_Of the Vitriolic Acid._
The vitriolic acid, so called because it was originally procured from
_vitriol_, is now generally procured from sulphur; the dephlogisticated
part of the air uniting with it in the act of burning.
That dephlogisticated air is essential to this acid is evident from the
decomposition of it; for if the vapour of it be made to pass through a
red-hot earthen tube, a great quantity of dephlogisticated air is
procured.
This acid has a strong affinity to water, with which it unites with much
heat; and it is capable of greater concentration, or of being made
specifically heavier, than any other acid. When pure, it is entirely
free from colour and smell, owing, probably, to its being free from
phlogiston, which is inseparable from the nitrous or marine acids.
The vitriolic acid will dislodge the nitrous, or marine, or any other
acid, from their earthy or metallic bases; from which property it is
called the strongest of all the acids.
By means of the superior affinity of the vitriolic acid to earths, and
especially to _terra ponderosa_, the smallest quantity of it in water
may be discovered by a solution of this earth in the marine acid. In
this acid the terra ponderosa is held in perfect solution; but with the
vitriolic acid it forms a substance that is insoluble in water, and
therefore it instantly appears in the form of a white cloud.
Perhaps chiefly from the strong affinity which this acid has with water,
_pyrophorus_, consisting of a mixture of alum and several substances
containing phlogiston, takes fire spontaneously on exposure to the air.
It is commonly made of three parts of alum and one of brown sugar, or of
two parts alum, one of salt of tartar, and one of charcoal. They must be
heated till they have for some time emitted a vapour that burns with a
blue flame.
The saline substances produced by the union of this acid with the
several earths and metals, are best exhibited in tables constructed for
the purpose. When united to three of the metals, viz. iron, copper, and
zinc, they are called _vitriols_, green, blue, and white. And all the
substances which this acid unites with crystallize, and do not
deliquesce.
This acid unites with oil, and the mixture is always black.
When any substance containing phlogiston is heated in the vitriolic
acid, another species of the acid, called _sulphureous_, is formed, of a
pungent smell. In reality, it is water impregnated with vitriolic acid
air. It makes, however, a distinct species of acid, and is dislodged
from its base by most of the others.
_Of the Marine Acid._
The marine acid is procured from common salt by the vitriolic acid,
which unites with its base, the fossil alkali.
This acid is generally of a straw-colour; but this is owing to an
impregnation with some earthy matter, most of which it readily
dissolves, especially the metallic ones. It is less capable of
concentration than the vitriolic or nitrous acids, perhaps from a more
intimate union of phlogiston with it. No heat can extract from it any
dephlogisticated air.
Though this is denominated a weaker acid than the nitrous, yet it will
take silver, lead, or mercury, from their union with the nitrous acid.
Upon this principle, a solution of these metals in the nitrous acid will
readily discover whether any water contains the marine acid, the latter
uniting with the metal dissolved in the former, and forming with it, if
it be silver, a _luna cornea_; which being a substance insoluble in
water, discovers itself by a cloudy appearance.
The union of the marine acid with earths forms salts that easily
deliquesce, but with the metals such as are capable of crystallization;
and so also is that formed by the union of this acid to terra ponderosa.
Neither this acid nor the nitrous will dissolve gold or platina; but a
mixture of them, called _aqua regia_, will do it.
The marine acid has a strong affinity to dephlogisticated air, and will
take it from manganese and other substances; and with this union it
becomes a different acid, called _dephlogisticated marine acid_, being
water impregnated with dephlogisticated marine acid air, described
above.