They are called platiniferous metals; and they have not
only the relation of being always found associated in this manner, but
they have other relations of a curious nature, which I shall point out to
you by a reference to one of the tables behind me. This substance is
always native--it is always in the metallic state; and the metals with
which it is found connected, and which are rarely found elsewhere, are
palladium, rhodium, iridium, osmium, and ruthenium. We have the names in
one of the tables arranged in two columns, representing, as you see, two
groups--platinum, iridium, and osmium constituting one group; and
ruthenium, rhodium, and palladium the other. Three of these have the
chemical equivalent of 98-1/2, and the others a chemical equivalent of
about half that number. Then the metals of one group have an extreme
specific gravity--platinum being, in fact, the lightest of the three, or
as light as the lightest. Osmium has a specific gravity of 21.4, and is
the heaviest body in nature; platinum is 21.15, and iridium the same; the
specific gravity of the other three being only about half that, namely,
11.3, 12.1, and 11.8. Then there is this curious relation, that palladium
and iridium are very much alike, so that you would scarcely know one from
the other, though one has only half the weight of the other, and only half
the equivalent power.
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