It is almost incompressible, a pressure equal to 2000 atmospheres occasioning a diminution of only one-ninth of its bulk; or, when submitted to a compressing force equal to 30,000 lbs. on the square inch, 14 volumes of this fluid

are condensed into 13 volumes ; proving that it is elastic. Water being the substance most easily procured in every part of the earth in a state of purity, it has been chosen by universal consent, to represent the unit of the specific gravity of

all solid and liquid bodies. A cubic inch of water at 60° Fah. weighs 255.5 grains; so that this fluid is about 815 times heavier than atmospheric air, but being the standard to which the weight of all other substances is referred, its specific weight is said to be 1. Accordingly when we say that the specific gravity of a body is two we mean that it weighs twice as much as the same volume of water would do. Water unites with both acids and bases, but without destroying their acid or

basic properties. Thus the crystallized vegetable acids, tartaric, citric, and oxalic, are atomic combinations of water with acids. Caustic potash (potassa fusa) and slaked lime may be instanced as compounds of water, and basic substances ;

these are therefore called hydrates. The crystallized salts, such as alum, common salt, sulphate of soda, sulphate of magnesia, borate of soda, (borax,) &c., contain

a large amount of water as a chemical constituent, called water of crystallization. Water rapidly absorbs some gases, as ammonia, fluoride of boron, &c, but it is neither combustible, nor, under ordinary circumstances, a supporter of combustion.