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.

Composition. The composition of water is determined both by analysis and synthesis. If this liquid be submitted to the influence of a volcanic battery, it is

decomposed into two gases, namely one volume of oxygen and two volumes of hydrogen. These gases, in the proportions just mentioned, may be made to recombine, and form water by heat, electricity, or spongy platinum, as water consists of one equivalent of hydrogen, 1 and one of oxygen, 8 = 9; and in volume, of one volume of hydrogen, and half a volume of oxygen, condensed into aqueous vapor or steam we can easily calculate the specific gravity of steam, for its density will be, .0689 (Sp. gr. of hydrogen) + .5512 (half the Sp. gr. of oxygen)=.6201.

Water as affected by the laws of Heat.

As the extensive and important functions which water discharges in the economy of nature, depend mainly on the manner in which it is affected by the laws of heat, a few remarks on this subject may not be inappropriate to this place. Heat is communicated through water in a different manner, from that observed in relation to solids, for it is not conducted as in them, from one particle to another, but carried with the parts of the fluid by means of an intestine motion. Water expands and becomes lighter by heat, and therefore it is, that if the upper portion of water be cooled below the lower, the former descends, and the latter rises to take its place.