3815.] On Iridium and Osmium. AAS 
blue colour, and its solution furnishes, by evaporation, a black 
salt, which is a muriate of iridium-and-potash. Sometimes the 
alkaline solution of iridiam is purple, because a portion of the 
metal has passed to a red colour, and has dissolved in the alkali at 
the same time with the blue portion. 
Thus the fixed alkalies have a greater action on this metal than 
the strongest acids. 
It is doubtful whether we can obtain a blue solution of iridium 
in the acids without the assistance of potash; for to dissolve it we 
must in that case employ boiling nitro-muriatic acid, and then we 
constantly obtain a red solution. 
The red muriatic solution of iridium, sufficiently concentrated, 
is entirely converted by means of ammonia, in a triple salt of a 
purple colour so deep, that it appears black like charcoal powder. 
If into 50 parts of the solution of pure platinum we put one 
part of concentrated muriate of iridium, and afterwards add sal 
ammoniae, we obtain a brick-red precipitate, instead of the lemon- 
yellow precipitate which pure platinum gives. 
_ There can be no doubt then that it is iridium, as we have before 
remarked, which gives a red colour, sometimes very intense, to 
the ammoniaco-muriate of platinum, obtained from the last 
portions of crude platinum. 
The ammoniaco-muriate of iridium erystallized and well dried, 
being exposed to heat in a distilling vessel, gives out azotic gas, 
muriatic acid, sal ammoniac, and leaves for residue 45 per cent. 
of its weight of pure metal. The azotic gas, which comes over, 
shows that part of the ammonia is decomposed. 
This salt is very little soluble in cold water. At the tempe- 
rature of 57°, 20 parts of water are required to dissolve one part of 
ammonio-muriate of iridium. 
The solution of the salt has an orange-red colour, very intense, 
considering the small quantity of salt which it contains. 
Five centigrammes (0°772 grain) were sufficient to give a very 
distinct colour to two litres (122056 cubic inches) of water. 
Hence it follows, that one part is capable of colouring 40,000 
parts of water: a property which is extraordinary for a metallic 
salt. The muriate of rhodium, which possesses this colour in a 
high degree, is, notwithstanding, four times less colouring than 
the muriate of iridium. 
Ammonia discolours the solution of this salt in a few minutes, 
without, however, producing a precipitate in it. 
The green sulphate of iron discolours it instantly, and renders 
it white like water. 
Sulphureted hydrogen, iron, zine, and tin in the metallic state, 
produce the same effect as the sulphate of iron; but if oxymuriatic¢ 
ncid be put into the liquids thus discoloured, they immediately 
assume their natural colour, ; 
When we heat the ammoniaco-muriate of iridium, by means of 
the blow pipe, upon charcoal, it burns with a yellow flame and a 
