ALLOTROPY (from άλλος, other, and τρόπος, manner), a name applied to a property, whereby certain substances, chemically simple, assume different forms and conditions without undergoing chemical change. Sulphur and phosphorus, for instance, occur sometimes in crystals and sometimes in an amorphous state, being in the latter case sometimes translucent and sometimes opaque, and present very different properties under these different conditions. Ozone is an allotropic form of oxygen. The name isomerism is given to the similar by no means uncommon property whereby compound bodies, although entirely distinct, are made up of the same chemical elements in precisely the same proportions.