252 M. C. Lea on the Platinum Metals. 
- The hyposuiphite is a valuable test for the purity of iridium, 
and affords an easy indication as to whether other metals of the 
latinum group are present, Let the chloriridiate of ammonium 
= boiled with HCl, and then ammonia be added until the solution 
assumes the pale olive color produced by alkalies in solutions of 
bichlorid of iridium. The solution should be sufficiently dilute 
that, after the ammonia has been added, it becomes nearly color- 
less. Now add the hyposulphite and boil. Jf any increase of 
color whatever takes place, it is a certain indication of impurity. If 
the liquid becomes rose color, ruthenium is present; if wine color, 
platinum is probably present; if brown, palladium is probably 
indicated. 
REACTIONS WITH TETRATHIONIC ACID, 
Tetrathionic acid is capable of giving useful reactions with 
metals of the platinum group, and especially with palladium. 
Ru, Cl, boiled with tetrathionic acid is somewhat decolorized, 
and finally becomes muddy and grayish. : 
uCl, boiled with tetrathionic acid gradually darkens in color, 
becomes muddy, and finally throws down a brown precipitate. 
But if the acid be at first supersaturated with ammonia, the s0- 
lution becomes yellow and remains clear, 
ir,Cl,, when boiled with tetrathionic acid, the pale, almost 
colorless dilute solution darkens rapidly, and by some moments 
tation without heat is highly characteristic of the protochlorid 
5 
of palladium, and the tes 
of water. Ina few drops of this very dilute solution, the pres” 
ence of palladium was made evident by this test. When the 
quantity of palladium present is so very minute as in this cast 
no precipitation takes place, but a brown coloration is developed. 
And as this coloration is produced in the cold, it is highly chat 
acteristic of the metal in question, 
: PtCl,. Tetrathionie acid produces no effect in the cold. DY 
_ boiling, a wine brown color is developed, but no precipitation 
___As this test for palladium appeared likely to be a valuable 
__ One, a series of experiments was undertaken to ascertain whethey 
___ Tike so many of the old tests for metals of the platinum group» 
