them positively to water. In his trials, a diminution of bulk was at first observed, insomuch that where five parts of vital air were added to three of common air, almost the whole disappeared: but, when phlogisticated was substituted for common air, the whole product then appeared as water; more than forty-nine parts in fifty. Thus was he enabled, as he conceived, to shew that vital air was the same thing as water deprived of phlogiston: and that the union of phlogisticated and dephlogisticated air formed the element of water.

This condensation of airs into water, by Cavendish, soon drew the attention of the ingenious of all nations. It was every where tried, and I believe every where generally subscribed to, excepting by the celebrated Mons. Achard, who thought the phænomenon which had been employed to prove that water is a combination of dephlogisticated and inflammable air, proves rather that air results from the combination of water with the igneous fluid. Wherefore, according to him, the decomposition of air must produce water, and consequently the experiments, on which Cavendish and Lavoisier's theory of the composition of water is founded, cannot be considered as a proof that water is

composed

composed of the two kinds of air, from whose combustion it is obtained; as the water obtained is not the production, but merely one of the constituent parts of the mixed air, which has undergone combustion. It has likewise been said, that a doctrine, giving to the oxigene and hydrogene gases, two of the most combustible bodies in nature, the property of forming water, is little less than philosophical extravagancy : the same materials, are moreover given to the formation of the nitrous acid. Why, it is asked, may not water be considered in fact, as Boyle considered it, as an aerial earth, possessing a considerable quantity of latent fire? Ice, by having a greater quantity of heat thrown into it, passes into water; and why may not earth, by having a greater quantity of heat thrown into it, pass into water also? Moreover, although it is the present fashion, not to consider water as one of the kingdoms of nature, why has it a better right to be distinguished from a solid, elastic, diaphanous substance, than a melted metal hath to be distinguished from the same metal, when concreted into a solid form? In their different states of fluidity and solidity they will have different properties; but, should they, from such accidental changes as are effected by minute variations of heat, bereferred to different classes?

VOL. I.

U

Had

Had water been called melted ice, who would have scrupled to consider it as belonging to the mineral kingdom? The reducing quicksilver into a solid, malleable metal, by a degree of cold, was an important discovery in physics. We learn, thence, to consider all fluid bodies, such as water, oils, spirits, æther, and probably the air itself, as convertible into solids, without the introduction of any frigorific particles, but simply by a diminution of heat; and all solid bodies as convertible into fluids, without suffering any other change in their constitution, except what arises from the volatilization of such of their principles as cannot sustain the degree of heat requisite to render the rest fluid.*

To all this, however, it is said, that accurate experiments have compelled chymists to deprive water of its dignity as an elementary principle, and to class it among compound substances; for that all the phænomena of nature and of art conspire to prove the same truth. At the samé time it is allowed, that water may be considered as the general cement of nature. Existing in a state of combination in bodies, it concurs in imparting to them hardness and transparency.

*Bishop Watson.

transparency. It exists in this form in crystals, &c. which immediately lose their transparency on being deprived of their water of crystallization, or their generative water, as it has been emphatically styled. Some bodies are indebted to it for their fixity. The acids, for example, acquire fixity only by combining with water. In a word, it is agreed upon all hands, that water, when disengaged from its combination, and in a state of absolute liberty, is one of the most considerable agents in the operations of this globe. It bears a part in the formations and decomposition of all the bodies of the mineral kingdom; it is necessary to vegetation, and to the free exercise of most of the functions of animal bodies; and it hastens and facilitates the destruction of these bodies, as soon as they are deprived of the principle of life. And thus, all philosophers, until these very few years, in a similar spirit to that of Thales, looked upon water as the elemental matter, or stamen of all things. Even Newton says, "all birds, "beasts and fishes, insects, trees and vegetables, "with their several parts, do grow out of water, "and watery tinctures and salts; and by putre"factions, return again to watery substances."

On whichsoever of these grounds, however, this subject comes to be considered, the close affinity of the elements will be demonstratively proved; together with the chymical position, that bodies never blend, excepting their natures be different, or they be united by the intervention of a third substance. As for instance, oil and water will not mix, and yet when the oil is combined with a salt, there results a soap which is soluble in water. Bodies of the same nature, only increase the bulk of the same matter. And hence it is, that acid salts opposed to alkalis, so intimately combine; that we find the same opposition between alkalis and sulphur; salts and oil; acids and metals; spirit of wine and water; all of which have a great tendency to unite, and to form a most intimate combination.*

From considering water in its constituent parts, let us proceed to contemplate it in the aggregate. Fluid in physiology, is an appellation given to all bodies, whose particles easily yield to the least partial pressure, or force impressed. Some philosophers, however, make the following distinctions in fluids: those which flow or spread themselves till their surfaces become level

* Fourcroy.