on of any medium, whereas
metallic substances are incapable of forming this combination without
being previously less or more oxygenated; strictly speaking, therefore,
metals are not soluble in acids, but only metallic oxyds. Hence, when we
put a metal into an acid for solution, it is necessary, in the first
place, that it become oxygenated, either by attracting oxygen from the
acid or from the water; or, in other words, that a metal cannot be
dissolved in an acid unless the oxygen, either of the acid, or of the
water mixed with it, has a stronger affinity to the metal than to the
hydrogen or the acidifiable base; or, what amounts to the same thing,
that no metallic solution can take place without a previous
decomposition of the water, or the acid in which it is made. The
explanation of the principal phenomena of metallic solution depends
entirely upon this simple observation, which was overlooked even by the
illustrious Bergman.

The first and most striking of these is the effervescence, or, to speak
less equivocally, the disengagement of gas which takes place during the
solution; in the solutions made in nitric acid this effervescence is
produced by the disengagement of nitrous gas; in solutions with
sulphuric acid it is either sulphurous acid gas or hydrogen gas,
according as the oxydation of the metal happens to be made at the
expence of the sulphuric acid or of the water. As both nitric acid and
water are composed of elements which, when separate, can only exist in
the gasseous form, at least in the common temperature of the atmosphere,
it is evident that, whenever either of these is deprived of its oxygen,
the remaining element must instantly expand and assume the state of gas;
the effervescence is occasioned by this sudden conversion from the
liquid to the gasseous state. The same decomposition, and consequent
formation of gas, takes place when solutions of metals are made in
sulphuric acid: In general, especially by the humid way, metals do not
attract all the oxygen it contains; they therefore reduce it, not into
sulphur, but into sulphurous acid, and as this acid can only exist as
gas in the usual temperature, it is disengaged, and occasions
effervescence.

The second phenomenon is, that, when the metals have been previously
oxydated, they all dissolve in acids without effervescence: This is
easily explained; because, not having now any occasion for combining
with oxygen, they neither decompose the acid nor