For"mu*la (?), n.; pl. E. Formulas (#), L. Formulæ (#). [L., dim. of forma form, model. SeeForm, n.] 1. A prescribed or set form; an established rule; a fixed or conventional method in which anything is to be done, arranged, or said.

2. (Eccl.) A written confession of faith; a formal statement of foctrines.

3. (Math.) A rule or principle expressed in algebraic language; as, the binominal formula.

4. (Med.) A prescription or recipe for the preparation of a medicinal compound.

5. (Chem.) A symbolic expression (by means of letters, figures, etc.) of the constituents or constitution of a compound.

Chemical formulæ consist of the abbreviations of the names of the elements, with a small figure at the lower right hand, to denote the number of atoms of each element contained.

Empirical formula (Chem.), an expression which gives the simple proportion of the constituents; as, the empirical formula of acetic acid is C2H4O2. -- Graphic formula, Rational formula (Chem.), an expression of the constitution, and in a limited sense of the structure, of a compound, by the grouping of its atoms or radicals; as, a rational formula of acetic acid is CH3.(C:O).OH; -- called also structural formula, constitutional formula, etc. See also the formula of Benzene nucleus, under Benzene. -- Molecular formula (Chem.), a formula indicating the supposed molecular constitution of a compound.