1815.] Gn Lridium and Osmium. 449 
blow pipe with oxygen gas. This enabled me to observe a very 
interesting phenomenon, the volatilization éf the silver. : 
There rose during the operation a very copious yellowish white 
fume, and the flame from the charcoal formed a cone, the»base of 
which was coloured yellow, the middle purple, and the summit 
blue. Ina short time nothing but the pure iridium remained upon 
the charcoal. . 
This phenomenon, of which I had not before seen so remarkable 
an example, led me to wish to subject silver alone to the same trial. 
I therefore’ placed four grains of this metal in a hole dug in 
charcoal, and heating by means of a current of oxygen gas, in less 
than a minute the whole was dissipated. During this operation, a 
portion of the smoke exhaled was collected in a glass vessel reversed 
above it. It formed a yellowish brown crust, which dissolved in a 
great measure in weak and cold nitric acid. This nitric acid was 
then abundantly precipitated by a solution of common salt. The 
greatest part of the silver burns when thus volatilized. At least 
the yellow colour of the flame, that of the condensed fumes, and 
their dissolving cold in dilute nitric acid, seems to prove it. . 
Chemists, assayers, and founders. know that silver is volatile; 
but I am persuaded that they are far from thinking that it possesses 
this property in so great a degree. ‘This ought to be attended to by 
all who refine and melt silver. 
The malleability of all the alloys of iridium leads to the idea 
that this metal would not be brittle if its parts could be united by 
fusion, or at least that certain brittle metals do not much diminish 
the malleability of those with which they are capable of. uniting. 
Certainly tin united to copper in the same proportion as the iridium 
produces a great change on its properties.* 
Mr. Tennant has remarked, that iridium does not change the 
colour nor the malleability of gold and silver, and that it was not 
ible to separate it from these bodies by the ordinary. methods. 
This might easily have been seen beforehand, in consequence of 
the properties which it possesses. 
The specific characters of iridium are then: 1. A greyish white 
colour. 2. Very difficult to fuse. 3. It forms blue, purple, yel- 
lowish red solutions in acids and alkalies, according to tlie state of 
its oxidation. 4.. It is not acted upon by the ordinary acids, and 
even very little by nitro-muriatic acid. 5. It forms triple salts of 
a black colour, and very little soluble with potash and ammonia, 
when in solution in acids in the state of red oxide. 
THIRD PART. 
§ 1. Properties of Osmium. 
‘Osmium has received its name from the strong smell which its 
* Since the reading of this paper, having succeeded in fusing a certain quam 
tity of iridium, Ihave found that. it possesses some ductility, 
Vox. VI. N° VI. 2F 
