_Of Vitriolic Acid Air._
Vitriolic acid air is procured by heating in hot acid of vitriol almost
any substance containing phlogiston, especially the metals which are
soluble in that acid, as copper, mercury, &c. This kind of air is
heavier than common air, and extinguishes a candle, but without any
particular colour of its flame. It will not dislodge the nitrous or
marine acids from any substance containing them.
By its affinity to water it deprives borax of it.
One measure of this air saturates two of alkaline air, and with it forms
the vitriolic ammoniac.
Water imbibes between 30 and 40 times its bulk of this air, and retains
it when frozen. Water thus impregnated dissolves some metals, and
thereby yields inflammable air.
If this water be confined in a glass tube, together with common air, and
be exposed to a long continued heat, it forms real sulphur, the
dephlogisticated part of the common air being imbibed, and forming real
vitriolic acid, which uniting with the phlogiston in the air, forms the
sulphur. Also this air mixed with atmospheric air will, without heat,
imbibe some part of it, and thereby become the common acid of vitriol;
so that water impregnated with vitriolic acid air, commonly called
_sulphureous_, or _phlogisticated acid of vitriol_, wants
dephlogisticated air to make it the common acid of of vitriol.
This kind of air is imbibed by oils, which thereby change their colour;
whale oil becoming red, olive oil of an orange colour, and spirit of
turpentine of the colour of amber.
If this air be confined in a glass tube by mercury, and the electric
spark be taken in it, a black tinge will be given to the glass
contiguous to the spark, and this black substance appears to be mercury
super-phlogisticated; since by exposure to air it becomes running
mercury: so that the vapour of mercury must be diffused through every
part of this air, to the distance of at least several feet from the
surface of the mercury.
_Of Fluor Acid Air._
Fluor acid air is procured by dissolving the earthy substance called
_fluor_ in vitriolic acid.
This kind of air extinguishes a candle, and, like vitriolic acid air,
one measure of it saturates two of alkaline air. It is peculiar to this
kind of air to dissolve glass when it is hot.
It seems to consist of a peculiar acid vapour united to the stony
substance of the fluor; for water being admitted to it absorbs the acid
vapour, and the stony substance is deposited. By this means it exhibits
an amusing appearance, whether water be admitted to a glass jar
previously filled with that air, or the bubbles of air be admitted, as
they are formed, to a quantity of water resting on mercury.