That branch of science which treats of the composition
of substances, and of the changes which they undergo in consequence of
alterations in the constitution of the molecules, which depend upon
variations of the number, kind, or mode of arrangement, of the
constituent atoms. These atoms are not assumed to be indivisible, but
merely the finest grade of subdivision hitherto attained. Chemistry
deals with the changes in the composition and constitution of
molecules. See Atom, Molecule.