SECTION II.. _of_ Soap.

Of SOAP.

Alkalis also have the same property. When an Oil is combined with an acid or an alkali in such a manner, that the compound resulting from their union is soluble in water; such a compound may in general be called a Soap. Soap itself hath the property of rendering fat bodies in some measure soluble in water; on which account it is very useful for scouring or cleansing any thing greasy.

Oily and saline substances, combined together, observe the same general rules as all other combinations; that is, they mutually communicate the properties belonging to each: thus Oils, which naturally are not soluble in water, acquire, by their union with saline matters, the property of dissolving therein; and salts lose, by their conjunction with Oils, part of their natural tendency to incorporate with water; so that, while they serve to constitute soap, they do not, as before, attract the moisture of the air, &c. and, in like manner, as they are not inflammable, they considerably lessen the inflammability of the Oils combined with them.

Acid Soaps are decompounded by alkalis, as alkaline Soaps are by acids, according to the general rules of affinities.

The acids of nitre and vitriol, when highly concentrated, dissolve Oils with such violence as to heat them, make them black, burn them, and even set them on fire. How sea-salt affects Oils is not yet sufficiently ascertained.

All Oils have the property of dissolving sulphur; which is not at all surprising, seeing each of its component principles hath an affinity with Oil.

It is also a property common to all Oils to become more fluid, subtile, light, and limpid, the oftener they are distilled. On the contrary, by being incorporated with saline substances they acquire a greater consistence, and sometimes form compounds that are most solid.

CHAP. XI.

Of the several Sorts of OILS.

Oils are distinguished by the substances from which they are drawn: and as Oils are extracted from minerals, from vegetables, and from animals, there are of course Mineral, Vegetable, and Animal Oils.