observed at ordinary temperatures only in the Li20-U205 system, it may be assumed that in this case stabilized U205 is present due to incorporation of very small amounts of LizO. With very low amounts of Liz0 (1 LizO: 15-20 U2O5), the lines of the hexagonal modification diverge in the direction of the lines of the orthorhombic a-U308 modification, and at the same time UO2.25 lines make their appearance in the Xray photograph. The compounds MgO.U205 and CdO.Uz05 crystallize in a fluorite-type lattice with statistical distribution of the cations ( M e~> 3 U~~6 , ) 0 2 .The cadmium compound reacts with additional CdO to give a rhombohedral phase, the upper phase limit of which lies near 2 CdO.UzO5. No 1 : 1 compound appears in the system PbO-U205. On the other hand, two phases richer in PbO exist; a cubic phase, whose homogeneity range extends from approximately 1.6 PbO.Uz05 to 2.25 PbO.U205, and a rhombohedral phase with the approximate composition 2.5 PbO.U205. Received, March 7th. 1962 [Z 229162 IE][*I Dedicated to Prof. Dr. G. Witfig on his 65th. birthday.