M. C. Lea on the Platinum Metals. 87 
not precipitate the sesquioxyd, but seems to hold it in solution. 
On the application of heat the sesquioxyd’ gradually oxydizes © 
itself at the expense of the atmosphere, and is then precipitated 
as deutoxyd of iridium. If to the cold solution containing ex- 
cess of alkali, an acid be added, in small quantity, an impure 
sesquioxyd is precipitated in consequence of the neutralization 
of the alkali which held it in solution. But the sesquioxyd 
thus precipitated always contains a considerable quantity of the 
alkali used. It is very unstable, and by the action of the air is 
rapidly converted into blue oxyd. This is nearly all that we 
know of the sesquioxyd of iridium. 
Under these circumstances it appeared to me desirable to in- 
vestigate the action of some of the alkaline earths upon iridium 
solutions which it seemed possible, might throw a clearer light 
upon the relations of the sesquioxyd. 
Vhen a solution of caustic baryta is poured over iridium-sal- 
ammoniae, the iridium salt rapidly dissolves with a slight effer- 
vescence, the solution presently becomes comparatively decolor- 
ized, and a dark olive-green precipitate falls. This reaction, it 
will be observed, is completely different from that caused by 
ash 
_ The filtrate from this precipitate, which precipitate is but small 
In quantity, still contains a large quantity of iridium. If it be 
exposed to heat, as soon as it is moderately warm, its dark olive 
color changes almost suddenly to an Isabella color, it becomes 
erties observed. : ; 
The olive green precipitate seemed to be permanent in the air, 
and contained no baryta, or, at most, only traces, It dissolved 
in acids, leaving however a trace of black powder behind, and 
& 
