438 On Iridium and Osmium. [Dec. 
stroyed by the alkali of the nitre, while the last solutions contain 
only the iron that was united with the iridium. 
From this it follows, that if we divide into three equal portions 
the quantity of muriatic acid necessary to dissolve the black powder, 
-and if the first portion is sufficient to dissolve all the iron, the 
colour of the first solution will be yellow ; of the second, blue, with 
a shade of green; and of the third, pure blue ; supposing that we 
have. carefully washed the residue after each portion of acid has 
acted on it. 
This shows that the green colour of the first solution is not 
simple, but composed of iron, which gives a yellow and a blue 
matter, which, by mixing with the yellow, produces a green. This 
proves likewise that the iron dissolves the first; and that probably, 
if we were to pour on the black powder only the quantity of acid 
necessary to dissolve the iron, this metal almost alone would be 
dissolved. 
Yet I must acknowledge, that though I applied the acid to the 
black powder in a great number of doses, 1 always found iron, 
though in small quantity indeed, even in the last solutions. 
Before explaining the method which I followed in analyzing the 
different solutions of the black powder in muriatic acid, and in 
separating the iridium from them, I think I ought to point out the 
phenomena which they presented with certain re-actives with which 
I mixed them. 
1. The first solution, or that which contains the most iron, and 
which of consequence is of a yellowish-green colour, gives with 
ammonia a bottle-green precipitate, and the liquid remains colour- 
less. But if oxymuriatic acid be introduced into the filtered liquid, 
it assumes a fine red colour, a phenomenon which, showing that 
some metallic body remains in the liquid, will enable us immediately 
to explain several interesting facts. 
2. Sulphate of iron and sulphureted hydrogen deprive this liquid 
almost entirely of its colour, especially if it be diluted with water. 
3. If into the solution thus deprived of its colour by sulphate of 
iron and sulphureted hydrogen, oxymuriatic acid be put, it assumes 
a green colour, and then becomes violet-red, if the acid be in suffi- 
cient quantity. 
“4. The solution rendered violet-red by oxymuriatic acid being 
exposed to the air recovers its green colour in proportion as the acid 
evaporates. 
5. The heat of boiling continued for some time produces in this 
solution a bottle-green precipitate (which we have denoted by the 
letter.B), and changes its colour to a very deep red. The precipi- 
tate which ammonia afterwards forms in this liquid is red, and con- 
tains only iron. 
6. If after having separated the precipitate which falls when the 
liquid is kept boiling, we evaporate the whole to the consistence of 
a syrup, it furnishes, on cooling, tetrahedral crystals of a black 
