metameric

isomeric i`so*mer"ic ([imac]`s[-o]*m[e^]r"[i^]k), a. [Iso- + Gr. me`ros part: cf. F. isom['e]rique.] (Chem.) Having the same chemical composition and molecular weight; having the same number of atoms of each kind in the molecule; -- said of chemical compounds with known chemical composition. This property used to be called {metameric} to distinguish it from other forms of isomerism. [PJC]

Note: Formerly the term isomeric applied also to comopounds having the same percentage chemical composition, even if the number of atoms in a molecule differed. In the 1913 dictionary isomeric was defined as: ``Having the same percentage composition; -- said of two or more different substances which contain the same ingredients in the same proportions by weight, often used with with. Specif.: (a) Polymeric; i. e., having the same elements united in the same proportion by weight, but with different molecular weights; as, acetylene and benzine are isomeric (polymeric) with each other in this sense. See {Polymeric}. (b) Metameric; i. e., having the same elements united in the same proportions by weight, and with the same molecular weight, but with a different structure or arrangement of the ultimate parts; as, ethyl alcohol and methyl ether are isomeric (metameric) with each other in this sense. See {Metameric}.'' [1913 Webster]