REMAINING AFTER THE SOLUTION OF PLATINA. 



27 



oxide, but are capable of retaining a part in folution, be- 

 coming of a yellow colour. All the metals which I tried, 

 except ing gold and platina, produced a dark or black pre- 

 cipitate from the muriated folution, which is at the fame time 

 deprived of its colour. The iridium may be obtained in a The metal iridi- 

 pure fiate, merely by expofing the octaedral cryftals to heat, um is white > 



u- u i .u ■ a Ti >■ -a t* infufible, and 



which expels the oxigen and the muriatic acid. It appeared r eje#s fulphat 



of a white colour, and was not capable of being melted, by andarfenic. 

 any degree of heat I could apply. I could not combine it 

 with fulphur, nor with arfenic. Lead eafily unites with it ; its habitudes 

 but is feparated by cupellation, leaving the iridium upon the wit ^ tlle me' 3 ' 8 ' 

 cupel, as a coarfe black powder. Copper forms with it a very 

 malleable alloy, which, after cupellation with the addition of 

 lead, left a (mall proportion of the iridium, but much lefs 

 than in the former cafe. Silver may be united with it, and 

 the compound remains perfectly malleable. The iridium was 

 not feparated from it by cupellation, but occafioned on the 

 furface a dark or tarnifhed hue. It appeared not to be per- 

 fectly combined with the filver, but merely diffufed through 

 the fubfiance of it, in the flate of a fine powder. Gold 

 alloyed with iridium is not freed from it by cupellation, nor 

 by quartation with filver. The compound was malleable; 

 and did not differ much in colour from pure gold, though 

 the proportion of alloy was very confiderable. If the gold 

 or filver is difiblved, the iridium is left, in the form of a 

 black powder. 



The yellow alkaline folution, which I have already men- The alkaline 

 tioned as containing a metallic oxide, diftincl from the former, folut '. on did not 

 is confidered by M. Vauquelin as a folution of the oxide of 

 chrome in alkali ; but I could not, by any teft, difcover the 

 prefence of chrome. After the fuperfiuous alkali had been 

 neutralized by an acid, it produced a pale or buff-coloured 

 precipitate with a folution of lead, and not the bright yellow 

 which is given by chrome. But, as we are indebted to the 

 above diftinguiflied chemift, among many other important 

 difcoveries, for our knowledge of the exigence of chrome, it 

 is not improbable that fome kinds of platina may contain that 

 fubftance, befides the other bodies ufually mixed with it. 

 When the alkaline folution is firft formed, by adding water it contains the 

 to the dry alkaline mafs in the crucible, a pungent and pe- volatile oxide of 

 culiar fmell is immediately perceived. This fmell, as I after- o/mim- C 



wards 



