessel, The apparatus being cold, the neek of 
the Tetort wa’ cut near the white crystals, in order to colléct them 
