This work is an investigation of the mixing of the nozzle fluid of a round turbulent jet with the entrained reservoir fluid, using laser-Rayleigh scattering methods. Our measurements, at a Reynolds number of 5000, cover the axial range from 20 to 80 jet exit diameters and resolve the full range of temporal & spatial concentration scales. The measured mean & rms values of the concentration, and the mean scalar dissipation rate, when estimated from the time derivative of concentration, are consistent with jet similarity laws. Concentration fluctuation power spectra are found to be self-similar along rays emanating from the jet virtual origin. The probability density functions for the concentration, the time derivative of concentration, and the square of the time derivative of concentration, are compiled and are also self-similar along rays.