PART ae

THE WATER.

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By contact. of air with the water-areas, an immense quantity of invisible vapor passes into the
atmosphere, from which, when sufficiently cooled, it re-appears and descends as fog, dew, rain, hail, sleet,
or snow. It then, in greater part, drains through various lake- and river-systems into the ocean, where
it is either again evaporated, or carried about'in waves, tides, or currents. T'his circulation of water
never ceases, and upon it depends the existence of all life on the earth.

SSS eee

SECTION

CHAP EER «1.

Physical Properties of Water.

146. Composition Water is formed by the
combination: of oxygen and hydrogen, in the pro-
portion, by weight, of eight parts of oxygen to
one part of hydrogen; or, by volume, of one part
of oxygen to two parts of hydrogen.

147. Properties. — Pure water is a colorless,
transparent, tasteless, and inodorous liquid. It

CONTINENTAL WATERS.

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freezes at 82° Fahr., and, under the ordinary
pressure of the atmosphere, boils at 212° Fahr.

Water exists in three states: solid, liquid, and gaseous. |
Under ordinary circumstances it freezes at 32°. It evapo-
rates, or passes off from the surface as vapor, at all tempera-
tures, even at 32°; but it is only at the boiling-point that
the vapor escapes from the mass of the liquid. as well as
from the surface.

Heated in open vessels, under the ordinary pressure of
the atmosphere, its temperature cannot be raised higher than
212°, any increase of heat only causing it to boil more rap-
idly. Heated in closed vessels, which prevent ne escape