Water. A fluid, of which a cubic foot weighs 1,000 ounces, or 825 times more than a cubic foot of atmospheric air; the constituents of which are one part, by weight, of hydrogen, and 7 1/2 of oxygen; and two parts, by bulk, of hydrogen, and one of oxygen. It becomes solid at 32° of Fahrenheit, and boils or evaporates, and becomes no hotter, St 212°, though, by compression, it has been heated red-hot. When expanded in steam, at 212°, it acquires 1,800 times its bulk, and presses with the force of atmospheric air ; at 226o it expands 9,000 times, and 36,000 times at 257o. A volume of ice is made fluid by as much excitement as will raise an equal volume of water 140°.

Vegetables decompose it, the hydrogen forming their unctuous, resinous, and saccharine principles, in combination with the carbon of the soil; the oxygen being evolved by the leaves, and a supply thereby kept up of what is fixed by animal respiration and combustion. In the ocean, it is combined with l-30th of its weight of muriate of soda, or sea-salt; but, as salt does not crystallize so soon as water, sea-water remains liquid till the thermometer is 3.5 lower than for other water. In like manner, the salt does not evaporate at the heat which vaporizes water, and, therefore, the two processes of crystallizing and evaporating separate the water from the salt. Hence, the clouds which rise from the sea. rain, fresh water, and water evaporated by art, yield salt in the proportion of one ton from 3-5 of water. In crystallizing, vacuities arise, which enlarge the bulk : hence, frozen water splits rocks and trees, and ice floats upon water. Water combines with iron, sulphur, lime, and various substances, under a great variety of names; hard water arises from carbonic acid in water which then combines with lime. Waters are called hard when they contain a salt which decomposes the soap instead of dissolving it. The deductions drawn, in regard to the decomposition of water, from the experiment of discharging a galvanic battery through water are erroneous; for the poles of the battery themselves produce the oxygen and hydrogen supposed to be produced by the water, being, in fact, the constituents of the solution lying between the plates, and identical with positive and negative electricity in all cases and circumstances. (See p. 16).