Ultrasound studies of the high T sub c superconducting La sub (1.85) Sr sub (.15) CuO sub 4.

Sound velocity, attenuation and thermal expansion measurements are reported on La sub (1.85) Sr sub (.15) Cu O sub 4. From room temperature to just above T sub c the sound velocity is found to soften significantly as the temperature is reduced. At T sub c there is a drop of ~150 ppm in accord with the thermodynamics of the superconducting transition and below T sub c, as the gap opens, there is a large increase in the sound velocity. The magnitude of these effects are anomalously large.