Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAPTER VI. THE ATMOSPHERE — NITROGEN. The Atmosphere is the great mass of gas surrounding the earth and extending into space. Its estimated height is fifty to several hundred miles. We live at the bottom of this vast ocean of air, as it is often called. Aristotle (384-322 B.c.) regarded air as one of the four elementary principles whose combinations made up all substances in the universe. The other three were earth, fire, and water. He taught that air possesses two fundamental properties,—heat and dampness. The early chemists used the word air in the sense in which the word gas is now employed. Thus, we have already learned that hydrogen was first called inflammable air. The terms atmosphere and air are often used interchangeably, though by air we usually mean a limited portion of the atmosphere. Many skillful chemists have studied the action of air on living things, its relation to combustion, the effect of its weight, its composition, and its varied properties. Their work has contributed many fundamental facts to science. General Properties of the Atmosphere. — Air has weight. We often use the expression " light as air." But a cubic foot of air weighs 1.28 oz. and a room 40 X 50 x 25 ft. contains about two tons of air. The total weight of the atmosphere has been estimated to be five thousand millions of millions of tons. This enormous mass resting upon the earth exerts a pressure which is about fifteen pounds on every square inch. This amount of pressure upon asquare inch is called "an atmosphere," and it is sometimes used as a unit of pressure. Thus, three atmospheres means a pressure of forty-five pounds per square inch. It is this pressure which causes water to rise in pumps and flow through siphons. Atmospheric pressure is exerted in all directions and is va...