Abstract
WHEN we find a substance capable of existing in two fluid states different in density and other properties, while the temperature and pressure are the same in both; and when we find also that an introduction or abstraction of heat without change of temperature or of pressure will effect the change from the one state to the other; and also find that the change either way is perfectly reversible, we speak of the one state as being an ordinary gaseous and the other as being an ordinary liquid state of the same matter; and the ordinary transition from the one to the other we would designate by the terms boiling, or condensing; or occasionally by other terms nearly equivalent, such as evaporation, gasification, liquefaction from the gaseous state, &c. Cases of gasification from liquids, or of condensation from gases, when any chemical alteration accompanies the abrupt change of density, are not among the subjects proposed to be brought under consideration in the present paper. In such cases I presume there would be no perfect reversibility in the process; and if so, this would of itself be a criterion sufficing to separate them from the proper cases of boiling or condensing at present intended to be considered. If now the fluid substance, in the rarer of the two states—that is, in what is commonly called the gaseous state—be still further rarefied, by increase of temperature or diminution of pressure, or be changed considerably in other ways by alterations of temperature and pressure jointly, without its receiving any abrupt collapse in volume, it will still, inordinary language and ordinary mode of thought, be regarded as being in a gaseous state. Remarks of quite a corresponding kind may be made in describing various conditions of the fluid (as to temperature, pressure, and volume), which would in ordinary language be regarded as belonging to the liquid state.
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Continuity of the Fluid and Gaseous States of Matter * . Nature 5, 106–108 (1871). https://doi.org/10.1038/005106a0
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DOI: https://doi.org/10.1038/005106a0