Ac"id, n. 1. A sour
2. (Chem.) One of a class of compounds,
generally but not always distinguished by their sour taste, solubility in
water, and reddening of vegetable blue or violet colors. They are also
characterized by the power of destroying the distinctive properties of
alkalies or bases, combining with them to form salts, at the same time
losing their own peculiar properties. They all contain hydrogen, united
with a more negative element or radical, either alone, or more generally
with oxygen, and take their names from this negative element or radical.
Those which contain no oxygen are sometimes called hydracids in
distinction from the others which are called oxygen acids or
☞ In certain cases, sulphur, selenium, or tellurium may take the
place of oxygen, and the corresponding compounds are called respectively
sulphur acids or sulphacids, selenium acids, or
tellurium acids. When the hydrogen of an acid is replaced by a
positive element or radical, a salt is formed, and hence acids are
sometimes named as salts of hydrogen; as hydrogen nitrate for nitric
acid, hydrogen sulphate for sulphuric acid, etc. In the old
chemistry the name acid was applied to the oxides of the negative or
nonmetallic elements, now sometimes called anhydrides.
Ac"id (?), a. [L. acidus sour, fr.
the root ak to be sharp: cf. F. acide. Cf. Acute.]
1. Sour, sharp, or biting to the taste; tart; having
the taste of vinegar: as, acid fruits or liquors. Also fig.: Sour-
He was stern and his face as acid as ever.
2. Of or pertaining to an acid; as, acid