# Man's physical universe

MATTER IN THE GASEOUS STATE 207

The Properties of Gases Have Many Practical Applications.

Robert Boyle (1627-1691) proved that air is a material and has

weight, but he is chiefly remembered for his discovery that the volume

of a given quantity of gas is inversely proportional to the pressure, provided

that the Temperature remains constant. This behavior of gases is

called Boyle's Law. This law is simply the statement of a property of

gas already famihar to you {i.e., its compressibility),

for everyone realizes that the volume

of gas compressed into an automobile tire,

for

example, depends upon the pressure exerted.

If the pressure on a tire is suddenly released,

the tire blows out, i.e. , the gas suddenly greatly

increases in volume.

Man is

so well adjusted to life in the atmosphere

that he scarcely realizes the pressure

which the atmosphere exerts. At sea level, the

Fig. 64. The pressure

of the atmosphere

prevents the card from

dropping from the glass

and thus allowing the

pressure of the atmosphere is equivalent to the

water contained therein

pressure which an ocean of water 34 feet deep to pour out.

would exert. To give an idea of the weight of the

atmosphere, it is interesting to note that although the carbon dioxide

content of the air is only 0.04 per cent, it is estimated that there are

2,200,000,000,000 tons of carbon dioxide in the earth's atmosphere.

The pressure of the atmosphere is readily shown by the experiment

in which a glass filled with water is covered with a card and inverted.

Otto von Guericke (1602-1686), the Magdeburg physicist, invented

the air pump, which made it possible for him to evacuate containers.

In one of his spectacular experiments he had fifty men tug on a rope

attached to a piston in a cylinder and then sent them sprawling by

allowing air to enter the cylinder.

Altitude

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