g, we are only acquainted with one compound radical from
the mineral kingdom, the nitro-muriatic, which is formed by the
combination of azote with the muriatic radical. The other compound
mineral acids have been much less attended to, from their producing less
striking phenomena.

SECT. III.--_Observations upon the Combinations of Light and Caloric
with different Substances._

I have not constructed any table of the combinations of light and
caloric with the various simple and compound substances, because our
conceptions of the nature of these combinations are not hitherto
sufficiently accurate. We know, in general, that all bodies in nature
are imbued, surrounded, and penetrated in every way with caloric, which
fills up every interval left between their particles; that, in certain
cases, caloric becomes fixed in bodies, so as to constitute a part even
of their solid substance, though it more frequently acts upon them with
a repulsive force, from which, or from its accumulation in bodies to a
greater or lesser degree, the transformation of solids into fluids, and
of fluids to aeriform elasticity, is entirely owing. We have employed
the generic name _gas_ to indicate this aeriform state of bodies
produced by a sufficient accumulation of caloric; so that, when we wish
to express the aeriform state of muriatic acid, carbonic acid, hydrogen,
water, alkohol, &c. we do it by adding the word _gas_ to their names;
thus muriatic acid gas, carbonic acid gas, hydrogen gas, aqueous gas,
alkoholic gas, &c.

The combinations of light, and its mode of acting upon different bodies,
is still less known. By the experiments of Mr Berthollet, it appears to
have great affinity with oxygen, is susceptible of combining with it,
and contributes alongst with caloric to change it into the state of gas.
Experiments upon vegetation give reason to believe that light combines
with certain parts of vegetables, and that the green of their leaves,
and the various colours of their flowers, is chiefly owing to this
combination. This much is certain, that plants which grow in darkness
are perfectly white, languid, and unhealthy, and that to make them
recover vigour, and to acquire their natural colours, the direct
influence of light is absolutely necessary. Somewhat similar takes place
even upon animals: Mankind degenerate to a certain degree when employed
in sedentary manufactures, or from living in crowded houses, or in the
narrow lanes of large ci