A most important class of chemical compounds, which have for the most part the following properties. They have a sour, or sourish taste, the stronger kinds being acrid and corrosive. They change the vegetable blues and purples to a bright red. They unite with water in almost every proportion With a few exceptions, they are decomposed or volatilized by a moderate heat They combine with all the alkalies, and most of the metallic earths and oxides, and form with them that class of bodies termed salts. The varieties of acids are extremely numerous, and will be generally noticed under the head Chemistry. The four principal acids of commerce, viz. the acetic, sulphuric, nitric, and muriatic, which are manufactured on the great scale, we shall describe in this place.