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The room temperature longitudinal and shear acoustic velocities in polycrystalline NaCI have been measured at static pressures in the range of 25-270 kbar (2.5-27.0 GPa). The measurements were made by ultrasonic interferometry in a variable lateral support Bridgeman anvil device. The velocity data are developed with the aid of the Decker equation of state. Previous measurements of acoustic velocities made in the range of 0-100 kbar are in agreement with the data. At higher pressures the shear mode velocity is approximately constant or slowly increasing with increasing pressure. This is in agreement with predictions made with next nearest neighbor interatomic force calculations. Nearest neighbor only and fourthorder finite strain theory calculations which use the assumption that the elastic parameter c, goes to zero at the 292-kbar phase transition are determined to be inaccurate near the transition. It is suggested that the ratio of the acoustic velocities of polycrystalline NaCI can be used in the future as a parameter for calibration of ultrahigh-pressure devices.

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The observation of flux exclusion approaching Meissner proportions (Xy~^^/^ cgs units) in pressure-quenched CdS at 77 K is reported. The results can be naturally and simply interpreted on the basis of superconductivity at 77 K. If the superconductive state is not the appropriate description, then a new high-temperature collective quantum state must be invoked.