Cohesion
the force which unites two molecules of the same nature; as, for instance, two molecules of iron or two molecules of water. It is strongly excited in solids, less strongly in liquids, and not at all in gases. It varies not merely according to the nature of different bodies, but also with the arrangement of molecules in the same body; thus the tempering of steel alters the molecular arrangement in that substance, with the effect also of altering its cohesion. Tenacity, hardness, ductility, etc., arise from modifications in their cohesion.