substance, the name of the class
or the genus ought to be taken; the other is peculiar to each acid, and
distinguishes it from the rest, and from this substance is to be taken
the name of the species. But, in the greatest number of acids, the two
constituent elements, the acidifying principle, and that which it
acidifies, may exist in different proportions, constituting all the
possible points of equilibrium or of saturation. This is the case in the
sulphuric and the sulphurous acids; and these two states of the same
acid we have marked by varying the termination of the specific name.

Metallic substances which have been exposed to the joint action of the
air and of fire, lose their metallic lustre, increase in weight, and
assume an earthy appearance. In this state, like the acids, they are
compounded of a principle which is common to all, and one which is
peculiar to each. In the same way, therefore, we have thought proper to
class them under a generic name, derived from the common principle; for
which purpose, we adopted the term _oxyd_; and we distinguish them from
each other by the particular name of the metal to which each belongs.

Combustible substances, which in acids and metallic oxyds are a specific
and particular principle, are capable of becoming, in their turn, common
principles of a great number of substances. The sulphurous combinations
have been long the only known ones in this kind. Now, however, we know,
from the experiments of Messrs Vandermonde, Monge, and Berthollet, that
charcoal may be combined with iron, and perhaps with several other
metals; and that, from this combination, according to the proportions,
may be produced steel, plumbago, &c. We know likewise, from the
experiments of M. Pelletier, that phosphorus may be combined with a
great number of metallic substances. These different combinations we
have classed under generic names taken from the common substance, with a
termination which marks this analogy, specifying them by another name
taken from that substance which is proper to each.

The nomenclature of bodies compounded of three simple substances was
attended with still greater difficulty, not only on account of their
number, but, particularly, because we cannot express the nature of their
constituent principles without employing more compound names. In the
bodies which form this class, such as the neutral salts, for instance,
we had to consider, 1st, The acidifying principle, which i