AFFINITY, see  Kindred.

The attraction of atoms and in some cases perhaps of molecules for each other by the force of chemical attraction. When the affinity is allowed to act or is carried out, a chemical change, as distinguished from a physical or mechanical change, ensues. Thus if sulphur and iron are each finely powdered and are mixed the change and mixture are mechanical. If slightly heated the sulphur will melt, which is a physical change. If heated to redness the iron will combine with the sulphur forming a new substance, ferric sulphide, of new properties, and especially characterized by unvarying and invariable ratios of sulphur to iron. Such change is a chemical one, is due to chemical affinity, is due to a combination of the atoms, and the product is a chemical compound.