In common with sulphuric acid, and several other acids, the muriatic is
capable of different degrees of oxygenation; but the excess of oxygen
produces quite contrary effects upon it from what the same circumstance
produces upon the acid of sulphur. The lower degree of oxygenation
converts sulphur into a volatile gasseous acid, which only mixes in
small proportions with water, whilst a higher oxygenation forms an acid
possessing much stronger acid properties, which is very fixed and cannot
remain in the state of gas but in a very high temperature, which has no
smell, and which mixes in large proportion with water. With muriatic
acid, the direct reverse takes place; an additional saturation with
oxygen renders it more volatile, of a more penetrating odour, less
miscible with water, and diminishes its acid properties. We were at
first inclined to have denominated these two degrees of saturation in
the same manner as we had done with the acid of sulphur, calling the
less oxygenated _muriatous acid_, and that which is more saturated with
oxygen _muriatic acid_: But, as this latter gives very particular
results in its combinations, and as nothing analogous to it is yet known
in chemistry, we have left the name of muriatic acid to the less
saturated, and give the latter the more compounded appellation of
_oxygenated muriatic acid_.
Although the base or radical of the acid which is extracted from nitre
or saltpetre be better known, we have judged proper only to modify its
name in the same manner with that of the muriatic acid. It is drawn from
nitre, by the intervention of sulphuric acid, by a process similar to
that described for extracting the muriatic acid, and by means of the
same apparatus (Pl. IV. Fig. 1.). In proportion as the acid passes over,
it is in part condensed in the baloon or recipient, and the rest is
absorbed by the water contained in the bottles L,L,L,L; the water
becomes first green, then blue, and at last yellow, in proportion to
the concentration of the acid. During this operation, a large quantity
of oxygen gas, mixed with a small proportion of azotic gas, is
disengaged.
This acid, like all others, is composed of oxygen, united to an
acidifiable base, and is even the first acid in which the existence of
oxygen was well ascertained. Its two constituent elements are but weakly
united, and are easily separated, by presenting any substance with which
oxygen has a stronger affinity than with the acidifiable base peculiar
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