The interiors of two large Kentucky caves — Mammoth Cave and nearby Salts Cave, both within Mammoth Cave National Park — were much visited and utilized by prehistoric Indians. Large quantities of artifacts and numerous other evidences of human activity are still present in both caves, especially in undisturbed portions of Salts Cave. Most of the remains comprise perishable materials of vegetable fiber and wood, and plants or plant parts carried into the caves by the aboriginal inhabitants of the region. Several collections of artifacts gathered 40 or 50 years ago from the surface in the Mammoth Cave area have recently been examined by D. W. Schwartz of the University of Kentucky. One such collection hints at a village site of the late Archaic-Early Woodland time range somewhere near the entrance to Salts Cave. In 1961, specimens of the black-brown ceiling and wall deposits which are quite extensive in parts of both Salts and Mammoth caves were collected and analyzed. The deposits were found to be soot, presumably from aboriginal torches and hearths whose remains occur plentifully in some areas of the caves. A sample of soot from Salts Cave was submitted for radiocarbon determination; the resulting date is 3075 ± 140 B.P. Two dates had been previously obtained by the National Park Service from artifacts in Mammoth Cave: 2230 ± 40 B.P. and 2370 ± 60 B.P. These three dates support the suggestion of a late Archaic-Early Woodland placement for the prehistoric activity in Salts and Mammoth caves.

Reactions designed to reduce the oxygen content of UO2 below stoichiometric composition are described. No evidence was found for the existence of substoichiometric U02-The reaction of metal with UOj + ^ yields a phase described in the literature as uranium monoxide, UO. However, the reaction proceeds at a low rate and the reaction products are contaminated with a large amount of U02-The reaction of UC with UOj is described: this reaction is capable of producing a single-phase material of composition ^^x^Ux ^'-^'^^ ^y *«*'»•»« «•« vacuum at 1600 to 1800 C.

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study has been made of the wear and friction phenomena associated ivith sliding molybdenum surfaces lubricated by liquid sodium. Operating conditions included sodium temperatures from 250 F to 1300 F, sliding speeds of from 0.22 to 2.5 mm per sec, and contact stresses of 80,000 psi. Sliding specimens consisted of a ball and a flat rectangle. Sodium was found to influence the sliding behavior of molybdenum br modifying reacted films which provided boundary lubrication. These effects were also found to be temperature dependent. Addition of clean sodium between dry rubbing molybdenum surfaces in an argon atmosphere of high purity produced a marked drop in friction coefficient, and the character of the wear scar changed from galling to superficial scratching. Furthermore, these effects persisted after removal of sodium by evaporation. Studies of the films formed on molybdenum surfaces during sliding in liquid sodium and under controlled atmospheres ivere carried out using electron and K-ray diffraction, electron microscope, and differential thermal-analysis techniques. It was established that a sodium molybdate film on the molybdenum surfaces can be associated with low friction and diminished surface damage. Studies in vacuums up to 10 mm of mercury showed that native oxides on molybdenum also influence its sliding behavior.