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 it remains solid, and is called ice. Above that degree of temperature, its particles beign no longer held together by reciprocal attraction, it becomes liquid; and, when we raise its temperature above 80°, (212°) its particles, giving way to the repulsion caused by the heat, assume the state of vapour or gas, and the water is changed into an aëriform fluid.

The same may be affirmed of all bodies in nature: They are either solid or liquid, or in the state of elastic aëriform vapour, according to the proportion which takes place between the attractive force inherent in their particles, and the repulsive power of the heat acting upon these; or, what amounts to the same thing, in proportion to the degree of heat to which they are exposed.

It is difficult to comprehend these phenomena, without admitting them as the effects of a real and material substance, or very subtile fluid, which, insinuating itself between the particles of bodies, separates them from each other; and, even allowing the existence of this fluid to be hypothetical, we shall see in the sequel, that it explains the phenomena of nature in a very satisfactory manner.

This substance, whatever it is, being the cause of heat, or, in other words, the sensation which we call warmth being caused by the accumulation of this substance, we cannot, in strict language,