ACID

a chemical compound containing hydrogen, which can be replaced by electro-positive elements of radicals (cations), or which, di ociating in aqueous solution, produces hydrogen ions. Most a‘s contain oxygen, but this _{s by no means a nece ary condition, as was formerly held by Lavoisier and others. Davy and Dulong were the first to state that hydrogen was the acidifying principle, and Liebig added final proof by showing that a’s containing more, than one atom of hydrogen (polybasic a.) can either have the entire hydrogen replaced by a metal (cation) to form normal salts, or only partially to form a. salts, or by different metals to form compound salts. Organic a’s are compounds containing one or more monovalent CO.OH groups called carboxyl, forming salts when hydrogen is replaced by a metal, and esters when replaced by alkyl radicals. A characteristic quality of a’s is to redden vegetable blues like litmus. Acidimetry, measurement of the percentage of acid in a solution. If no other substances are present it may be determined by the specific weight; in other cases the usual methods are either by titration or by determining the quantity of an insoluble salt precipitated, or by calculating the amount of carbon dioxide liberated by the addition of a carbonate.