440 On Iridium and Osmium. [Dee: 
odour similar to that of oxymuriatic acid, and at the same) time 
assumes a red colour. As this production of oxymuriatic acid may 
serve to explain the change of the colour of the solution from green 
to red, a quantity of it was put into a retort furnished with a re- 
ceiver, and heated till it acquired a reddish-brown colour. | 
The product obtained had the smell of oxymuriatic acid, and de- 
stroyed the colour of litmus, so that it could not be restored by the 
alkalies, : 
Thus the discolouration of the green liquid by sulphureted 
hydrogen and the sulphate of iron, and its change into violet-red 
by oxymuriatic acid, seems. to announce that the metal is in a mean 
state of oxidation when it is blue, and that it descends to a 
minimum when it passes to white. It is not probable: that the 
production of the oxymuriatic acid of which we have spoken is the 
effect of the change of the blue colour into red, since, on the con- 
trary, this last is changed into violet-red by the addition of oxymu- 
riaticacid. In fact, the blue liquid discoloured by sulphate of iron, 
by sulphureted hydrogen, by a plate of zinc, or by any other body, 
passes at once into blue by the addition of a small quantity of oxy- 
muriatic acid.. This seems to leave no doubt that the most oxygen- 
ated state of this substance is that which exists in the red solution. 
Such are the properties of the bottle-green substance, precipi- 
tated during boiling from the first muriatic solution of the black 
powder from platum, previously treated with nitre. 
50 grammes of the black powder furnished 10 grammes of this 
bottle-green precipitate. After washing and calcination, it had a 
black colour, a smooth and brilliant fracture, like that of glass: 
then, though well pounded, it dissolved no longer entirely in 
miuriatie acid. Of these 10 grammes, which were boiled with five 
parts of nitro-muriatic acid, 2°6 grammes only were dissolved, and 
7°4 grammes remained under the form of a greenish-brown 
powder. This matter, being dried, and pulverized again, was sub- 
jected a second time to the action of a great quantity of nitro+ 
muriatic acid, without dissolving. It had merely communicated to 
the acid a reddish-brown colour. The solutions, being united and 
concentrated by evaporation, did not furnish crystals; but muriate 
of ammonia being added to it, a black salt was obtained, similar'to 
the one mentioned before, and which is an ammoniaco-muriate of 
iridium. If when these solutions yield no more of the salt by con- 
centration, we dilute them with water, and add to them a sufficient 
quantity of ammonia to saturate all the acid, a precipitate falls, 
which has all the appearance of oxide of iron, and which in reality 
contains nothing else, except a little oxide of titanium and silica. 
The liquid from which this precipitate has been ‘separated is 
colourless, though it still contains ammoniaco-muriate of iridium, 
as is shown by the red colour produced in it by oxymuriatic acid. 
‘Our precipitate being no longer acted upon by acids, I treated it 
with twice its weight of caustic potash, which rendered it soluble in 
mariatic acid. . ‘The solution was yellow, and presented all the pro- 
