Page:The fairy tales of science.djvu/70

 the elegant varieties of marble, are examples of this union.

The solid portions of our globe are almost as rich in oxygen as the atmosphere and ocean. Every rock is a compound of oxygen with certain metallic and non-metallic bodies. Silica contains about half its weight of this abundant element; alumina no less than one-third; and lime two-fifths.

In some compounds oxygen is replaced by another metalloid. Common salt, the chief saline matter of sea-water, is a compound of sodium, a metal closely allied to potassium, with chlorine, a remarkable gaseous body, which in some respects resembles oxygen. The glistening yellow mineral called iron pyrites, contains iron, and the metalloid sulphur. The variegated crystalline substance known as fluorspar, is a compound of calcium, the metallic base of lime, with fluorine, a mysterious body which the chemist has never yet been able to procure in a separate state.

The so-called noble metals—namely, gold, silver, mercury, platinum, and a few others—are usually found in a state of purity; sulphur is frequently met with uncombined; and carbon is found pure in the diamond. With these few exceptions, the material world may be said to be an assemblage of compounds formed by the union of thirteen metalloids with fifty metals.

Plants and animals are almost wholly composed of oxygen, hydrogen, nitrogen, and carbon; hence