1815.) On Iridium and Osmium. 44} 
perties‘of muriate of titanium mixed with a minute quantity of 
iron. — : 
Thus the precipitate under examination is composed of- iridium, 
iron, titanium, and silica. 
It follows from this that though the liquid from. which these 
different substances come was sensibly acid, a portion of the iron, 
most of the titanium and iridium at a medium point of oxidation 
are precipitated by means of heat. It is to be presumed that the 
titanium, the solutions of which are decomposed by heat, is the 
cause of the precipitation of the iron and iridium, which would 
not take place with either of them separately. ‘These bodies seem 
to exert a reciprocal action on each other, which produces a com- 
pound insoluble at least in a weak acid. 
Now that we know the nature of the substances contained in the 
muriatic acid solutions, and the way in which they are acted on by 
Te-aetives, we can trace with more accuracy the method that must 
be followed in order to extract the iridium ina state of purity, 
which is our principal object. 
_» We have remarked that iridium, when in the state in which it 
gives red solutions, is no longer precipitated by heat, even when 
assisted by the action of titanium, nor by the alkalies, from. its 
solutions when sufficiently diluted: that it is preeipitated in the 
state of a triple salt by sal-ammoniac when its solutions are) con- 
centrated. 
We must therefore bring iridium into this state, by adding to the 
solution a certain quantity of nitric acid, and boiling the mixture 
for along time. When the greatest part of the superabundant acid 
is dissipated, the solution is diluted with a considerable quantity of 
water, and the quantity of ammonia is added necessary to bring the 
liquid nearly to a neutral state. When the liquid is now boiled, a 
precipitate falls, consisting chiefly of oxide of titanium with a little 
iron, without any mixture of iridium, if the precipitate be) pro- 
perly washed. ‘The liquid, now containing only iridium and iron, 
is concentrated and mixed with sal-ammoniac. A black crystalline 
precipitate of ammoniaco-miuriate of iridium falls, from which the 
supernatant liquid is separated by decantation. When the concen- 
trated liquid furnishes no more salt, it is diluted with water, the 
iron is precipitated by ammonia, the precipitate washed with, hot 
water, and the liquids evaporated to dryness. The residual salt 
being exposed to a red heat, leaves very pure iridium in) the 
metallic state. 
The ammonio-muriate of iridium being obtained ina state of 
purity, we have only to heat it to redness in a covered crucible in 
order to obtain metallic iridium in a state of powder. 1 ought to 
observe, however, that the salt of which I have just spoken con- 
taining always a small quantity of muriate of potash, the metal 
which it furnishes requires to be washed in boiling water before it 
is pure, 
* This muriate of potash comes from a small quantity of potash 
