I*som"er*ism (?), n. Chem.

The state, quality, or relation, of two or more isomeric substances.

Physical isomerism Chem., the condition or relation of certain (metameric) substances, which, while chemically identical (in that they have the same composition, the same molecular weights, and the same ultimate constitution), are yet physically different, as in their action on polarized light, as dextro- and laevo-tartaric acids. In such compounds there is usually at least one unsymmetrical carbon atom. See Unsymmetrical.

© Webster 1913.