remaining after the Solution of Platina. 415 
iridium may be obtained in a pure state, merely by exposing 
the octaedral crystals to heat, which expels the oxygen and the 
muriatic acid. It appeared of a white colour, and was not 
capable of being melted, by any degree of heat I could apply. I 
Could not combine it with sulphur, nor with arsenic. I^ead 
easily unites with it ; but is separated by cupellation, leaving 
the iridium upon the cupel, as a coarse black powder. Copper 
forms with it a very malleable alloy, which, after cupellation 
with the addition of lead, left a small proportion of the iridium, 
but much less than in the former case. Silver may be united 
with it, and the compound remains perfectly malleable. The 
iridium was not separated from it by cupellation, but occasioned 
on the surface a dark or tarnished hue. It appeared not to be 
perfectly combined with the silver, but merely diffused through 
the substance of it, in the state of a fine powder. Gold alloyed 
with iridium is not freed from it by cupellation, nor by quartation 
with silver. The compound was malleable; and did not differ 
much in colour from pure gold, though the proportion of alloy 
was very considerable. If the gold or silver is dissolved, the 
iridium is left, in the form of a black powder. 
The yellow alkaline solution, which I have already mentioned 
as containing a metallic oxide, distinct from the former, is con- 
sidered by M. Vauquelin as a solution of the oxide of chrome 
in alkali ; but I could not, by any test, discover the presence of 
chrome. After the superfluous alkali had been neutralized by 
an acid, it produced a pale or buff-coloured precipitate with a 
solution of lead, and not the bright yellow which is given by 
chrome. But, as we are indebted to the above distinguished 
chemist, among many other important discoveries, for our 
knowledge of the existence of chrome, it is not improbable that 
MDCCCIV. 3 H 
