ponent 1 do not appear to be satisfactorily described component 1 is less than M,, to obtain sufficiently by the molecular theory in its present form. It may direct and precise information for a complete analysis. be necessary to measure them by diff ereiit experi-Acknowledgment.-This work was supported in mental means, especially when the molecular weight of part by a grant from the National ScTence Foundation.The actinide elements neptunium,.plutonium, and americium are materials of considerable interest to the high pressure investigator. The possibility of pressure-induced electronic transitions such as those in cerium and cesium is suggested by the electronic configurations of the actinides. Such transitions are usually detectable by a discontinuous change in the electrical resistance of the sample. A matter of additional interest is the known one atmosphere polymorphism of plutonium with six allotropic forms between room temperature and its melting point, of neptunium with two allotropic forms, and a suspected allotropism in americium. The program therefore involved the development of apparatus capable of developing high pressures and temperatures which could allow electrical resistance measurements to be made on milligram quantities of metal. In addition, the apparatus was t o be resistant t o breakage or blowout which could contaminate the laboratory, permanent equipment, and, of course, laboratory personnel.
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