The "heavyweight champion" among the metals is osmium. One cubic centimetre of this noble metal weighs 22.6 grams. To balance one cube of osmium we would have to put on the other tray, say, three cubes of copper, two cubes of lead or four cubes of yttrium. The "performance" of osmium's closest neighbours, namely, platinum and iridium, is almost as high. The noble metals are also the heaviest metals.

   The hardness of metals has become proverbial. If a man is always composed and cool-headed, we say he has "iron nerves." But in the world of metals the situation is different.

   Here iron is hardly a model of hardness. The hardness champion is chromium which is just slightly inferior to diamond. By the way, paradoxical though it sounds, the hardest chemical elements are not metals at all. At the top of the conventional hardness scale stand diamond (a form of carbon) and crystalline boron. Iron should rather be classed as a soft metal; it is only half as hard as chromium. And as to the lightweights, the alkali metals, they are as soft as wax.

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