525 Northwestern Ave
West Lafayette,IN 47907-2036
We calculate the dependence of the Casimir force on the isotopic composition of the interacting objects. This dependence arises from a subtle influence of the nuclear masses on the electronic properties of the bodies. We discuss the relevance of these results to current experiments utilizing the isoelectronic effect to search at very short separations for new weak forces suggested by various unification theories. Preliminary results from an ongoing experiment will be presented.