We have not pretended to make any alteration upon such terms as are sanctified by ancient custom; and, therefore, continue to use the words _water_ and _ice_ in their common acceptation: We likewise retain the word _air_, to express that collection of elastic fluids which composes our atmosphere; but we have not thought it necessary to preserve the same respect for modern terms, adopted by latter philosophers, having considered ourselves as at liberty to reject such as appeared liable to occasion erroneous ideas of the substances they are meant to express, and either to substitute new terms, or to employ the old ones, after modifying them in such a manner as to convey more determinate ideas. New words have been drawn, chiefly from the Greek language, in such a manner as to make their etymology convey some idea of what was meant to be represented; and these we have always endeavoured to make short, and of such a nature as to be changeable into adjectives and verbs. Following these principles, we have, after Mr Macquer's example, retained the term _gas_, employed by Vanhelmont, having arranged the numerous class of elastic aeriform fluids under that name, excepting only atmospheric air. _Gas_, therefore, in our nomenclature, becomes a generic term, expressing the fullest degree of saturation in any body with caloric; being, in fact, a term expressive of a mode of existence. To distinguish each species of gas, we employ a second term from the name of the base, which, saturated with caloric, forms each particular gas. Thus, we name water combined to saturation with caloric, so as to form an elastic fluid, _aqueous gas_; ether, combined in the same manner, _etherial gas_; the combination of alkohol with caloric, becomes _alkoholic gas_; and, following the same principles, we have _muriatic acid gas_, _ammoniacal gas_, and so on of every substance susceptible of being combined with caloric, in such a manner as to assume the gasseous or elastic aeriform state.