A transparent fluid without colour, smell, or taste, and compressible only in a very slight degree; when pure, not liable to spontaneous change; liquid at the common temperature of our atmosphere, assuming a solid form at 32° of Fahr. and agaseous state at 212° Fahr., but returning unaltered to its liquid state on resuming any degree of heat between these points. Water is capable of dissolving a greater number of natural bodies than any other fluid whatever, and especially those known by the name of the saline; performing the most important functions in the animal and vegetable kingdoms, and entering largely into their compositions as a constituent part; water exists therefore in three different states: in the solid state or state of ice, in the liquid, and in the state of vapour or steam. It assumes the solid form, as observed above, when cooled down to the temperature of 32°, in which state it increases in bulk, and hence exerts a prodigious expansive force, owing to the new arrangement of its particles, which assume a crystalline form, the crystals crossing each other at an angle of 60° or 120°. The specific gravity of ice is therefore less than that of water.
When ice is exposed to a temperature above 32°, it absorbs caloric, which then becomes latent, and is converted into a liquid state, or that of water. At the temperature of 42° 5' water is at its maximum of density; and according to some accurate experiments upon water in this state, a French cubic foot of it weighs 70 pounds 223 grains French, which is equal to 529452.9492 troy grains. An English cubic foot, at the same temperature, weighs 437102.4946 grains troy. By professor Robinson's experiments, it is ascertained that a cubic foot of water, at the temperature of 55o, weighs 998.74 avoirdupois ounces, of 437.5 grams troy each, or about 1 1/2 ounce less than 1000 ounces avoirdupois, which latter, however, is the usual estimate. When water is exposed to the temperature of 212°, it boils; and if this temperature be continued, the whole is converted into elastic vapour or steam. In this state it expands to about 1600 times its bulk when in the state of water, which shows what an astonishing expansive force it must exert when it is confined; and hence its application to the steam engine, of which it is the moving power.
Water was formerly considered as a simple elementary substance, and the contrary was not satisfactorily ascertained till towards the end of the eighteenth century, when it was found that 100 parts, by weight, of water is composed of 85 parts of oxygen gas, and 15 of hydrogen gas. In the common tables of specific gravities, that of water is assumed as 1.000, or the unit of measurement, because, as has been already observed, a cubic foot of water weighs very nearly 1000 ounces; it follows, therefore, that the number expressed in the table as the specific gravity of any other substance, gives also the real weight of a cubic foot of such substance.
Boring for Water. See Boring the Earth.