Its modern meaning and general
introduction into the chemical vocabulary,
however, is usually attributed to the
French chemist, Guillaume-François
Rouelle (1703–1770), who used the
term in a memoir on salts written in
1754 (5). In this paper, which was an
extension of an earlier memoir on the
same subject written in 1744 (6),
Rouelle pointed out that the number of
known salts had increased significantly
during the 17th and early 18th centuries,
due not only to the preparation of
new salts, but also to an increasing ability
to distinguish between sodium and
potassium compounds, and to a generalization
of the concept so as to include
many substances, such as the alums and
vitriols (i.e., sulfates), that had been previously
excluded.
In order to incorporate this extended
concept of salt formation,
Rouelle explicitly defined a neutral salt
as the product formed by the union of
an acid with any substance, be it a watersoluble
alkali, a volatile alkali, an absorbent
earth, a metal, or an oil, capable of
serving as “a base” for the salt “by giving
it a concrete or solid form”.