Formula

* 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.