88 M. C. Lea on the Platinum Metals. 
dry at ordinary nares even by exposure to the air, it was 
only oxydized in small par 
To observe the action of som on this compound, a portion 
of the Isabella colored precipitate was placed in a watch glass, 
and a little caustic potash solution was poured over it. Ina few 
minutes a blue tint was observable along the borders of the solu- 
tion, and by exposure for a few hours the whole precipitate be- 
came intensely blue. We thus see that while potash is capable 
of reducing the bi-salts of iridium to sesqui-salts, its presence 
eauses the sesquioxyd to take up oxygen from the atmosphere, 
with production of bioxyd. And that, for this action to take 
place, it is not necessary that the sesquioxyd should be in that 
anomalous state of solution in alkali, in which it seems to exist 
in solutions of bichlorid decolorized with excess of alkali; but 
that the barytic pomyouse here described, which is compara- 
tively permanent by itself, commences immediately to oxydize 
rapidly when placed in contact with potas 
ther reactions of platinum metals with baryta are as follows: 
Sesquichlorid of ruthenium and ammonium is immediately and 
completely pene by baryta in the cold. 
Bichlorid of r mand ammonium gives no precipitate to 
the cold. Heated, it sited yellowish brown and becomes trou- 
bled. This troubling is completely removed by the addition of 
a large excess of the ‘precipitant. If the baryta have been added 
to large excess at first, no troubling is occasioned by the appli- 
cation of heat. 
Protochlorid of anaes is precipitated immediately in the 
cold by Ba. The brownish yellow precipitate does not redis- 
solve in excess of the presipitaat In this the reaction of baryta 
differs — that of 
Bichlorid of i pease is “scarcely affected by baryta water in 
the aid. Heat immediately produces a dirty white precipitate, 
the supernatant liquid remaining of a yellow color 
Sesquichlorid of rhodium gives an immediate light colored pre- 
cipitate with baryta, which sya, pes wa ass ina very large 
excess of the precipitant, even in the 
It will be seen from the one that the reactions of baryta 
with the platinum metals differ widely from those produced by 
tee and are highly characteristic. 
Two of these solutions which — resemble each a 
otro of a well marked precipitate is generally 
a mere pine of color, as produ 
been cons the’ beat reagent to distin 
