444 On Iridium and Osmiuin. [Dxc. 
I observed that at the moment I poured the concentrated muriati¢ 
acid upon the powder an effervescence was produced, accompanied 
by a kind of noise, and that the mixture exhaled very distinctly the 
odour of oxymuriatic acid. 
When the muriatic acid had no further action on the black 
powder, I boiled it for a long time in a great quantity of nitro- 
muriatic acid ; that solution took place, was announced by the very 
deep colour which the liquid assumed. 
The residue, being now washed and dried, weighed only 3°2 
grammes. I fused it with twice its weight of potash in a silver 
crucible. 
The mass being dissolved in hot water communicated to it a fine 
blue colour. The undissolved, portion was treated with murilatic 
acid, which dissipated a part of it, and assumed likewise a blue 
colour with a tint of violet. 
By repeated treatments with potash and muriatic acid the whole 
of the black matter was at last dissolved. _ 
I mixed together all the alkaline solutions, and after having 
saturated them with muriatic acid, 1 evaporated, in order to obtain 
by crystallization the muriate of iridium-and-potash, 
I mixed together likewise all the acid solutions, concentrated 
them, and when they yielded no more muriate of iridium-and- 
potash, I added ammonia, in order to convert the muriate of iri- 
dium, still held in solution, into ammoniaco-muriate of iridium. 
We see by the above statement, that the black powder obtained 
by repeated washings from the insoluble residue of crude pla- 
tinum, is composed of a great quantity of iridium and osmium ; 
that it scarcely contains any chromium, and much less titanium 
and iron, than the black powder which we subjected to the first 
analysis. 
PART SECOND. 
§ I. Properties of Iridium. 
The name iridium, given to this metal by Mr. Tennant, is 
derived from the various colours which it presents in its solutions, 
and which M. Fourcroy and I first made known. 
But in the metallic state the colour of iridium is greyish-white, 
nearly like that of platinum. It appears to be brittle, and conse- 
quently hard. 
I cannot give its specific gravity, because I have not yet been 
able to melt it completely. ; 
It is not attacked by the simple acids, and only with great difli- 
culty by the most concentrated nitro-muriatic acid. 
Potash and nitre convert it into an oxide and then combine with 
it. A black powder is produced, which, being put into water, 
communicates to it a fine blue colour. It is a portion of the metal 
dissolved in the excess of alkali which produces this colour; but 
the portion insoluble in water is still a combination of the metal 
with alkali; for it is soluble in muriatic acid, to which it gives a 
a) 
a 
