446 On Iridium and Osmium. [Dec. 
kind of fulguration,, It leaves a porous metallic mass of a grey 
colour, but which assumes a white colour, and a strong lustre, 
when rubbed between two hard bodies. This colour and lustre 
strongly resemble those of platinum. 
We have seen by what has been said, that iridium, according to 
the state of its oxidation, gives, when it combines with  muriatic 
acid, a yellowish red colour. 
I have endeavoured to ascertain if these two colours were due to 
two states of oxidation, as we thought before, and, in that case, 
which of the two contains most oxygen. The experiments which 
I have made leave me in my former opinion ; but they only furnish 
probabilities respecting the quantity of oxygen existing in these 
oxides. 199 
All the information they have given is; 1. That we canno 
obtain the blue solution of iridium in acids, without having 
first treated this. metal with potash or nitre. 2. That these blue 
solutions become yellowish red when long boiled; and, as tne 
change takes place gradually, we can perceive, if we pay attention 
to it, the shade becoming first green, then violet purple, and 
finally yellowish red. 3. ‘That the blue solutions are not precipi- 
tated in the state of triple salts by the alkalies, either fixed or 
volatile. 4. That the blue solutions become red when sufficiently 
diluted; but still are not precipitated by the alkalies, and when 
sufficiently concentrated, give a black triple salt, soluble in twenty 
parts of water. There is then a difference in the state of. the iri- 
dium in these solutions, since the one forms triple salts but little 
soluble, and the other salts which are very soluble. 
If. the blue and red solutions be equally discoloured by the com- 
bustible bodies of which we have spoken above, oxymuriatic acid 
restores to each of them its primitive colour; but if, after restoring 
the blue colour, we adda new quantity of oxymuriatic acid,’ that 
colour passes into a purple red. 
If we suppose that these two solutions are reduced to the same 
state of oxidation by the combustible substances, the sulphate of 
iron for example, we must see it, when we mix with it oxymuriatic 
acid, pass through the same shades to arrive at the maximum, 
which does not happen. ‘The blue becomes blue without inter- 
mediate shade, and the red becomes immediately red without pass- . 
ing through blue. The purple red colour, which oxymuriatie acid 
in excess gives to the blue liquid, does not appear to change the 
state of the oxidation of the metal; for it is sufficient to leave this 
solution for some time in the air, to enable it to resume its blue 
eolour, in proportion as the oxymuriatic acid exhales, Thus, 
though there is an obvious difference between the oxide of iridium 
in the blue and in the red solutions, I am obliged to acknowledge 
my ignorance of the relative quantity of oxygen in each. I pre- 
sume, merely, that the red contains more oxygen than the blue, 
We have said-above that the blue solution of iridium is not pre- 
cipitated by alkalies. This is true when the solution is pure ;’ but 
