Note 9 — PART III. Scientific Pursuits: (continued 2)

It may be well to state here, that by vapour is generally understood the aërial form of a substance usually existing in a solid or fluid form at ordinary temperatures; as the vapour of iodine, a solid; of mercury, water, spirits, and other fluids: while the term gas is applied to those bodies usually known in the aërial state; thus oxygen, nitrogen, carbonic acid, hydrogen, &c. &c., are called gases. It is, however, but an arbitrary distinction; for many of these gases have, by the combined influence of cold and powerful pressure, been converted into fluids, and even solids—carbonic acid gas for instance!