3. One atom of hydrogen in acetic acid (HC_{2}H_{3}O_{2})[6] may be replaced by the basic radical ammonium (NH_{4}), producing the salt ammonium acetate (NH_{4}C_{2}H_{3}O_{2}). [Footnote 6: Symbols indicating the number of atoms of replaceable hydrogen occupy the foremost position in the formulæ of acids, as shown in the text.] Acids which, like those mentioned in the foregoing examples, contain one atom of replaceable hydrogen are called monobasic; those which contain two such atoms (_e.g._ sulphuric acid, H_{2}SO_{4}; tartaric acid, H_{2}C_{4}H_{4}O_{6}),[7] dibasic; those which contain three such atoms (_e.g._ phosphoric acid, H_{3}PO_{4}; citric acid, H_{3}C_{6}H_{5}O_{7}),[7] tribasic; and so on with acids of higher basicity. Acids of greater basicity than unity are frequently termed polybasic. [Footnote 7: See footnote, p. 26.] Besides containing replaceable or basic hydrogen, acids are further characterised by the property of combining with alkaloids to form salts; _e.g._—— Sulphuric Acid. Quinia. H_{2}SO_{4} + 2C_{24}H_{24}N_{2}O_{2} = Quinia Sulphate. (C_{20}H_{24}N_{2}O_{2})_{2} . H_{2}SO_{4} Acetic Acid. Morphia. HC_{2}H_{3}O_{2} + C_{17}H_{19}NO_{3} = Morphia Acetate. C_{17}H_{19}NO_{3} . HC_{2}H_{3}O_{2} =Dibasic Acids.= See ACID. =Fatty Acids.= Acids separable from fats or oils; _e.g._ stearic acid, oleic acid, butyric acid, &c. =Inorganic Acids.= Same as MINERAL ACIDS (which _see_). =Mineral Acids.= Acids chiefly or wholly derived from the mineral kingdom. In _medicine_, sulphuric, hydrochloric, and nitric acids, are commonly so called. =Monobasic Acids.= See ACID. =Organic Acids.= Acids formed by, or derived from organic substances; _e.g._ acetic acid, tartaric acid, uric acid, &c. =Polybasic Acids.= See ACID. =Pyro-acids.= Acids resulting from the decomposition by heat of other acids, _e.g._ gallic acid, when heated, yields pyro-gallic acid. =Tribasic Acids.= See ACID. =ACIDIFICA′TION.= [Eng., Fr.] _Syn._ ACIDIFICA′TIO, L. In _chemistry_, the act, process, or state of acidifying, or of making, becoming, or impregnated with acid. =ACIDIM′ETER.= _Syn._ ACIDOM′ETER; ACIDIME′TRUM, &c., L.; ACIDIMÈTRE, Fr. An instrument or apparatus employed in acidimetry. The ordinary acidimeters of the chemist are small tubes, constructed to hold exactly 1000 grains of distilled water, at 60° Fahr., within the limits of their scale, which is accurately graduated into 100 divisions. They are used to contain the alkaline solutions (TEST-LIQUORS, NORMAL or STANDARD SOLUTIONS) employed in the following processes. Beaumé’s Acidimeter, and others of the same class, are HYDROMETERS, and are described under that ‘head.’