It is strange that this metal is almost always found associated with some four or five other metals, most curious in their qualities and characteristics. 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 98½, 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. So with iridium and rhodium, and osmium and ruthenium, which are so closely allied that they make pairs, being separated each from its own group. Then these metals are the most infusible that we possess. Osmium is the most difficult to fuse: indeed, I believe it never has been fused, while every other metal has. Ruthenium comes next, iridium next, rhodium next, platinum next (so that it ranks here as a pretty fusible metal, and yet we have been long accustomed to speak of the infusibility of platinum), and next comes palladium, which is the most fusible metal of the whole. It is a curious thing to see this fine association of physical properties coming out in metals which are grouped together somehow or other in nature, but, no doubt, by causes which are related to analogous properties in their situation on the surface of the earth, for it is in alluvial soils that these things are found.