1815.] On Tridium and Osmium. 443 
in water; for the matter from which it was extracted had been 
sufficiently washed. It is possible, indeed, that this oxide may 
form with the other matters contained in the precipitate a combi- 
nation which renders it insoluble in water. 
After having separated the osmium, I poured into the concen- 
trated liquid sal-ammoniac, to form ammoniaco-muriate of iridium, 
which precipitated in the state of a black powder. ‘The liquid, 
being evaporated to dryness, and the residue digested in water, J 
obtained a small-additional quantity of the same salt mixed with 
silica. The solution had then a fine green colour of chromium, 
which neither sulphate of iron nor sulphureted hydrogen destroyed. 
It could not, therefore, be ascribed to iridium. 
To discover what substance produced that colour, I poured 
ammonia into the solution, which threw down a brownish-green 
precipitate, and the liquid, though containing an excess of alkali, 
was colourless. : 
This precipitate, when fused with borax, communicated to it a 
fine green colour. When heated with potash, the mixture, being 
washed, gave a yellow liquid, possessing the properties of chromate 
of potash, and a little oxide of iron remained behind. 
Hence the precipitate is composed of 
1. Oxide of iridium. 
2, ————— osmium. 
3. ——— chromium, 
4, ——_————- iron. 
5. Silica. 
The second water which I poured on the black powder treated by 
nitre did not become clear like the first. It was of a milky-green 
colour, Nitric acid poured into this liquid formed a precipitate in 
it, as in the first water; but it was more flocculent, and of a 
blackish-green colour. It was composed of oxide of iridium, silica, 
and titaniuin. 
Water producing no more effect, I put upon the matter a small 
quantity of weak muriatic acid. It acquired no colour, but sepa- 
rated a light flocky substance, very distinct from the powder itself, 
which, falling quickly to the bottom in consequence of its weight, 
enabled me easily to separate the flocky part. It was composed of 
oxide of iridium, silica in great abundance, titanium, and iron. 
I distilled the liquid to separate the osmium, of which it had a 
strong smell. IL poured, for the second time, upon the powder, a 
considerable quantity of diluted muriatic acid. The acid assumed 
a violet colour, which it would have been difficult to have distin- 
uished by the eye from a strong infusion of the flowers of violets. 
Phis second portion of acid was succeeded by a third portion of con- 
centrated acid, which remained upon the matter for 15 hours. 
The acid had a very deep and pure blue colour; but, notwith- 
standing its great quantity, and its concentration, all the matter 
was not dissolved. 
