Sour, sharp or biting to the taste, having the taste of vinegar, as acid fruits or liquors.

In chimistry, acids are a class of substances, so denominated from their taste, or the sensation of sourness which they produce on the tongue. But the name is now given to several substances, which have not this characteristic in an eminent degree. The properties, by which they are distinguished, are these:

When taken into the mouth, they occasion the taste of sourness. They are corrosive, unless diluted with water; and some of them are caustic.

They change certain vegetable blue colors to red, and restore blue colors which have been turned green, or red colors which have been turned blue by an alkali.

Most of them unite with water in all proportions, with a condensation of volume and evolution of heat; and many of them have so strong an attraction for water, as not to appear in the solid state.

They have a stronger affinity for alkalies, than these have for any other substance; and in combining them, most of them produce effervescence.

They unite with earths, alkalies and metallic oxyds, forming interesting compounds, usually called salts.

With few exceptions, they are volatilized or decomposed by a moderate heat. The old chimists divided acids into animal, vegetable, and mineral - a division now deemed inaccurate. They are also divided into oxygen acids, hydrogen acids, and acids destitute of these acidifiers. Another division is into acids with simple radicals, acids with double radicals, acids with triple radicals, acids with unknown radicals, compound acids, dubious acids, and acids destitute of oxygen.