, in other words, by introducing caloric into the
interstices between their particles; and, as the attraction of these
particles for each other is diminished in the inverse ratio of their
distance, it is evident that there must be a certain point of distance
of particles when the affinity they possess with each other becomes less
than that they have for oxygen, and at which oxygenation must
necessarily take place if oxygen be present.

We can readily conceive that the degree of heat at which this phenomenon
begins must be different in different bodies. Hence, on purpose to
oxygenate most bodies, especially the greater part of the simple
substances, it is only necessary to expose them to the influence of the
air of the atmosphere in a convenient degree of temperature. With
respect to lead, mercury, and tin, this needs be but little higher than
the medium temperature of the earth; but it requires a more considerable
degree of heat to oxygenate iron, copper, &c. by the dry way, or when
this operation is not assisted by moisture. Sometimes oxygenation takes
place with great rapidity, and is accompanied by great sensible heat,
light, and flame; such is the combustion of phosphorus in atmospheric
air, and of iron in oxygen gas. That of sulphur is less rapid; and the
oxygenation of lead, tin, and most of the metals, takes place vastly
slower, and consequently the disengagement of caloric, and more
especially of light, is hardly sensible.

Some substances have so strong an affinity with oxygen, and combine with
it in such low degrees of temperature, that we cannot procure them in
their unoxygenated state; such is the muriatic acid, which has not
hitherto been decomposed by art, perhaps even not by nature, and which
consequently has only been found in the state of acid. It is probable
that many other substances of the mineral kingdom are necessarily
oxygenated in the common temperature of the atmosphere, and that being
already saturated with oxygen, prevents their farther action upon that
element.

There are other means of oxygenating simple substances besides exposure
to air in a certain degree of temperature, such as by placing them in
contact with metals combined with oxygen, and which have little affinity
with that element. The red oxyd of mercury is one of the best substances
for this purpose, especially with bodies which do not combine with that
metal. In this oxyd the oxygen is united with very little force to the
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