442 On: Iridium and Osmium: [Dze. 
which remains combined with the iridium and titanium after treat~ 
ing the black powder with nitre, and which washing with water has 
not been able to separate. 7 : 
§ X. Experiments on the Black Powder obtained by Washing from 
the Residue of Platinum. 
If we agitate in water the insoluble residue of platinum treated 
with nitro-muriatic acid, and decant off the liquid after an interval 
of a few seconds, we obtain by deposition from the liquid a_bril- 
liant black substance, soft to the touch, and staining paper like 
plumbago. I 
By repeating this process a great number of times, we deprive 
the residue almost entirely of this substance. What then. remains 
is a brown coarse sand, harsh to the feel, and which does not, stain 
paper. It is almost entirely composed of chromate of iron, oxide 
of titanium, quartz, and still retains a little of the brilliant matter; 
for it is easy to see that by this mechanical method we cannot com- 
pletely separate the elements which compose the residue of pla- 
tinum. Accordingly in the brilliant powder there is still a small 
quantity of chromate of iron, quartz, and oxide of titanium in the 
state of a finer powder. 
I have already given the analysis of the coarse portion, and mean 
here to speak of the lightest and most brilliant part. 
I treated 20 grammes of this powder in a porcelain retort with 
40 grammes of nitre, in the way already described. 
The water through which the gas was made to pass gave out a 
strong smell of osmium. 
The washings of the matter thus treated showed other properties 
than those which we observed in the other powder. Instead of 
being yellowish-green, they were violet-red. 
When the alkali was saturated with nitric acid, a reddish-brown 
precipitate fell, and the liquid, after the separation of this preci- 
pitate, was reddish-purple, instead of being yellow, as was the case 
with the coarse powder. 
I distilled this liquid in order to separate from it the osmium, of 
which it contained a great deal. The residue of the distillation 
contained no sensible quantity of chromic acid, while the coarse 
powder furnished this acid in this solution alone. ‘This shows that 
by the washing the chromate of iron was almost completely re- 
moved. 
Examination of the Precipitate formed in the Alkaline Liquid by 
Nitric Acid. 
This precipitate, being washed, and put into muriatic acid while 
still moist, dissolved entirely, communicating a very strong smell of 
osmium. By distilling the liquid, I obtained a considerable quan- 
tity of this metal. 
This seems to prove that the osmium may be dissolved by the 
alkali in a state of oxidation different from that in which it is soluble 
