[CHAP. IV.]
Of the several Sorts of Saline Substances.
SECTION I.
Of the Universal Acid.
The Universal Acid is so called, because it is in fact the Acid which is most universally diffused through all nature, in waters, in the atmosphere, and in the bowels of the earth. But it is seldom pure; being almost always combined with some other substance. That from which we obtain it with most ease, and in the greatest quantity, is Vitriol, a mineral which we shall consider afterwards: and this is the reason why it is called the Vitriolic Acid; the name by which it is best known.
When the Vitriolic Acid contains but little phlegm, yet enough to give it a fluid form, it is called Oil of Vitriol, on account of a certain unctuosity belonging to it. In truth this name is very improperly bestowed on it; for we shall afterwards see that, bating this unctuousness, it has none of the properties of oils. But this is not the only impropriety in names that we shall have occasion to censure.
If the Vitriolic Acid contain much water, it is then called Spirit of Vitriol. When it does not contain enough to render it fluid, and so is in a solid form, it is named the Icy Oil of Vitriol.
When Oil of Vitriol highly concentrated is mixed with water, they rush into union with such impetuosity, that, the moment they touch each other, there arises a hissing noise, like that of red-hot iron plunged in cold water, together with a very considerable degree of heat, proportioned to the degree to which the Acid was concentrated.
If, instead of mixing this concentrated Acid with water, you only leave it exposed to the air for some time, it attracts the moisture thereof, and imbibes it most greedily. Both its bulk and its weight are increased by this accession; and if it be under an icy form, that is, if it be concreted, the phlegm thus acquired will soon resolve it into a fluid.