(14.)

The same body may, by the agency of heat, be made to pass successively through the different states of solid, liquid, and gas, or vapour. The most familiar and obvious example of these successive transitions is presented by water. Exposed to a certain temperature, water can only exist as a solid; as the temperature is increased, the ice, or solid water, is liquefied; and by the continued application of heat, this water again undergoes a change, and assumes the form, and acquires the mechanical qualities, of air or gas: in such a state it is called STEAM.

This is a common property of all liquids. If they be exposed for a sufficient length of time to a sufficient degree of heat, they will always be converted into elastic fluids. These are usually distinguished from air and other permanent gases, which never are known to exist in the liquid form, by the term vapour, by which, therefore, must be understood an elastic fluid which at common temperatures exists in the liquid or solid state; by steam is expressed the vapour of water; and by gases, those elastic fluids which like air are never known—at least, under ordinary circumstances—to exist in any other but the elastic form.